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Chemistry of neogene basalts of British Columbia and the adjacent pacific ocean floor : a test of tectonic.. 1985

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CHEMISTRY OF NEOGENE BASALTS OF BRITISH COLUMBIA AND THE ADJACENT PACIFIC OCEAN FLOOR: A TEST OF TECTONIC DISCRIMINATION DIAGRAMS by LINDA RUTH ERDMAN B.Sc. UNIVERSITY OF BRITISH COLUMBIA, 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA OCTOBER, 1985 © LINDA RUTH ERDMAN, 1985 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the The U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree that p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s or her r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permi s s i o n . DEPARTMENT OF GEOLOGICAL SCIENCES The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Pl a c e Vancouver, Canada V5T 1W5 Date: OCTOBER, 1985 ABSTRACT Seventy-one samples of s u b a l k a l i n e and a l k a l i n e b a s a l t s from B r i t i s h Columbia and the adjacent P a c i f i c s e a f l o o r were analyzed f o r 33 major, t r a c e and rare e a r t h elements using X-ray f l o u r e s c e n c e (XRF) and ins t r u m e n t a l neutron a c t i v a t i o n a n a l y s i s (INAA). These b a s a l t s are a l l l e s s than 22 Ma i n age and come from v a r i o u s magmatic b e l t s , each with a d i s t i n c t , well-known, t e c t o n i c s e t t i n g ; (1) Convergent margin ( G a r i b a l d i and Pemberton B e l t s ) , (2) Back-arc ( C h i l c o t i n B a s a l t s ) , (3) Hotspot (Anahim V o l c a n i c B e l t ) , (4) I n c i p i e n t r i f t ( S t i k i n e V o l c a n i c B e l t ) , (5) A r c - t r e n c h gap ( A l e r t Bay V o l c a n i c B e l t ) and (6) Ocean f l o o r (Offshore b a s a l t s of the Juan de Fuca-Explorer Ridge Systems). Element abundances and r a t i o s were p l o t t e d on eighteen diagrams that have been proposed to d i s c r i m i n a t e between t e c t o n i c s e t t i n g s on the b a s i s of magma chemistry. Although e r u p t i o n through c o n t i n e n t a l c r u s t has mo d i f i e d the abundances of Ba, Th, U, K and Sr, i n most cases t h i s d i d not a f f e c t the a b i l i t y of the diagrams t o d i s t i n g u i s h t e c t o n i c s e t t i n g . On most diagrams b a s a l t s from back-arc, hotspot, i n c i p i e n t r i f t and a r c - t r e n c h gap s e t t i n g s p l o t t e d i n the wi t h i n p l a t e b a s a l t (WPB) f i e l d , but d i s t i n c t i o n between these d i f f e r e n t WPB s e t t i n g s c o u l d not be made. Two samples from the Masset Formation on the Queen C h a r l o t t e I s l a n d s , i n c l u d e d with the Anahim B e l t hotspot s u i t e , were c o n s i s t e n t l y c l a s s i f i e d as convergent margin. Samples from the ocean f l o o r p l o t t e d i n the N-MORB or E-MORB f i e l d s . i i Three convergent margin samples from the Pemberton B e l t always p l o t t e d i n the convergent margin f i e l d , but on most diagrams a l l e i g h t samples from the G a r i b a l d i B e l t p l o t t e d in the WPB f i e l d because of t h e i r d e p l e t i o n i n LIL elements. La i s the only ra r e e a r t h element obtained by INAA that i s e s s e n t i a l f o r i d e n t i f y i n g the t e c t o n i c environment of magma g e n e s i s . The r a t i o La/Nb, i s an e f f e c t i v e separator of wi t h i n p l a t e b a s a l t s (WPB), i n c l u d i n g E-MORB, (La/Nb l e s s than 1.2) from convergent margin b a s a l t s (La/Nb g r e a t e r than 2.0). N-MORB l i e between the r a t i o s 1.2 and 2.0. Th, Ta and Hf a l s o o b t a i n e d by INAA, are important d i s c r i m i n a n t elements. However, Nb and Zr, o b t a i n e d by XRF a n a l y s i s convey much of the same i n f o r m a t i o n . The r a t i o Nb/16 as an estimate of Ta and Zr/39 as an estimate f o r Hf produced a c c e p t a b l e r e s u l t s on diagrams that o r i g i n a l l y i n c o r p o r a t e d Ta and Hf. E f f e c t i v e d i s c r i m i n a t i o n can t h e r e f o r e u s u a l l y be ach i e v e d u s i n g XRF elements alo n e . Convergent margin, w i t h i n p l a t e and ocean f l o o r t e c t o n i c s e t t i n g s were best d i s t i n g u i s h e d on Th-Hf/3-Ta, T i - Z r - Y and T i - Z r - S r , T i / Y v s . Nb/Y, Th/Yb vs. Ta/Yb, ( B a / L a ) C H vs. (La/Sm) C H and V vs. Ti/1000. S l i g h t l y l e s s e f f e c t i v e p l o t s were MnO-Ti0 2-P 20 5, La vs. Th, La vs. Nb and K 20/Yb vs. Ta/Yb. On the other hand T i 0 2 - K 2 0 - P 2 0 5 , MgO-Fe0*-Al 20 3 and La vs. Ba p r o v i d e d l i t t l e i n f o r m a t i o n concerning the t e c t o n i c s e t t i n g of i n d i v i d u a l samples. T i / C r v s. N i , Sm/Ce vs. Sr/Ce, Cr vs. Ce/Sr and Cr vs. Y diagrams were u s e f u l f o r d i s t i n g u i s h i n g u n f r a c t i o n a t e d convergent margin b a s a l t s from MORB pl u s WPB. Table of Contents ABSTRACT i i LIST OF TABLES x LIST OF FIGURES x i i ACKNOWLEDGMENTS x v i i GLOSSARY x v i i i 1 . OBJECTIVES 1 1.1 SAMPLE SELECTION AND METHODS OF ANALYSIS 1 1.2 TECTONIC SETTING 3 2. REVIEW OF MAJOR AND TRACE ELEMENT TECTONIC DISCRIMINATION DIAGRAMS 9 2.1 CHEMICAL DISTINCTIONS BASED ON MAJOR ELEMENTS 9 2.1.1 ALKALINE vs. SUBALAKLINE 9 2.1.2 THOLEIITIC vs. CALCALKALINE 11 2.1.3 OCEANIC vs. NON-OCEANIC 13 2.1.3.1 T i 0 2 - K 2 0 - P 2 0 5 1 3 2.1.3.2 MnO-Ti0 2-P 2O s 13 2.1.3.3 MgO-FeO*-Al 20 3 1 5 2.2 TRACE ELEMENT GEOCHEMISTRY 15 2.2.1 OCEAN FLOOR BASALTS (MORB) 17 2.2.2 OCEAN ISLAND BASALTS (WPB) 18 2.2.3 CONVERGENT MARGIN BASALTS (ARC) 19 2.3 RARE EARTH ELEMENT GEOCHEMISTRY 20 2.4 TRACE ELEMENT DIAGRAMS 22 2.4.1 T i - Z r - Y and T i - Z r - S r 22 2.4.2 V vs. Ti/1000 22 2.4.3 Ti/Y vs. Nb/Y 24 2.4.4 T i / C r vs. Ni 24 v 2.5 TRACE AND REE DIAGRAMS 27 2.5.1 Sm/Ce vs. Sr/Ce and Cr vs. Ce/Sr 27 2.5.2 Cr vs. Y 29 2.5.3 ( B a / L a ) C H vs. (La/Sm) C H 29 2.5.4 La vs. Ba La vs. Th La vs. Nb 31 2.5.5 K 20/Yb vs. Ta/Yb 34 2.5.6 Th/Yb vs. Ta/Yb 34 2.5.7 Th vs. Ta La vs. Ta Th vs. Hf 34 2.5.8 Th-Hf/3-Ta 36 2.6 BULK EARTH NORMALIZED TRACE AND REE DIAGRAMS (BEND) 40 2.6.1 MORB 41 2.6.2 WPB 41 2.6.3 CONVERGENT MARGIN BASALTS 43 3. GARIBALDI and PEMBERTON BELTS 47 3.1 MAJOR ELEMENT CHEMISTRY 47 3.2 DISCRIMINATION DIAGRAMS 49 3.2.1 MAJOR ELEMENT CLASSIFICATIONS ...49 3.2.2 TRACE ELEMENT CLASSIFICATIONS 53 3.2.3 TRACE AND REE CLASSIFICATIONS 53 3.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) 63 3.3 TRACE ELEMENT CHEMISTRY 68 3.3.1 Th and U 69 3.3.2 TRANSITION ELEMENTS 70 3.4 Sr ISOTOPES 70 3.5 DISCUSSION OF DISCRIMINATION DIAGRAMS 71 3.6 SUMMARY 73 v i 4. CHILCOTIN BASALTS 78 4.1 MAJOR ELEMENT CHEMISTRY 78 4.2 DISCRIMINATION DIAGRAMS 80 4.2.1 MAJOR ELEMENT CLASSIFICATIONS 80 4.2.2 TRACE ELEMENT CLASSIFICATIONS 82 4.2.3 TRACE AND REE CLASSIFICATIONS 85 4.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) 92 4.3 TRACE ELEMENT CHEMISTRY 96 4.3.1 Th and U 97 4.3.2 TRANSITION ELEMENTS 97 4.4 Sr ISOTOPES 98 4.5 DISCUSSION OF DISCRIMINATION DIAGRAMS 98 4.6 SUMMARY . 100 5. ANAHIM VOLCANIC BELT 103 5.1 MAJOR ELEMENT CHEMISTRY 103 5.2 DISCRIMINATION DIAGRAMS 105 5.2.1 MAJOR ELEMENT CLASSIFICATIONS 105 5.2.2 TRACE ELEMENT CLASSIFICATIONS 107 5.2.3 TRACE AND REE CLASSIFICATIONS 109 5.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) .....118 5.3 TRACE ELEMENT CHEMISTRY 121 5.3.1 Th AND U 125 5.3.2 TRANSITION ELEMENTS 125 5.4 Sr ISOTOPES 126 5.5 DISCUSSION OF DISCRIMINATION DIAGRAMS 126 5.6 SUMMARY 129 6. STIKINE VOLCANIC BELT 133 v i i 6.1 MAJOR ELEMENT CHEMISTRY 135 6.2 DISCRIMINATION DIAGRAMS 136 6.2.1 MAJOR ELEMENT CLASSIFICATIONS 136 6.2.2 TRACE ELEMENT CLASSIFICATIONS 139 6.2.3 TRACE AND REE CLASSIFICATIONS 139 6.2.4 BULK EARTH NRMALIZED DIAGRAMS (BEND) 147 6.3 TRACE ELEMENT CHEMISTRY 156 6.3.1 Th AND U 157 6.3.2 TRANSITION ELEMENTS 157 6.4 Sr ISOTOPES 158 6.5 DISCUSSION OF DISCRIMINATION DIAGRAMS 159 6 . 6 SUMMARY 161 7. ALERT BAY VOLCANIC BELT 166 7.1 MAJOR ELEMENT CHEMISTRY 166 7.2 DISCRIMINANT DIAGRAMS 168 7.2.1 MAJOR ELEMENT CLASSIFICATIONS 168 7.2.2 TRACE ELEMENT CLASSIFICATIONS 171 7.2.3 TRACE AND REE CLASSIFICATIONS 171 7.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) 176 7.3 TRACE ELEMENT CHEMISTRY 180 7.3.1 Th and U 181 7.3.2 TRANSITION ELEMENTS 181 7.4 ISOTOPIC DATA 181 7.5 DISCUSSION OF DISCRIMINATION DIAGRAMS 182 7.6 SUMMARY 183 8. OFFSHORE BASALTS 186 8.1 MAJOR ELEMENT CHEMISTRY 186 v i i i 8.2 DISCRIMINATION DIAGRAMS 188 8.2.1 MAJOR ELEMENT CLASSIFICATIONS 188 8.2.2 TRACE ELEMENT CLASSIFICATIONS 192 8.2.3 TRACE AND REE CLASSIFICATIONS 195 8.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) 199 8.3 TRACE ELEMENT CHEMISTRY 206 8.3.1 Th AND U . . : 208 8.3.2 TRANSITION ELEMENTS 208 8.4 Sr ISOTOPES 209 8.5 DISCUSSION OF DISCRIMINATION DIAGRAMS 210 8 . 6 SUMMARY 212 9. SUMMARY OF DISCRIMINATION DIAGRAM DISCUSSIONS 216 10. CONCLUSIONS 227 REFERENCES 230 APPENDIX I - SAMPLE SOURCES AND PREVIOUS ANALYSES 243 APPENDIX II - NEUTRON ACTIVATION ANALYSIS 249 APPENDIX III - MAJOR AND TRACE ELEMENT ANALYSIS BY XRF 271 APPENDIX IV - TA CONTAMINATION 286 ix =2.124 DR=0 LIST OF TABLES TABLE I. N o r m a l i z a t i o n Values f o r Bulk E a r t h Normalized Diagrams 42 TABLE I I . G a r i b a l d i and Pemberton B e l t s : Major, t r a c e and rare e a r t h element abundances, Sr iotope r a t i o s and K-Ar dates 76 TABLE I I I . . C h i l c o t i n B a s a l t s : Major, t r a c e and rare e a r t h element abundances, Sr iotope r a t i o s and K-Ar dates . 102 TABLE IV. Anahim V o l c a n i c B e l t : Major, t r a c e and r a r e e a r t h element abundances, Sr iotope r a t i o s , K-Ar dates and ages 131 TABLE V. S t i k i n e V o l c a n i c B e l t : Major, t r a c e and r a r e e a r t h element abundances, Sr iotope r a t i o s , K-Ar dates and ages 163 TABLE VI. A l e r t Bay V o l c a n i c B e l t : Major, t r a c e and rare e a r t h element abundances, Sr iotope r a t i o s and K-Ar dates 185 TABLE V I I . O f f s h o r e B a s a l t s : Major, t r a c e and rare e a r t h element abundances, Sr iotope r a t i o s and estimated ages 214 TABLE V I I I . C l a s s i f i c a t i o n of Sample S u i t e s Using D i s c r i m i n a t i o n Diagrams 217 TABLE IX. E f f i c i e n c y of T e c t o n i c D i s c r i m i n a t i o n Diagrams 222 TABLE X. Element Isotope Data 251 TABLE XI. Standard Abundnces of S e l e c t e d Trace and Rare E a r t h Elements i n Standards Used f o r INAA . . . . 253 TABLE X I I . Table of I n t e r f e r e n c e s 257 x TABLE X I I I . P r e c i s i o n of INAA Based on R e p l i c a t e Analyses 260 TABLE XIV. R e l a t i v e P r e c i s i o n s Based on R e p l i c a t e Analyses 264 TABLE XV. Test of A n a l y t i c a l Accuracy f o r INAA . 265 TABLE XVI. Systematic E r r o r i n INAA Analyses . . . 268 TABLE XVII. Element Abundances i n I n t r a l a b Standards WP1 and PI 270 TABLE XVIII. P r e c i s i o n of Major Element Analyses . . 273 TABLE XIX. P r e c i s i o n of Trace Element Analyses . . 277 TABLE XX. C a l c u l a t e d Abundances of Nb and Ta i n Analyzed B a s a l t i c Samples 290 TABLE XXI. Abundances of Nb and Ta i n Standards (Abbey, 1983) 293 TABLE XXII. Abundances of Nb and Ta i n T e r r e s t r i a l Rocks (Wood, 1980) 294 LIST OF FIGURES F i g . 1.1. Neogene v o l c a n i c t r e n d s of B r i t i s h Columbia and o f f s h o r e p l a t e boundaries 4 F i g . 2.1. K 20 + Na 20 vs. S i 0 2 d i s t i n g u i s h i n g a l k a l i n e and s u b a l k a l i n e rocks 10 F i g . 2.2. AFM diagram s e p a r a t i n g c a l c a l k a l i n e from t h o l e i i t i c v o l c a n i c rocks 12 F i g . 2.3. FeO*/MgO vs. S i 0 2 diagram s e p a r a t i n g c a l c a l k a l i n e from t h o l e i i t i c v o l c a n i c rocks 12 F i g . 2.4. T i 0 2 - K 2 0 - P 2 0 5 s e p a r a t i n g oceanic from non-oceanic b a s a l t s 14 F i g . 2.5. MnO-Ti0 2-P 20 5 with f i e l d s f o r MORB, IAT, CAB, OIT and OIA 14 F i g . 2.6. MgO-FeO*-Al 20 3 diagram d i s t i n g u i s h i n g f i e l d s f o r ARC, CB, OI , N-MORB and E-MORB 16 F i g . 2.7. T i - Z r - Y showing f i e l d s f o r WPB, LKT, OFB and CAB 23 F i g . 2.8. T i - Z r - S r showing f i e l d s f o r LKT, OFB and CAB. . 23 F i g . 2.9. V vs. Ti/1000 d i s t i n g u i s h i n g f i e l d s f o r WPB, MORB and t h o l e i i t i c convergent margin b a s a l t s 25 F i g . 2.10. Ti / Y vs. Nb/Y with f i e l d s f o r WPB, MORB and convergent margin b a s a l t 25 F i g . 2.11. T i / C r vs. Ni diagram with f i e l d s f o r t h o l e i i t i c convergent margin b a s l t and t h o l e i i t i c MORB 26 F i g . 2.12. Sm/Ce vs. Sr/Ce d i s t i n g u i s h i n g convergent margin rocks from oceanic v o l c a n i c rocks 28 F i g . 2.13. Cr vs. Ce/Sr with a f i e l d f o r convergent margin b a s a l t s separated from o v e r l a p p i n g MORB and WPB f i e l d s . . 28 F i g . 2.14. Cr vs. Y with convergent margin, MORB and WPB f i e l d s . 30 F i g . 2.15. ( B a / L a ) C H vs. (La/Sm) C H diagram d i s t i n g u i s h i n g b a s a l t s from convergent margins ana oceanic areas (ocean r i d g e and i n t r a p l a t e ) 32 F i g . 2.16. La vs. Ba with f i e l d s f o r N-MORB, E-MORB p l u s WPB and orogenic a n d e s i t e s 32 F i g . 2.17. La vs. Th with f i e l d s f o r N-MORB, E-MORB p l u s WPB and orogenic a n d e s i t e s 33 F i g . 2.18. La vs. Nb with f i e l d s f o r N-MORB, E-MORB p l u s WPB and orogenic a n d e s i t e s 33 F i g . 2.19. K 20/Yb vs. Ta/Yb d i s t i n g u i s h i n g convergent margin b a s a l t s from s l i g h t l y o v e r l a p p i n g MORB and WPB f i e l d s 35 F i g . 2.20. Th/Yb vs. Ta/Yb d i s t i n g u i s h i n g convergent margin b a s a l t s from s l i g h t l y o v e r l a p p i n g MORB and WPB f i e l d s 35 F i g . 2.21. Th vs. Ta d i s t i n g u i s h i n g convergent margin b a s a l t s from N-MORB pl u s E-MORB p l u s WPB 37 F i g . 2.22. La vs. Ta with f i e l d s f o r convergent margin b a s a l t s , N-MORB and E-MORB 37 F i g . 2.23. Th vs. Hf diagram d i s t i n g u i s h i n g f i e l d s f o r WPB, N-MORB and E-MORB . 3 8 x i i F i g . 2.24. Th-Hf/3-Ta with f i e l d s f o r N-MORB, E-MORB pl u s t h o l e i i t i c WPB, a l k a l i n e WPB and convergent margin b a s a l t s . 39 F i g . 2.25. BEND p a t t e r n s f o r N-MORB and E-MORB 44 F i g . 2.26. BEND p a t t e r n s f o r a l k a l i n e oceanic WPB, a l k a l i n e c o n t i n e n t a l WPB and t h o l e i i t i c c o n t i n e n t a l WPB. 45 F i g . 2.27. BEND p a t t e r n s f o r c a l c a l k a l i n e and a l k a l i n e convergent margin b a s a l t s 46 F i g . 3.1. Sample l o c a t i o n map f o r the Convergent Margin S u i t e 48 F i g . 3.2. T o t a l a l k a l i s v s . s i l i c a 51 F i g . 3.3. AFM diagram 51 F i g . 3.4. FeO*/NgO vs. S i 0 2 51 F i g . 3.5. T i 0 2 - K 2 0 - P 2 0 5 52 F i g . 3.6. MnO-Ti0 2-P 20 5 52 F i g . 3.7. MgO-FeO*-Al 20 3 52 F i g . 3.8. T i - Z r - Y 54 F i g . 3.9. T i - Z r - S r 54 F i g . 3.10. V vs. Ti/1000 54 F i g . 3.11. T i / Y vs. Nb/Y 55 F i g . 3.12. T i / C r vs. Ni 55 F i g . 3.13. Sm/Ce vs. Sr/Ce 57 F i g . 3.14. Cr vs. Ce/Sr 57 F i g . 3.15. Cr vs. Y 58 F i g . 3.16. La vs. Ba 59 F i g . 3.17. (Ba/La) r„ vs. (La/Sm) r„ 59 F i g . 3.18. La vs. TH 7 60 F i g . 3.19. La vs. Nb 60 F i g . 3.20. K 20/Yb vs. Ta*/Yb 62 F i g . 3.21. Th/Yb vs. Ta*/Yb 62 F i g . 3.22. Th-Hf/3-Ta* 62 F i g . 3.23. BEN diagram f o r samples C0Q253, C0Q632 and COQ63 64 F i g . 3.24. BEN diagram f o r samples ELAHO, GARIBALD, CHEAK and MEAGER 65 F i g . 3.25. BEN diagram f o r samples SALAL1, SALAL2, SALAL3 and SILVERH 66 F i g . 3.26. BEN diagram f o r samples CAYLEY and SILVERA. 67 F i g . 4.1. Sample l o c a t i o n map f o r the C h i c o t i n B a s a l t S u i t e 79 F i g . 4.2. T o t a l a l k a l i s v s . s i l i c a 81 F i g . 4.3. AFM diagram 81 F i g . 4.4. Fe0*/NgO vs. S i 0 2 81 F i g . 4.5. T i 0 2 - K 2 0 - P 2 0 5 83 F i g . 4.6. MnO-Ti0 2-P 20 5 83 F i g . 4.7. MgO-FeO*-Al 20 3 83 F i g . 4.8. T i - Z r - Y 84 F i g . 4.9. V vs. Ti/1000 84 F i g . 4.10. T i / Y vs. Nb/Y 86 F i g . 4.11. T i / C r vs. Ni 86 x i i i F i g . 4.12. Cr vs. Ce/Sr 87 F i g . 4.13. Cr vs. Y 87 F i g . 4.14. La vs. Ba 89 F i g . 4.15. (Ba/La) r„ vs. (La/Sm) r 89 F i g . 4.16. La vs. Tn 7 90 F i g . 4.17. La vs. Nb 90 F i g . 4.18. K 20/Yb vs. Ta*/Yb 91 F i g . 4.19. Th/Yb vs. Ta*/Yb 91 F i g . 4.20. Th-Hf/3-Ta* 91 F i g . 4.21. BEN diagram f o r samples QUESW, WOOD LK and BLIZZARD 93 F i g . 4.22. BEN diagram f o r samples REDSTONE, NAZKO, CAMEL, DOG CK, EDMUND and DE ADMAN 94 F i g . 4.23. BEN diagram f o r samples BULL CAN and CARD. . 95 F i g . 5.1. Sample l o c a t i o n map for the Anahim V o l c a n i c B e l t 104 F i g . 5.2. T o t a l a l k a l i s vs. s i l i c a 106 F i g . 5.3. AFM diagram 106 F i g . 5.4. Fe0*/NgO vs. S i 0 2 106 F i g . 5.5. T i 0 2 - K 2 0 - P 2 0 5 1 08 F i g . 5.6. Mn0-Ti0 2-P 20 5 1 08 F i g . 5.7. MgO-FeO*-Al 20 3 1 08 F i g . 5.8. T i - Z r - Y 110 F i g . 5.9. T i - Z r - S r 110 F i g . 5.10. V vs. Ti/1 000 1 10 F i g . 5.11. T i / Y vs. Nb/Y 111 F i g . 5.12. T i / C r vs. Ni 111 F i g . 5.13. Sm/Ce vs. Sr/Ce 113 F i g . 5.14. Cr vs. Ce/Sr 113 F i g . 5.15. Cr vs. Y 114 F i g . 5.16. La vs. Ba 116 F i g . 5.17. (Ba/La) r„ vs. (La/Sm)_ H 116 F i g . 5.18. La vs. Tn 7 117 F i g . 5.19. La vs. Nb 117 F i g . 5.20. K 20/Yb vs. Ta*/Yb 119 F i g . 5.21. Th/Yb vs. Ta*/Yb 119 F i g . 5.22. Th-Hf/3-Ta* 119 F i g . 5.23. BEN diagram f o r samples KITASU, LAKE IS, RAINBOW, ANAHIM, ITCHA1 and ITCH A 2 120 F i g . 5.24. BEN diagram f o r samples ALEX, QUES LK, WGRAYN, SPAN CK and TROPHY 122 F i g . 5.25. BEN diagram f o r samples MASSET1, MASSET2 and ARIS IS 123 F i g . 6.1. Sample l o c a t i o n map for the S t i k i n e V o l c a n i c B e l t 134 F i g . 6.2. T o t a l a l k a l i s vs. s i l i c a 138 F i g . 6.3. AFM diagram 138 F i g . 6.4. Fe0*/NgO vs. S i 0 2 138 F i g . 6.5. T i 0 2 - K 2 0 - P 2 0 5 1 40 F i g . 6.6. Mn0-Ti0 2-P 20 5 140 xi v F i g . 6.7. MgO-FeO*-Al 20 3 1 40 F i g . 6.8. T i - Z r - Y 141 F i g . 6.9. V vs. Ti/1000 141 F i g . 6.10. T i / Y vs. Nb/Y 142 F i g . 6.11. T i / C r vs. Ni 142 F i g . 6.12. Cr vs. Ce/Sr." 144 F i g . 6.13. Cr vs. Y. 144 F i g . 6.14. La vs. Ba 145 F i g . 6.15. ( B a / L a ) r H vs. (La/Sm)_ H 145 F i g . 6.16. La vs. Tn 7 146 F i g . 6.17. La vs. Nb 146 F i g . 6.18. K 20/Yb vs. Ta*/Yb 147 F i g . 6.19. Th/Yb vs. Ta*/Yb 147 F i g . 6.20. Th-Hf/3-Ta* 147 F i g . 6.21. BEN diagram f o r samples PRINCER, LEVELD and SATLIN 149 F i g . 6.22. BEN diagram f o r samples AYNSH1, AYNSH2 and BOWSER 151 F i g . 6.23. BEN diagram f o r samples MTDUNN, ISKUT, ISKUTW and BORDERLK 152 F i g . 6.24. BEN diagram f o r samples EDZ1, SPEC1, SPEC2 and EDZ2 153 F i g . 6.25. BEN diagram f o r samples NEDZ1, NEDZ2, NEDZ3 and NEDZ4 154 F i g . 6.26. BEN diagram f o r samples LEVEL 1, LEVEL2 and NATLIN 155 F i g . 7.1. Sample l o c a t i o n map f o r the A l e r t Bay V o l c a n i c B e l t . 167 F i g . 7.2. T o t a l a l k a l i s vs. s i l i c a 169 F i g . 7.3. AFM diagram 169 F i g . 7.4. Fe0*/MgO vs. S i 0 2 169 F i g . 7.5. T i 0 2 - K 2 0 - P 2 0 5 1 70 F i g . 7.6. MnO-Ti0 2-P 20 5 1 70 F i g . 7.7. MgO-FeO*-Al 20 3 1 70 F i g . 7.8. T i - Z r - Y 172 F i g . 7.9. V vs. Ti/1000 172 F i g . 7.10. T i / Y vs. Nb/Y 172 F i g . 7.11. T i / C r vs. Ni 173 F i g . 7.12. Sm/Ce vs. Sr/Ce 173 F i g . 7.13. Cr vs. Ce/Sr 174 F i g . 7.14. Cr vs. Y 174 F i g . 7.15. La vs. Ba 175 F i g . 7.16. (Ba/La) r„ vs. (La/Sm) r„ 175 F i g . 7.17. La vs. TR 177 F i g . 7.18. La vs. Nb 177 F i g . 7.19. K 20/Yb vs. Ta*/Yb 178 F i g . 7.20. Th/Yb vs. Ta*/Yb 178 F i g . 7.21. Th-Hf/3-Ta* 178 F i g . 7.22. BEN diagram f o r samples ALERT1, ALERT2 and ALERT3 179 xv F i g . 8.1. Sample l o c a t i o n map f o r the Ocean F l o o r B a s a l t S u i t e 187 F i g . 8.2. T o t a l a l k a l i s vs. s i l i c a 190 F i g . 8.3. AFM diagram 190 F i g . 8.4. Fe0*/NgO vs. S i 0 2 190 F i g . 8.5. T i 0 2 - K 2 0 - P 2 0 5 1 91 F i g . 8.6. Mn0-Ti0 2-P 20 5 191 F i g . 8.7. MgO-FeO*-Al 20 3 1 91 F i g . 8.8. T i - Z r - Y 193 F i g . 8.9. T i - Z r - S r 193 F i g . 8.10. V vs. Ti/1000 193 F i g . 8.11. T i / Y vs. Nb/Y 194 F i g . 8.12. T i / C r vs. Ni 194 F i g . 8.13. Sm/Ce vs. Sr/Ce 196 F i g . 8.14. Cr vs. Ce/Sr 196 F i g . 8.15. Cr vs. Y 197 F i g . 8.16. La vs. Ba 198 F i g . 8.17. ( B a / L a ) r vs. (La/Sm) 198 F i g . 8 . 1 8 . La vs. Tn 7 200 F i g . 8.19. La vs. Nb 200 F i g . 8.20. K 20/Yb vs. Ta*/Yb 201 F i g . 8.21. Th/Yb vs. Ta*/Yb 201 F i g . 8.22. Th-Hf/3-Ta* 201 F i g . 8.23. BEN diagram f o r samples EXMOUNT1, EXMOUNT2 and EXMOUNT3 202 F i g . 8.24. BEN diagram f o r samples BRBEAR1, BRBEAR2, COBB 1 and COBB2 204 F i g . 8.25. BEN diagram f o r samples SEXRIDGE, PREVRDG, EXRIFT and EXDEEP 205 x v i ACKNOWLEDGMENTS I would l i k e to thank Dr. R.L. Armstrong f o r suggesting the t h e s i s t o p i c , f o r p r o v i d i n g guidance and f o r c r i t i c a l l y reviewing the manuscript many times before the f i n a l d r a f t . I am a l s o g r a t e f u l f o r the comments and suggestions from Drs. R.L. Chase, W.H. Mathews and K. R u s s e l l which g r e a t l y improved the f i n a l manuscript. Many thanks i s extended to NOVATRAK f o r i r r a d i a t i o n of the samples, f o r l e t t i n g me use t h e i r equipment f o r INAA and to J . Humphries who spent time t e a c h i n g me the techniques of INAA. I would a l s o l i k e to thank B. Cousens of the Department of Oceanography fo r doing the XRF a n a l y s e s , S. Horsky of the Departmant of Geology who p r o v i d e d a s s i s t a n c e with a n a l y t i c a l procedures and R. Berman, G. Nixon, B. Cousens and E. P e r k i n s who wrote the computer programs f o r data r e d u c t i o n and p l o t t i n g . I am indebted to the i n d i v i d u a l s who c o l l e c t e d the samples f o r t h e i r B . S c , M.Sc, and Ph.D. t h e s i s p r o j e c t s , and by doing so c r e a t e d the r e s e a r c h c o l l e c t i o n s from which the samples f o r t h i s study were s e l e c t e d . A d d i t i o n a l samples were p r o v i d e d by Dr. T. Hamilton of the P a c i f i c Geoscience Center and Dr. J . G. Souther of the G e o l o g i c a l Survey of Canada. Funding f o r t h i s p r o j e c t was from N a t u r a l Sciences and E n g i n e e r i n g Research C o u n c i l of Canada o p e r a t i n g grant 67-8841 to Dr. R.L Armstrong and from an NSERC s c h o l a r s h i p and Graduate Teaching A s s i s t a n t s h i p awarded to the author. x v i i GLOSSARY ARC - convergent margin = v o l c a n i c arc BEND - bulk e a r t h normalized diagram CAB - c a l c a l k a l i n e b a s a l t CA - c a l c a l k a l i n e CB - c o n t i n e n t a l b a s a l t E-MORB - e n r i c h e d MORB HREE - heavy rare e a r t h element I AT - i s l a n d arc t h o l e i i t e INAA - instrumental neutron a c t i v a t i o n a n a l y s i s LIL - l a r g e ion l i t h o p h i l e LREE - l i g h t rare e a r t h element MORB - mid-ocean r i d g e b a s a l t N-MORB - normal MORB OFB - ocean f l o o r b a s a l t OI - ocean i s l a n d OIA - ocean i s l a n d a l k a l i n e OIT - ocean i s l a n d t h o l e i i t e REE - r a r e e a r t h element TH - t h o l e i i t e TH MORB - t h o l e i i t i c MORB XRF - X-ray f l o u r e s c e n c e WPB - w i t h i n p l a t e b a s a l t < >CH — c h o n d r i t e normalized x v i i i SCHEMATIC DIAGRAM OF TECTONIC SETTING TERMS IN GLOSSARY Convergent Margin (ARC) Cont inental WPB (Rift , H o t s p o t , l a c k - a r c ) Ocean Island WPB M i d - o c e a n (OIT) Ridge (OIA) (MORB) O c e a n i c Crust iĈ yj, Cont inental Crust Depleted Mantle L e s s D e p l e t e d M a n t l e Diagram after: Thompson et a l . , 1884 and DePao lo , 1981 1. OBJECTIVES T e c t o n i c d i s c r i m i n a t i o n diagrams which use major and t r a c e element abundances i n b a s a l t i c rocks have been used to i n f e r t e c t o n i c s e t t i n g . These diagrams were produced using a n a l y t i c a l data from u n a l t e r e d b a s a l t s from known t e c t o n i c s e t t i n g s , many of them erupted through oceanic c r u s t . In subsequent a p p l i c a t i o n s the same diagrams have been used to i d e n t i f y t e c t o n i c s e t t i n g s of metamorphosed and/or deformed b a s i c rocks, now i n c o r p o r a t e d i n t o and o f t e n erupted through c o n t i n e n t a l c r u s t . The present i n v e s t i g a t i o n was undertaken t o : 1. provide more complete chemical data f o r each s u i t e , and 2. a s c e r t a i n the a p p l i c a b i l i t y of v a r i o u s t e c t o n i c d i s c r i m i n a t i o n diagrams to s u i t e s of Neogene b a s a l t s from B r i t i s h Columbia and the adjacent P a c i f i c and E x p l o r e r p l a t e s which have been erupted i n a v a r i e t y of known t e c t o n i c s e t t i n g s . 1.1 SAMPLE SELECTION AND METHODS OF ANALYSIS The samples s t u d i e d e x i s t e d i n r e s e a r c h c o l l e c t i o n s at U.B.C. and at the G.S.C. i n Vancouver. Since t h i s t h e s i s was concerned with d i s c r i m i n a t i o n diagrams f o r b a s a l t i c rocks, most samples s e l e c t e d had e i t h e r a S i 0 2 content of l e s s than 55 wt.% (known from p r e v i o u s a n a l y s e s ) or they had been d e s c r i b e d ( v e r b a l l y ) as b a s a l t s . These c r i t e r i a were met f o r a l l samples except C0Q61 (58.75% S i 0 2 ) , CAYLEY (60.34% S i 0 2 ) , SILVERA (59.81% S i 0 2 ) , ALERT1 (61.15% S i 0 2 ) and 1 2 HOODOO (59.18% S i 0 2 ) . Many of the samples chosen f o r t h i s study had already been d e s c r i b e d , analyzed by XRF f o r major and t r a c e elements, and had Sr i s o t o p i c d e terminations and K-Ar dates. A few of them were not p r e v i o u s l y analyzed. Sample source i n f o r m a t i o n and a l i s t of p r e v i o u s a n a l y t i c a l work i s given i n Appendix I. Incomplete major and t r a c e element data s e t s were f i l l e d i n by new XRF an a l y s e s and some of the p r e v i o u s l y analyzed samples were re a n a l y z e d i n order to estimate p r e c i s i o n of r e s u l t s . T o t a l Fe was measured as F e 2 0 3 and c a l c u l a t e d as FeO*. Sample p r e p a r a t i o n , method of a n a l y s i s , abundances obtained from d u p l i c a t e analyses and p r e c i s i o n of analyses are given i n Appendix I I I . Instrumental neutron a c t i v a t i o n a n a l y s i s (INAA) (see Appendix II) was used f o r s e l e c t e d t r a c e and r a r e earth elements (REE) with the e x p e c t a t i o n that f u t u r e s t u d i e s at U.B.C. might r o u t i n e l y use INAA. Estimates of p r e c i s i o n based on r e p l i c a t e a n a l y s e s are presented i n Appendix I I , Table X I I I , and Table XIV; t e s t s of a n a l y t i c a l accuracy are l i s t e d i n Table XV, and systematic e r r o r s i n a n a l y s i s are presented i n Table XVI. Because systematic e r r o r s were g r e a t e r than the p r e c i s i o n of a n a l y s i s f o r La, Hf, Yb and Sc c a l c u l a t e d abundances of these elements were r e v i s e d by an amount equal t o the systematic e r r o r . In a d d i t i o n , t r a c e and REE abundances obtained by INAA were determined f o r i n t r a l a b standards WP1 and P-1. These 3 are presented i n Appendix I I , Table XVII. A n a l y s i s f o r Ta was u n s u c c e s s f u l because of contamination so Ta abundances were estimated u s i n g the r a t i o Nb/16, denoted Ta*. A more d e t a i l e d e x p l a n a t i o n i s given i n Appendix IV. 1.2 TECTONIC SETTING The Neogene and younger v o l c a n i c trends from western B r i t i s h Columbia and southwestern Yukon, and the present p l a t e boundaries are shown i n F i g u r e 1.1. The Queen C h a r l o t t e r i g h t l a t e r a l transform f a u l t which separates the P a c i f i c P l a t e and North American p l a t e s p a r a l l e l s the edge of the c o n t i n e n t from southeast A l a s k a to a t r i p l e j u n c t i o n i n the v i c i n i t y of Delwood K n o l l s at l a t i t u d e 50° N. (Yorath and Hyndman, 1983; Riddihough, 1984). Earthquake f i r s t motion s t u d i e s along t h i s f a u l t show almost pure s t i k e - s l i p motion on a near v e r t i c a l plane (Milne et a l . , 1981), however S r i v a s t a v a (1973), Horn et a l . , (1981) and Yorath and Hyndman (1983) suggest there may be a component of u n d e r t h r u s t i n g of the P a c i f i c p l a t e beneath the North 'America p l a t e along the f a u l t zone s i n c e Miocene time. To the north, the Queen C h a r l o t t e f a u l t c o n t i n u e s i n t o A laska as the Fairweather f a u l t system ( P l a f k e r et a l . , 1978). Southwest of the t r i p l e j u n c t i o n at 50° N, spreading axes (Tuzo Wilson and Delwood K n o l l s , E x p l o r e r Ridge and the Juan de Fuca Ridge) and transform f a u l t s (Paul Revere and Sovanco f r a c t u r e zones) separate the P a c i f i c from Juan de 4 F i g . 1 . 1 . N e o g e n e v o l c a n i c t r e n d s o f B r i t i s h C o l u m b i a a n d s o u t h w e s t e r n Y u k o n a n d p r e s e n t p l a t e t e c t o n i c b o u n d a r i e s , s h o w i n g e x t e n t o f G a r i b a l d i V o l c a n i c B e l t ( A ) , P e m b e r t o n B e l t ( • ) , A l e r t B a y V o l c a n i c B e l t ( * ) , A n a h i m V o l c a n i c B e l t ( • ) , S t i k i n e V o l c a n i c B e l t ( T ) a n d s o u t h e a s t e r n W r a n g e l l V o l c a n i c B e l t ( * ) . O u t l i n e d d o t t e d a r e a s s h o w t h e e x t e n t o f t h e C h i l c o t i n G r o u p B a s a l t s . P P - P a c i f i c p l a t e , E P - E x p l o r e r p l a t e , J d F P - J u a n d e F u c a p l a t e , N A P - N o r t h A m e r i c a p l a t e , P R f z - P a u l R e v e r e f r a c t u r e z o n e ( r i d g e ) , S f z - S o v a n c o f r a c t u r e z o n e , N F Z - N o o t k a f r a c t u r e z o n e , C B - C o b b s e a m o u n t , B B - B r o w n B e a r s e a m o u n t . D i a g r a m m o d i f i e d f r o m B e v i e r e t a l . , 1 9 7 9 . 5 Fuca and E x p l o r e r p l a t e s . These two smaller p l a t e s are separated by the n o r t h e a s t e r l y t r e n d i n g Nootka l e f t l a t e r a l t r a n s f o r m f a u l t , which formed i n P l i o c e n e time (Riddihough, 1977, Hyndman et a l . , 1979). The p l a t e boundary s e p a r a t i n g the Juan de Fuca and E x p l o r e r p l a t e s from the North American p l a t e i s one of convergence. Although an eastward d i p p i n g s e i s m i c zone beneath the continent i s p o o r l y d e f i n e d and a major bathymetric trench at the foot of the c o n t i n e n t a l slope i s l a c k i n g , Riddihough (1979) concludes that the Juan de Fuca-Explorer p l a t e s are moving under the North American p l a t e thereby producing the arc type volcanism of the present day G a r i b a l d i V o l c a n i c B e l t and the e a r l i e r Pemberton V o l c a n i c B e l t . The Quaternary G a r i b a l d i V o l c a n i c B e l t comprises a narrow l i n e a r chain of v o l c a n i c c e n t r e s that t r e n d approximately N20° W, p a r a l l e l to and approximately 250 km i n l a n d from the Juan de Fuca-North American p l a t e boundary (Green, 1981). Fa r t h e r northwest, near the S i l v e r t h r o n e Complex, a few v o l c a n i c c e n t r e s of s i m i l a r age and chemistry l i e a s i m i l a r d i s t a n c e from the convergent p l a t e boundary between E x p l o r e r and North American p l a t e s . East of the G a r i b a l d i B e l t and f o l l o w i n g a more no r t h w e s t e r l y trend i s the l a r g e l y Miocene Pemberton V o l c a n i c B e l t . Bevier et a l . (1979) suggest t h a t c e s s a t i o n of volcanism i n the Pemberton B e l t and the s h i f t to volcanism i n the G a r i b a l d i B e l t was caused by r e o r i e n t a t i o n 6 of p l a t e motion about 3 m.y. ago, when the Nootka f r a c t u r e zone was c r e a t e d . The Anahim V o l c a n i c B e l t runs approximately east-west along l a t i t u d e 52° N and i n c l u d e s v o l c a n i c c e n t r e s that range i n age from 14.5 to l e s s than 0.01 m.y. Three hypotheses have been proposed to e x p l a i n t h i s magmatic b e l t . They a r e : magmas r i s i n g through deep f r a c t u r e s developed along the northern edge of the "subducting Juan de Fuca p l a t e (Stacey, 1974). magmas from a mantle hotspot (Bevier et a l . , 1979). magmas generated i n an east-west r i f t zone (Bevier et a l . , 1979). V o l c a n i c rocks of the upper Oligocene t o lower Miocene Masset Formation occur i n the Queen C h a r l o t t e I s l a n d s and o f f s h o r e basins to the southeast. Bevier et a l . (1979) suggest that these v o l c a n i c rocks form the western end of a hotspot t r a c e whose propogation eastward produced the Anahim V o l c a n i c B e l t . Northward movement of the Queen C h a r l o t t e I s l a n d s , a f t e r volcanism had oc c u r r e d , was accomplished by t r a n s c u r r e n t motion along the Louscoone I n l e t - S a n d s p i t f a u l t systems (Young, 1981; Yorath and Chase, 1981). Other models suggest Masset volcanism i s : a s s o c i a t e d with the c r u s t a l r i f t i n g t h a t generated the f i r s t phase of Queen C h a r l o t t e Basin subsidence (Yorath and Hyndman, 1983) the northwestern end of the Pemberton V o l c a n i c B e l t ( J . 7 Souther, o r a l comm.). Adjacent t o , l o c a l l y i n c o n t a c t , and c o e v a l with the Anahim V o l c a n i c B e l t are the Miocene t o P l i o c e n e C h i l c o t i n Group B a s a l t s , forming a l a v a p l a i n elongate p a r a l l e l to the c o n t i n e n t a l margin ( B e v i e r , 1982). These l a v a s were erupted in a back-arc t e c t o n i c s e t t i n g and are contemporaneous with voicanism i n the Pemberton arc (Souther, 1977). The Miocene to Quaternary S t i k i n e V o l c a n i c B e l t i s s i t u a t e d i n l a n d and to the north of the Queen C h a r l o t t e I s l a n d s and trends toward the n o r t h e a s t , c u t t i n g d i a g o n a l l y a c r o s s the o l d e r rocks of the n o r t h w e s t e r l y t r e n d i n g Coast Mountains and Intermontane B e l t . I t i s b e l i e v e d to be a zone of i n c i p i e n t Cenozoic extension r e l a t e d to t r a n s c u r r e n t motion along the adjacent c o n t i n e n t a l margin (Souther, 1977). Near the c e n t r e of the S t i k i n e V o l c a n i c B e l t i s the Edziza-Spectrum Range complex i n which a l k a l i b a s a l t s to h i g h l y f r a c t i o n a t e d p e r a l k a l i n e r h y o l i t e s and t r a c h y t e s were erupted (Souther, 1977; Souther et a l . , 1984). The Wrangell V o l c a n i c B e l t , a broad arc that curves around the northern and ea s t e r n edge of the S t . E l i a s Mountains i n southwest Yukon and s o u t h c e n t r a l Alaska, r e s u l t s from subduction of the P a c i f i c p l a t e beneath the North American p l a t e (Souther, 1977). F a r t h e r to the west the same subduction produces the A l e u t i a n arc system. The P l i o c e n e A l e r t Bay V o l c a n i c B e l t i n northern Vancouver I s l a n d , formed d u r i n g a h i a t u s i n the voicanism of the Pemberton-Garibaldi V o l c a n i c B e l t s and was l i k e l y a 8 r e s u l t of magma generat i o n along the edge of the descending Juan de Fuca p l a t e (Armstrong et a l . , i n p r e s s ) . 2. REVIEW OF MAJOR AND TRACE ELEMENT TECTONIC DISCRIMINATION DIAGRAMS 2.1 CHEMICAL DISTINCTIONS BASED ON MAJOR ELEMENTS R e s u l t s from c o n v e n t i o n a l bulk chemical a n a l y s i s of igneous rocks are g e n e r a l l y presented as major element oxide percentages by weight, and consequently a v a r i e t y of t e c t o n i c d i s c r i m i n a t i o n diagrams have been formulated based e n t i r e l y on major element chemistry. A complete review of major element geochemical c h a r a c t e r i s t i c s i n MORB, WPB and convergent margin b a s a l t s i s p r o v i d e d by the B a s a l t i c Volcanism Study P r o j e c t (1981). Major element chemistry i s used to c a l c u l a t e normative mineralogy and to d i s t i n g u i s h a l k a l i n e from s u b a l k a l i n e and t h o l e i i t i c from c a l c a l k a l i n e s e r i e s rocks ( I r v i n e and Baragar, 1971). As some of the t e c t o n i c d i s c r i m i n a t i o n diagrams are p r e d i c a t e d on s e p a r a t i o n of a l k a l i n e , or t h o l e i i t i c , or c a l c a l k a l i n e s e r i e s rocks, these c l a s s i f i c a t i o n s must f i r s t be e s t a b l i s h e d . 2.1.1 ALKALINE VS. SUBALAKLINE To d i s t i n g u i s h the a l k a l i n e from the s u b a l k a l i n e v o l c a n i c rock s e r i e s the a l k a l i s v s . s i l i c a (wt.%(Na 20 + K 20) vs. S i 0 2 ) and 01' -Ne'-Qz' diagrams were used (MacDonald, 1968; I r v i n e and Baragar, 1971) ( F i g . 2.1). I r v i n e and Baragar c o n s i d e r e d the Ol'-Ne'-Qz' diagram the most r e l i a b l e f o r s e p a r a t i n g s u b a l k a l i n e from 9 10 F i g 2.1. K 20 + Na 20 vs. S i 0 2 d i s t i n g u i s h i n g a l k a l i n e and s u b a l k a l i n e v o l c a n i c rocks. The s o l i d l i n e i s MacDonald's (1968) d i v i d i n g l i n e f o r Hawaiian t h o l e i i t i c and a l k a l i n e rocks, the dashed curve i s I r v i n e and Baragar's (1971) d i v i d i n g l i n e f o r a general d i s t i n c t i o n between a l k a l i n e and s u b a l k a l i n e compositions. 11 a l k a l i n e b a s a l t s , t h e r e f o r e i n the few cases i n t h i s study where the two d i s c r i m i n a t i o n diagrams d i s a g r e e d , Ol'-Ne'-Qz' c l a s s i f i c a t i o n s were given the most weight. 2.1.2 THOLEIITIC VS. CALCALKALINE S u b a l k a l i n e rocks i n c l u d e both the c a l c a l k a l i n e and the t h o l e i i t i c b a s a l t s e r i e s and were d i s t i n g u i s h e d from one another by Wager and Deer (1939) on the b a s i s of Fe enrichment tr e n d s . Pronounced Fe enrichment d u r i n g d i f f e r e n t i a t i o n t y p i f i e s the t h o l e i i t i c s e r i e s while absence of t h i s enrichment t y p i f i e s the c a l c a l k a l i n e s e r i e s . T h i s d i f f e r e n c e i s commonly shown on an AFM diagram ( I r v i n e and Baragar, 1971), or on the FeO*/MgO vs. S i 0 2 diagram of M i y a s h i r o (1974) ( F i g s . 2.2 and 2.3). The l a t t e r diagram i s more a p p r o p r i a t e f o r s u i t e s of d i f f e r e n t i a t e d rocks, as trends are more important than i n d i v i d u a l p o s i t i o n s . In a d d i t i o n to lower Fe/Mg r a t i o s I r v i n e and Baragar noted that c a l c a l k a l i n e b a s a l t s and a n d e s i t e s g e n e r a l l y c o n t a i n 16% to 20% A l 2 0 3 , whereas s i m i l a r t h o l e i i t i c rocks have onl y 12% to 16% A 1 2 0 3 . T h i s was i l l u s t r a t e d on a p l o t of A 1 2 0 3 vs. normative p l a g i o c l a s e composition, c o n s i d e r e d by them to be b e t t e r than the AFM diagram f o r d i s c r i m i n a t i n g t h o l e i i t i c from c a l c a l k a l i n e rocks i n the b a s a l t - a n d e s i t e range. 12 F i g s . 2.2 and 2.3. AFM diagram (above) and FeO*/MgO vs. S i 0 2 diagram (below) s e p a r a t i n g c a l c a l k a l i n e from t h o l e i i t i c v o l c a n i c r o c k s . On the AFM diagram the dotted l i n e i s from I r v i n e and Baragar (1971) and the d i f f e r e n t i a t i o n trends f o r Hawaiian b a s a l t s are from MacDonald and Katsura (1964). The s o l i d l i n e on FeO*/MgO vs. S i 0 2 i s from M i y a s h i r o (1974) and the dashed l i n e s are d i f f e r e n t i a t i o n trends f o r v o l c a n i c s u i t e s from Japan (Kuno, 1968). 1 3 2.1.3 OCEANIC VS. NON-OCEANIC 2.1.3.1 T i 0 2 - K 2 0 - P 2 0 5 S u b a l k a l i n e b a s a l t s may be separated i n t o oceanic or non-oceanic ( c o n t i n e n t a l ) environments using a p l o t of T i 0 2 - K 2 0 - P 2 0 5 (Figure 2.4) (Pearce et a l . , 1975). These three oxides e f f e c t i v e l y d i s c r i m i n a t e d 93% of the oceanic (MORB and WPB) and great e r than 80% of the c o n t i n e n t a l b a s a l t data p l o t t e d by the above authors. Important ex c e p t i o n s were the Scoresby Sund b a s a l t s of East Greenland and the Deccan Plateau b a s a l t s of I n d i a , both of which p l o t t e d i n the oceanic f i e l d . T h i s supported the suggestion that these exeptions were produced by i n i t i a l r i f t i n g of a co n t i n e n t which generated new sea f l o o r , hence t h e i r oceanic c h a r a c t e r . 2.1.3.2 MnO-Ti0 2-P 20 5 Mullen (1983) r e p l a c e d the K 20 component of the above diagram with MnO and p l o t t e d a l k a l i n e and s u b a l k a l i n e v o l c a n i c rocks which had S i 0 2 abundances between 45%-54% ( F i g . 2.5). T h i s d i s t i n g u i s h e d f i v e oceanic p l a t e t e c t o n i c and p e t r o g e n e t i c environments: MORB, i s l a n d a r c t h o l e i i t e (IAT), i s l a n d arc c a l c a l k a l i n e (CAB), ocean i s l a n d t h o l e i i t e (OIT), and ocean i s l a n d a l k a l i n e (OIA) b a s a l t . C o n t i n e n t a l t h o l e i i t i c WPB's s c a t t e r a c r o s s a l l of these f i e l d s and cannot be r e s o l v e d from the oceanic b a s a l t s as there i s no component i n t h i s diagram which i s more e n r i c h e d i n 14 F i g s . 2.4 and 2.5. T i 0 2 - K 2 0 - P 2 0 5 (above) s e p a r a t i n g oceanic b a s a l t s from non-oceanic b a s a l t s (Pearce et a l . , 1975). MnO-Ti0 2-P 20 5 (below) with f i e l d s f o r MORB, IAT ( i s l a n d arc t h o l e i i t e ) , CAB ( i s l a n d arc c a l c a l k a l i n e ) , OIT (ocean i s l a n d t h o l e i i t e ) and OIA (ocean i s l a n d a l k a l i n e ) (Mullen, 1983). 15 b a s a l t s erupted through or a s s o c i a t e d with c o n t i n e n t s . B a s a l t s from back-arc b a s i n s and r i f t s g e n e r a l l y p l o t i n the ocean i s l a n d t h o l e i i t e f i e l d i f they are s u b a l k a l i n e , or i n the ocean i s l a n d a l k a l i n e f i e l d i f they are a l k a l i n e (Mullen, 1983). 2.1.3.3 MgO-FeO*-Al 20 3 Pearce et a l . (1977) d i s t i n g u i s h e d f i v e d i f f e r e n t t e c t o n i c environments on a MgO-FeO*-Al 20 3 diagram by p l o t t i n g a n a l y s e s of 8400 s u b a l k a l i n e v o l c a n i c rocks with s i l i c a contents between 51 and 56 wt% ( F i g . 2.6). F i e l d s d e s c r i b e d were: 1. orogenic b a s a l t s (ARC) 2. c o n t i n e n t a l b a s a l t s (CB) 3. ocean i s l a n d b a s a l t s (OI) 4. ocean r i d g e / f l o o r b a s a l t s (N-MORB), and 5. oceanic i s l a n d s which are adjacent to or s t r a d d l i n g a mid-ocean ri d g e ( E-MORB). However, none of the t e c t o n i c f i e l d s had sharp boundaries, e s p e c i a l l y the orogenic f i e l d , which enclosed only 55% of the orogenic data p o i n t s . 2.2 TRACE ELEMENT GEOCHEMISTRY Magmas from s p e c i f i c t e c t o n i c environments can be d i s t i n g u i s h e d by t h e i r c h a r a c t e r i s t i c t r a c e and r a r e e a r t h element c o n c e n t r a t i o n s . In g e n e r a l , abundances of incompatible t r a c e elements are lower i n t h o l e i i t i c than in a l k a l i n e s e r i e s rocks from 16 F i g . 2.6. MgO-FeO*-Al 20 3 diagram d i s t i n g u i s h i n g f i e l d s f o r ARC (convergent margin b a s a l t s ) , CB ( c o n t i n e n t a l b a s a l t s ) , 01 (ocean i s l a n d b a s a l t s ) , N-MORB and E-MORB (ocean i s l a n d s which are adjacent to or s t r a d d l i n g a mid-ocean ri d g e (Pearce et a l . , 1977).. 1 7 the same t e c t o n i c environment, but r e l a t i v e interelement enrichments and d e p l e t i o n s are s i m i l a r , p r o v i d i n g the source regions were homogeneous and c r y s t a l f r a c t i o n a t i o n before e r u p t i o n was minimal. In c o n t r a s t , the compatible ( t r a n s i t i o n ) elements Co, Cr, N i , Sc and V g e n e r a l l y have l a r g e abundance ranges even w i t h i n a s i n g l e s u i t e , and t h e r e f o r e are not very d i a g n o s t i c of source environments. They are however, important i n d i c a t o r s of f r a c t i o n a t i o n . F r a c t i o n a t i o n of o l i v i n e and pyroxene c o n t r o l s Ni and Co content whereas, f r a c t i o n a t i o n of pyroxene ± C r - s p i n e l c o n t r o l s Cr abundances (Gast, 1968; Miy a s h i r o and Shido, 1975; H a k l i and Wright, 1970). Sc i s p r e f e r e n t i a l l y i n c o r p o r a t e d i n t o c l i n o p y r o x e n e and low Sc abundances may i n d i c a t e h i g h p r e s s u r e pyroxene f r a c t i o n a t i o n ( B a s l t i c Voicanism Study P r o j e c t , 1981). Abundances of V are p r i m a r i l y c o n t r o l l e d by c l i n o p y r o x e n e f r a c t i o n a t i o n , but under c o n d i t i o n s of high f02 magnetite i s p r e c i p i t a t e d and t h i s r a p i d l y f r a c t i o n a t e s V. 2.2.1 OCEAN FLOOR BASALTS (MORB) N-MORB are de p l e t e d i n L I L (Ba, Rb, K, Sr and U) r e l a t i v e to a l l other v o l c a n i c r o c k s , with Ba and Rb being more de p l e t e d than K and Sr . Thus, K/Rb and Sr/Rb r a t i o s are g e n e r a l l y higher i n b a s a l t s from N-MORB than r a t i o s from WPB but the N-MORB r a t i o s can be s i m i l a r to r a t i o s i n b a s a l t s from convergent margin s e t t i n g s . T h i s i s p o s s i b l e because of the enrichment i n K and Sr i n the 18 l a t t e r b a s a l t s . However, N-MORB g e n e r a l l y have d i s t i n c t l y higher r e l a t i v e abundances of Nb, Ta, Zr and Hf than the convergent margin b a s a l t s ( B a s a l t i c Volcanism Study P r o j e c t , 1981; Sun, 1980). E-MORB have higher abundances of LIL than N-MORB but they are s t i l l d e p l e t e d r e l a t i v e to b a s a l t s from other t e c t o n i c environments (Sun et a l . , 1979; Sun, 1980; Pearce, 1982). N- and E-MORB abundances f o r Th and U g e n e r a l l y range from 0.1 to 0.7 ppm and 0.05 and 0.3 ppm, r e s p e c t i v e l y , the higher abundances o c c u r r i n g i n E-MORB. Th/U r a t i o s range from 2 to 5. Er l a n k and Kable (1976) used Zr/Nb r a t i o s from MORB as a measure of source d e p l e t i o n , a low r a t i o i n d i c a t i n g an undepleted source. Most N-MORB have Zr/Nb r a t i o s between 25 and 110, av e r a g i n g 40 to 50, whereas most E-MORB have Zr/Nb r a t i o s of 15 or l e s s . 2.2.2 OCEAN ISLAND BASALTS (WPB) WPB have a l a r g e range of t r a c e element abundances, n e v e r t h e l e s s a l l t r a c e elements are en r i c h e d r e l a t i v e to N- and E-MORB (Thompson et a l . , 1983; Pearce, 1982). I t i s more d i f f i c u l t to c h e m i c a l l y d i s t i n g u i s h w i t h i n - p l a t e and subduct i o n - r e l a t e d b a s a l t s because abundance ranges completely o v e r l a p . R e l a t i v e to convergent margin b a s a l t s oceanic WPB b a s a l t s are g e n e r a l l y l e s s e n r i c h e d i n Ba, K and Sr, but they are 19 s t r o n g l y enriched i n Nb r e l a t i v e to Rb and K so that Rb/Nb and K/Nb r a t i o s i n WPB are lower. T h o l e i i t i c oceanic WPB have a Th abundance range between 0.3 and 1.2 ppm and U contents between 0.1 and 0.3 ppm. A l k a l i n e s e r i e s b a s a l t s g e n e r a l l y have higher Th abundances (1 to 6 ppm) but U abundances are s i m i l a r (0.2 to 0.3 ppm). Th/U r a t i o s range from 2 to 5. Oceanic WPB c h a r a c t e r i s t i c s are a l s o seen i n most c o n t i n e n t a l WPB, but a few c o n t i n e n t a l t h o l e i i t e s are de p l e t e d i n Nb r e l a t i v e to Rb and K, and are thus s i m i l a r to b a s a l t s from convergent margins (Dupuy and D o s t a l , 1984; Thompson et a l . , 1984; Sun, 1980). Th and U are en r i c h e d i n the c r u s t r e l a t i v e to mantle source regions and consequently i n c o r p o r a t i o n of c r u s t a l m a t e r i a l w i l l i n c r e a s e abundances of both Th and U ( G i l l , 1981). Thus, very h i g h Th and U contents and high Th/U r a t i o s suggest i n t e r a c t i o n with c o n t i n e n t a l c r u s t . 2.2.3 CONVERGENT MARGIN BASALTS (ARC) R e l a t i v e to both N- and E-MORB convergent margin b a s a l t s have higher abundances of LIL (Ba, Rb, K and Sr) but lower abundances of Nb, Ta, Zr and Hf., e s p e c i a l l y Nb and Ta. Lower Nb and Ta r e l a t i v e abundances a l s o d i s t i n g u i s h them from most WPB. Consequently, t h e i r Rb/Nb and K/Nb r a t i o s are much higher than r a t i o s from e i t h e r MORB or WPB ( C u l l e r s and Graf, 1984; Kay, 1980; 20 Pearce, 1982; Kay, 1978 and 1980; White and P a t c h e t t , 1984; Hawkesworth et a l . , 1977; Saunders et a l . , 1980). Th and U abundances i n oceanic convergent margin b a s a l t s c o r r e l a t e p o s i t i v e l y with K 20 content and magmatic s e r i e s , from t h o l e i i t i c through c a l c a l k a l i n e to s h o s h o n i t i c , and range from 0.1 to g r e a t e r than 5 ppm and 0.07 to 1.5 ppm, r e s p e c t i v e l y . Abundances are s l i g h t l y higher i n c o n t i n e n t a l convergent margin b a s a l t s . Th/U r a t i o s range from 2 to 5. E r u p t i o n of convergent margin b a s a l t s through c o n t i n e n t a l c r u s t f u r t h e r i n c r e a s e s abundances of Ba, Rb, K and Sr (Dostal et a l . , 1977; Jackes and White, 1972). 2.3 RARE EARTH ELEMENT GEOCHEMISTRY The group of elements with atomic numbers 57 to 71 a l l have very s i m i l a r chemical and p h y s i c a l p r o p e r t i e s . L i g h t r a r e e a r t h elements (LREE) have atomic numbers 57-63 (La-Eu) and heavy r a r e e a r t h elements (HREE) have atomic numbers 64-71 (Gd-Lu). Y t t r i u m (Y) has an atomic number of 39 but i s c h e m i c a l l y very s i m i l a r to HREE, t h e r e f o r e i t i s o f t e n i n c l u d e d when REE are being d i s c u s s e d . In g e n e r a l REE are c o n s i d e r e d to be very incompatible, but c l i n o p y r o x e n e and garnet can f r a c t i o n a t e HREE from the l i q u i d , so that o n l y LREE are t r u l y incompatible (Langmuir et a l . , 1977). ( L a / Y b ) C H r a t i o s i n d i c a t e the degree of HREE f r a c t i o n a t i o n . 21 U n l i k e most other REE E u + 3 may be reduced to E u + 2 , i n which s t a t e i t can enter p l a g o i c l a s e . Abundance of Eu i s t h e r e f o r e c o n t r o l l e d by p l a g i o c l a s e f r a c t i o n a t i o n ( C u l l e r s and Graf, 1984; G i l l , 1981). N-MORB have low abundances of t o t a l REE r e l a t i v e to c h o n d r i t e s and are dep l e t e d in LREE r e l a t i v e to HREE. ( L a / Y b ) C H and ( L a / C e ) C H r a t i o s are g e n e r a l l y l e s s than 1.0. E-MORB have higher t o t a l REE abundances and i n most samples ( L a / Y b ) C H and ( L a / C e ) ^ H r a t i o s are gr e a t e r than 1.0 (Henderson, 1984). B a s a l t s from convergent margin and w i t h i n - p l a t e s e t t i n g s have higher abundances of REE than N-MORB, and are u s u a l l y e n r i c h e d i n LREE r e l a t i v e to HREE, but i n most cases REE abundances from these two environments are i n d i s t i n g u i s h a b l e . A few oceanic i s l a n d a r c s have negative Ce anomalies and can thus be separated from WPB, but as the Ce anomaly i s a t t r i b u t e d to the subduction of p e l a g i c sediments, convergent margin b a s a l t s which have a l a r g e p r o p o r t i o n of c o n t i n e n t a l d e t r i t u s e n t e r i n g the tr e n c h , i . e . convergent margin b a s a l t s s i t e d on c o n t i n e n t a l c r u s t , do not have these d i s t i n g u i s h i n g Ce anomalies (Hole et a l . , 1984; White and P a t c h e t t , 1984). ( L a / Y b ) C H r a t i o s i n w i t h i n - p l a t e and convergent margin b a s a l t s are g e n e r a l l y g r e a t e r than 1.0, but l e s s than 10.0. A l k a l i n e s e r i e s b a s a l t s have higher abundances of REE and LREE than s u b a l k a l i n e s e r i e s b a s a l t s and g e n e r a l l y have ( L a / Y b ) r H r a t i o s g r e a t e r than 5.0 ( C u l l e r s and Graf, 1984). 22 2.4 TRACE ELEMENT DIAGRAMS 2.4.1 TI-ZR-Y AND TI-ZR-SR Pearce and Cann (1973) p l o t t e d data from 300 u n a l t e r e d b a s a l t i c samples and d i s c r i m i n a t e d four d i f f e r e n t t e c t o n i c environments u s i n g the elements T i , Zr, Y and Sr. A T i - Z r - Y diagram d i s t i n g u i s h e s WPB from c a l k a l k a l i n e b a s a l t s (CAB), low-K t h o l e i i t i c b a s a l t s (LKT) and ocean f l o o r b a s a l t s (OFB). A f t e r e x c l u d i n g WPB samples from the data set the l a t t e r three t e c t o n i c environments are then separated much more e f f e c t i v e l y using a T i - Z r - S r diagram ( F i g s . 2.7 and 2.8). Note that a l t e r e d b a s a l t s cannot be p l o t t e d on the T i - Z r - S r diagram and a T i vs. Zr p l o t must be used i n s t e a d (Pearce and Cann, 1973). Holme (1982) argues t h a t some t h o l e i i t i c WPB cannot be d i s t i n g u i s h e d from OFB and CAB on the T i - Z r - Y diagram suggesting t h i s diagram should be used with c a u t i o n . 2.4.2 V VS. TI/1000 P l o t t i n g V vs. Ti/1000 d i s t i n g u i s h e s s u i t e s of t h o l e i i t i c and a l k a l i n e b a s a l t i c rocks from mid-ocean r i d g e s , ocean i s l a n d s and convergent margins ( F i g . 2.9) (Sh e r v a i s , 1982). C a l c a l k a l i n e b a s a l t s cannot be d i s t i n g u i s h e d because t h e i r T i / V r a t i o s are extrememly v a r i a b l e . T h i s p l o t i s based on the c r y s t a l / l i q u i d p a r t i t i o n c o e f f i c i e n t f o r V which i s a f u n c t i o n of the 23 Ti/100 F i g s . 2.7 and 2.8. T i - Z r - Y (above) and T i - Z r - S r (below) showing f i e l d s f o r WPB ( w i t h i n - p l a t e b a s a l t ) , LKT (low-K t h o l e i i t e ) , OFB (ocean f l o o r b a s a l t ) and CAB ( c a l c a l k a l i n e b a s a l t ) (Pearce and Cann, 1973). 24 f02 of the magma and i t s source, the degree of p a r t i a l m e l t i n g and subsequent f r a c t i o n a l c r y s t a l l i z a t i o n . Arc t h o l e i i t e s have the sma l l e s t T i / V r a t i o s , 10-20, MORB have T i / V r a t i o s between 20-50 and most WPB's, whether t h o l e i i t i c or a l k a l i n e have r a t i o s of 50-100. B a s a l t i c rocks from back-arc basins p l o t i n a f i e l d that o v e r l a p s both the MORB and arc t h o l e i i t e f i e l d s , although MORB l i k e abundances and r a t i o s are more common. 2.4.3 TI/Y VS. NB/Y The T i / Y vs. Nb/Y diagram d i s t i n g u i s h e s WPB from MORB and convergent margin b a s a l t s but the l a t t e r two environments cannot be separated ( F i g . 2.10) (Pearce, 1982). 2.4.4 TI/CR VS. NI I s l a n d arc t h o l e i i t e and t h o l e i i t i c MORB samples with s i l i c a contents between 40 and 56 wt% were p l o t t e d on a T i / C r vs. Ni diagram and an e m p i r i c a l boundary was pla c e d between the two data sets ( F i g . 2.11) (Beccaluva et a l . , 1979). Data from ocean i s l a n d s were excluded. Although t h i s diagram was designed to d i s t i n g u i s h IAT from t h o l e i i t i c MORB, i t can a l s o be used to d i s t i n g u i s h u n f r a c t i o n a t e d WPB samples. These l a t t e r samples g e n e r a l l y l i e w i t h i n the TH MORB f i e l d , whereas most of the more f r a c t i o n a t e d samples l i e w i t h i n the IAT f i e l d . F r a c t i o n a l c r y s t a l l i z a t i o n of o l i v i n e p a r a l l e l s the 25 600 400- 200 Ti/1000 1000 0 1 Nb/Y 1 F i g s . 2.9 and 2.10. V vs. Ti/1000 (above) d i s t i n g u i s h i n g f i e l d s f o r MORB, WPB and t h o l e i i t i c convergent margin b a s a l t s (Shervais, 1982). T i / Y vs. Nb/Y (below) with f i e l d s f o r WPB, MORB and convergent margin (ARC) b a s a l t s (Pearce, 1982). 1 0 0 0 F i g . 2.11. T i / C r v s. Ni diagram with f i e l d s f o r t h o l e i i t i c convergent margin b a s a l t s and t h o l e i i t i c MORB (Beccaluva et 1979). 27 boundary, so that more d i f f e r e n t i a t e d rocks have i n c r e a s e d T i / C r r a t i o s and decreased Ni abundances. 2.5 TRACE AND REE DIAGRAMS 2.5.1 SM/CE VS. SR/CE AND CR VS. CE/SR The Sm/Ce vs. Sr/Ce and Cr vs. Ce/Sr diagrams both separate convergent margin b a s a l t s from MORB ± WPB ( F i g s . 2.12 and 2.13) (Hawkesworth and Powell, 1980; Pearce, 1982). These diagrams are e f f e c t i v e f o r s e p a r a t i n g convergent margin b a s a l t s f o r two reasons: 1. B a s a l t s from a convergent margin s e t t i n g are enr i c h e d i n Sr r e l a t i v e to MORB. 2. Some convergent margin b a s a l t s have negative Ce anomlies. These two f a c t o r s c o n t r i b u t e to higher Sr/Ce or lower Ce/Sr r a t i o s i n convergent margin b a s a l t s r e l a t i v e to MORB or WPB. However, ext e n s i v e p l a g i o c l a s e f r a c t i o n a t i o n can lower the Sr content i n a convergent margin b a s a l t , so that p o i n t s p l o t t i n g c l o s e to the convergent margin- MORB/WPB f i e l d boundary l i n e cannot be d i s t i n g u i s h e d with c o n f i d e n c e . In a d d i t i o n the Cr vs. Ce/Sr diagram i s a l s o a f f e c t e d by o l i v i n e and cli n o p y r o x e n e f r a c t i o n a t i o n . 28 Ce/Sr F i g s . 2.12 and 2.13. Sm/Ce vs. Sr/Ce (above) d i s t i n g u i s h i n g convergent margin rocks from oceanic v o l c a n i c rocks (Hawkesworth and Powell, 1980). Cr vs. Ce/Sr (below) with a f i e l d f o r convergent margin b a s a l t s separated from o v e r l a p p i n g MORB and WPB f i e l d s (Pearce, 1982). 29 2.5.2 CR VS. Y The Cr v s . Y diagram separates convergent margin b a s a l t s from MORB and WPB, but both of these l a t t e r f i e l d s o v e r l a p the high Y edge of the convergent margin f i e l d ( F i g . 2.14) (Pearce, 1982) T h e r e f o r e , t h i s diagram appears to be u s e f u l only as an i n d i c a t o r of o l i v i n e and/or pyroxene f r a c t i o n a t i o n , e s p e c i a l l y i n rocks with Y abundances between 28 and 48 ppm. 2.5.3 ( B A / L A ) c n VS. (LA/SM) c n A p l o t of ( B a / L a ) C H vs. (La/Sm) C H can a l s o be used to d i s t i n g u i s h b a s a l t s from convergent margin and ocean f l o o r environments ( F i g . 2.15) (Kay, 1980). P r i m i t i v e mid-ocean r i d g e b a s a l t s have ( B a / L a ) ^ H r a t i o s l e s s than 1, but as the LREE f r a c t i o n a t i o n ( ( L a / S m ) C H r a t i o ) i n c r e a s e s , the ( B a / L a ) ^ r a t i o a l s o i n c r e a s e s , to s l i g h t l y l e s s than 2. In c o n t r a s t the ( B a / L a ) C H r a t i o s of convergent margin b a s a l t s are g e n e r a l l y higher at low (La/Sm)^ H r a t i o s ( l e s s than 1.5) and as the ( L a / S m ) ^ r a t i o i n c r e a s e s the (Ba/La) (_ H r a t i o decreases. Convergent margin and ocean f l o o r b a s a l t s are w e l l separated when the samples are u n f r a c t i o n a t e d , (samples with low ( L a / S m ) C H r a t i o s ) , but as f r a c t i o n a t i o n i n c r e a s e s (higher (La/Sm) C H r a t i o s ) data from the two environments o v e r l a p ( B a s a l t i c Voicanism Study P r o j e c t , 1981). Back arc b a s i n b a s a l t s were a l s o p l o t t e d on t h i s diagram but c o u l d not be d i s t i n g u i s h e d from convergent 30 100 F i g . 2.14. Cr vs. Y with convergent margin, MORB and WPB f i e l d s (Pearce, 1982). 31 margin and/or ocean f l o o r b a s a l t s . 2.5.4 LA VS. BA LA VS. TH LA VS. NB P l o t s of La vs. Ba, Th, or Nb separate orogenic a n d e s i t e s from N-MORB or from E-MORB, t h i s l a t t e r group i n c l u d i n g WPB as w e l l ( G i l l , 1981). On La vs. Ba, N-MORB have Ba/La r a t i o s between 4 and 11, E-MORB have r a t i o s between 11 and 15 and Ba/La r a t i o s i n orogenic a n d e s i t e s range from 15 to 80 ( F i g . 2.16) However, when t h i s p l o t i s compared with the ( B a / L a ) C H vs. (La/Sm) C H p l o t ( F i g u r e 2.15) i t appears G i l l ' s orogenic f i e l d i s too r i g i d l y c o n s t r a i n e d , e s p e c i a l l y f o r the more f r a c t i o n a t e d samples, and there i s probably a great d e a l of o v e r l a p between the orogenic and E-MORB f i e l d s . The La vs. Th diagram i s very s i m i l a r to the La vs. Ba p l o t : N-MORB have La/Th r a t i o s between 25 and 15, E-MORB r a t i o s l i e between 15 and 7 and orogenic a n d e s i t e s p r i m a r i l y p l o t between La/Th r a t i o s of 7 and 2 ( F i g . 2.17). At Th contents l e s s than 3 ppm the E-MORB and orogenic f i e l d s o v e r l a p . On La vs. Nb orogenic a n d e s i t e s have La/Nb r a t i o s between 2 and 5, N-MORB have r a t i o s between 2 and 1 and La/Nb r a t i o s i n E-MORB are l e s s than 1 ( F i g 2.18). Histograms of La/Nb r a t i o s i n unambiguous examples of convergent margin b a s a l t s , oceanic WPB, and c o n t i n e n t a l WPB p l a c e d convergent margin b a s a l t s between r a t i o s of 1 32 F i g s . 2.15 and 2.16. ( B a / L a ) ^ vs. (La/Sm) C H diagram (above) d i s t i n g u i s h i n g b a s a l t s from convergent margins and oceanic areas (ocean r i d g e and i n t r a p l a t e ) (Kay, 1980). La vs. Ba (below) with f i e l d s f o r N-MORB, E-MORB pl u s WPB and orogenic a n d e s i t e s ( G i l l , 1.981). 33 F i g s . 2.17 and 2.18. La vs. Th (above) and La vs. Nb (below) with f i e l d s f o r N-MORB, E-MORB and orogenic a n d e s i t e s ( G i l l , 1981). Ocean i s l a n d s and c o n t i n e n t a l b a s a l t s t y p i c a l l y l i e i n the E-MORB f i e l d . 34 and 5 and c o n t i n e n t a l t h o l e i i t i c WPB between 0.5 and 2. Oceanic WPB plus c o n t i n e n t a l a l k a l i n e WPB had r a t i o s l e s s than 1.3, but the m a j o r i t y of r a t i o s were l e s s than 1.0 (Thompson et a l . , 1983). 2.5.5 K 20/YB VS. TA/YB Pearce (1982) p l o t t e d K 20/Yb vs. Ta/Yb to d i s t i n g u i s h convergent margin b a s a l t s from MORB and WPB ( F i g . 2.19). The convergent margin f i e l d i s f u r t h e r d i v i d e d i n t o areas f o r t h o l e i i t i c , c a l c a l k a l i n e and s h o s h o n i t i c b a s a l t s . MORB and WPB f i e l d s are s l i g h t l y o v e r l a p p i n g . 2.5.6 TH/YB VS. TA/YB The Th/Yb vs. Ta/Yb diagram i s s i m i l a r to the K 20/Yb vs. Ta/Yb diagram but because Th i s much l e s s mobile i n aqueous f l u i d s t h i s diagram i s u s e f u l when a l t e r e d rocks are being analyzed ( F i g . 2.20) (Pearce, 1982) . I t has a l s o been suggested that t h i s diagram can d i s t i n g u i s h WPB which have been contaminated with c o n t i n e n t a l c r u s t because consequent enrichment i n Th d i s p l a c e s WPB i n t o the v o l c a n i c arc f i e l d (Pearce, 1983) . 2.5.7 TH VS. TA LA VS. TA TH VS. HF Wood et a l . (1979) p l o t t e d three b i a x i a l diagrams using incompatible elements Th, Ta, Hf and La to 35 100 F i g s . 2 .19 and 2.20. K ?0/Yb v s . Ta/Yb (above) and Th/Tb vs. Ta/Yb (below) d i s t i n g u i s h i n g convergent margin b a s a l t s (ARC) from s l i g h t l y o v e r l a p p i n g MORB and WPB f i e l d s (Pearce, 1982). The convergent margin f i e l d i s subdivided i n t o TH ( t h o l e i i t i c ) , CA ( c a l c a l k a l i n e ) and SHO ( s h o s h o n i t i c ) areas. 36 d i s t i n g u i s h b a s a l t s e r i e s erupted i n d i f f e r e n t t e c t o n i c environments. P l o t t i n g Th vs. Ta Japanese t h o l e i i t i c and c a l c a l k a l i n e l a v a s were separated from WPB and N- and E-MORB's at a Th/Ta r a t i o equal to 2 ( F i g . 2.21). Se p a r a t i o n of N-MORB from the above grouping i s aide d by us i n g a p l o t of La vs 0. Ta ( F i g 2.22). In t h i s p l o t the Japanese convergent margin samples have La/Ta r a t i o s g r e a t e r than 30, and WPB and E-MORB have La/Ta r a t i o s l e s s than 14. N-MORB data p o i n t s p l o t with La/Ta r a t i o s between 14 and 30. The Th vs. Hf p l o t i s not used f o r d i s c r i m i n a t i n g Japanese t h o l e i i t i c and c a l c a l k a l i n e samples but but i t e f f e c t i v e l y separates WPB from N-MORB from E-MORB ( F i g . 2.23). WPB have Hf/Th r a t i o s l e s s than 2.5, N-MORB have Hf/Th r a t i o s g r e a t e r than 12.5 and E-MORB samples p l o t i n the area between these other two (12.5 > Hf/Th > 2.5) 2.5.8 TH-HF/3-TA Based on in f o r m a t i o n from the three p l o t s j u s t d i s c u s s e d Wood et a l . (1979) and Wood (1980) proposed a t r i a n g u l a r d i s c r i m i n a n t diagram with Th-Hf/3-Ta at the ap i c e s ( F i g . 2.24). T h i s diagram i s not r e s t r i c t e d to b a s a l t s but can be used f o r more s i l i c e o u s rocks as w e l l , and t h e r e f o r e i n the remainder of t h i s study the three p r e v i o u s diagrams w i l l not be p l o t t e d . F i e l d s d i s t i n g u i s h e d a re: 37 F i g s . 2.21 and 2.22. Th vs. Ta (above) and La vs. Ta (below) with f i e l d s f o r Japanese t h o l e i i t i c and c a l c a l k a l i n e l a v a s (convergent margin), WPB plus E-MORB and N-MORB (Wood et a l . , 1979). 38 39 Hf/3 F i g . 2.24. Th-Hf/3-Ta with f i e l d s f o r N-MORB, E-MORB plus t h o l e i i t i c WPB, a l k a l i n e WPB and convergent margin (Wood, 1980). The convergent margin f i e l d i s f u r t h e r d i v i d e d i n t o p r i m i t i v e a r c t h o l e i i t e s (TH) and c a l c a l k a l i n e l a v a s (CAB). 40 A. N-MORB B. E-MORB pl u s t h o l e i i t i c WPB C. A l k a l i n e WPB D. Convergent margins In a d d i t i o n f i e l d D i s f u r t h e r d i v i d e d i n t o a c a l c a l k a l i n e f i e l d and a p r i m i t i v e arc t h o l e i i t e f i e l d by an Hf/Th r a t i o equal to 3. P o s s i b l e o v e r l a p s e x i s t between f i e l d A and B and between f i e l d s B and C . Th e r e f o r e , any analyzed v o l c a n i c s which p l o t c l o s e to the boundary l i n e s between these f i e l d s cannot be c l a s s i f i e d with c e r t a i n t y . To d i s c r i m i n a t e t h o l e i i t i c WPB from E-MORB Wood (1980) suggests r e - p l o t t i n g data from f i e l d B on a Zr-Ti-Y d i s c r i m i n a n t diagram (Pearce and Cann, 1973). 2.6 BULK EARTH NORMALIZED TRACE AND REE DIAGRAMS (BEND) Ch o n d r i t e normalized REE diagrams allow comparisons to be made between numerous samples which have d i v e r s e elemental data, and give i n f o r m a t i o n about magma sources and p e t r o g e n e s i s . To in c r e a s e t h i s i n f o r m a t i o n Sun (1980) added s e l e c t e d bulk e a r t h normalized t r a c e element data. The order of the elements i s based on t h e i r degree of m o b i l i t y i n an aqueous f l u i d as w e l l as t h e i r degree of i n c o m p a t i b i l i t y at a small degree of p a r t i a l m e l t i n g (Sun, 1980; Pearce, 1983; Thompson et a l . , 1983). F o l l o w i n g Thompson et a l . (1983) the data were normalized to bulk e a r t h abundances, c h o n d r i t i c except f o r K 41 and Rb (see Table I f o r n o r m a l i z a t i o n f a c t o r s ) . The bulk e a r t h normalized data were then r e c a l c u l a t e d to make (Yb) VT= 1 0. 0. T h i s l a t t e r n o r m a l i z a t i o n decreases the e f f e c t s of f r a c t i o n a l c r y s t a l l i z a t i o n of e s s e n t i a l l y Yb-free phases and makes comparisons of p a t t e r n s more convenient by spreading them apart without changing t h e i r shape (Thompson et a l . , 1983). For the purposes of d i s c u s s i o n these diagrams w i l l be c a l l e d BEN diagrams or BEND. Although MORB, WPB and convergent margin b a s a l t s have c h a r a c t e r i s t i c p a t t e r n shapes on BEN diagrams, minor i r r e g u l a r i t i e s do occur as a r e s u l t of v a r i a b l e p a r t i a l m e l t i n g and f r a c t i o n a l c r y s t a l l i z a t i o n . 2.6.1 MORB Ordering from most to l e a s t incompatible elements causes the BEND p a t t e r n f o r N-MORB to slope p o s i t i v e l y from Ba to Y with a shallow concave-up trough from Sm to T i , and a f l a t to negative slope from Y to Lu ( F i g . 2.25) (Sun, 1980). E-MORB p a t t e r n s are r e l a t i v e l y e n r i c h e d i n LIL. They slope p o s i t i v e l y from Ba to Nb, slope n e g a t i v e l y from Nb to Zr and are s i m i l a r to N-MORB pa t t e r n s from Zr to Lu ( F i g . 2.25). 2.6.2 WPB BEND p a t t e r n s from oceanic WPB and c o n t i n e n t a l a l k a l i n e WPB are e s s e n t i a l l y i n d i s t i n g u i s h a b l e , with i r r e g u l a r convex-up shapes which 'peak' at Nb ( F i g . 42 TABLE I NORMALIZATION VALUES FOR BEND Ba 2 6.9 Rb 1 0.35 T h 2 0.042 U 1 0.013 K 1 120.0 Nb 1 0.35 L a 2 0.328 Ce 2 0.865 S r 2 11.8 Nd 2 0.63 Sm2 0.203 Z r 2 6.84 Hf 2 0.2 T i 1 620.0 E u 3 0.0735 Tb 2 0.052 Y 1 2.0 Yb 2 0.22 L u 3 0.0322 1 2 3 Sun (1980) Thompson et a l . ( l 9 8 3 ) Henderson (1984) 43 2.26) . However, BEND p a t t e r n s from c o n t i n e n t a l t h o l e i i t e s are h i g h l y i r r e g u l a r ( F i g . 2.26). Some are s i m i l a r to p a t t e r n s from oceanic WPB but others have w e l l d e f i n e d 'troughs' at Nb s i m i l a r to convergent margin b a s a l t s (see below) (Norry and F i t t o n , 1983; Weaver and Tarney, 1983; Thompson et a l . , 1983). 2.6.3 CONVERGENT MARGIN BASALTS In c o n t r a s t to MORB and WPB most BEND p a t t e r n s from t h o l e i i t i c and c a l c a l k a l i n e convergent margin b a s a l t s have 'peaks' at Ba, K, Sr ± Rb, a 'trough' at Nb, and are concave-up from Sm to Eu ( F i g . 2.27). Six out of seven convergent margin b a s a l t s s t u d i e d by White and Pat c h e t t (1984) had 'troughs' at Ce, and mixing models fo r p a r e n t a l oceanic i s l a n d arc l a v a s c o n s t r u c t e d by Hole et a l . (1984) a l s o produced negative Ce anomalies. BEND p a t t e r n s from a l k a l i n e s e r i e s convergent margin b a s a l t s g r o s s l y resemble p a t t e r n s from some WPB ( F i g . 2.27) . 44 1000 -i co ui < > Q UJ N 100- ,V| -MORB >T7 10- 7—V x—x— -X" / X N - M O R B MORB X — i 1 — i — i — i 1 I 1 I i 1—r—| i l l 1 1 1 Ba RbTh U K NbLaCe SrNdSmZr Hf Ti Eu Tb Y Yb Lu F i g . 2.25. BEND p a t t e r n s f o r N-MORB (X) and E-MORB ( V ) (Sun, 1980; Sun e t a l . , 1979; White and Bryan, 1977). 45 1000 n CO UJ < > Q LU N O 100- 10 AALK. CONT. \£ALK. OCEANIC TH. CONT. WPB — I — I — I — I — I — I — I I I I I I I I—I I I — I I Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F i g . 2.26. BEND p a t t e r n s f o r a l k a l i n e oceanic WPB ( X ) , a l k a l i n e c o n t i n e n t a l WPB ( A ) and t h o l e i i t i c c o n t i n e n t a l WPB (•) (Thompson et a l . , 1983 and 1984). 46 1000 -i co UJ =? 100 H Q HI N < cr o .ALKALINE 10- C A L C ALKALINE 1 CONVERGENT MARGIN BASALT T T r i — i i I i i i—i i i i—r— Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F i g . 2.27. BEND p a t t e r n s f o r c a l c a l k a l i n e convergent margin b a s a l t (+ ) ( B a s a l t i c Voicanism Study P r o j e c t , 1981) and a l k a l i n e convergent margin b a s a l t ( A ) (Shimizu and A r c u l u s , 1975). 3. GARIBALDI AND PEMBERTON BELTS T h i r t e e n samples from two magmatic b e l t s were used to study the convergent margin v o l c a n i c rocks i n B r i t i s h Columbia. E i g h t of the samples are from the Quaternary G a r i b a l d i V o l c a n i c B e l t east of 125°, two are from Quaternary Mt. S i l v e r t h r o n e , and three are from the Miocene Pemberton V o l c a n i c B e l t ( F i g . 3.1). For the purposes of t h i s d i s c u s s i o n the two samples from Mt. S i l v e r t h r o n e w i l l be i n c l u d e d with the samples from the G a r i b a l d i V o l c a n i c B e l t as these two v o l c a n i c areas are c o e v a l . At the present time they r e s u l t from the subduction of d i f f e r e n t p l a t e s , but p r i o r t o 3 m.y. ago these p l a t e s were j o i n e d as one. T h e r e f o r e any c o n t r i b u t i o n to the erupted magma from the subducting s l a b should be s i m i l a r , r e s u l t i n g i n comparable geochemical p a t t e r n s . A v a i l a b l e K-Ar dates from G a r i b a l d i B e l t b a s a l t s and a n d e s i t e s range from 0.09 Ma to 0.97 Ma (Table I I ) . The three samples from the C o g u i h a l l a area had not been dated but Rb-Sr isochron and K-Ar dates from other C o q u i h a l l a samples give an age of approximately 22 Ma (Berman, 1979). 3.1 MAJOR ELEMENT CHEMISTRY Abundances of T i 0 2 , A l 2 0 3 and P 2 0 5 i n c a l c a l k a l i n e samples COQ251, COQ632, C0Q61, CAYLEY and SILVERA resemble abundances i n the average c a l c a l k a l i n e b a s a l t of Jakes and White (1972) or G i l l (1981), but K 20 abundances are s l i g h t l y higher (Table I I ) . Mg' numbers range from 38 to 52. 47 48 Fig. 3.1. Sample l o c a t i o n map f o r the Converqent Margin S u i t e . A l l subsequent diagrams i n t h i s chapter use i d e n t i c a l symbols. 49 G a r i b a l d i B e l t b a s a l t s ELAHO, GARIBALD and CHEAK are e n r i c h e d i n T i 0 2 and d e p l e t e d i n A l 2 0 3 and K 20 r e l a t i v e to an average arc b a s a l t ( B a s a l t i c Volcanism Study P r o j e c t , 1981) or the C o q u i h a l l a b a s a l t s (Table II) but P 2 0 5 abundances are s i m i l a r . Mg' numbers l i e between 54 and 59. Sample MEAGER has a T i 0 2 content of 1.55 wt.%, s i m i l a r to T i 0 2 abundance i n the other three G a r i b a l d i B e l t b a s a l t samples, but i t s abundances of A l 2 0 3 , K 20 and P 2 0 5 are s i m i l a r to abundances i n the a l k a l i n e samples (see below). A l k a l i n e samples SALAL1, SALAL2, SALAL3 and SILVERH have abundances of T i 0 2 , A 1 2 0 3 and P 2 0 5 which are s i m i l a r to abundances i n an average a l k a l i n e WPB but K 20 abundances are m a r g i n a l l y higher (Thompson et a l . , 1984; B a s a l t i c Volcanism Study P r o j e c t , 1981). Mg' numbers range from 41 to 61. 3.2 DISCRIMINATION DIAGRAMS 3.2.1 MAJOR ELEMENT CLASSIFICATIONS On the t o t a l a l k a l i s v s . s i l i c a diagram three of the samples are c l e a r l y a l k a l i n e (SALAL1, SALAL3 and SILVERH), f i v e are c l e a r l y s u b a l k a l i n e (CAYLEY, SILVERA, COQ251, COQ632, and C0Q61) and the remaining f i v e s i t a s t r i d e MacDonald's (1968) s u b a l k a l i n e and a l k a l i n e f i e l d boundary ( F i g . 3.2). On Ol'-Ne'-Qz' (not shown) the t h r e e a l k a l i n e samples are i n agreement with the a l k a l i s v s . s i l i c a c l a s s i f i c a t i o n , and a l l remaining samples are c l a s s i f i e d 50 as s u b a l k a l i n e . However, SALAL2 w i l l be p l o t t e d with the a l k a l i n e samples r a t h e r than the s u b a l k a l i n e ones because o v e r a l l i t has a l k a l i n e t r a c e element chemical c h a r a c t e r i s t i c s (documented i n a l a t e r s e c t i o n ) . S u b a l k a l i n e samples p l o t t e d on AFM and FeO*/MgO vs. S i 0 2 diagrams s t r a d d l e the boundary l i n e between t h o l e i i t i c and c a l c a l k a l i n e f i e l d s ( F i g s . 3.3 and 3.4), but the lack of a pronounced iron-enrichment t r e n d d u r i n g d i f f e r e n t i a t i o n c l a s s i f i e s them as c a l c a l k a l i n e . On A l 2 0 3 vs. normative p l a g i o c l a s e composition (not shown) a l l samples were c l a s s i f i e d as c a l c a l k a l i n e , except sample MEAGER which was b a r e l y t h o l e i i t i c . On T i 0 2 - K 2 0 - P 2 0 5 a l l s u b a l k a l i n e b a s a l t i c samples l i e w i t h i n the non-oceanic f i e l d ( F i g . 3.5). On MnO-Ti0 2-P 20 5 COQ251 and COQ632 l i e w i t h i n the CAB f i e l d , and COQ61 and SALAL2 l i e w i t h i n the IAT f i e l d ( F i g . 3.6). The remainder l i e j u s t w i t h i n the the OIA f i e l d , along the boundary l i n e s e p a r a t i n g OIA from IAT. Su b a l k a l i n e b a s a l t i c samples p l o t t e d on an MgO-FeO*-Al 20 3 diagram l i e i n two separate groups ( F i g . 3.7). COQ251, COQ632 and COQ61 l i e w i t h i n the orogenic f i e l d and ELAHO, MEAGER, GARIBALD and CHEAK p l o t around the t r i p l e p o i n t between ocean i s l a n d , c o n t i n e n t a l and ocean r i d g e / f l o o r f i e l d s . 7- 6- O 5 H CM + A - \ O CM ru «3 —7 J 2 - 1 - 1 I I I L A L K . F i g . 3.2. T o t a l a l k a l i s vs. s i l i c a . S u b a l k a l i n e / a l k a l i n e boundary fom MacDonald (1968). 51 F i g . 3.3. AFM diagram. T h o l e i i t i c / c a l c a l k a l i n e boundary from I r v i n e and Baragar (1971). Na 20 + K 20 ELAHO • G A R I B A L D X CHEAK • MEAGER V CAYLEY B SALAL1 • SALAL2 A SALAL3 + S I L V E R A S S I L V E R H 0 COQ251 • COQ632 • C0Q61 0 S i O , F i g . 3.4. FeO*/MgO vs. S i 0 2 . T h o l e i i t i c / c a l c a l k a l i n e boundary from M i y a s h i r o (1974). F i g . 3.5. T i 0 2 - K 2 0 - P 2 O s . 53 3.2.2 TRACE ELEMENT CLASSIFICATIONS On T i - Z r - Y a l l G a r i b a l d i B e l t samples, except SILVERH, l i e w i t h i n the WPB f i e l d along the boundary l i n e s e p a r a t i n g WPB from LKT-OFB-CAB ( F i g . 3.8). Samples COQ251, COQ632 and COQ61 l i e w i t h i n the CAB f i e l d on T i - Z r - S r , and SILVERH p l o t s j u s t w i t h i n the LKT f i e l d ( F i g . 3.9) Although c a l c a l k a l i n e b a s a l t i c samples cannot be d i s t i n g u i s h e d on V vs. Ti/1000 a l l samples were p l o t t e d and two groups are c l e a r l y seen ( F i g . 3.10). Samples from the C o q u i h a l l a Complex l i e w i t h i n the MORB f i e l d , toward the convergent margin f i e l d boundary, whereas the ei g h t remaining samples l i e w i t h i n or c l o s e to the WPB f i e l d . COQ251, COQ632 and COQ61 l i e w i t h i n or adjacent to the o v e r l a p p i n g convergent margin-MORB f i e l d s on Ti / Y vs. Nb/Y ( F i g . 3.11). The e i g h t remaining b a s a l t i c samples l i e w i t h i n the WPB f i e l d . C o q u i h a l l a samples COQ251, COQ632 and COQ61 l i e w i t h i n the IAT f i e l d on T i / C r vs. Ni ( F i g . 3.12). The remaining b a s a l t i c samples l i e w i t h i n the TH MORB f i e l d . 3.2.3 TRACE AND REE CLASSIFICATIONS On Sm/Ce vs. Sr/Ce b a s a l t i c samples l i e w i t h i n the convergent margin f i e l d ( F i g . 3.13). Most b a s a l t i c samples l i e w i t h i n or c l o s e to the convergent margin f i e l d on Cr vs. Ce/Sr, but SALAL1  55 1 000 -J 1 00 0-0 1 — , r 0.1 1 Nb/Y 1 0 ELAHO • GARIBALD X CHEAK • MEAGER V CAYLEY B SALAL1 • SALAL2 A SALAL3 + SILVERA H SILVERH 0 COQ251 • COQ632 • C0Q61 a 1 ooo -A 1 oo -\ 10 H 1 o Ni 1 oo 1000 F i g s . 3.11 and 3.12. Ti/Y vs. Nb/Y (above) and T i / C r vs. Ni (below). 56 p l o t s i n the o v e r l a p p i n g MORB-WPB f i e l d s ( F i g . 3.14). On Cr vs. Y a l l eleven b a s a l t i c samples l i e w i t h i n the convergent margin f i e l d , or o v e r l a p p i n g WPB-convergent margin f i e l d s d e s p i t e a wide range of Cr abundances ( F i g . 3.15). Both b a s a l t s and a n d e s i t e s were p l o t t e d on La vs. Ba, La vs. Th and La vs. Nb diagrams. On La vs. Ba most samples l i e w i t h i n or c l o s e to the orogenic a n d e s i t e f i e l d , with Ba/La r a t i o s g r e a t e r than 15 ( F i g . 3.16). SALAL1 and GARIBALD l i e w i t h i n the f i e l d f o r E-MORB. However, on ( B a / L a ) ^ v s . (La/Sm) C H only b a s a l t i c samples COQ251, COQ632 and COQ61 are c l e a r l y c l a s s i f i e d as convergent margin ( F i g . 3.17). The ei g h t remaining b a s a l t i c samples l i e w i t h i n the oceanic f i e l d . Sample MEAGER and the four a l k a l i n e samples have the h i g h e s t ( L a / S m ) ^ r a t i o s . On La vs. Th samples COQ251, COQ632 and COQ61 l i e w i t h i n the orogenic a n d e s i t e f i e l d with La/Th r a t i o s l e s s than 3.3 ( F i g . 3.18). Samples MEAGER and SILVERH l i e w i t h i n the N-MORB f i e l d , and the e i g h t remaining samples l i e w i t h i n the f i e l d f o r E-MORB. Of these e i g h t , three have Th contents l e s s than 1.5 ppm (ELAHO, GARIBALD and CHEAK) and l i e w i t h i n the area which o v e r l a p s with the orogenic a n d e s i t e f i e l d . COQ251, COQ632, COQ61, CAYLEY and MEAGER l i e w i t h i n the orogenic a n d e s i t e f i e l d on La vs. Nb, with La/Nb r a t i o s between 2 and 5 ( F i g . 3.19). Samples SILVERH and 57 1 H CD o E CO 0.1 H ELAHO • GARIBALD CHEAK • MEAGER V CAYLEY B SALAL1 T SALAL2 A SALAL3 + SILVERA H SILVERH 0 COQ251 O COQ632 • C0Q61 a -\ r 1 0 1 0 0 Sr/Ce 1 0 0 0 1 0 0 0 o 1 'A '\ ' c 'A *\ X *.\MORB:\ 1 ''\ 1 | \ W P B \ A R C * | • 1 " 1 | 1 1 1 ! f 0 . 0 1 0.1 Ce/Sr F i g s . 3.13 and 3.14. Sm/Ce vs. Sr/Ce (above) and Cr vs. Ce/Sr (below). ELAHO • GARIBALD X CHEAK • MEAGER V CAYLEY B SALAL1 • SALAL2 A SALAL3 + SILVERA H SILVERH 0 COQ251 O COQ632 • COQ61 0 100 F i g . 3.15. Cr vs. Y. 59 F i g s . 3.16 and 3.17. La vs. Ba (above) and (Ba/La) vs. (La/Sm) (below). 60 F i g s . 3.18 and 3.19. La vs. Th (above) and La vs. Nb (below). 61 SILVERA c l e a r l y l i e w i t h i n the N-MORB f i e l d (La/Nb r a t i o s between 1 and 2) and the remainder l i e a s t r i d e the N-MORB/E-MORB f i e l d boundary with La/Nb r a t i o s approximately equal to 1. Most b a s a l t data p l o t t e d on K 20/Yb v s . Ta*/Yb l i e w i t h i n the space between the WPB and convergent margin f i e l d s ( F i g . 3.20). E x c e p t i o n s are COQ251, COQ632 and COQ61 which l i e w i t h i n the convergent margin f i e l d . Samples SALAL1, SALAL2 and SALAL3 have the hig h e s t Ta*/Yb r a t i o s . On Th/Yb vs. Ta*/Yb samples COQ251, COQ632 and COQ61 l i e w i t h i n the convergent margin f i e l d ( F i g . 3.21). A l l remaining b a s a l t i c samples l i e w i t h i n the ov e r l a p p i n g MORB-WPB f i e l d s . To p l o t Th-Hf/3-Ta* abundances of Hf i n samples COQ251, COQ632 and COQ61 were estimated u s i n g the r a t i o Zr/Hf = 39. According to G i l l (1982) t h i s r a t i o remains q u i t e constant i n b a s a l t s from a l l t e c t o n i c environments. On t h i s diagram samples COQ251, COQ632, COQ61 and CAYLEY l i e w i t h i n the convergent margin f i e l d ( F i g . 3.22). A l k a l i n e samples SALAL1, SALAL2, SALAL3 and SILVERH l i e w i t h i n the a l k a l i n e WPB f i e l d and the remaining four b a s a l t samples, p l u s SILVERA, l i e w i t h i n the E - M O R B - t h o l e i i t i c WPB f i e l d . 62 1 0 0 10 J > O CM 1 H o. 1 0 . 0 1 — I f - 0.1 1 TaVYb F i g . 3.20. K 20/Yb vs, Ta*/Yb. ELAHO • GARIBALD X CHEAK • MEAGER V CAYLEY H SALAL1 • SALAL2 A SALAL3 + SILVERA H SILVERH 0 COQ251 • COQ632 • C0Q61 a 1 0 1 0 F i g . 3.21. Th/Yb vs, Ta*/Yb. J2 > Hf/3 0 .0 1 0 0 1 0.1 1 0 Ta*/Yb F i g . 3.22. Th-Hf/3-Ta*. 0.2 0.4 0.6 0.8 Th 63 3.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) BEND p a t t e r n s on F i g . 3.23 are from COQ251, COQ632 and COQ61. Pa t t e r n s are e n r i c h e d i n Ba, Rb, Th and K r e l a t i v e to LREE, have a pronounced 'trough' at Nb and a l e s s d i s t i n c t 'trough' at T i . Eu anomalies are not e v i d e n t . From Eu to Lu the p a t t e r n i s f a i r l y f l a t . F i g . 3.24 shows BEND p a t t e r n s f o r s u b a l k a l i n e G a r i b a l d i B e l t b a s a l t s , ELAHO, GARIBALD, CHEAK and MEAGER. The f i r s t three samples have n e a r l y i d e n t i c a l p a t t e r n s and the l a t t e r sample's p a t t e r n i s g r o s s l y s i m i l a r . A l l p a t t e r n s have an i r r e g u l a r , s l i g h t l y convex-up shape with 'peaks' at Ba, K and Sr and 'troughs' at Nb and Hf. In a d d i t i o n , a l l p a t t e r n s have a small 'peak' at Eu so that they have a concave-up 'dip' from Sm to Eu. BEND p a t t e r n s on F i g . 3.25 are from G a r i b a l d i B e l t h a w a i i t e s , SALAL1, SALAL2, SALAL3 and SILVERH. From Ba to Rb the p a t t e r n s are f l a t , or have s l i g h t l y negative s l o p e s , but from Rb to Lu they are i r r e g u l a r l y convex-up, with a 'trough' at Hf, so that they have a concave-up d i p from Sm to Eu. In a d d i t i o n , SALAL2 has a 'peak' at Sr and SILVERH has a 'trough' at Th. A l l p a t t e r n s suggest a p o s i t i v e Eu anomaly, although Tb was not analyzed. BEND p a t t e r n s on F i g . 3.26 are from a n d e s i t i c samples CAYLEY and SILVERA. Both p a t t e r n s are e n r i c h e d in LIL r e l a t i v e to HREE, with 'peaks' at Sr, K, Eu ± Rb 6 4 1000 -i F i g . 3 2 3 . BEN d i a g r a m f o r s a m p l e s C 0 0 2 5 1 , C 0 0 6 3 2 and C 0 0 6 1 F i g . 3 . 2 4 . BEN d i a g r a m f o r s a m p l e s ELAHO. GARIBALD, CHEAK and MEAGER 66 F i g . 3 . 2 5 . BEN d i a g r a m f o r s a m p l e s S A L A L 1 , SALAL2, SALAL3 and SILVERH. 67 1000 n F i g . 3 . 2 6 . BEN d i a g r a m f o r s a m p l e s CAYLEY and SILVERA 68 and 'troughs' at Nb and T i . The magnitude of 'peaks' and 'troughs' are much gr e a t e r i n the p a t t e r n f o r CAYLEY. None of the p a t t e r n s d i s p l a y negative Ce anomalies. 3.3 TRACE ELEMENT CHEMISTRY Samples from the C o q u i h a l l a V o l c a n i c Complex and a n d e s i t i c samples CAYLEY and SILVERA from the G a r i b a l d i B e l t have abundances of t r a c e and REE and BEND p a t t e r n s s i m i l a r to an average c a l c a l k a l i n e convergent margin b a s a l t erupted through c o n t i n e n t a l c r u s t (Thompson et a l . , 1984; Wilson and Davidson, 1984; Pearce, 1983). La abundances range from 45 to 84 times c h o n d r i t i c , Yb abundances l i e between 6 and 13 times c h o n d r i t i c and ( L a / Y b ) ^ r a t i o s range from approximately 4 to 14 (Yb abundances estimated f o r C o q u i h a l l a samples). La/Nb r a t i o s are g r e a t e r than 1.3 and Rb/Nb r a t i o s range from 1.6 to 9, c h a r a c t e r i s t i c of convergent margins. R e l a t i v e to an 'average' convergent margin b a s a l t b a s a l t i c samples ELAHO, GARIBALD and CHEAK are s l i g h t l y t o very d e p l e t e d i n L I L and are e n r i c h e d i n Nb ( B a s a l t i c Voicanism Study P r o j e c t , 1981; Thompson et a l . , 1984). These three samples have BEND p a t t e r n s s i m i l a r to p a t t e r n s from WPB. La abundances range from 31 to 37 times c h o n d r i t i c , Yb abundances range from 7 to 8 times c h o n d r i t i c and ( L a / Y b ) ^ H r a t i o s l i e between 4.1 and 4.6. La/Nb r a t i o s range from 0.94 to 1.08 and Rb/Nb r a t i o s range from 0.55 to 0.75, more t y p i c a l of WPB than b a s a l t s from convergent margins. Cascade 69 b a s a l t i c l a v a s a l s o have a t y p i c a l l y low Rb/Nb r a t i o s ( 0.6) and are i n f e r r e d to have o r i g i n a t e d w i t h i n the the mantle wedge ( i . e . w i t h i n - p l a t e ) (Leeman and Smith, i n pr e p a r a t i o n ) . B a s a l t i c sample MEAGER i s s l i g h t l y to g r e a t l y e n r i c h e d in a l l t r a c e and REE r e l a t i v e to the other s u b a l k a l i n e G a r i b a l d i B e l t b a s a l t s . I t has an Rb/Nb r a t i o of 0.66, s i m i l a r to Rb/Nb from WPB, but i t s La/Nb r a t i o of 2.08 i s t y p i c a l of a convergent margin b a s a l t . A l k a l i n e samples SALAL1, SALAL2, SALAL3 and SILVERH have t r a c e and REE abundances and BEND p a t t e r n s g r o s s l y s i m i l a r to an average a l k a l i n e WPB but Ba abundances are s l i g h t l y h i g h e r (Table I I ) . La abundances range from 65 to 84 times c h o n d r i t i c . Yb abundances l i e between 8 and 12 times c h o n d r i t i c and ( L a / Y b ) C H r a t i o s range from 6.6 to 8.6. La/Nb r a t i o s range from 0.9 to 1.2 and Rb/Nb r a t i o s l i e between 0.55 and 0.68. 3.3.1 TH AND U Th abundances i n G a r i b a l d i B e l t samples l i e between 1.0 and 2.5 ppm and U abundances l i e between 0.3 and 1.0 ppm (Table I I ) . Th/U r a t i o s are h i g h l y v a r i a b l e , range from 1.9 to 3.5 and average 2.6. Samples from the C o q u i h a l l a V o l c a n i c Complex have Th abundances g r e a t e r than 4 ppm. These samples were not analyzed f o r U. 70 3.3.2 TRANSITION ELEMENTS Cr and Ni abundances and v a r i a t i o n s i n Mg' numbers are presumably c o n t r o l l e d by f r a c t i o n a t i o n of o l i v i n e ± c l i n o p y r o x e n e and C r - s p i n e l . Samples with Mg' numbers g r e a t e r than 56 (GARIBALD, CHEAK, SALAL1 and SALAL2) a l s o have r e l a t i v e l y high abundances of Cr and Ni i n d i c a t i n g they are l e s s f r a c t i o n a t e d than the r e s t of the samples. Lower Mg' numbers and lower Cr and Ni abundances p o i n t to more e x t e n s i v e f r a c t i o n a t i o n . With the exception of samples CAYLEY and SILVERA, Sc contents range from 17 to 29 ppm and average 22 ppm. Samples CAYLEY AND SILVERA have Sc abundances of 11.2 ppm and 11.6 ppm r e s p e c t i v e l y . They a l s o have the lowest Yb contents and highest ( L a / Y b ) C H r a t i o s . Low Sc abundance suggests high p r e s s u r e pyroxene f r a c t i o n a t i o n , whereas low contents of Yb suggest a garnet r i c h r e s i d u e , perhaps an e c l o g i t e . 3.4 SR ISOTOPES A l l samples i n t h i s study have 8 7 S r / 8 6 S r r a t i o s between 0.7030 ± 0.00007 to 0^7036 ± 0.00008 (Table I I ) . Average 8 7 S r / 8 6 S r r a t i o s of b a s a l t s erupted at subduction zones l i e between 0.7030 and 0.7040 (Faure, 1977). 71 3.5 DISCUSSION OF DISCRIMINATION DIAGRAMS On elemental d i s c r i m i n a t i o n diagrams the three c a l c a l k a l i n e samples from the C o q u i h a l l a V o l c a n i c Complex always l i e w i t h i n the convergent margin f i e l d and on a BEND t h e i r p a t t e r n s have a ' t y p i c a l ' convergent margin shape (Thompson et a l . , 1984). C a l c a l k i n e a n d e s i t e s CAYLEY and SILVERA c o u l d be p l o t t e d on only a few diagrams and c l a s s i f i c a t i o n s were not as c o n s i s t e n t . On La vs. Th ( F i g . 3.18) both CAYLEY and SILVERA l i e i n the E-MORB f i e l d , whereas on the La vs. Nb and Th-Hf/3-Ta* diagrams ( F i g s . 3.19 and 3.22) CAYLEY l i e s w i t h i n the convergent margin f i e l d but SILVERA l i e s w i t h i n N-MORB and E-MORB ( t h o l e i i t i c WPB) f i e l d s r e s p e c t i v e l y . BEND pa t t e r n s f o r both of these samples i n d i c a t e they are s l i g h t l y e n r i c h e d i n La r e l a t i v e to a ' t y p i c a l ' convergent margin a n d e s i t e thereby e x p l a i n i n g the La vs. Th c l a s s i f i c a t i o n . The BEND p a t t e r n from SILVERA a l s o i n d i c a t e s i t i s s l i g h t l y e n r i c h e d i n Nb, r e l a t i v e to a convergent margin b a s a l t , hence the MORB c l a s s i f i c a t i o n on La vs. Nb and Th-Hf/3-Ta*. In c o n t r a s t , b a s a l t samples ELAHO, GARIBALD, CHEAK and MEAGER l i e w i t h i n the WPB or E-MORB f i e l d s on s e v e r a l of the d i s c r i m i n a t i o n diagrams and have BEND p a t t e r n s with c h a r a c t e r i s t i c s of both WPB and convergent margin b a s a l t . R e l a t i v e to a ' t y p i c a l ' convergent margin b a s a l t t h e i r higher T i abundances c l a s s i f i e s them as WPB on Ti0 2-MnO-P 20 5, T i - Z r - Y and Ti / Y vs. Nb/Y diagrams and t h e i r 72 undepleted Nb content produces the same c l a s s i f c a t i o n s on T i / Y vs. Nb/Y, La vs. Nb, K 20 vs. Ta*/Yb, Th/Yb vs. Ta*/Yb and Th-Hf/3-Ta* diagrams. A t y p i c a l l y low A l 2 0 3 abundance i s evident on the MgO-FeO*-Al 20 3 diagram, low Ba content moves them towards or w i t h i n the WPB f i e l d s on La vs. Ba and ( B a / L a ) C H vs. (La/Sm) C H diagrams and low abundances of Th c l a s s i f y them as WPB on La vs. Th, Th/Yb vs. Ta*/Yb and Th-Hf/3-Ta*. On Sm/Ce vs. Sr/Ce. Cr vs. Ce/Sr and Cr vs. Y the samples l i e w i t h i n the convergent margin f i e l d because of t h e i r Sr and Y abundances. Sr enrichment i s caused by e i t h e r : a subduction component (Armstrong, 1971; Kay, 1980; Hole et a l . , 1984), or p l a g i o c l a s e accumulation, whereas Y d e p l e t i o n i s most l i k e l y r e l a t e d to a garnet r i c h source residuum, perhaps an e c l o g i t e . T h i s type of arc b a s a l t has been c a l l e d ' m i l d l y a l k a l i n e ' or ' t r a n s i t i o n a l ' by Best and B r i m h a l l (1974) and 'anomalous' by Pearce (1982). Green (1981) c l a s s i f i e s the G a r i b a l d i B e l t b a s a l t s as ' m i l d l y a l k a l i n e ' . Hawaiite samples SALAL1, SALAL2, SALAL3 and SILVERH most o f t e n l i e w i t h i n the WPB or E-MORB f i e l d s . An ex c e p t i o n i s the La vs. Ba p l o t ( F i g . 3.16) which c l a s s i f i e s them a l l as convergent margin because of t h e i r s l i g h t enrichment i n Ba. However t h i s enrichment cannot be very s i g n i f i c a n t as i t i s not evident on ( B a / L a ) C H v s . (La/Sm) C H ( F i g . 3.17). The in c r e a s e d abundance of K 20 r e s u l t s i n an ambiguous p o s i t i o n 73 on K 20/Yb vs. Ta*/Yb ( F i g . 3.20) but on Th/Yb vs. Ta*/Yb ( F i g . 3.21) these four samples are c l e a r l y c l a s s i f i e d as WPB. Data p l o t e d on Cr vs. Ce/Sr ( F i g . 3.14) i s probably a f f e c t e d by p l a g i o c l a s e , o l i v i n e ± pyoxene and C r - s p i n e l f r a c t i o n a t i o n . The f r a c t i o n a t i o n of pyroxene ± C r - s p i n e l almost c e r t a i n l y c o n t r o l s the p o s i t i o n of SALAL3 and SILVERH, whereas p l a g i o c l a s e f r a c t i o n a t i o n (accumulation ?) may be the reason SALAL2 l i e s w i t h i n the convergent margin f i e l d . However, the la c k of a corresponding p o s i t i v e Eu anomaly i n t h i s l a t t e r sample c a s t s some doubt on t h i s i n t e r p r e t a t i o n . The c l e a r l y d i s t i n g u i s h e d alkaline-WPB G a r i b a l d i B e l t samples are unusual because members of the a l k a l i n e rock s e r i e s are present only r a r e l y i n an a r c s e t t i n g (Delong et a l . , 1975). In a recent study of the S a l a l Creek V o l c a n i c s Lawrence et a l . (1984) r e l a t e t h e i r a l k a l i n e geochemistry to t h e i r p o s i t i o n at the end of the G a r i b a l d i V o l c a n i c a r c and p o s t u l a t e they may be e i t h e r the consequence of a change from arc to back-arc volcanism, or sm a l l e r degrees of me l t i n g as v o l c a n i c arc magma generat i o n ceases (Jakes and White, 1969), or a descending p l a t e edge e f f e c t ( A r c u l u s et a l . , 1977). 3.6 SUMMARY The three samples from the C o q u i h a l l a Complex (part of the Pemberton V o l c a n i c Arc) belong to the c a l c a l k a l i n e s e r i e s , l i e w i t h i n the ARC f i e l d i n a l l of the t e c t o n i c 74 d i s c r i m i n a t i o n diagrams s t u d i e d and have BEND p a t t e r n s and La/Nb r a t i o s which are ' t y p i c a l ' of a v o l c a n i c a r c . In c o n t r a s t , b a s a l t i c samples from the G a r i b a l d i B e l t are t r a n s i t i o n a l ( m i l d l y a l k a l i n e ) i n nature and are c l a s s i f e d as WPB on many of the s t u d i e d diagrams. BEND pa t t e r n s have c h a r a c t e r i s t i c convex-up (WPB) shapes and La/Nb and Rb/Nb r a t i o s a l s o suggest a w i t h i n - p l a t e t e c t o n i c s e t t i n g . B a s a l t i c lavas from the Cascades a l s o d i s p l a y these w i t h i n - p l a t e geochemical c h a r a c t e r i s t i c s . T h i s has been, i n t e r p r e t e d by Leeman and Smith ( i n prep.) as evidence f o r a source o r i g i n w i t h i n the mantle wedge o v e r l y i n g the subduction zone. A n d e s i t i c sample CAYLEY i s c l a s s i f i e d as convergent margin on the few diagrams on which i t c o u l d be p l o t t e d and has a BEND p a t t e r n and an La/Nb r a t i o c h a r a c t e r i s t i c of a v o l c a n i c a r c . A n d e s i t i c samples SILVERA i s more a l k a l i n e i n nature but s t i l l has some convergent margin c h a r a c y t e r i s t i e s . B a s a l t i c samples from the S a l a l Creek area of the G a r i b a l d i B e l t and one from Mt. S i l v e r t h r o n e belong to the a l k a l i n e s e r i e s , l i e w i t h i n the WPB f i e l d on almost a l l of the t e c t o n i c d i s c r i m i n a t i o n diagrams and have BEND p a t t r e n s and La/Nb r a t i o s ' t y p i c a l ' of a WPB. A l k a l i n e s e r i e s rocks are unusual i n a convergent margin s e t t i n g and these are probably r e l a t e d to t h e i r p o s i t i o n at the end of the G a r i b a l d i B e l t (Lawrence et a l . , 1984). 75 Both t r a n s i t i o n a l and a l k a l i n e G a r i b a l d i B e l t samples are e n r i c h e d in Sr and d e p l e t e d i n Y r e l a t i v e t o a 'normal' WPB. Consequently they l i e w i t h i n the ARC f i e l d on Sm/Ce vs. Sr/Ce, Ce vs. Ce/Sr and Cr vs. Y. Sr enrichment i s e i t h e r from p l a g i o c a l s e accumulation or r e l a t e d to a subduction component, whereas Y d e p l e t i o n suggests r e s i d u a l garnet i n the source. 76 TABLE II Garibaldi and Pemberton Belts Major, trace and rare earth element abundances, Sr isotope ratios and K/Ar dates. ELAHO 1 G A R I B A L O 2 C H E A K 3 MEAGER 1 C A Y L E Y S A L A L 1 4 S A L A L 2 4 S A L A L 3 4 S e r t e s C A / T r a n s C A / T r a n s C A / T r a n s C A / T r a n s C a l c a l k . A l k a l i n e A l k a l Ine A l k a l i n e Name B a s a l t B a s a 1 t B a s a l t B a s a l t Anc les 1 t e Hawa i 1 t e Hawa* t t e H a w a i I t e L A T . 5 0 2 6 . 9 7 4 9 5 8 . 3 5 0 0 3 . 0 5 0 4 0 . 2 5 0 1 2 . 1 5 0 4 7 . 0 5 0 4 7 . 5 5 0 4 7 . 9 L O N G . 123 3 4 . 8 8 123 0 9 123 0 8 . 0 . 123 3 4 . 9 5 123 1 8 . 1 123 - 2 2 . 6 123 21 123 2 3 . 5 S I 0 2 51 . 2 4 4 9 . 3 0 51 . 8 2 4 9 . 5 0 • 6 0 . 3 4 4 7 . 2 7 4 9 . 0 0 5 0 . 9 2 T 1 0 2 1 . 56 1 . 5 2 1 . 4 4 1 . 5 5 0 . 8 9 1 . 9 7 1 . 7 1 2 . 2 8 A 1 2 0 3 1 5 . 7 7 1 5 . 55 1 5 . 9 4 1 6 . 3 0 1 6 . 6 4 1 4 . 3 7 1 5 . 9 9 1 6 . 9 6 F e 2 0 3 1 . 9 1 1 1 . 78 1 . 4 5 4 . 0 4 5 . 6 0 1 . 75 1 . 6 4 1 . 6 4 F e O 9 . 46 0 . 0 8 . 7 7 8 . 1 1 0 . 0 9 . 94 9 . 29 9 . 2 9 MnO 0 . 15 0 . 14 0 . 14 0 . 15 0 . 0 9 0 . 19 0 . 19 0 . 17 MgO 7 . 2 8 8 . 5 6 7 . 4 3 6 . 5 9 3 . IO 9 . 9 2 7 . 7 9 4 . 28 C a O S . 4 2 8 . 9 0 8 . 5 1 8 . 8 5 7 . 2 7 8 . 62 9 48 7 . 6 1 N a 2 0 3 . 18 3 . 4 6 3 . 7 3 3 . 1 1 4 . 4 4 4 . 4 3 3 . 3 4 4 . 7 6 K 2 0 0 . 7 5 0 . 5 0 0 . 5 4 1 . 2 9 1 . 36 1 . 0 9 1 . 1 3 1 . 33 P 2 0 5 0 . 26 0 . 2 9 0 . 2 3 0 . 5 0 0 . 27 0 . 4 6 0 . 4 3 0 . 7 5 H 2 0 N/A 0 . 2 2 0 . 4 9 N/A N/A 0 . 0 7 0 . 27 0 . 1 3 B a 2 4 7 . 0 1 4 3 . 0 1 7 9 . 0 6 4 7 . 0 4 0 7 . 0 3 1 7 . 0 362 . 0 4 0 0 . 0 Rb 9 . 0 5 . 0 6 . 0 1 0 . 0 1 5 . 0 1 7 . 0 1 4 . 0 1 5 . 0 T h 1 . 4 0 . 9 1 . 0 1 . 6 2 . 4 2 . 4 2 . 2 2 . 3 U 0 . 6 0 . 4 0 . 3 0 . 7 0 . 8 0 . 7 1 . 0 1 . 0 Nb 1 2 . 0 9 . 0 1 0 . 0 1 5 . 0 6 . 0 25 . 0 21 . 0 27 . 0 L a 1 2 . 0 1 0 . 3 1 0 . 5 3 1 . 3 2 6 . 8 23 . 9 2 1 . 3 2 7 . 5 C e 24 . 7 22 . 3 2 1 . 2 5 9 . 0 4 8 . 2 54 . 8 36 . 3 5 2 . 8 S r 5 5 4 . 0 4 3 7 . 0 4 8 9 . 0 1695 0 1944 . 0 6 3 4 . 0 749 . 0 6 1 3 . 0 N d (7 . 8 12 . 2 1 3 . 2 3 5 . 3 3 0 . 0 27 . 5 23 6 3 4 . 3 Sm 4 . 2 3 . 9 3 . 6 7 . 5 5 . 5 5 . 9 5 . 5 7 . 3 Z r 1 1 6 . 0 95 . 0 94 . 0 137 . 0 1 3 4 . 0 152 . 0 1 4 5 . 0 2 1 2 . 0 H f 2 . 1 1 . 5 2 . 3 2 . 3 3 . 6 2 . 1 2 . 1 3 . 1 E u 1 . 0 1 . 2 1 . 1 1 6 1 . 4 1 . 4 1 . 3 2 . 0 T b N/A 0 . 6 0 . 5 N/A 0 . 3 N/A N/A N/A Y 21 . 0 2 0 . 0 1 8 . 0 2 3 . 0 1 4 . 0 2 0 . 0 24 . 0 3 0 . 0 Yb 1 . 8 1 . 7 . 1 . 6 2 . 3 1 . 3 2 . 0 1 . 7 2 . 3 L u 0 . 3 0 . 2 0 . 3 0 . 2 0 . 1 0 . 3 0 . 3 0 . 3 C o 3 6 . 0 54 . 0 5 6 . 0 3 0 . 0 27 . 0 51 . 0 42 . 0 3 0 . 0 C r , 2 2 1 . 0 108 . 4 2 1 9 . 0 6 5 . 5 1 6 . 3 1 7 4 . 3 1 4 3 . 1 34 . 6 C u 3 9 . 0 56 . 0 37 . 0 67 . 0 6 6 . 0 6 0 . 0 6 0 . 0 3 8 . 0 NI 9 5 . 0 152 . 0 1 1 2 . 0 5 3 . 0 2 5 . 0 277 . 0 107 . 0 4 0 . 0 S c 22 . 1 2 1 . 4 1 8 . 0 2 3 . 7 1 1 . 2 2 2 . 4 24 . 9 1 8 . 6 V 87 1 7 3 . 0 1 7 7 . 0 1 6 0 . 0 1 9 6 . 0 1 0 4 . 0 188 . 0 207 . 0 181 . 0 S r l a 0 . 7 0 3 1 N/A N/A 0 . 7 0 3 6 N/A- 0 . 7 0 3 3 N/A 0 . 7 0 3 0 K/Rb 6 9 1 . 7 5 8 3 0 . 1 0 7 4 7 . 0 9 1 0 7 0 . 8 3 7 5 2 . 6 2 5 3 2 . 2 4 6 7 0 . 0 1 7 3 6 . 0 2 ( L a / Y b ) 4 . 54 4 . 10 4 . 4 0 9 . 0 4 1 4 . 1 8 7 . 9 0 8 . 6 1 8 . 2 0 L a / N b 1 . 0 0 1 . 1 4 1 . 0 5 2 . 0 9 4 . 4 7 0 . 9 6 1 . 0 1 1 . 0 2 M g ' 5 4 5 9 57 5 0 52 61 56 41 K / A r OATE 0 . 1 4 ± 0 . 1 < 1 < 1 0 . 0 9 + 0 . 0 6 < 1 0 . 5 9 ± 0 . 0 5 < 1 0 . 9 7 + 0 . 0 5 (Ma) continued 77 S I L V E R A S I L V E R H C O 0 2 5 1 C 0 0 6 3 2 C 0 0 6 1 S e r 1 e s C a l c a l k . A l k a l i n e C a 1 c a 1 k . C a l c a 1 k . C a l c a l k . Name A n d e s ) t e H a w a i t t e B a s a l t . B a s a l t B a s a l t L A T . 51 2 4 . 5 51 3 3 . 2 5 4 9 53 4 9 5 3 49 54 L O N G . 126 1 5 . 2 5 126 2 1 . 5 121 0 4 121 0 5 121 0 4 S 1 0 2 5 9 . 8 1 4 9 . 3 0 5 3 . 5 3 5 5 . 4 0 5 7 . 7 5 T I 0 2 1 . 0 8 2 . 0 0 1 . 0 2 1 . 0 2 0 . 8 3 A 1 2 0 3 1 7 . 14 1 6 . 2 2 1 6 . 3 8 1 6 . 3 4 1 5 . 3 8 F e 2 0 3 6 . 5 5 1 2 . 10 8 . 8 9 8 . 3 8 8 . 0 5 F e O 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 MnO 0 . 10 0 . 18 0 . 19 0 . 15 0 . 14 MgO 2 . 0 4 5 . 0 8 6 . 7 5 5 . 4 7 6 . 1 1 C a O 6 . 67 8 . 9 5 9 . 7 0 8 . 12 6 . 4 2 N a 2 0 4 . 8 8 4 . 7 6 2 . 2 6 3 . 0 8 2 . 9 6 K 2 0 1 . 5 4 0 . 8 8 0 . 9 6 1 . 6 7 2 . 16 P 2 ° 5 0 . 28 0 . 5 3 0 . 3 1 0 . 37 0 . 2 1 H 2 0 N/A N/A 1 . 10 0 . 4 7 2 . 3 2 B a 6 4 4 . 0 4 4 5 . 0 . 5 7 6 . 0 6 4 6 . 0 8 4 2 . 0 Rb 33 . 0 16 . 0 21 . 0 42 . 0 54 . 0 T h 2 . 5 1 . 3 4 0 6 . 0 1 1 . 0 U 1 . 0 0 . 7 N/A N/A N/A Nb 2 0 . 0 2 3 . 0 5 . 0 6 . 0 6 . 0 L a 27 . 4 26 . 8 1 4 . 8 2 1 . 2 2 1 . 2 C e 3 5 . 6 6 2 . 6 2 9 . 0 34 . 0 4 8 . 0 S r 6 2 5 . 0 5 0 2 . 0 6 0 5 . 0 5 0 0 . 0 4 7 9 . 0 N d 1 7 . 4 2 0 . 1 1 6 . 0 2 2 . 0 2 9 . 0 Sm 3 . 9 6 . 2 6 . 0 7 . 0 6 . 0 Z r 172 . 0 1 5 9 . 0 9 5 . 0 1 2 0 . 0 1 4 9 . 0 H f 3 . 6 3 . 1 N/A N/A N/A E u 1 . 3 1 . 8 1 . 0 1 . 0 1 . 1 T b N/A N/A 0 . 7 0 . 8 0 . 8 Y 2 0 . 0 32 . 0 2 3 . 0 2 8 . 0 2 8 . 0 Yb 1 . 3 2 . 7 2 . 4 * 2 . 7 * 2 . 9 * L u 0 . 3 0 . 4 0 . 3 0 . 4 0 . 4 C o 44 . 0 6 3 . 0 5 8 . 0 41 0 4 5 . 0 C r 9 . 1 1 5 . 0 5 0 . 0 22 . 0 6 5 . 0 C u 37 . 0 2 1 . 0 28 . 0 2 6 . 0 28 . 0 N l 14 . 0 3 5 . 0 2 7 . 0 1 2 . 0 1 2 . 0 S c 1 1 . 6 2 8 . 7 22 . 1 2 3 . 0 1 7 . 5 V 87 132 . 0 2 8 0 . 0 241 . 0 2 1 3 . 0 191 . 0 S r a s 0 . 7 0 3 6 0 . 7 0 3 6 0 . 7 0 3 6 N/A N/A K/Rb 3 8 7 . 3 8 4 5 6 . 5 5 3 7 9 . 4 7 3 3 0 . 0 6 3 3 2 . 0 4 ( L a / Y b ) 1 3 . 7 9 6 . 6 4 4 . 14* 5 2 7 * 4 . 9 0 * L a / N b 1 . 37 1 . 17 2 . 9 7 3 . 5 3 3 . 5 3 M g - 3 8 4 5 5 0 48 52 K / A r D A T E 0 . 4 ± 0.1 0 . 9 5 ± 0 . 2 ~ 2 2 ~ 2 2 ~ 2 2 M a j o r e l e m e n t a b u n d a n c e s f r o m : 1 A n d e r s o n ( 1 9 7 5 ) ' G r e e n ( 1 9 8 1 ) ^ F e l s l n g e r ( 1 9 7 5 ) L a w r e n c e ( 1 9 7 9 ) ' E s t i m a t e d f r o m BEND N/A = not analyzed (Ma) 4. CHILCOTIN BASALTS Eleven samples of the Miocene to P l i o c e n e C h i l c o t i n Group b a s a l t s were s e l e c t e d f o r a n a l y s i s ( F i g . 4.1). The b a s a l t s were generated i n a back-arc t e c t o n i c s e t t i n g due to a sthenospheric up w e l l i n g e v i d e n t l y r e l a t e d to the Pemberton and G a r i b a l d i a r c s . In a d d i t i o n the upwelling may have been i n f l u e n c e d by the p r o x i m i t y of the Anahim hot-spot ( B e v i e r , 1982). According to Bevier (1982), the bulk of the C h i l c o t i n b a s a l t s are 6 to 10 Ma o l d with an e a r l i e r episode of b a s a l t i c voicanism at 19 to 25 Ma and a l a t e r episode at 2 to 3 Ma. Samples s e l e c t e d f o r t h i s study range in age from 2.2. to 18.1 Ma (Table I I I ) . 4.1 MAJOR ELEMENT CHEMISTRY Abundances of major element oxides i n C h i l c o t i n Group b a s a l t s (Table I I I ) resemble abundances from oceanic WPB ( B a s a l t i c Voicanism Study P r o j e c t , 1981). T o t a l a l k a l i s range from 3.23 to 5.06 wt. %, the highest abundance i n sample WOOD LK. P 2 0 5 abundances i n samples DOG CK, BULL CAN and CAMEL are s i m i l a r to P 2 0 5 abundances i n MORB from the Nazca P l a t e , East P a c i f i c R i se or mid-Indian Ocean Ridge, whereas P 2 0 5 abundances i n the e i g h t remaining samples are h i g h e r , w i t h i n the range of oceanic WPB (Rhodes et a l . , 1976; Sun et a l . , 1979; Mullen, 1983). Mg' numbers range from 40 to 60 and average 53, suggesting the b a s a l t s are not primary and have f r a c t i o n a t e d on t h e i r way to the s u r f a c e . 78 79 F i g . 4.1. Sample l o c a t i o n map f o r the C h i l c o t i n B a s a l t S u i t e . A l l subsequent diagrams i n t h i s chapter use i d e n t i c a l symbols. 80 4.2 DISCRIMINATION DIAGRAMS 4.2.1 MAJOR ELEMENT CLASSIFICATIONS On t o t a l a l k a l i s vs. s i l i c a one sample, WOOD LK, i s d i s t i n c t l y a l k a l i n e and the remainder l i e s t r a d d l i n g MacDonald's (1968) boundary between a l k a l i n e and s u b a l k a l i n e f i e l d s ( F i g . 4.2). The Ol'-Ne'-Qz' diagram i d e n t i f i e s three samples as a l k a l i n e (CAMEL, EDMUND and WOOD LK) and the r e s t as s u b a l k a l i n e (REDSTONE, BULL CAN, NAZKO, QUESW, CARD, DOG CK, DEADMAN and BLIZZARD). AFM and FeO*/MgO vs. S i 0 2 diagrams show a l l s u b a l k a l i n e samples from the a l k a l i s v s . s i l i c a diagram to be t h o l e i i t i c ( F i g s . 4.3 and 4.4). On A 1 2 0 3 vs. normative p l a g i o c l a s e sample BULL CAN i s s u f f i c i e n t l y aluminous to be c l a s s i f i e d as c a l c a l k a l i n e . Petrography of the C h i l c o t i n B a s a l t s , d e s c r i b e d by Bevier (1982), i n d i c a t e s they c o n t a i n only one pyroxene, a c l i n o p y r o x e n e . T h i s i s c h a r a c t e r i s t i c of an a l k a l i n e b a s a l t , but normative mineralogy c l a s s i f i e s most of them as o l i v i n e t h o l e i i t e s (Yoder and T i l l e y , 1962; I r v i n e and Baragar, 1971), t h e r e f o r e , Bevier p r e f e r s to c a l l these b a s a l t s t r a n s i t i o n a l . In t h i s study a l l b a s a l t s are t r a n s i t i o n a l except WOOD LK which i s c l a s s i f i e d as a nepheline normative a l k a l i n e b a s a l t . On T i 0 2 - K 2 0 - P 2 0 5 three of the ten t r a n s i t i o n a l samples c l e a r l y l i e w i t h i n the non-oceanic f i e l d , three 81 j i J l l i i I I . F i g . 4.2. T o t a l a l k a l i s vs. s i l i c a . S u b a l k a l i n e / a l k a l i n e boundary fom MacDonald (1968)' . FeO* F i g . 4.3. AFM diagram. T h o l e i i t i c / c a l c a l k a l i n e boundary from I r v i n e and Baragar (1971). Na 20 + K 20 rigO F i g . 4.4. FeO*/MgO vs. S i 0 2 . T h o l e i i t i c / c a l c a l k a l i n e boundary from M i y a s h i r o (1974). REDSTONE • NAZKO 0 CARD 0 DOG CK • DEADMAN • BLIZZARD + BULL CAN A QUESW X CAMEL V EDMUND • WOOD LK A SiO, 82 l i e w i t h i n the oceanic f i e l d and the remaining four s t r a d d l e the boundary l i n e d i v i d i n g these two f i e l d s ( F i g . 4.5). On MnO-Ti0 2-P 20 5 samples CARD, QUESW and WOOD LK c l e a r l y l i e w i t h i n the OIA f i e l d and CAMEL and DOG CK are c l a s s i f i e d as MORB ( F i g . 4.6). BULL CAN l i e s on the MORB-IAT f i e l d boundary and the f i v e remaining samples l i e w i t h i n the OIA f i e l d , along the OIA-IAT f i e l d boundary. On FeO*-MgO-Al 20 3 e i g h t t r a n s i t i o n a l samples l i e around the t r i p l e p o i n t between c o n t i n e n t a l , ocean i s l a n d and N-MORB f i e l d s ( F i g . 4.7). CARD s t r a d d l e s the boundary s e p a r a t i n g ocean i s l a n d and N-MORB and DEADMAN l i e s w i t h i n the ocean i s l a n d f i e l d . 4.2.2 TRACE ELEMENT CLASSIFICATIONS Except f o r BULL CAN, a l l samples l i e w i t h i n or c l o s e to the WPB f i e l d on T i - Z r - Y ( F i g . 4.8). BULL CAN c l e a r l y l i e s w i t h i n the f i e l d c o n t a i n i n g OFB, LKT and CAB. On T i - Z r - S r i t l i e s w i t h i n the LKT f i e l d (not shown) . On V vs. Ti/1000 a l l samples have T i / V r a t i o s between n e a r l y 50 and 100 and l i e w i t h i n the WPB f i e l d ( F i g . 4.9). REDSTONE, BULL CAN and EDMUND l i e c l o s e to the boundary between the MORB and WPB f i e l d s . Ten of the eleven samples l i e w i t h i n the WPB f i e l d on T i / Y vs. Nb/Y ( F i g . 4.10). Sample BULL CAN has 83 Ti/100 0 4 8 12 16 20 24 Ti/1000 F i g s . 4.8. and 4.9. T i - Z r - Y (above) and V vs. Ti/1000 (below), (below). 85 s l i g h t l y lower T i / Y and Nb/Y r a t i o s and l i e s j u s t w i t h i n the f i e l d of ov e r l a p p i n g MORB and convergent margin b a s a l t s . On T i / C r vs. Ni most samples have approximately the same T i / C r r a t i o and l i e w i t h i n the TH MORB f i e l d , but BLIZZARD has a s l i g h t l y lower abundance of Ni and l i e s j u s t w i t h i n the IAT f i e l d ( F i g . 4.11). WOOD LK has a much higher T i / C r r a t i o and l i e s f a r from the other samples, adjacent to the IAT-TH MORB f i e l d boundary. 4.2.3 TRACE AND REE CLASSIFICATIONS Sm/Ce vs. Sr/Ce was not p l o t t e d because t h i s diagram does not have a WPB f i e l d . On Cr vs. Ce/Sr ten of the eleven samples l i e i n a broad band near the top of the diagram ( F i g . 4.12). Of these ten, s i x l i e w i t h i n the o v e r l a p p i n g MORB-WPB or ARC-MORB f i e l d s and four c l e a r l y l i e w i t h i n the convergent margin f i e l d . WOOD LK has a much lower Cr content and l i e s w i t h i n the convergent margin f i e l d , f a r from the other ten samples. On Cr vs. Y ten samples l i e w i t h i n or c l o s e to the ove r l a p p i n g convergent margin-WPB f i e l d s ( F i g . 4.13). As on F i g 4.12 WOOD LK l i e s f a r from the other ten samples. On La vs. Ba ei g h t samples have Ba/La r a t i o s g r e a t e r than 15 and l i e w i t h i n the orogenic a n d e s i t e f i e l d ( F i g . 4.14). BLIZZARD l i e s s t r a d d l i n g the boundary between the orogenic a n d e s i t e and WPB f i e l d s , and F i g s . 4.10 and 4.11. T i / Y vs. Nb/Y (above) and T i / C r vs. Ni (below). Figs.4.12 and 4.13. Cr vs. Ce/Sr (above) and Cr vs. Y (below). 88 REDSTONE and WOOD LK l i e w i t h i n the WPB f i e l d . On ( B a / L a ) C H vs. (La/Sm) C H a l l samples l i e w i t h i n the ocean f i e l d ( F i g . 4.15). Two of these, CARD and CAMEL, l i e w i t h i n the area which o v e r l a p s with the convergent margin f i e l d . On La vs. Th, WOOD LK . l i e s w i t h i n the WPB f i e l d but the remaining ten samples l i e w i t h i n or c l o s e to the orogenic a n d e s i t e f i e l d ( F i g . 4.16). However, e i g h t of these ten have La/Th r a t i o s between n e a r l y seven and ten and l i e w i t h i n the o v e r l a p p i n g orogenic andesite-WPB f i e l d s . On La vs. Nb ten samples l i e w i t h i n the WPB f i e l d , with La/Nb r a t i o s l e s s than 1 ( F i g . 4.17). CARD l i e s a s t r i d e the N-MORB-WPB f i e l d boundary. On K 20/Yb vs. Ta*/Yb most samples l i e w i t h i n or c l o s e to the area between the convergent margin and MORB-WPB f i e l d s ( F i g . 4.18). A few samples l i e j u s t w i t h i n the o v e r l a p p i n g MORB-WPB f i e l d , along that f i e l d ' s upper boundary l i n e . A l l samples except CARD l i e w i t h i n the WPB f i e l d on Th/Yb v s. Ta*/Yb ( F i g . 4.19). CARD has a s l i g h t l y higher Th/Yb r a t i o and l i e s on the lower boundary l i n e of the convergent margin f i e l d . On Th-Hf/3-Ta* a l l samples except CARD l i e w i t h i n the f i e l d s f o r t h o l e i i t i c and a l k a l i n e WPB ( F i g . 4.20). CARD p l o t s away from the other samples, towards Th and l i e s on the convergent margin f i e l d boundary. F i g s . 4.14 and 4.15. La vs. Ba (above) and (Ba/La) vs. (La/Sm)_ u (below). F i g s . 4.16 and 4.17. (below). La vs. Th (above) and La vs. Nb 91 1 oo 1 0 Si > O CN 0.1 ' .»*M ORB .*** F i g . 4 . 1 8 . K 2 0 / Y b v s , T a * / Y b . REDSTONE • BULL CAN • NAZKO 0 QUESW X CARD 0 DOG CK • CAMEL V EDMUND • DEADMAN • WOOD LK A BLIZZARD + 0.0 1 F i g . 4 . 1 9 . T h / Y b v s T a * / Y b . F i g . 4 . 2 0 . T h - H f / 3 - T a * . Th Ta* 92 4.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) Element data p l o t t e d on BEND d i s t i n g u i s h e s three groups of samples ( F i g s . 4.21, 4.22 and 4.23). The BEND p a t t e r n s on F i g . 4.21 are from a l k a l i n e sample WOOD LK, and t r a n s i t i o n a l samples QUESW and BLIZZARD. These p a t t e r n s have convex-up shapes which peak at Nb or K, and have f a i r l y r e g u l a r negative s l o p e s from La to Lu, with a concave-up d i p from Sm to Eu. WOOD LK has a moderate 'trough' at Nd and QUESW i s s l i g h t l y e n r i c h e d i n Ba r e l a t i v e to Rb. A l l samples have small p o s i t i v e Eu anomalies. BEND p a t t e r n s on F i g . 4.22 are from samples REDSTONE, NAZKO, CAMEL, DOG CK, EDMUND, and DEADMAN. A l l p a t t e r n s have convex-up shapes which 'peak' at K (NAZKO, CAMEL, DOG CK, EDMUND and DEADMAN) or Nb (REDSTONE). The pa t t e r n s are n e a r l y f l a t from La to Sm, are f l a t to shallow concave-up from Sm to Eu and have negative s l o p e s from Eu to Lu. A l l p a t t e r n s have a small to l a r g e 'peak' at Sr (Sr enrichment), but they do not have a corresponding 'peak' at Eu. NAZKO and EDMUND are s l i g h t l y e n r i c h e d i n Ba r e l a t i v e to Rb and CAMEL i s enr i c h e d i n LIL r e l a t i v e to Zr, Hf, T i and REE. BEND p a t t e r n s on F i g . 4.23 are from samples CARD and BULL CAN. Both p a t t e r n s show enrichment i n Ba r e l a t i v e to Rb, enrichment i n Sr (Sr 'peak') and have convex-up 'humps' from Rb to Nb, i n d i c a t i n g r e l a t i v e enrichment i n Th, U and K. CARD has a 'peak' at Eu but 1000 n CO S < > o LU N CC O 100 H ioH QUESW X WOOD LK A BLIZZARD + — i — i — i — i — i — i — i — i — i — i — i — r — I — I — | — | — 1 — I — I — Ba RbTh U K NbLa Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F1g. 4.21. BEN diagram f o r samples QUESW, WOOD LK and BLIZZARD. 94 1000 n co UJ DOG CK • EDMUND • DEADMAN • 1 — I — I — H — I — I — I — I — I — I — I — I — I T~~T—I I I — I — r — Ba RbTh u K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F i g . 4 . 2 2 . BEN d i a g r a m f o r s a m p l e s REDSTONE, NAZKO, CAMEL, DOG CK, EDMUND and DEADMAN. 95 1000 - i CO 1 — i — i — i — ' — i — i — i — i — i — i 1 — i — i 1 — i — r — i — i — | — Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F i g . 4 . 2 3 . BEN d i a g r a m f o r s a m p l e s BULL CAN and CARD. 96 BULL CAN does not. F i g . 4.22. 4.3 TRACE ELEMENT CHEMISTRY T r a n s i t i o n a l samples QUESW and BLIZZARD have abundances of t r a c e and REE s i m i l a r to abundances i n an a l k a l i n e oceanic WPB and have BEND p a t t e r n s s i m i l a r to the p a t t e r n from a l k a l i n e sample WOOD LK ( F i g . 4.21), but major element chemistry and normative mineralogy c l a s s i f i e s them as t h o l e i i t e s . Thus t h e i r t r a c e element chemistry i s c o n s i s t e n t with t h e i r t r a n s i t i o n a l nature. The e i g h t remaining t r a n s i t i o n a l samples have lower t r a c e element abundances, s i m i l a r to a t h o l e i i t i c oceanic WPB but r e l a t i v e to a t h o l e i i t i c oceanic WPB t h e i r LREE abundances are lower (Thompson et a l . , 1984). The ten t r a n s i t i o n a l samples have La abundances ranging from 16 to 69 times c h o n d r i t i c , Yb abundances from 5 to 13 times c h o n d r i t i c and ( L a / Y b ) C H r a t i o s between 3.09 and 6.5. Nine of the ten samples have La/Nb r a t i o s ranging from 0.44 to 0.85, resembling La/Nb r a t i o s i n oceanic WPB, but CARD has a r a t i o , o f 0.99, w i t h i n the range of e i t h e r oceanic WPB or convergent margin b a s a l t (Thompson et a l . , 1983). In g e n e r a l a l k a l i n e sample WOOD LK has the hig h e s t abundances of t r a c e and ra r e e a r t h elements i n t h i s s u i t e (CARD has higher abundances of Ba, Th, U and S r ) . I t s La content i s 96 times c h o n d r i t i c , Yb content i s 11 times c h o n d r i t i c and (La/Yb)_„ r a t i o i s 8.93. La/Nb equals 0.85. 97 4.3.1 TH AND U Th abundances range from 0.7 ppm to 1.9 ppm i n samples REDSTONE, BULL CAN, NAZKO, QUESW, CAMEL, DOG CK, EDMUND and DEADMAN, and from 3.0 to 4.3 ppm in CARD, WOOD LK and BLIZZARD (Table I I I ) . U abundances are l e s s than or equal to 0.5 ppm i n the f i r s t e i g h t samples l i s t e d above, and g r e a t e r than or equal to 1.1 ppm i n the l a t t e r three samples. Both Th and U abundances are higher than abundances i n an average oceanic WPB but Th/U r a t i o s which range from 1.75 to 3.95 and average 2.9, are s i m i l a r to r a t i o s i n many oceanic WPB ( B a s a l t i c Volcanism Study P r o j e c t , 1981). 4.3.2 TRANSITION ELEMENTS Abundances of Cr and Ni i n most C h i l c o t i n Group lav a s range from 175 to 296 ppm and 50 to 271 ppm r e s p e c t i v e l y . As Ni abundance n e g a t i v e l y c o r r e l a t e s with Mg' number, Bevier (1982) concludes that none of the C h i l c o t i n b a s a l t s a re primary magmas, but were d e r i v e d by p a r t i a l m e l t i n g of a s p i n e l p e r i d o t i t e with 10 - 15 % of subsequent o l i v i n e f r a c t i o n a t i o n . Sample WOOD LK, which has an Mg' number of 40, has the lowest Cr and Ni abundances i n t h i s s u i t e (Cr = 15.7 ppm, Ni = 30 ppm). These v a l u e s presumably i n d i c a t e l o s s of o l i v i n e which i n c l u d e d C r - s p i n e l . Sc abundances range from 19.4 to 26.8 ppm and average 23.5 ppm. 98 4.4 SR ISOTOPES 8 7 S r / 8 6 S r r a t i o s were not a v a i l a b l e from samples REDSTONE, NAZKO, EDMUND and WOOD LK. Ex c l u d i n g CARD ( 8 7 S r / 8 6 S r = 0.7042), the remaining f i v e samples have Sr isotope r a t i o s between 0.70316 ± 8 and 0.70346 ± 6 (Table I I I ) . These r a t i o s are w i t h i n the range of 8 7 S r / B 6 S r r a t i o s from oceanic WPB (Faure, 1977). 4.5 DISCUSSION OF DISCRIMINATION DIAGRAMS On K 20/Yb vs. Ta*/Yb ( F i g . 4.18) a l l samples l i e w i t h i n or c l o s e to the area between convergent margin and MORB-WPB, but on Th/Yb vs. Ta*/Yb ( F i g . 4.19) a l l samples, e x c l u d i n g CARD l i e w i t h i n the MORB-WPB f i e l d . T h i s i m p l i e s the C h i l c o t i n b a s a l t s are s l i g h t l y e n r i c h e d i n K r e l a t i v e to Nb and suggests i n t e r a c t i o n with a K - r i c h metasomatic f l u i d . K enrichment i s a l s o e v i d e n t from BEND p a t t e r n s . As w e l l , a l l samples except REDSTONE and WOOD LK l i e w i t h i n the convergent margin f i e l d on La vs. Ba ( F i g . 4.14) but on ( B a / L a ) C H vs. ( L a / S m ) C H ( F i g . 4.15) these 'convergent margin' samples l i e w i t h i n the ocean(WPB) f i e l d . T h e r e f o r e , although some samples are en r i c h e d i n Ba r e l a t i v e to Rb (metasomatism?, a n a l y t i c a l e r r o r ? ) Ba enrichment r e l a t i v e to La i s not great enough to a f f e c t the ( B a / L a ) C H vs. (La/Sm) C H diagram. Samples CAMEL, BULL CAN and DOG CK are c l a s s i f i e d as oceanic or MORB on T i 0 2 - K 2 0 - P 2 0 5 ( F i g . 4.5) and MnO-Ti0 2-P 20 5 ( F i g . 4.6), and as convergent margin b a s a l t s 99 on Cr vs. Ce/Sr ( F i g . 4.12). These c l a s s i f i c a t i o n s r e f l e c t t h e i r r e l a t i v e d e p l e t i o n i n P 2 0 5 and enrichment i n Sr. Enrichment i n Sr suggests e i t h e r : metasomatism, p l a g i o c l a s e accumulation, low pressure f r a c t i o n a t i o n of phases other than p l a g i o c l a s e (eg. o l i v i n e , pyroxene), or i n t e r a c t i o n with c o n t i n e n t a l c r u s t ( c o n t a m i n a t i o n ) . Lack of p o s i t i v e Eu anomalies and 'average' WPB Sr iso t o p e r a t i o s support n e i t h e r of these l a t t e r two suggestions. BULL CAN a l s o l i e s w i t h i n or c l o s e t o the MORB f i e l d on many of the other diagrams because of i t s low elemental abundances. T h i s suggests a d e p l e t e d source r e g i o n , perhaps deplet e d d u r i n g a previous m e l t i n g event. Both CAMEL and DOG CK l i e w i t h i n the convergent margin f i e l d on Cr vs. Y ( F i g . 4.13) because of t h e i r d e p l e t i o n i n Y r e l a t i v e t o the r e s t of the sample s u i t e . T h i s suggests a garnet r i c h source residuum. W.H. Mathews ( o r a l comm., 1985) th i n k s these two samples are l i k e l y to have had a common source, at or north of DOG CK. CARD a l s o l i e s w i t h i n the convergent margin f i e l d on ( B a / L a ) C H vs. (La/Sm) C H and La vs. Th, as w e l l as on Cr vs. Ce/Sr ( F i g . 4.12), and l i e s a s t r i d e the convergent margin f i e l d boundary on La vs. Nb ( F i g . 4.17), Th/Yb v s. Ta*/Yb ( F i g . 4.19) and Th-Hf/3-Ta* ( F i g . 4.20). The convergent margin c l a s s i f i c a t i o n i s caused by t h i s samples r e l a t i v e enrichment i n Ba, Th, K and Sr and s l i g h t d e p l e t i o n i n Nb. 100 CARD, the most 'orogenic', i s nearest to the co e v a l Pemberton arc and may have i n h e r i t e d an LIL r i c h component form the subducting s l a b . In recent years s l a b components in back-arc basins and even ocean i s l a n d s have been suggested by McKenzie and O'Nions (1983), Cohen and O'Nions (1982) and Thompson et a l . (1983, 1984). A d d i t i o n a l evidence arguing for a s l a b component i n CARD i s suggested by i t s r e l a t i v e l y high 8 7 S r / 8 6 S r r a t i o of 0.7042. A l t e r n a t i v e l y these c h a r a c t e r i s t i c s may be caused by c r u s t a l contamination (Dupuy and D o s t a l , 1984). 4.6 SUMMARY The C h i l c o t i n Group b a s a l t samples have t h o l e i i t i c / t r a n s i t i o n a l chemistry, except sample WOOD LK which i s c l a s s i f i e d as a nepheline normative a l k a l i n e b a s a l t . Major, t r a c e and r a r e e a r t h element abundances are g e n e r a l l y s i m i l a r to abundances i n a t h o l e i i t i c oceanic WPB, and on most t e c t o n i c d i s c r i m i n a t i o n diagrams these samples l i e w i t h i n the WPB f i e l d . Some of the diagrams imply an enrichment i n Ba, K ± Sr and Th, suggesting i n t e r a c t i o n with an a l k a l i r i c h metasomatic f l u i d . BULL CAN comes from a de p l e t e d source with some of the chemical c h a r a c t e r i s t i c s of a MORB. Ex c l u d i n g CARD, Sr isotope r a t i o s imply no i n t e r a c t i o n with the c o n t i n e n t a l c r u s t . CARD has both an Sr isotope r a t i o and some geochemical c h a r a c t e r i s t i c s of e i t h e r ; c r u s t a l l y contaminated WPB, or 101 the presence of a subduction - r e l a t e d component. TABLE III. Chilcotin Basalts Major, trace and rare earth element abundances, Sr isotope ratios and K/Ar dates. REDSTONE B U L L CAN NAZKO QUESW CARD CAMEL DOG CK EDMUND DEADMAN WOOD LK B L I Z Z A R D S e r i e s T h o l / T r a n s T h o l / T r a n s T h o l / T r a n s A t k / T r a n s T h o l / T r a n s A l k / T r a n s T h o l / T r a n s A l k / T r a n s T h o l / T r a n s A l k a l i n s A l k / T r a n s Name B a s a l t B a s a l t B a s a l t B a s a l t B a s a l t B a s a l t B a s a l t B a s a l t B a s a l t H a w a i I t e B a s a l t L A T . 52 0 7 . 2 52 0 5 . 5 53 0 3 . 6 7 52 5 6 . 6 51 0 5 . 4 7 5 0 5 8 . 2 51 3 5 . 0 51 3 6 . 8 5 0 5 8 . 0 5 0 0 3 . 6 49 3 7 . 5 L O N G . 123 4 0 . 0 123 2 3 . 3 123 3 4 . 6 7 122 3 3 . 5 122 5 7 . 5 3 121 5 5 . 4 122 1 5 . 0 121 2 2 . 7 120 5 8 . 0 119 2 1 . 0 1 18 5 5 . 0 S i 0 2 5 1 . 7 7 4 9 . 7 1 51 . 24 5 0 . 5 4 4 9 . 5 0 51 . 89 51 25 5 0 . 5 5 4 8 4 1 4 8 . 19 48 . 19 T 1 0 2 1 . 6 2 1 . 35 1 . 8 4 2 . 3 0 2 . 5 7 1 . 93 1 . 9 3 1 . 5 3 1 . 9 0 2 . 6 6 1 . 9 6 A 1 2 0 3 1 5 . 0 8 15 . 5 8 15 . 0 7 14 . 44 14 . 84 15 . 25 14 . 6 9 1 5 . 6 4 14 . 62 1 6 . 01 1 5 . 3 1 F e 2 0 3 . 1 1 . 0 2 13 . 2 0 1 2 . 1 2 1 2 . 4 3 1 1 . 8 4 1 1 . 04 1 2 . 8 2 1 1 . 78 1 3 . 84 1 3 . 6 5 1 2 . 7 0 F e O 0 . 0 0 0 0 . 0 0 . 0 0 0 0 . 0 0 . 0 0. 0 0 . 0 0. 0 0 . 0 MnO 0 . 15 0 . 17 0. 16 0 . 17 0 . 14 0 . 14 0 . 16 0. 16 0 . 18 0 . 18 0 . 18 MgO 7 . 10 7 . 4 2 6 . 8 2 7 . 0 4 8 . 9 5 ' 6 . 02 6 . 7 0 6 . 28 9 . 81 4 . 6 0 7 . 9 9 CaO 8 . 9 6 8 . 5 6 8 . 4 6 8 . 5 9 7 . 72 8 . 51 8 . 4 7 8 . 9 5 7 . 54 7 . 6 0 9 . 2 1 N a 2 0 3 . 3 4 3 . 4 2 3 . 3 8 3 . 0 9 2 . 8 2 • 4 . 25 3 . 2 7 4 . 0 3 2 . 19 4 . 9 3 2 . 8 9 K 2 0 . 0 . 6 6 0 . 4 1 0 . 6 2 1 . 0 2 1 . 15 0 . 81 0 . 5 7 0. 6 7 1 . 0 4 1 . 38 1 . 0 7 P 2 0 5 0 . 3 0 0 . 17 0 30 0 . 37 0 . 46 0 . 15 0 . 14 0 . 42 0 - 4 5 0 . 8 0 0 . 4 8 H 2 0 N/A N/A N/A 0 . 5 5 N/A N/A N/A N/A N/A N/A N/A B a 1 8 3 . 0 108 0 2 0 6 . 0 3 4 0 . 0 54 1 . 0 235 . 0 1 7 0 . 0 2 2 2 . 0 . 264 . 0 4 4 0 . 0 3 3 6 . 0 Rb 1 1 . 0 4 . 0 8 . 0 1 5 . 0 1 4 . 0 12 . 0 9 . 0 8 . 0 13 . 0 24 . 0 1 8 . 0 T h 1 5 0 . 7 1 . 3 1 . 9 4 . 3 1 .4 0 . 8 1 . 6 1 8 3 . 0 3 . 1 U 0 . 4 0 . 4 0 . 5 0 . 8 1 . 3 0 .4 0 . 3 0 . 4 0 . 5 1 . 1 1 . 1 Nb 1 8 . 0 6 . 0 1 3 . 0 2 3 . 0 1 9 . 0 13 . 0 1 2 . 0 16 . 0 22 . 0 37 . 0 2 9 . 0 L a 1 5 . 2 5 . 2 1 1 . 3 18 . 4 1 8 . 8 7 . 8 5 . 3 1 1 . 4 15 2 31 . 6 22 . 5 C e 37 . 1 1 3 . 4 27 . 3 43 . 2 44 . 3 20 . 2 14 . 1 25 . 3 36 . 7 53 . 2 48 8 S r 496 . 0 3 0 0 . 0 387 . 0 5 0 8 . 0 1 0 8 6 . 0 491 . 0 3 7 5 . 0 421 0 6 0 1 . 0 6 6 4 0 5 8 9 . 0 Nd 2 2 . 8 9 . 5 17 2 1 6 . 4 2 8 . 6 12 . 6 10 . 1 17 . 2 17 3 33 6 27 . 2 Sm 5 . 0 3 2 4 . 4 6 . 0 7 1 3 . 1 3 . 2 4 . 5 4 . 7 8 . 2 7 . 0 Z r 1 2 0 . 0 68 . 0 104 . 0 157 . 0 1 4 2 . 0 127 . 0 1 1 4 . 0 106 . 0 132 . 0 2 5 6 . 0 157 . 0 H f 2 . 4 2 3 3 . 0 2 . 7 3 . 8 2 . 8 3 . 2 2 . 8 . 3 . 1 5 . 5 3 . 6 E u 1 . 3 1 . 1 1 . 5 1 . 9 2 . 2 1 . 3 1 . 2 1 . 4 ' 1 . 6 2 5 2 . 0 T b 0 . 7 0 . 5 0 . 4 N/A 0 . 6 0 . 5 0 . 5 0 . 9 0 . 4 1 . 0 N/A Y 2 0 . 0 23 . 0 2 2 . 0 25 . 0 2 5 . 0 IB . 0 1 9 . 0 23 . 0 2 1 . 0 32 . 0 2 5 . 0 Yb 1 6 1 . 3 1 . 3 2 . 0 2 . 1 1 .2 1 . 1 1 8 1 . 6 2 . 4 2 . 7 L u 0 . 2 0 . 2 0 . 2 0 . 3 0 . 2 0 . 1 0 . 2 0 . 2 0 . 1 0 3 0 . 3 C o 6 0 . 0 5 0 . 0 56 . 0 45 . 0 51 . 0 4 1 . 0 48 . 0 49 . 0 61 . 0 45 . 0 4 0 . 0 C r 2 4 5 . 9 207 . 8 2 5 0 . 0 175 . 4 2 7 9 . 9 189 . 6 2 1 7 . 9 2 4 5 . 9 232 . 8 15 . 7 . 2 9 6 . 3 C u 6 1 . 0 59 . 0 101 . 0 77 . 0 1 7 0 . 0 26 . 0 4 3 . 0 35 . 0 6 9 . 0 3 0 . 0 3 8 . 0 N l 64 . 0 2 1 1 . 0 1 8 1 0 1 7 6 . 0 182 . 0 96 . 0 1 8 3 . 0 1 1 1 . 0 27 1 . 0 3 0 . 0 5 0 . 0 SC 2 0 . 6 2 3 . 0 22 . 3 2 1 .2 2 1 . 1 22 . 4 22 1 24 . 4 18 . 2 17 . 9 24 . 7 V 87 1 8 5 . 0 1 6 5 . 0 154 . 0 172 . 0 234 . 0 185 . 0 161 . 0 176 . 0 168 . 0 181 . 0 2 1 7 . 0 S r 8 6 N/A 0 . 7 0 3 4 6 N/A 0 . 7 0 3 4 0 . 7 0 4 2 0 . 7 0 3 2 0 0 . 7 0 3 1 6 N/A 0 . 7 0 3 1 6 N/A 0 . 7 0 3 3 K/Rb 4 9 8 . 0 6 8 5 0 85 6 4 3 . 3 3 5 6 4 . 4 7 6 8 1 . 8 7 5 6 0 . 3 2 5 2 5 . 7 3 6 9 5 . 2 1 6 6 4 . 0 8 4 7 7 . 31 4 9 3 . 4 5 U a / Y b ) C H 6 . 2 3 2 62 5 . 8 5 6 . 17 6 . 12 12 . 2 9 3 . 0 9 4 . 24 6 . 4 8 8 . 93 5 . 6 1 L a / N b 0 . 8 5 0 86 0 . 8 7 0 . 8 0 0 . 9 9 1 65 0 . 4 4 0 . 7 1 0 6 9 0 8 5 0 . 78 M g ' 56 53 53 53 6 0 52 51 51 58 4 0 55 K/Ar date N/A 6 1 ± 0 . 2 6 . 3 ± 0 . 3 8 . 7 1 0 . 6 1 8 . 1 ± 0 . 6 2 . 2 ± 0 . 3 2 . 9 ± 0 2 7 . 8 ± 0 . 3 8 . 2 ± 0 . 3 1 4 . 8 1 1 5 5 . 0 + 0 (Ma) N/A = not analyzed O to 5. ANAHIM VOLCANIC BELT Nine samples from the Anahim V o l c a n i c B e l t west of the F r a s e r R i v e r were s e l e c t e d f o r a n a l y s i s ( F i g . 5.1). Two of these nine are from the Masset Formation on the Queen C h a r l o t t e I s l a n d s to determine i f they are c h e m i c a l l y s i m i l a r to b a s a l t s from the Anahim B e l t i n c e n t r a l B r i t i s h Columbia because Bevier et a l . (1979) suggest the Masset v o l c a n i c s may form the western end of the Anahim hotspot t r a c e . An a d d i t i o n a l f i v e samples from v o l c a n i c c e n t e r s east of the F r a s e r River were i n c l u d e d i n t h i s s u i t e , as these l o c a t i o n s are of t e n p l a c e d on f i g u r e s which d e f i n e the Anahim B e l t ( B e v i e r , 1978). However, recent work by C. Hickson ( o r a l comm., 1984) suggests e r u p t i o n s from the Anahim hotspot source end i n the v i c i n i t y of the Nazko Cones, west of Quesnel, and J.E. Souther ( i n press) s p e c u l a t e s that a second hotspot t r a c e forms t h i s eastward cont inuat i o n . Samples from t h i s s u i t e range i n age from 23.8 Ma to 0.28 Ma (Table I V ) . The o l d e s t dates are from the Masset Formation and the youngest age i s from a sample l o c a t e d i n Wells Gray Park. 5.1 MAJOR ELEMENT CHEMISTRY Major element oxide abundances (Table IV) g e n e r a l l y l i e w i t h i n the range of major element abundances i n oceanic t h o l e i i t i c and a l k a l i n e WPB ( B a s a l t i c Voicanism Study P r o j e c t , 1981; Carmichael et a l . , 1974). Mg' numbers d i v i d e 103 F i g 5.1. Sample l o c a t i o n map f o r the Anahim V o l c a n i c B e l t . A l l subsequent diagrams i n t h i s chapter use i d e n t i c a l symbols. 105 the samples i n t o two groups. The nine samples west of the F r a s e r R i v e r p l u s ALEX have Mg' numbers between 30 and 56, whereas the four remaining samples, i n and near Wells Gray Park, have Mg' numbers between 56 and 62. Thus, these l a t t e r four samples are l e s s f r a c t i o n a t e d (more p r i m i t i v e ) . 5.2 DISCRIMINATION DIAGRAMS 5.2.1 MAJOR ELEMENT CLASSIFICATIONS On the t o t a l a l k a l i s vs. s i l i c a diagram e i g h t of the f o u r t e e n samples c l e a r l y l i e w i t h i n the a l k a l i n e f i e l d , f i v e p l o t a s t r i d e MacDonalds (1968) s u b a l k a l i n e / a l k a l i n e f i e l d boundary and one (ALEX) i s c l e a r l y s u b a l k a l i n e ( F i g . 5.2). Ol'-Ne'-Qz' (not shown) c l a s s i f i e s nine samples as a l k a l i n e (ARIS IS, KITASU, LAKE IS, RAINBOW, ANAHIM, ITCHA1, ITCHA2, SPAN CK and TROPHY) and the remaining f i v e as s u b a l k a l i n e . A p e t r o g r a p h i c study of TROPHY by F i e s i n g e r (1975) suggests i t should be c l a s s i f i e d as t r a n s i t i o n a l . On AFM and FeO*/MgO vs. S i 0 2 diagrams, s u b a l k a l i n e and t r a n s i t i o n a l b a s a l t i c samples l i e w i t h i n the t h o l e i i t i c f i e l d s ( F i g s . 5.3 and 5.4). A l 2 0 3 vs. normative p l a g i o c l a s e (not shown) confirms the AFM d i s c r i m i n a t i o n except f o r samples MASSET1 and MASSET2 which were s u f f i c i e n t l y aluminous to be c l a s s i f i e d as c a l c a l k a l i n e . 106 F i g . 5.2. T o t a l a l k a l i s vs. s i l i c a . S u b a l k a l i n e / a l k a l i n e boundary fom MacDonald (1968). Feu* F i g . 5.3. AFM diagram. T h o l e i i t i c / c a l c a l k a l i n e boundary from I r v i n e and Baragar (1971). Na20 + K 20 MgO J I I I I I I L F i g . 5.4. FeO*/MgO vs. S i 0 2 . T h o l e i i t i c / c a l c a l k a l i n e boundary from M i y a s h i r o (1974). MASSET1 A ARIS IS + LAKE ISB ANAHIM • ITCHA2 • QUES LK • SPAN CK X. MASSET2A KITASU X RAINBOW V ITCHA1 O ALEX • WGRAYN 0 TROPHY A t S i O , 1 07 Because T i 0 2 - K 2 0 - P 2 0 5 can only be used f o r s u b a l k a l i n e samples with t o t a l a l k a l i s l e s s than or equal to 20% on an AFM diagram samples MASSET1 and MASSET2 were excluded. The four remaining samples l i e c l o s e to the boundary l i n e between the oceanic and non-oceanic f i e l d s ( F i g . 5.5). ALEX and WGRAYN l i e w i t h i n the oceanic f i e l d , TROPHY l i e s w i t h i n the non-oceanic f i e l d and QUES LK l i e s on the boundary l i n e . Most samples p l o t t e d on MnO-Ti0 2-P 20 5 l i e w i t h i n the OIA f i e l d ( F i g . 5.6). Exceptions are: ANAHIM which l i e s w i t h i n the OIT f i e l d . QUES LK which l i e s w i t h i n the MORB f i e l d . TROPHY which l i e s on the boundary l i n e between the MORB and IAT f i e l d s , and MASSET1 which l i e s on the boundary betwen the IAT and CAB f i e l d s . On MgO-FeO*-Al 20 3 four s u b a l k a l i n e and t r a n s i t i o n a l samples s t r a d d l e the boundary between the ocean i s l a n d (OI) and MORB f i e l d s , MASSET2 l i e s w i t h i n the orogenic (ARC) f i e l d and ALEX l i e s a t the approximate cent e r of the c o n t i n e n t a l f i e l d ( F i g . 5.7). Thus t h i s diagram i s i n c o n c l u s i v e . 5.2.2 TRACE ELEMENT CLASSIFICATIONS Eleven of the fourteen samples p l o t w i t h i n the WPB f i e l d on T i - Z r - Y ( F i g . 5.8). The three remaining samples were r e p l o t t e d on T i - Z r - S r ( F i g . 5.9). On t h i s l a t t e r TiO, 5.5. T i 0 2 - K 2 0 - P 2 0 5 0.8 OCEANIC/ • A t NON-OCEANIC 0 . 4 MASSET1 A ARIS IS + LAKE I S " ANAHIM T ITCHA2 • QUES LK • SPAN CK X„ MASSET2A KITASU X RAINBOW V ITCHA1 0 ALEX • WGRAYN 0 TROPHY A t 0.2 109 diagram c a l c a l k a l i n e samples MASSET1 and MASSET2 l i e w i t h i n the CAB f i e l d and sample LAKE IS l i e s w i t h i n the OFB f i e l d , adjacent to the OFB-CAB f i e l d boundary. V vs. Ti/1000 cannot d i s c r i m i n a t e samples belonging to the c a l c a l k a l i n e s e r i e s , t h e r e f o r e MASSET1 and MASSET2 were excluded from t h i s p l o t . Eleven of the remaining twelve samples have T i / V r a t i o s g r e a t e r than 50 and p l o t w i t h i n the WPB f i e l d ( F i g . 5.10). ARIS IS l i e s w i t h i n the MORB f i e l d with a T i / V r a t i o of 48. On Ti/Y vs. Nb/Y samples MASSET1 and MASSET2 p l o t w i t h i n the f i e l d f o r MORB, adjacent to the MORB-convergent margin f i e l d boundary ( F i g . 5.11). Three of the remaining twelve samples (ARIS IS, KITASU and LAKE IS) have r e l a t i v e l y low Ti/Y r a t i o s and p l o t a s t r i d e the lower boundary of the WPB f i e l d . The other nine samples are c l e a r l y c l a s s i f i e d as WPB. Samples MASSET1, LAKE IS, RAINBOW, ITCHA1 and ALEX p l o t w i t h i n the IAT f i e l d on the T i / C r v s . Ni diagram ( F i g . 5.12). MASSET2 and KITASU l i e on the f i e l d boundary and the remaining seven samples p l o t w i t h i n the TH MORB f i e l d . T h i s diagram does not have a f i e l d f o r WPB. 5.2.3 TRACE AND REE CLASSIFICATIONS Only the two samples from the Masset Formation were p l o t t e d on Sm/Ce vs. Sr/Ce because t h i s diagram was designed to c l a s s i f y convergent margin b a s a l t s , and does 110 0.6 Ti/100 0.8 F i g . 5.8. Ti-Zr-Y, n.2 Ti/100 111 iooo -\ > 100 MASSET1 A ARIS IS + LAKE I S ! ANAHIM T ITCHA2 • QUES LK • SPAN CK X c 0 0 1 0.1 1 Nb/Y 1 0 MASSET2 • KITASU X RAINBOW V ITCHA1 O ALEX • WGRAYN 0 TROPHY A, F i g s . 5.11 and 5.12. T i / Y vs. Nb/Y (above) and T i / C r vs. Ni (below). 1 1 2 not have a WPB f i e l d ( F i g . 5.13). MASSET 1 and MASSET2 l i e w i t h i n the convergent margin f i e l d . On Cr vs. Ce/Sr s i x samples l i e w i t h i n the ov e r l a p p i n g MORB-WPB f i e l d s ( F i g . 5.14). Four of these s i x from east of the Fr a s e r R i v e r and l i e removed from a l l of the remaining samples. The other e i g h t samples l i e w i t h i n or c l o s e to the convergent margin f i e l d . Seven of these e i g h t samples have Ce/Sr r a t i o s which are s i m i l a r to r a t i o s from the samples which p l o t i n the MORB-WPB f i e l d s , but they are de p l e t e d i n Cr, thus t h e i r convergent margin c l a s s i f i c a t i o n . The e i g h t h sample, ARIS IS, has a much lower Ce/Sr r a t i o than the other t h i r t e e n samples and l i e s at the center of the convergent margin f i e l d . On Cr vs. Y a l l samples l i e w i t h i n the f i e l d f o r WPB ( F i g . 5.15). MASSET1, MASSET2, ITCHA1, RAINBOW and ALEX l i e w i t h i n the area which o v e r l a p s with the convergent margin f i e l d , ARIS IS, ANAHIM, ITCHA2, QUES LK, SPAN CK and TROPHY l i e w i t h i n the o v e r l a p p i n g WPB-MORB- convergent margin f i e l d s and WGRAYN l i e s w i t h i n the o v e r l a p p i n g WPB-MORB f i e l d s . On La vs. Ba e i g h t samples l i e w i t h i n the orogenic a n d e s i t e f i e l d with Ba/La r a t i o s g r e a t e r than 15 ( F i g . 5.16). KITASU and ITCHA2 have Ba/La r a t i o s l e s s than 11 and l i e w i t h i n the N-MORB f i e l d and the remaining four (RAINBOW, ITCHA1, QUES LK and WGRAYN) l i e w i t h i n the E-MORB (WPB) f i e l d . 113 1 -\ O •«». E CO 0.1 MASSET1 A ARIS IS + LAKE IS a ANAHIM • ITCHA2 • QUES LK • SPAN CK X,. 1 0 1 0 0 Sr/Ce 1 0 0 0 MASSET2A KITASU X RAINBOW V ITCHA1 0 ALEX • WGRAYN 0 TROPHY A t 1 0 0 0 F i g s . 5.13 and 5.14. Sm/Cevs. .Sr/Ce (above) and Cr vs. Ce/Sr (below). MASSET1 A ARIS IS + LAKE I S * ANAHIM • ITCHA2 • QUES LK • SPAN CK X s MASSET2A KITASU X RAINBOW V ITCHA1 O ALEX • WGRAYN 0 TROPHY A t F i g . 5.15. Cr vs. Y. 1 15 On ( B a / L a ) C H vs. (La/Sm) C H nine of the fourteen samples c l e a r l y l i e w i t h i n the ocean f i e l d ( F i g . 5.17). MASSET1 and MASSET2 l i e w i t h i n the ocean f i e l d adjacent to the ocean-ARC f i e l d boundary, ARIS IS and SPAN CK l i e j u s t w i t h i n the o v e r l a p p i n g ocean-ARC f i e l d s and RAINBOW l i e s f a r from the other t h i r t e e n samples, c l e a r l y w i t h i n the ARC f i e l d . On La vs. Th eleven samples l i e wi t h i n the E-MORB (WPB) f i e l d with La/Th r a t i o s g r e a t e r than 7 ( F i g . 5.18) . The remaining three (MASSET2, QUES LK and WGRAYN) have La/Th r a t i o s l e s s than 7. MASSET1, QUES LK and WGRAYN l i e j u s t w i t h i n the orogenic a n d e s i t e f i e l d boundary. On La vs. Nb nine samples have La/Nb r a t i o s l e s s than 1 and l i e w i t h i n the E-MORB (WPB) f i e l d ( F i g . 5.19) . The remaining f i v e samples (MASSET1, MASSET2, ARIS IS, RAINBOW and ITCHA2) have La/Nb r a t i o s between 1 and 2 and l i e w i t h i n the N-MORB f i e l d . On K 20 vs. Ta*/Yb samples l i e w i t h i n : (a) the o v e r l a p p i n g MORB-WPB f i e l d s , and (b) the area between the o v e r l a p p i n g MORB-WPB f i e l d s and the convergent margin f i e l d ( F i g . 5.20). Samples which l i e w i t h i n t h i s l a t t e r area are MASSET1, MASSET2, ARIS IS, RAINBOW, ANAHIM and TROPHY. They have the same range of Ta*/Yb r a t i o s as the other e i g h t samples but t h e i r K 20/Yb r a t i o s are h i g h e r . 1 16 Ba 3 I \ I \ \ \ \ \ * ARC \ \ \ \ \ \ \ \ \ \ \ •OCEAN > • • • • • • X i i 1 r 0 1 2 3 (La/Sm) F i g s . 5.16 and 5.17. La v s . Ba (above) and (Ba/La) vs. (La/Sin)-., (below). F i g s . 5.18 and 5.19. La vs. Th (above) and La vs. Nb (below). 1 18 On Th/Yb vs. Ta*/Yb MASSET1, MASSET2 and ARIS IS have the highest Th/Yb r a t i o s and l i e 'above' the WPB f i e l d ( F i g . 5.21). MASSET2 has a s u f f i c i e n t l y h i g h Th/Yb r a t i o to l i e w i t h i n the convergent margin f i e l d . The remaining twelve samples l i e w i t h i n the o v e r l a p p i n g MORB-WPB f i e l d s . On Th-Hf/3-Ta* eleven of the t h i r t e e n samples l i e w i t h i n the a l k a l i n e WPB and E-MORB- t h o l e i i t i c WPB f i e l d s ( F i g . 5.22) The remaining three samples, MASSET1, MASSET2 and ARIS IS, l i e towards and w i t h i n the CAB f i e l d . 5.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) Trace and rare e a r t h element data p l o t t e d on BEN diagrams d i v i d e s the samples i n t o three groups ( F i g u r e s 5.23, 5.24 and 5.25). Samples KITASU, LAKE IS, RAINBOW, ANAHIM, ITCHA1 and ITCHA2 are p l o t t e d on F i g . 5.23. T h e i r BEND p a t t e r n s are g r o s s l y s i m i l a r with convex-up shapes peaking at Nb (KITASU, ITCHA1), K (RAINBOW, ANAHIM) or La (LAKE IS, ITCHA2). A l a r g e 'peak' at La i s unusual. Both LAKE IS and RAINBOW are e n r i c h e d i n Ba r e l a t i v e to Rb. A l l p a t t e r n s have l a r g e p o s i t i v e Eu anomalies, but none of them have c o r r e l a t i v e p o s i t i v e Sr anomalies. In f a c t , KITASU and LAKE IS d i s p l a y negative Sr anomalies! The p a t t e r n f o r LAKE IS i s f a i r l y f l a t from Ba to La i n c o n t r a s t to the other f i v e p a t t e r n s which have a 119 1 oo 1 0 > O CM 1 - 0. 1 / / A R C / J% / '.WPB v - - 0 . 0 1 —i r 0.1 1 Ta*/Yb F i g . 5.21. Th/Yb vs. Ta*/Yb. Hf/3 F i g . 5.20. K 20/Yb vs. Ta*/Yb. MASSET1A ARIS IS + LAKE ISB ANAHIM • ITCHA2 • QUES LKO SPAN CK X, MASSET2A KITASU X RAINBOW V ITCHA1 0 ALEX • WGRAYN 0 TROPHY A, 1 0 1 0 1 - > 0.1 - 0 .0 1 0 .01 0.1 Ta*/Yb 1 o F i g . 5.22. Th-Hf/3-Ta*. Th Ta* 120 1000 -i 1 f " - 1 — i — 1 — i — i — r — i — i — i 1 — i — i 1 — i — r — i — i — r - Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu 1g. 5.23. BEN d i a g r a m f o r s a m p l e s KITASU, LAKE I S . RAINBOW, ANAHIM, ITCHA1 and ITCHA2 121 d i s t i n c t l y p o s i t i v e s l o p e . BEND p a t t e r n s on F i g . 5.24 are from the f i v e l o c a t i o n s east of the F r a s e r R i v e r ; ALEX, QUES LK, WGRAYN, SPAN CK and TROPHY. Pat t e r n s are s i m i l a r to those on F i g . 5.23, but F i g . 5.24 p a t t e r n s are more i r r e g u l a r from Ba to La, and they a l l have a concave-up d i p from Sm to T i . A l l samples, e x c l u d i n g QUES LK, are enr i c h e d i n Ba r e l a t i v e to Rb and WGRAYN i s e n r i c h e d i n Th and U. A l l p a t t e r n s have small p o s i t i v e Eu anomalies and ALEX has a 'trough' at Sr. The p a t t e r n s from TROPHY and ALEX are almost i d e n t i c a l and are g r o s s l y s i m i l a r to the p a t t e r n from LAKE IS on F i g . 5.23. BEND p a t t e r n s on F i g u r e 5.25 are from samples MASSET1, MASSET2 and ARIS IS. Th i s l a t t e r sample has 'peaks' at Ba and Sr, but b a r r i n g these two exc e p t i o n s the three p a t t e r n s are n e a r l y i d e n t i c a l . They are a l l s l i g h t l y e n r i c h e d i n LIL r e l a t i v e to La, have a 'trough' at Nb and are s l i g h t l y d e p l e t e d i n Hf and T i r e l a t i v e to Y. A l l p a t t e r n s have small p o s i t i v e Eu anomalies. 5.3 TRACE ELEMENT CHEMISTRY A l l samples from F i g s . 5.23 and 5.24 have abundances of tr a c e and REE and BEND p a t t e r n s which are s i m i l a r to those from oceanic and some c o n t i n e n t a l WPB (Thompson et a l . , 1983; Kay, 1984) (Table I V). Samples belonging to the a l k a l i n e s e r i e s g e n e r a l l y have higher abundances of LIL and LREE than the t h o l e i i t i c and t r a n s i t i o n a l samples. Most La 1 2 2 1000-. CO QUES LK • WGRAYN 0 SPAN CK X s TROPHY • ALEX • -~1 r—r—i—i—i—i—i—i—i 1— i — | 1—|—i 1—|—p- Ba RbTh U K NbLaCe SrNdSmZr Hf Ti Eu Tb Y Yb Lu F i g . 5-24. BEN d i a g r a m f o r s a m p l e s ALEX, QUES LK, WGRAYN, SPAN CK and TROPHY. 1 23 1000 - i MASSET1 A MASSET2 • ARIS IS + 1 1 1 1 1 1 1 1 1 1 1 1 1 I I I 1 — I 1 | Ba RbTh U K NbLaCe SrNdSmZr Hf Ti Eu Tb Y Yb Lu F i g . 5.25. BEN d i a g r a m f o r s a m p l e s MASSET1, MASSET2 and ARIS I S . 124 abundances l i e between 48 and 59 times c h o n d r i t i c i n the t h o l e i i t i c / t r a n s i t i o n a l samples and 72 to 126 times c h o n d r i t i c i n the a l k a l i n e samples. Sample ITCHA2 i s an e x c e p t i o n with an La content of 211 times c h o n d r i t i c which r e s u l t s i n t h i s samples u n u s u a l l y shaped BEND p a t t e r n . In the t h o l e i i t i c / t r a n s i t i o n a l samples Yb abundances range from 7 to 12.5 times c h o n d r i t i c and are w i t h i n the range of Yb abundances i n the a l k a l i n e samples; Yb = 6 to 18 times c h o n d r i t i c . E x c l u d i n g ITCHA2, (La/Yb> C H r a t i o s l i e between 4.41 and 14.38 i n the a l k a l i n e samples, and 4.36 to 8.23 i n the t h o l e i i t i c / t r a n s i t i o n a l samples. A l k a l i n e samples KITASU and LAKE IS are e n r i c h e d i n HREE r e l a t i v e to the remaining f i v e a l k a l i n e samples, e x p l a i n i n g t h e i r lower ( L a / Y b ) C H r a t i o s , which are more l i k e those from the t h o l e i i t i c / t r a n s i t i o n a l samples. ITCHA2 has a ( L a / Y b ) C H * r a t i o of 31.30 because of i t s enrichment i n La. La/Nb r a t i o s range from 0.75 to 1.10, w i t h i n the range of r a t i o s from OIB (Thompson et a l , 1983). The three samples from F i g . 5.25 have t r a c e and REE abundances and BEND p a t t e r n s which are g r o s s l y s i m i l a r to e i t h e r c o n t i n e n t a l WPB contaminated with c o n t i n e n t a l c r u s t , or convergent margin b a s a l t s (Dupuy and D o s t a l , 1984; Thompson et a l . , 1983). La abundances range from 59 to 86 times c h o n d r i t i c , Yb contents l i e between 11 and 12 times c h o n d r i t i c and ( L a / Y b ) C H r a t i o s from 5.43 to 7.44. These samples have La/Nb r a t i o s which l i e between 1.3 and 1.6, p r o v i d i n g a d d i t i o n a l evidence f o r e i t h e r of the above 125 a l t e r n a t i v e s . 5.3.1 TH AND U Abundances of Th range from 1.4 to 4.8 ppm and U abundances l i e between 0.6 and 1.6 ppm. Th/U r a t i o s range from 1.87 to 4.92 and average 2.77. There i s no c o r r e l a t i o n between Th and U abundances or r a t i o s and a samples age or geographic l o c a t i o n . 5.3.2 TRANSITION ELEMENTS Abundances of Cr and Ni i n samples QUES LK, WGRAYN, SPAN CK and TROPHY are higher than Cr and Ni abundances in the remaining ten b a s a l t s , suggesting f r a c t i o n a t i o n of o l i v i n e , c l i n o p y r o x e n e ± C r - S p i n e l was more important in the p e t r o g e n e s i s of the l a t t e r b a s a l t s than i n the former. ANAHIM, which has an Ni content of 56 ppm, and Cr content of 108 ppm, presumably f r a c t i o n a t e d more o l i v i n e than e i t h e r c l i n o p y r o x e n e or C r - s p i n e l . Sc contents d i v i d e the samples i n t o two groups:(A) Sc g r e a t e r than 20 ppm, and (B) Sc l e s s than 16.5 ppm. Samples ANAHIM, ITCHA1 and ITCHA2 belong to the l a t t e r group. Low Sc contents suggest a h i s t o r y i n v o l v i n g high pressure pyroxene f r a c t i o n a t i o n ( B a s a l t i c Volcanism Study P r o j e c t , 1981). 1 26 5.4 SR ISOTOPES E x c l u d i n g MASSET1, MASSET2 and ARIS IS, a v a i l a b l e Sr i s o t o p i c data does not d i s t i n g u i s h samples west of the Fra s e r from those to the e a s t . Both western and e a s t e r n samples have 8 7 S r / B 6 S r r a t i o s r a nging from 0.7030 to 0.7035 (Table I V ) . Average r a t i o s of oc e a n i c WPB range from 0.7028 to 0.706 (Faure, 1977). Sr i s o t o p i c r a t i o s f o r MASSET1, MASSET2 AND ARIS IS are 0.7039, 0.7040 and 0.7042 r e s p e c t i v e l y . These r a t i o s are d i s t i n c t l y higher than r a t i o s from the other e l e v e n samples, and are s i m i l a r to r a t i o s from convergent margin s e t t i n g s , but they are s t i l l w i t h i n the range of oceanic WPB. 5.5 DISCUSSION OF DISCRIMINATION DIAGRAMS On most elemental d i s c r i m i n a t i o n diagrams, the eleven t h o l e i i t i c , a l k a l i n e and t r a n s i t i o n a l samples from F i g s . 5.23 and 5.24 p l o t as WPB or E-MORB, and t h e i r BEND p a t t e r n s have convex-up WPB-like shapes. However on some of the diagrams a few of these samples l i e w i t h i n N-MORB or convergent margin f i e l d s . These l a t t e r c l a s s i f i c a t i o n s g e n e r a l l y occur only s p o r a d i c a l l y and t h e r e f o r e they do not seem s i g n i f i c a n t f o r d i s c r i m i n a t i o n purposes. For example, ITCHA2 l i e s w i t h i n the N-MORB f i e l d on La vs. Ba ( F i g . 5.16) because of i t s very h i g h abundance of La, RAINBOW appears to be from a convergent margin s e t t i n g on (Ba/La)^, H vs. (La/Sm) C H ( F i g . 5.17) because i t i s enriched i n Ba, QUES LK and WGRAYN l i e w i t h i n the o r o g e n i c f i e l d on La v s . Th ( F i g . 1 27 5.18) because of t h e i r r e l a t i v e enrichment i n Th and RAINBOW, ANAHIM and TROPHY l i e 'above' the WPB f i e l d on K 20/Yb vs. Ta*/Yb ( F i g . 5.20) because they are s l i g h t l y e n r i c h e d i n K 20. O l i v i n e and pyroxene ± C r - s p i n e l f r a c t i o n a t i o n lower Cr abundance i n LAKE IS, ANAHIM, RAINBOW, ITCHA1, ITCHA2 and ALEX so that they l i e w i t h i n or c l o s e to the convergent margin f i e l d on Cr vs. Ce/Sr ( F i g . 5.14) even though t h e i r Ce/Sr r a t i o s are w i t h i n the range of r a t i o s from the samples c l a s s i f i e d as WPB. The b i g g e s t e x c e p t i o n to the WPB (E-MORB) c l a s s i f i c a t i o n comes from the La vs. Ba diagram ( F i g . 5.16). On t h i s diagram s i x of the eleven samples d i s c u s s e d above l i e w i t h i n the orogenic a n d e s i t e f i e l d . However on the ( B a / L a ) C H vs. (La/Sm) C H diagram ( F i g . 5.17) only RAINBOW i s u n e q u i v o c a l l y c l a s s i f i e d as convergent margin because of i t s high abundance of Ba. T h i s d i s c r e p a n c y c a s t s some doubt on the v a l i d i t y of the La v s . Ba f i e l d boundaries, e s p e c i a l l y when t h i s diagram i s a p p l i e d to b a s a l t s . A l k a l i n e samples KITASU and LAKE IS do not always p l o t with the four other a l k a l i n e Anahim B e l t samples from west of the F r a s e r R i v e r . T h i s suggests that i f the source f o r KITASU and LAKE IS was the Anahim hotspot, i t must have been heterogeneous and changing with time. The three t h o l e i i t i c and t r a n s i t i o n a l samples i n and near Wells Gray Park g e n e r a l l y p l o t i n a group separate from the four a l k a l i n e samples west of the F r a s e r R i v e r (RAINBOW, ANAHIM, ITCHA1 and ITCHA2), and a l k a l i n e sample SPAN CK, 1 28 a l s o from Wells Gray Park, p l o t s near the other "Wells Gray" samples on many of the diagrams. T h o l e i i t i c sample ALEX, from east of the F r a s e r R i v e r , g e n e r a l l y p l o t s with the four samples j u s t d i s c u s s e d , except on diagrams a f f e c t e d by o l i v i n e and pyroxene f r a c t i o n a t i o n ( i . e . diagrams using Cr or N i ) . In an attemt to e x p l a i n why samples east of the F r a s e r River p l o t s e p a r a t e l y from samples west of the F r a s e r R i v e r the f o l l o w i n g three suggestions are o f f e r e d : t h o l e i i t i c b a s a l t s c h a r a c t e r i s t i c a l l y have lower abundances of most elements r e l a t i v e to a l k a l i n e b a s a l t s ; the source was heterogeneous; the source f o r the f i v e samples east of the F r a s e r River was not the Anahim hotspot (C.J. Hickson, o r a l comm., 1985; J.E. Souther, i n p r e s s ) . C a l c a l k a l i n e samples MASSET1 and MASSET2 and a l k a l i n e sample ARIS IS p l o t w i t h i n or towards the convergent margin f i e l d on many of the diagrams, have BEND p a t t e r n s with some of the c h a r a c t e r i s t i c s of subduction r e l a t e d b a s a l t s (high LIL with respect to La and Nb and T i d e p l e t i o n ) , La/Nb r a t i o s g r e a t e r than 1.3 and 8 7 S r / 8 6 S r r a t i o s g r e a t e r than 0.7039. On some diagrams ARIS IS p l o t s s e p a r a t e l y from MASSET1 and MASSET2 and c l o s e to KITASU and/or LAKE IS. T h i s l a t t e r grouping of samples i s seen on M n 0 - T i 0 2 - P 2 ° 5 > T i - Z r - Y , V vs. Ti/1000, T i / Y vs. Nb/Y, T i / C r v s . Ni and La vs. Ba diagrams. T h i s suggests that ARIS IS may have o r i g i n a t e d i n a source c h e m i c a l l y s i m i l a r to the KITASU and 1 29 LAKE IS source, but there were s l i g h t m o d i f i c a t i o n s towards a "convergent margin' chemistry. The convergent margin a f f i n i t y observed i n MASSET1, MASSET2 and ARIS IS decreases from west to east and with time, suggesting t h i s chemistry i s perhaps r e l a t e d t o : p o s s i b l e o b l i q u e subduction of the P a c i f i c p l a t e along the Queen C h a r l o t t e f a u l t which may have been o c c u r r i n g at that time, or volcanism i n the Pemberton Arc ( J . Souther, o r a l comm., 1985). A l t e r n a t i v e l y , Dupuy and D o s t a l (1984) suggest WPB BEND pa t t e r n s s i m i l a r to convergent margin p a t t e r n s may be produced by v a r y i n g degrees of c r u s t a l contamination. T h i s a l t e r n a t i v e might be t e s t e d with a d d i t i o n a l 0, Nd, and Pb i s o t o p i c d ata. 5.6 SUMMARY B a s a l t samples from the Anahim V o l c a n i c B e l t west of the F r a s e r R i v e r belong to the a l k a l i n e s e r i e s and are c l a s s i f i e d as WPB. B a s a l t samples from east of the Fr a s e r River belong p r i m a r i l y to the t h o l e i i t i c s e r i e s , although one sample i s a l k a l i n e , and they too are c l a s s i f i e d as WPB. These l a t t e r samples, e x c l u d i n g ALEX, are more ' p r i m i t i v e ' than the 'western' samples. Chemistry and Sr isotope r a t i o s lend no support to the suggestion that 'western' (Anahim B e l t ) and 'eastern' samples came from d i f f e r e n t sources. The observed chemical 130 d i f f e r e n c e s may e a s i l y be r e l a t e d to abundance d i f f e r e n c e s i n t h o l e i i t i c v s . a l k a l i n e s e r i e s rocks. Chemical d i f f e r e n c e s which on a few diagrams separate a l k a l i n e samples KITASU and LAKE IS from the remaining a l k a l i n e samples suggest a heterogeneous hotspot which changed with time. Two b a s a l t i c samples from the Masset Formation on the Queen C h a r l o t t e I s l a n d s belong to the c a l c a l k a l i n e s e r i e s and have chemical c h a r a c t e r i s t i c s and Sr isotope r a t i o s g r o s s l y s i m i l a r to a convergent margin b a s a l t . A l k a l i n e sample, ARIS IS, from the mainland a l s o has some convergent margin c h a r a c t e r i s t i c s . Chemistry of the Masset Formation samples suggest t h e i r source was not the Anahim hotspot, however c r u s t a l contamination of the hotspot magma c o u l d have caused the convergent m a r g i n - l i k e chemistry. A l t e r n a t i v e l y , Masset b a s a l t s may be r e l a t e d to the Pemberton Arc or they may have been produced by the p o s s i b l e o b l i q u e subduction of the P a c i f i c p l a t e along the Queen C h a r l o t t e F a u l t . However, as o b l i q u e subduction i s only e s t a b l i s h e d from recent p l a t e movements ( < 6 Ma) t h i s l a t t e r p o s s i b i l i t y i s only s p e c u l a t i v e l y a p p l i e d here. 131 TABLE IV ANAHIM VOLCANIC BELT Major, trace and rare earth element abundances, Sr Isotope rat ios, K/Ar dates and ages. M A S S E T 1 M A S S E T 2 A R I S i IS K I T A S U L A K E IS R A I N B O W 1 ANAHIM S e r i e s C a l c a l k . C a l c a l k . A l k a l I n e A l k a l i n e A l k a l I n e A l k a l I n e A l k a l I n Name B a s a l t B a s / A n d H a w a i 1 t e H a w a t 1 t e H a w a i 1 t e H a w a i 1 t e Hawa1< t L A T . 5 3 3 0 . 6 53 2 4 . 6 52 4 2 . 0 52 2 9 . 5 52 2 1 . 3 52 4 4 . 6 52 4 5 . L O N G . 132 2 0 . 0 131 5 5 . 5 129 1 5 . 5 128 4 3 . 5 128 2 1 . 0 125 4 4 . 6 125 3 7 . S i 0 2 5 0 . 3 8 5 3 . 3 1 5 0 . 38 5 0 . 15 . 47 . 24 " 5 0 . 3 0 ' - 5 0 . 3 3 T 1 0 2 1 . 5 4 1 . 6 8 1. 8 5 2 . 3 5 2 . 51 1 . 9 8 2 . 29 A 1 2 0 3 1 5 . 2 8 1 6 . 13 16 . 53 1 5 . 18 1 3 . 91 1 6 . 5 4 1 6 . 17 F e 2 0 3 1 1 . 9 5 11 . 0 3 9 . 9 0 1 3 . 0 7 1 6 . 2 0 1 2 . 8 9 1 2 . 8 4 F e O N/A N/A N/A N/A N/A N/A N/A MnO 0 . 2 2 0 . 17 0 . 15 0 . 19 0 . 2 0 0 . 19 0 . 14 MgO 7 . 3 9 4 . 3 0 6 . 46 3 . 6 6 6 . 31 3 . 18 4 . 32 C a O 8 . 0 8 7 . 7 8 8 . 6 4 7 . 62 8 . 0 0 8 . 5 2 8 . 0 1 N a 2 0 3 . 5 8 4 . 18 4 . 33 5 . 27 3 . Bfi 4 . 4 3 4 . 16 K 2 0 1 . 10 0 . 8 9 1 . 0 7 1 . 5 5 0 . 9 6 1 . 4 6 1 . 5 7 P 2 ° 5 0 . 4 7 0 . 5 3 0 . 6 9 0 . 96 0 . 81 0 . 5 1 0 . 17 H 2 0 N/A N/A N/A N/A N/A N/A 0 . 7 4 B a 3 7 0 . 0 4 6 3 . 0 5 7 9 . 0 4 0 4 . 0 4 5 7 . 0 1 1 1 3 . 0 4 3 4 . 0 Rb 3 0 . 0 21 . 0 12 . 0 28 . 0 18 . 0 1 9 . 0 24 . 0 T h 2 . 6 4 . 0 2 . 8 3 . 5 2 . 3 2 . 6 3 . 1 U 1 . 1 1 . 5 0 . 9 1 . 5 0 . 7 1 . 1 0 . 9 Nb 1 4 . 0 1 5 . 0 17 . 0 54 . 0 23 . 0 2 5 . 0 3 3 . 0 L a 1 9 . 5 2 5 . 5 28 . 1 4 1 . 4 23 . 9 2 9 . 2 3 0 . 3 C e 4 0 . 6 6 0 . 7 43 . 8 6 6 . 8 44 . 2 6 0 . 6 5 6 . 9 S r 3 5 5 . 0 6 0 1 . 0 8 9 8 . 0 4 2 0 . 0 4 4 9 . 0 7 1 4 . 0 ' 6 5 9 . 0 N d 22 . 3 2 2 . 3 22 . 5 37 . 4 29 . 4 3 3 . 2 3 3 . 7 Sm 5 . 3 6 . 2 6 . 8 10 . 7 8 . 3 7 . 5 8 . 8 Z r 176 . 0 1 8 2 . 0 161 . 0 2 4 6 . 0 188 . 0 1 8 1 . 0 2 5 0 . 0 H f 2 . 9 3 . 9 3 . 2 5 . 2 3 . 4 4 . 1 6 . 5 EU 1 . 5 1 . 7 1 . 7 2 . 7 2 . 2 3 . 9 2 . 6 T b N/A N/A 0 . 9 1 . 0 0 . 8 N/A N/A Y 3 5 . 0 3 1 . 0 29 . 0 39 . 0 41 . 0 28 . 0 2 9 . 0 Yb 2 . 4 2 . 5 2 . 5 3 . 9 3 . 6 1 . 4 1 . 8 L u 0 . 3 0 . 4 0 . 3 0 . 4 0 . 3 0 . 2 0 . 2 C o 2 6 . 0 31 . 0 21 .0 28 . 0 25 . 0 2 6 . 0 3 2 . 0 C r 4 4 . 0 5 4 . 0 84 . 0 6 3 . 4 6 0 . 3 3 6 . 2 1 0 7 . 7 C u 78 . 0 102 . 0 8 6 . 0 43 . 0 46 . 0 6 5 . 0 7 0 . 0 N i 1 6 . 0 4 2 . 0 44 . 0 42 . 0 29 . 0 24 . 0 5 6 . 0 S c 2 4 . 0 2 0 . 0 22 . 0 21 . 4 33 . 2 2 1 8 16 . 2 V 87 2 5 0 . 0 1 6 9 . 0 2 4 2 . 0 174 0 2 6 6 . 0 1 3 3 . 0 1 7 2 . 0 Sr|J 0 . 7 0 3 9 0 . 7 0 4 0 0 . 7 0 4 2 0 . 7 0 2 6 0 . 7 0 3 5 0 . 7 0 3 2 0 . 7 0 3 2 K / R b 3 0 4 . 3 7 3 5 1 . 8 0 7 4 0 . 17 4 5 9 . 5 2 4 4 2 . 72 6 3 7 . 8 7 5 4 3 . 0 2 ( L a / Y b ) r u 5 . 4 3 6 . 7 7 7 . 44 7 . 16 4 . 4 1 14 . 38 1 1 . 49 L a / N b 1 . 3 9 1 . 7 0 1 . 6 5 0 . 77 1 . 0 4 1 . 17 0 . 9 2 M g ' 5 5 44 56 36 44 33 4 0 Dates and 2 3 . 8 + 0 . 8 1 9 . 8 ± 0 . 7 ~ 1 4 ~ 1 4 ~ 1 4 7 . 9 + O . S 6 . 7 ± 0 . 3 Ages (Ma). N/A = not analyzed continued 132 I TCHA1 I T C H A 2 A L E X OUES LK W G R A Y N 2 SPAN CK T R O P H Y 2 Series A l k a l i n e A l k a l I n e T h o l T h o l T h o l . A l k a l i n e T h o l / T r a n s Name M u g e a r 1 t e H a w a i 1 t e B a s a 1 t B a s a 1 t B a s a l t B a s a n l t e B a s a 1 t L A T . 52 4 2 . 0 52 45 . 0 52 3 8 . 7 52 3 9 . 5 52 0 5 5 2 . 0 1 . 7 51 5 0 L O N G . 124 4 5 . 0 124 4 9 . 2 122 27 . 0 120 5 9 . 2 5 120 0 3 1 2 0 . 1 9 . 7 5 120 0 0 S 1 0 2 4 9 . 8 4 45 . 17 52 . 7 0 4 8 . 88 4 8 . 8 9 4 5 . 8 0 4 9 . 13 T 1 0 2 ' 2 . 6 5 2 . 98 3 . 0 8 1 . 6 5 2 . 0 8 2 . 0 7 1 . 8 5 * ' 2 ° 3 1 6 . 5 7 14 . 0 9 1 2 . 67 1 5 . 0 2 14 . 13 1 3 . 9 4 14 . 25 F e 2 ° 3 1 1 . 5 3 14 . 26 1 5 . 5 3 1 2 . 89 2 . 19 1 3 . 0 2 1 23 F e O N/A N/A N/A N/A 1 0 . 0 5 N/A 1 0 . 0 3 MnO 0 . 15 0 . 17 0 . 19 0 . 17 0 . 17 0 . 18 0 . 2 1 MgO 3 . 6 0 8 . 14 3 . 87 8 . 52 8 . 6 6 1 0 . 9 2 9 . 2 1 C a O 7 . 2 8 7 . 8 5 7 . 42 9 . 19 9 . 8 3 8 . 9 4 9 . 74 N a 2 0 6 . 0 6 4 . 78 3 . 28 2 . 71 3 . 0 2 3 . 4 1 3 . 28 K 2 0 1 . 6 3 1 . 9 0 0 . 75 0 . 78 0 . 6 7 1 . 3 0 0 . 8 0 P 2 ° S 0 . 6 9 0 . 6 8 0 . 5 0 0 . 19 0 . 3 0 0 . 4 2 0 . 2 7 H 2 0 N/A N/A N/A N/A 0 . 8 4 N/A 0 . 4 0 B a 4 1 6 . 0 5 5 3 . 0 3 0 7 . 0 2 5 7 . 0 2 4 7 . 0 701 . 0 2 6 4 . 0 Rb 2 6 . 0 33 . 0 13 . 0 18 . 0 6 . 0 26 . 0 1 2 . 0 T h 3 . 0 4 . 8 1 . 5 2 . 9 3 . 0 3 . 5 1 . 4 U 1 . 2 1 . 6 0 . 8 0 . 6 1 . 2 1 . 1 0 . 6 N b 4 5 . 0 61 . 0 2 0 . 0 21 . 0 2 2 . 0 4 2 . 0 1 6 . 0 L a 3 5 . 7 6 9 . 1 17 . 3 19 . 3 1 9 . 5 3 5 . 1 1 5 . 9 C e 71 . 4 94 . 6 4 1 . 4 31 . 3 3 5 . 3 6 5 . 7 3 9 . 4 S r 8 3 5 . 0 1004 . 0 3 3 0 . 0 391 . 0 4 1 5 . 0 6 2 5 . 0 421 . 0 N d 37 . 6 48 . 7 24 . 7 19 . 2 2 0 . 1 3 0 . 8 14 . 2 Sm 8 . 1 12 . 1 7 . 2 4 . 4 5 . 0 6 . 6 4 . 5 Z r 2 6 3 . 0 3 1 2 . 0 169 . 0 126 . 0 1 1 4 . 0 1 5 0 . 0 1 1 2 . 0 H f 6 . 2 6 . 3 3 . 8 2 . 8 2 . 6 3 . 2 2 .4 E u 2 . 5 2 . 9 1 . 8 1 . 5 1 . 6 1 . 7 1 . 4 T b 0 . 7 1 . 1 1 . 0 0 . 5 N/A 0 . 4 0 . 7 Y 2 9 . 0 24 . 0 34 . 0 22 . 0 2 7 . 0 2 1 . 0 22 . 0 Y b 2 . 3 1 . 5 2 . 7 1 . 7 1 . 6 2 . 1 2 . 1 L u 0 . 2 0 . 2 0 . 4 0 . 2 0 . 2 0 . 2 0 . 2 C o 2 9 . 0 121 . 0 33 . 0 100 . 0 8 6 . 0 5 9 . 0 1 1 2 . 0 C r 1 7 . 6 1 15 . 7 21 . 9 2 7 9 . 3 3 3 9 . 5 3 9 3 . 9 2 8 7 . 5 C u 3 3 . 0 7 9 . 0 24 . 0 52 . 0 47 . 0 6 9 . 0 38 . 0 N( 14 -0 1 19 . 0 10 . 0 160 . 0 2 0 3 . 0 3 5 7 . 0 1 3 9 . 0 S c 1 3 . 6 15 . 5 25 . 5 23 . 7 24 . 0 2 2 . 7 2 1 . 7 V 87 1 5 2 . 0 201 . 0 2 8 2 . 0 182 . 0 184 . 0 2 1 1 . 0 1 9 0 . 0 S r ? 6 0 . 7 0 3 0 N/A 0 . 7 0 3 0 N/A 0 . 7 0 3 4 0 . 7 0 3 5 0 . 7 0 3 2 K / R b 5 2 0 . 4 1 4 7 7 . 9 4 4 7 8 . 9 0 3 5 9 . 7 1 9 2 6 . 9 4 4 15 . 0 5 5 5 3 . 4 0 ( L a / Y b ) r H 1 0 . 5 8 31 . 3 0 4 . 36 7 . 8 1 8 . 2 3 1 1 . 2 0 5 . 0 5 L a / N b 0 . 7 9 1 . 13 0 . 8 7 0 . 9 2 0 . 8 9 0 . 8 4 0 . 9 9 M g ' 38 5 3 33 57 5 6 62 6 0 Dates and 0 . 7 8 + 0 . 0 7 N/A N/A N/A ~ 1 . 2 N/A ~ 0 . 28 Major element abundances f rom: 1 B e v i e r , 1978 2 F i e s i n g e r , 1975 Ages (Ma). N/A = not analyzed 6. STIKINE VOLCANIC BELT The S t i k i n e V o l c a n i c B e l t i s b e l i e v e d to be zone of i n c i p i e n t l a t e Cenozoic extension r e l a t e d to t r a n s c u r r e n t motion along the adjacent c o n t i n e n t a l margin (Souther, 1977). Large volumes of a l k a l i n e b a s a l t s to p e r a l k a l i n e r h y o l i t e s form the b a s a l t i c s h i e l d s , composite domes, flows and c e n t r a l volcanoes of the Mount E d z i z a V o l c a n i c Complex, L e v e l Mountain and Hart Peaks (Souther et a l . , 1984; Hamilton, 1981). Hoodoo Mountain, a d i f f e r e n t i a t e d v o l c a n i c complex to the south, i s not as voluminous. The remainder of the S t i k i n e V o l c a n i c B e l t i s comprised of small monogenetic cones and l a v a flows (Souther et a l . , 1984; R.L. Armstrong, p e r s . comm., 1985). Twenty-two samples from the S t i k i n e V o l c a n i c B e l t were s e l e c t e d f o r a n a l y s i s ( F i g . 6.1) Four are from the Mt. E d z i z a V o l c a n i c Complex and another four are from r e s i d u a l b a s a l t caps and v a l l e y flows north and northeast of Mt. E d z i z a at approximately 58° N. Three samples are from the L e v e l Mountain volcano, west of Dease Lake and two are from near A t l i n . One sample comes from an i s o l a t e d cone i n the northwest part of the Bowser Basin, two were c o l l e c t e d from the recent Aiyansh River flow i n the southwest Bowser B a s i n and one i s from a dyke l o c a t e d j u s t to the n o r t h of P r i n c e Rupert. Four of the f i v e remaining samples are from monogenetic v o l c a n i c c e n t e r s i n the S i k i n e r e g i o n northwest of Stewart and the f i f t h i s from Hoodoo Mountain. 133 F i g . 6 .1 . Sample l o c a t i o n map f o r the S t i k i n e V o l c a n i c B e l t . 1 35 K-Ar dates from samples i n the Mount E d z i z a V o l c a n i c Complex and l o c a t i o n s j u s t to the north range from 0.507 ± 0.070 to 7.8 ± 0.3 Ma (Table V ) , BOWSER has a K-Ar date of 1.6 ± 0.3 Ma and samples PRINCER and SATLIN have been dated at 7.2 ± 0.8 and 16.5 ± 3.1 Ma r e s p e c t i v e l y (U.B.C. K-Ar l a b ) . C 1 * dates obtained from the Aiyansh l a v a flow give an age of 220 years (Sutherland-Brown, 1969). Samples from near the Iskut River (BORDERLK, ISKUTW, MT DUNN and ISKUT) are approximately 0.04 Ma o l d and HOODOO has been dated at 0.02 ± 0.013 Ma (U.B.C. K-Ar l a b ) . The three samples from L e v e l Mountain have not been dated but other samples from L e v e l Mountain have K-Ar dates of 5.8 to 14.9 Ma. 6.1 MAJOR ELEMENT CHEMISTRY Abundances of major elements i n most of the b a s a l t i c samples are very s i m i l a r to abundances i n an average Hawaiian a l k a l i o l i v i n e b a s a l t (MacDonald, 1968), or the a l k a l i n e Anahim B e l t v o l c a n i c s ( t h i s study) (Table V ) . Mg' numbers range from 32 to 58, the lowest numbers from AYNSH1 and AYNSH2. Samples PRINCER and SATLIN are d i s t i n g u i s h e d from the remainder of the s u i t e by lower t o t a l a l k a l i s at a given S i 0 2 content, as w e l l as lower abundances of T i 0 2 . PRINCER has an Mg' number of 61, i n d i c a t i n g i t i s the l e a s t f r a c t i o n a t e d sample i n t h i s s u i t e . Abundances of most major elements i n LEVELD are g e n e r a l l y s i m i l a r to abundances in PRINCER and SATLIN, but 1 36 i t s T i 0 2 content i s hig h e r . HOODOO has a higher abundance of S i 0 2 (59 wt%), very low abundances of T i 0 2 , MgO, and CaO and a molecular excess of (Na 20+K 20) over A l 2 0 3 . Both acmite and sodium m e t a s i l i c a t e appear i n i t s l i s t of normative m i n e r a l s , d i s t i n g u i s h i n g i t as p e r a l k a l i n e (MacDonald, 1974; Carmichael et al.,1974), and i t s d i f f e r e n t i a t i o n index of 80 i d e n t i f i e s i t as a t r a c h y t e (Thompson et a l . , 1972; Thornton and T u t t l e , 1960). Trace element abundances are a l s o c h a r a c t e r i s t i c of a h i g h l y f r a c t i o n a t e d p e r a l k a l i n e l a v a ( F e r r a r a and T r e u i l , 1974). I t s Ba and Sr abundances are l e s s than 1 ppm, the t r a n s i t i o n elements (Co, Cr, Cu, N i , Sc, and V) occur i n very low abundances and i t i s g r e a t l y e n r i c h e d i n Rb, Th, U, K, Nb, Zr, Hf and a l l REE's, except Eu. These p e r a l k a l i n e chemical c h a r a c t e r i s t i c s p r e c l u d e comparisons with the S t i k i n e b a s a l t s u i t e , t h e r e f o r e i t w i l l not be p l o t t e d on any of the t e c t o n i c d i s c r i m i n a t i o n diagrams. 6.2 DISCRIMINATION DIAGRAMS 6.2.1 MAJOR ELEMENT CLASSIFICATIONS On t o t a l a l k a l i s vs. s i l i c a one sample (PRINCER) l i e s on MacDonalds (1968) d i v i d i n g l i n e between the s u b a l k a l i n e and a l k a l i n e f i e l d s , two (LEVELD and SATLIN) l i e j u s t w i t h i n the a l k a l i n e f i e l d c l o s e to the d i v i d i n g l i n e and the remaining e i g h t t e e n samples l i e w i t h i n the 1 37 a l k a l i n e f i e l d ( F i g . 6.2). On Ol'-Ne'-Qz' (not shown) PRINCER, SPEC 1, NEDZ1 and SATLIN are c l a s s i f i e d as s u b a l k a l i n e and the remainder are c l a s s i f e d as a l k a l i n e . Samples SPEC 1 and NEDZ1, c l a s s i f i e d as s u b a l k a l i n e on Ol'-Ne'-Qz' , but not on a l k a l i s v s . s i l i c a , have major element abundances which are i n d i s t i n g u i s h a b l e from a l k a l i n e samples ISKUT and BORDERLK. In c o n t r a s t , sample LEVELD, which i s a l k a l i n e on Ol'-Ne'-Qz', and b a r e l y a l k a l i n e on a l k a l i s vs. s i l i c a , has abundances of K 20 and P 2 0 5 which are s i m i l a r to abundances i n t h o l e i i t i c samples PRINCER and SATLIN. Because of these c o n t r a s t i n g elemental and normative m i n e r a l c l a s s i f i c a t i o n s these three samples w i l l be c a l l e d t r a n s i t i o n a l and p l o t t e d with the s u b a l k a l i n e samples from Ol'-Ne' -Qz' . A l l f i v e s u b a l k a l i n e and t r a n s i t i o n a l samples belong to the t h o l e i i t i c s e r i e s on AFM and FeO*/MgO vs. S i 0 2 ( F i g s . 6.3 and 6.4). On the AFM diagram, a l l f i v e samples have t o t a l a l k a l i s l e s s than 20% so a l l of them can be p l o t t e d on T i 0 2 - K 2 0 - P 2 0 5 ( F i g . 6.5). Four of the f i v e l i e w i t h i n the non-oceanic f i e l d , but LEVELD c l e a r l y l i e s w i t h i n the oceanic f i e l d . On MnO-Ti0 2-P 20 5 ISKUTW l i e s j u s t w i t h i n the OIT f i e l d , but the remaining twenty samples l i e w i t h i n the OIA f i e l d ( F i g . 6.6) . 1 3 8 F i g . 6 . 2 . T o t a l a l k a l i s v s . s i l i c a . S u b a l k a l i n e / a l k a l i n e b o u n d a r y f o m M a c D o n a l d ( 1 9 6 8 ) . AYNSH1 X PRINCER • ISKUT 0 BORDERLK 0 EDZ1 A SPEC 1 At NEDZ1 Dt NEDZ3 • LEVEL 1 • LEVELD Tt NATLIN V FeO* AYNSH2X MT DUNN 0 ISKUTW0 BOWSER + EDZ2 A SPEC2 A NEDZ 2 121 NEDZ4 0 LEVEL2 • SATLIN V t S i O , F i g . 6 . 3 . A F M d i a g r a m . T h o l e i i t i c / c a l c a l k a l i n e b o u n d a r y f r o m I r v i n e a n d B a r a g a r ( 1 9 7 1 ) . PRINCER • SPEC1 A NEDZ1 • LEVELD T SATLIN V 0.2 Na 20 + K 20 0.4 0.6 0.8 F i g . 6 . 4 . F e O * / M g O v s . S i 0 2 . T h o l e i i t i c / c a l c a l k a l i n e b o u n d a r y f r o m M i y a s h i r o ( 1 9 7 4 ) . SiCL 139 Four of the f i v e s u b a l k a l i n e and t r a n s i t i o n a l samples l i e w i t h i n the 01 f i e l d on MgO-FeO*-Al 20 3 ( F i g . 6 . 7 ) . LEVELD l i e s w i t h i n the c o n t i n e n t a l b a s a l t f i e l d . 6.2.2 TRACE ELEMENT CLASSIFICATIONS A l l twenty-one samples c l e a r l y l i e w i t h i n the WPB f i e l d on T i - Z r - Y ( F i g . 6.8), t h e r e f o r e T i - Z r - S r i s not needed. On V vs. Ti/1000 a l l samples analyzed f o r V have T i / V r a t i o s g r e a t e r than 50 and l i e w i t h i n the WPB f i e l d ( F i g . 6.9). T h o l e i i t i c samples PRINCER and SATLIN have the lowest T i / V r a t i o s and are s l i g h t l y separated from the remaining nineteen samples. A l l samples c l e a r l y l i e w i t h i n the WPB f i e l d on Ti/Y v s. Nb/Y ( F i g . 6.10). Samples from the l o c a t i o n s j u s t to the north of the Mount E d z i z a Complex (the NEDZ samples) have the hig h e s t T i / Y and Nb/Y r a t i o s . On T i / C r vs. Ni a l l samples p l o t w i t h i n the TH MORB f i e l d or along the boundary between the IAT and TH MORB f i e l d s ( F i g . 6.11). AYNSH1 and AYNSH2 l i e f a r from the remainder of the s u i t e because of t h e i r high T i / C r r a t i o s . 6 6.2.3 TRACE AND REE CLASSIFICATIONS On Cr vs. Ce/Sr approximately two-thirds of the samples l i e w i t h i n or c l o s e to the o v e r l a p p i n g MORB-WPB rigo F i g . 6.6. MnO-Ti0 2-P 20 5 0.8 AYNSH1 X PRINCER • ISKUT 0 BORDERLK< EDZ1 • SPEC1 At NEDZ1 Dt NEDZ3 a LEVEL1 • LEVELD Tt NATLINV AYNSH2X MT DUNN 0 ISKUTWO BOWSER + EDZ2 • SPEC2 A NEDZ2 0 NEDZ4 0 LEVEL2 • SATLIN V, FeO* 0.6 OIT IORI p 2 o 5 X F i g . 6.7. MgO-FeO*-Al 20 3 PRINCER • SPEC1 A NE0Z1 • LEVELD • SATLIN V 0.2 0.4 0.6 0.8 ni 2 o 3 TI/100 141 0.8 0.4 0.2 0.6 Zr 0.2 0.4 0.6 0.8 Y X 3 AYNSH1 X PRINCER • I S K U T 0 BORDERLK 0 EDZ1 • SPEC1 At NEDZ1 Dt NEDZ3 O L E V E L 1 • LEVELD f t N A T L I N V A Y N S H 2 X MT DUNN 0 ISKUTW O BOWSER + EDZ2 • SPEC2 A NEDZ2 0 NEDZ4 0 L E V E L 2 • S A T L I N V , > 300 H J J J I I I L F i g s . 6.8 and 6.9. T i - Z r - Y (above) and V vs. Ti/1000 (below). 142 AYNSH1 X PRINCER • ISKUT 0 BORDERLK < EDZ1 • SPEC 1 A t NEDZ1 Dt NEDZ3 • LEVEL 1 • LEVELD T t NATLIN V AYNSH2 X MT DUNN O ISKUTW 0 BOWSER + EDZ2 A SPEC2 A NEDZ 2 121 NEDZ 4 121 LEVEL2 • SATLIN V, 1 oooH 1 0 0 0 F i g s . 6.10 and 6.11. T i / Y vs. Nb/Y (above) and T i / C r vs. Ni (below). 143 f i e l d s ( F i g . 6.12). AYNSH1 and AYNSH2 have very low abundances of Cr and l i e below the WPB f i e l d although t h e i r Ce/Sr r a t i o s are w i t h i n the range of MORB-WPB samples. The f i v e remaining samples l i e w i t h i n the ARC f i e l d . On Cr vs. Y a l l samples, except NEDZ3, l i e w i t h i n or c l o s e to the ov e r l a p p i n g ARC-MORB-WPB or ARC-WPB f i e l d s ( F i g . 6.13). R e l a t i v e to the other samples NEDZ3 i s s l i g h t l y depleted i n both Cr and Y and c l e a r l y l i e s w i t h i n the ARC f i e l d . Twelve of the twenty-one samples have Ba/La r a t i o s g r e a t e r than 15 and l i e w i t h i n or c l o s e to the orogenic a n d e s i t e f i e l d on La vs. Ba ( F i g . 6.14). Seven samples l i e w i t h i n the f i e l d f o r WPB (E-MORB) and two l i e w i t h i n the N-MORB f i e l d , with Ba/La r a t i o s l e s s than 11. In c o n t r a s t , on ( B a / L a ) C H vs. (La/Sm) C H nineteen of the twenty-one samples l i e w i t h i n or c l o s e t o the ocean b a s a l t f i e l d and only two (AYNSH1 and AYNSH2) are s u f f i c i e n t l y e nriched i n Ba to c l e a r l y l i e w i t h i n the ov e r l a p p i n g ocean and ARC f i e l d s ( F i g . 6.15). A l l twenty-one samples are c l a s s i f i e d as WPB (E-MORB) on La vs. Th ( F i g . 6.16). Out of these, only two (NEDZ4 and SATLIN) l i e w i t h i n the o v e r l a p p i n g WPB and ARC f i e l d s . On La vs. Nb a l l samples l i e w i t h i n or on the border of the WPB (E-MORB) f i e l d ( F i g . 6.17). E x c l u d i n g NEDZ1, s u b a l k a l i n e and t r a n s i t i o n a l samples have the 1 0 0 0 1000 AYNSH1 X PRINCER • ISKUT 0 BORDERLK0 EDZ1 • SPEC1 At NEDZ1 Dt NEDZ3 • LEVEL1 T LEVELD Tt NATLIN V AYNSH2X MT DUNN 0 ISKUTWO BOWSER + EDZ2 • SPEC2 A NEDZ2 a NEDZ4 0 LEVEL2 T SATLIN V, 100 1 0 100 F i g s . 6.12 and 6.13. Cr vs. Ce/Sr (above) and Cr v s . Y (below). 145 AYNSH1 X PRINCER • ISKDT O BORDERLK < EDZ1 • SPEC1 At NEDZ1 Dt NEDZ3 O L E V E L 1 T L E V E L D Tt NATLIN V AYNSH2X MT DUNN O ISKUTWO BOWSER + EDZ2 A SPEC2 A NEDZ2 0 NEDZ4 0 L E V E L 2 • S A T L I N V t (La/Sm) CH F i g s . 6.14 and 6.15. La vs. Ba (above) and (Ba/La) vs. ( L a / S m ) r u (below). 146 AYNSH1 X PRINCER • ISKUT 0 BORDERLK< EDZ1 A SPEC 1 At NEDZ1Ot NEDZ3 • LEVEL 1 T LEVELD Tt NATLIN V AYNSH2 X MT DUNN 0 ISKUTWO BOWSER + EDZ2 A SPEC2 A NEDZ2 0 NEDZ4 0 LEVEL2 • SATLIN V, 60 Figs. 6.16 and 6.17. La vs. Th (above) and La vs. Nb (below). 1 47 lowest La and Nb abundances, although t h e i r La/Nb r a t i o s are s i m i l a r to r a t i o s from the a l k a l i n e samples. A l l samples l i e w i t h i n or j u s t o u t s i d e of the ov e r l a p p i n g WPB - MORB f i e l d s on K 20/Yb vs. Ta*/Yb ( F i g . 6.18). Three samples (NEDZ1, NEDZ3 and NATLIN) have r e l a t i v e l y high K 20/Yb and Ta*/Yb r a t i o s and l i e towards the non-overlapping WPB f i e l d , whereas LEVELD has much lower K 20/Yb and Ta*/Yb r a t i o s and l i e s toward the non-overlapping MORB f i e l d . On Th/Yb vs. Ta*/Yb a l l samples c l e a r l y l i e w i t h i n the o v e r l a p p i n g WPB-MORB f i e l d s ( F i g . 6.19) and on Th-Hf/3-Ta* a l l samples l i e w i t h i n the f e i l d s f o r a l k a l i n e and t h o l e i i t i c WPB (E-MORB) ( F i g . 6.20) 6.2.4 BULK EARTH NRMALIZED DIAGRAMS (BEND) To c l a r i f y BEND p a t t e r n s samples were d i v i d e d i n t o s i x groups ( F i g s . 6.21, 6.22, 6.23, 6.24, 6.25 and 6.26). In general a l l p a t t e r n s have convex-up WPB-like shapes, most of them d i s p l a y p o s i t i v e Eu anomalies and a l l of them show s l i g h t enrichment i n K r e l a t i v e to an oceanic WPB (Thompson et a l . , 1983 and 1984). T h o l e i i t i c samples PRINCER and SATLIN are p l o t t e d on F i g . 6.21. These p a t t e r n s are f a i r l y f l a t from Ba to La and then slope n e g a t i v e l y towards Lu, with a concave-up d i p from Sm to Eu. The p a t t e r n from t r a n s i t i o n a l sample LEVELD a l s o appears on F i g . 6.21. I t i s markedly e n r i c h e d i n Ba r e l a t i v e to Rb, has 'peaks' 148 1 oo 1 0 JQ >- •— O CM 1 1 0. 1 1 r 0 . 0 1 0.1 1 Ta#/Yb 1 0 F i g . 6.19. Th/Yb vs. Ta*/Yb. > F i g . 6.18. K20/Yb vs. Ta*/Yb. AYNSH1 X PRINCER • ISKUT 0 BORDERLK 0 EDZ1 • SPEC 1 At N E D Z 1 Dt NEDZ3 • L E V E L 1 T L E V E L D Tt NATLIN V AYNSH2X MT DUNN 0 ISKUTWO BOWSER + EDZ2 A SPEC2 A NEDZ2 0 NEDZ4 0 LEVEL2 T S A T L I N V , 1 0 0.1 Hf/3 0.0 1 0 .01 0.1 1 Ta*/Yb F i g . 6.20. Th-Hf/3-Ta*. 1 o Th Ta* 149 1000 -, CO B -I < > Q UJ N < cr O 100- 10 \7A PRINCER • LEVELD • SATLIN V — I 1 1 1 1 I 1 1 1 1 I I I I I I I 1 — 1 — Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F 1 g . 6 . 2 1 . BEN d i a g r a m f o r s a m p l e s PRINCER, LEVELD and SATL IN . 1 50 at Sr and T i and 'troughs' at Ce and Hf. Ex c l u d i n g Ba enrichment, t h i s l a t t e r p a t t e r n g r o s s l y resembles the BEND p a t t e r n from an E-MORB ( F i g . 2.25). F i g . 6.22 has p a t t e r n s from AYNSH1, AYNSH2 and BOWSER. The former two samples are en r i c h e d i n Ba r e l a t i v e to Rb and have 'troughs' at Sr. This i s unusual because both of them have l a r g e p o s i t i v e Eu anomalies. The p a t t e r n from BOWSER has a s l i g h t 'trough' at Nd and no Eu anomaly. Samples on F i g . 6.23 are from the Iskut River a r e a . A l l four p a t t e r n s are remarkably s i m i l a r with ' t y p i c a l ' WPB shapes (Thompson et a l . , 1983). ISKUT i s e n r i c h e d i n Ba r e l a t i v e to Rb and MT DUNN has 'troughs' at Ce and Hf . Patt e r n s d i s p l a y e d on F i g . 6.24 are from the Mount E d z i z a V o l c a n i c Complex. SPEC 1 and EDZ2 are en r i c h e d i n Ba r e l a t i v e to Rb, but otherwise the pa t t e r n s are almost i d e n t i c a l and s i m i l a r to those on F i g . 6.23. F i g . 6.25 has p a t t e r n s from the samples j u s t to the north of the Mount E d z i z a Complex. The o l d e s t samples, NEDZ1 and NEDZ3, are separated from the younger samples, NEDZ2 and NEDZ4, because of the formers s l i g h t l y higher abundances of LIL elements and lower abundances of Yb. NEDZ1 and NEDZ3 have the most f r a c t i o n a t e d p a t t e r n s but p a t t e r n shapes f o r a l l four samples are s i m i l a r . NEDZ2 and NEDZ4 are s l i g h t l y e n r i c h e d i n Ba r e l a t i v e to Rb, NEDZ2 has a small 'trough' at Sm and NEDZ1 has small 151 1000 -. F i g . 6 . 2 2 . BEN d i a g r a m f o r s a m p l e s AYNSH1, AYNSH2 and BOWSER. 152 1000 -i CO 1 — * — i — i — i — i — i — i — i — i — i i i — i i i i i i — i — i — Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F1g. 6.23. BEN diagram for samples MT DUNN, ISKUT, ISKUTW and BORDERLK. 153 1000 - i co 1 r ~ ~ ' — ' — • — i — r — i — i — i — r — i — i i i — i — i 1 — | — | — Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F i g . 6 . 2 4 . BEN d i a g r a m f o r s a m p l e s EDZ1, SPEC 1, SPEC2, and EDZ2. 154 1000 n 1 — ' — i — i — i — i — i — r — i — r — i — i r - 1 — I r — T — r — i — i — r - Ba RbTh U K NbLaCe SrNdSmZr Hf Ti Eu Tb Y Yb Lu F i g . 6 . 2 5 . BEN d i a g r a m f o r s a m p l e s NEDZ1, NEDZ2, NEDZ3, and NEDZ4 155 1000 n 1 — ' — " — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F i g . 6 . 2 6 . BEN d i a g r a m f o r s a m p l e s LEVEL 1, LEVEL2 and NATLIN. 156 'peaks' at Sr and Zr. The two a l k a l i n e samples from L e v e l Mountain and the b a s a n i t e from north of A t l i n are p l o t t e d on F i g . 6.26. A l l three p a t t e r n s have l a r g e p o s i t i v e Eu anomalies without a c o r r e s p o n d i n g 'peak' at Sr and LEVEL 1 and LEVEL2 are s l i g h t l y e n r i c h e d i n Ba r e l a t i v e to Rb. R e l a t i v e to the other 20 BEND p a t t e r n s , NATLIN's p a t t e r n i s the most f r a c t i o n a t e d . 6.3 TRACE ELEMENT CHEMISTRY As a group the S t i k i n e B e l t b a s a l t s have abundances of t r a c e and REE and BEND p a t t e r n s g r o s s l y s i m i l a r to oceanic WPB, but the s u i t e shows c o n s i d e r a b l e i n t e r n a l v a r i a t i o n . T h i s i s most evident i n abundances of Ba, Th, U and Sr. In g e n e r a l the a l k a l i n e and t r a n s i t i o n a l samples, e x c l u d i n g LEVELD, have higher abundances of t r a c e and r a r e e a r t h elements than the t w o • t h o l e i i t i c samples (PRINCER and SATLIN), although there i s a s m a l l amount of o v e r l a p . La abundances i n the nineteen a l k a l i n e and t r a n s i t i o n a l samples range from 46 to 144 times c h o n d r i t i c , Yb contents l i e between 4 and 14 times c h o n d r i t i c and ( L a / Y b ) ^ r a t i o s range from 5.9 to 24.5. The h i g h e s t ( L a / Y b ) C H r a t i o s are from NEDZ1, NEDZ3 and NATLIN, c o r r e s p n d i n g to t h e i r f r a c t i o n a t e d BEND p a t t e r n s . S i m i l a r abundances and r a t i o s i n the two t h o l e i i t i c samples a r e : La = 47 and 54 times c h o n d r i t i c , Yb = 6.8 and 7.7 times c h o n d r i t i c and ( L a / Y b ) ^ = 5.9 and 8. 157 A l l samples have La/Nb r a t i o s l e s s than or b a r e l y g r e a t e r than 1.0. These r a t i o s are c h a r a c t e r i s t i c of r a t i o s in oceanic WPB (Thompson et a l . , 1983). R e l a t i v e to the other twenty samples LEVELD has very low abundances of a l l LIL elements except Ba. I t has an La content of 34.2 times c h o n d r i t i c , a Yb abundance of 9.1 times c h o n d r i t i c and an ( L a / Y b ) o u r a t i o of 3.83. These geochemical c h a r a c t e r i s t i c s suggest i t came from a source r e g i o n d e p l e t e d i n LIL by a p r e v i o u s e x t r a c t i o n of melt, an i n t e r p r e t a t i o n c o n s i s t e n t with the E-MORB shape of i t s BEND p a t t e r n ( T h i r w a l l and Jones, 1983). 6.3.1 TH AND U Abundances of Th i n samples from the S t i k i n e s u i t e l i e between 0.8 and 4.4 ppm and U abundances range from 0.3 to 1.5 ppm (Table V ) . Th/U r a t i o s are h i g h l y v a r i a b l e , range from 1.5 to 4.6 and average 3.0, s i m i l a r to Th/U r a t i o s from many oceanic WPB ( B a s a l t i c Voicanism Study P r o j e c t , 1981). 6.3.2 TRANSITION ELEMENTS Samples with low abundances of Cr and N i , and low Mg' numbers (AYNSH1, AYNSH2, IKUTW, MT DUNN, ISKUT, EDZ1, NEDZ2 and LEVEL 1) have been more e x t e n s i v e l y f r a c t i o n a t e d than the remaining fourteen samples, e x c l u d i n g SPEC2 and NEDZ3, which have higher Cr and Ni abundances and higher Mg' numbers. SPEC2 and NEDZ3, 158 which are de p l e t e d i n Ni r e l a t i v e to Cr, probably had a f r a c t i o n a t i o n h i s t o r y which was dominated by the c r y s t a l l i z a t i o n of o l i v i n e r a ther than c l i n o p y r o x e n e and/or C r - s p i n e l . E x c l u d i n g NEDZ1, NEDZ3 and NATLIN, Sc contents range from 18.1 to 27.1 ppm and average 23 ppm. NEDZ1, NEDZ3 and NATLIN have Sc abundances of 15.7, 11.8 and 17 ppm r e s p e c t i v e l y . These l a t t e r three samples a l s o have very low abundances of Yb and Lu, with ( L a / Y b ) ^ H r a t i o s g r e a t e r than 24. Low abundances of Sc suggest f r a c t i o n a t i o n of pyroxene at high p r e s s u r e s , whereas low Yb and Lu abundances and f r a c t i o n a t e d ( L a / Y b ) C H r a t i o s suggest small degrees of p a r t i a l m e l t i n g of a garnet p e r i d o t i t e (Gast, 1968; Kay and Gast, 1973; B a s a l t i c Voicanism Study P r o j e c t , 1981; C u l l e r s and Graf, 1984). 6.4 SR ISOTOPES A v a i l a b l e 8 7 S r / 8 6 S r r a t i o s from the S t i k i n e B e l t samples range from 0.7030 to 0.7039, except sample BOWSER which has an 8 7 S r / 8 6 S r r a t i o of 0.7023 (Table V) (Hamilton, 1981; UBC geochronology l a b ) . These r a t i o s are mostly w i t h i n the range f o r ocean i s l a n d s (0.7028 to 0.706), are the same as those observed i n the Anahim V o l c a n i c B e l t and C h i l c o t i n Group B a s a l t s and i n d i c a t e an uncontaminated mantle source f o r these b a s a l t s . The low Sr i s o t o p i c r a t i o i n sample BOWSER i s t y p i c a l of a MORB rat h e r than a WPB, and suggests t h i s sample came from an i s o t o p i c a l l y d e p l e t e d source. 159 6.5 DISCUSSION OF DISCRIMINATION DIAGRAMS S t i k i n e V o l c a n i c B e l t samples are c l a s s i f i e d as WPB on almost a l l major, t r a c e and rare e a r t h element t e c t o n i c d i s c r i m i n a t i o n diagrams. Major exceptions to t h i s c l a s s i f i c a t i o n are seen on Cr vs. Ce/Sr ( F i g . 6.12), Cr vs. Y ( F i g . 6.13) and La vs. Ba ( F i g . 6.14) On these diagrams some of the samples l i e w i t h i n the ARC f i e l d because of t h e i r low Ce/Sr r a t i o s , low Y abundances or high Ba abundances. Low Ce/Sr r a t i o s , observed on Cr vs. Ce/Sr, are g e n e r a l l y caused by an in c r e a s e i n the Sr content, or more u n u s u a l l y as i n LEVELD and ISKUTW, by a decrease i n the abundance of Ce, both of which are evident on BEND. Increase d Sr abundances probably r e s u l t from an accumulation of p l a g i o c a l s e i n the analyzed samples (note a l s o the p o s i t i v e Eu anomalies) but Ce d e p l e t i o n i s l e s s e a s i l y e x p l a i n e d as there are no minerals which p r e f e r e n t i a l l y i n c o r p o r a t e Ce ( C u l l e r s and Graf, 1984). S l i g h t l y higher Ce/Sr r a t i o s i n samples from the A i y a n i s h flow r e f l e c t t h e i r n e g a t i v e Sr anomalies on BEND. These anomalies suggest p l a g i o c l a s e f r a c t i o n a t i o n and removal i n the source, but l a r g e p o s i t i v e Eu anomalies i n these same samples suggests the analyzed rocks may have co n t a i n e d cumulate p l a g i o c l a s e . V a r i a t i o n s i n the Y content, a f f e c t i n g c l a s s i f i c a t i o n s on Cr vs. Y, r e f l e c t e i t h e r a heterogeneous source, v a r i a b l e degree of p a r t i a l m e l t i n g , and/or the presence/absence of a r e s i d u a l phase which c o n t a i n s Y, such as garnet, z i r c o n , 1 60 sphene or a p a t i t e (Pearce, 1982; Clague and Frey, 1982). Ba enrichment which shows up on La vs. Ba and BEND i s a t y p i c a l f o r oceanic or c o n t i n e n t a l WPB and suggests i n t e r a c t i o n with an a l k a l i r i c h v o l a t i l e phase (Clague and Frey, 1982). I n t e r a c t i o n with such a phase c o u l d a l s o produce the s l i g h t enrichment in K r e l a t i v e to Nb, seen on BEND and K 20/Yb vs. Ta*/Yb. An a l k a l i - r i c h v o l a t i l e phase may a l s o provide an e x p l a n a t i o n f o r the i n c r e a s e d abundances of Sr. LEVELD l i e s towards the MORB (oceanic) f i e l d on many of the t e c t o n i c d i s c r i m i n a t i o n diagrams because of i t s d e p l e t i o n i n LIL elements r e l a t i v e to an 'average' WPB. The towards-MORB c l a s s i f i c a t i o n p r o v i d e s a d d i t i o n a l evidence of i t s MORB-like d e p l e t e d source. The only t h o l e i i t i c samples i n t h i s s u i t e are l o c a t e d at the western edge of the S t i k i n e B e l t . PRINCER i s a l s o the southernmost sample and SATLIN, n e a r l y the northernmost, i s o l d e r than a l l of the r e s t . From these o b s e r v a t i o n s i t i s p o s s i b l e t h at these t h o l e i i t e s do not s t r i c t l y r e present the S t i k i n e B e l t . Because SATLIN i s markedly o l d e r than a l l of the other samples and l i e s near the Miocene Wrangell B e l t i n the Yukon, i t may be an o u t l i e r of the Wrangell Arc whose a c t i v i t y i s now r e s t r i c t e d to Al a s k a , whereas PRINCER may be the r e s u l t of the small component of P a c i f i c P l a t e subduction along the Queen C h a r l o t t e f a u l t . However, a l l t e c t o n i c d i s c r i m i n a t i o n diagrams c l a s s i f y these two samples as WPB with no evidence f o r an ARC-like component. 161 6.6 SUMMARY Six t e e n of the twenty-one b a s a l t i c samples from the S t i k i n e V o l c a n i c B e l t were c l a s s i f i e d as a l k a l i n e WPB on a l l chemical and t e c t o n i c d i s c r i m i n a t i o n diagrams s t u d i e d . Three of the remaining samples were c l a s s i f e d as a l k a l i n e / t r a n s i t i o n a l WPB, and the l a s t two were c l a s s i f i e d as t h o l e i i t i c WPB. HOODOO was c l a s s i f e d as p e r a l k a l i n e and was not p l o t t e d on any of the t e c t o n i c d i s c r i m i n a t i o n diagrams. Most major, t r a c e and ra r e earth element abundances and Sr isotope r a t i o s i n the b a s a l t i c samples are s i m i l a r to abundances i n WPB from the Anahim V o l c a n i c B e l t , the C h i l c o t i n Group B a s a l t s and Hawaii. E n r i c h e d contents of Ba, K ± Sr which produce anomalous c l a s s i f i c a t i o n s on Cr vs. Ce/Sr, Cr vs. Y and La vs. Ba are a t t r i b u t e d to i n t e r a c t i o n with an a l k a l i - r i c h v o l a t i l e phase. Sr enrichment may a l s o be caused by cumulate p l a g i o c l a s e i n the sample, a more l i k e l y e x p l a n a t i o n when there i s a corresponding enrichment in Eu ( p o s i t i v e Eu anomaly). AYNSH1 and AYNSH2 are depleted i n Sr but enr i c h e d in Eu, suggesting a complex h i s t o r y i n v o l v i n g both p l a g i o c l a s e f r a c t i o n a t i o n and accumulation. LEVELD i s dep l e t e d i n LIL, has a low (La/Yb)-,„ r a t i o , CH l i e s towards the MORB f i e l d on many of the t e c t o n i c d i s c r i m i n a t i o n diagrams and has a BEND p a t t e r n with an E-MORB shape. These c h a r a c t e r i s t i c s imply a source region d e p l e t e d i n LIL by a pr e v i o u s e x t r a c t i o n of melt. 162 The two t h o l e i i t i c s e r i e s b a s a l t s are unusual i n t h i s predominantly a l k a l i n e - p e r a l k a l i n e v o l c a n i c b e l t and s i n c e they l i e nearest to the c o n t i n e n t a l margin may be r e l a t e d to P a c i f i c P l a t e subduction, although d i s c r i m i n a t i o n diagrams do not support t h i s suggestion. 163 TABLE V STIKINE VOLCANIC BELT Major, trace and rare earth element abundances, Sr Isotope rat ios , K/Ar dates and ages. P R I N C E R AYNSH1 AYNSH2 HOODOO BORDERLK ISKUTW MT DUNN ISKUT S e r i e s T h o l e i i t e A l k a l i n e A l k a l i n e P e r a l k . A l k a l i n e f I k a l i n e A l k a l i n e A l k a l i n e Name B a s a l t H a w a i I t e H a w a i i t e T r a c h y t e A l k . B a s . A l k . B a s . A l k . B a s . H a w a i i t e L A T . 54 2 6 . 0 5 5 0 6 . 5 5 5 1 1 . 0 56 4 6 . 5 56 2 1 . 5 56 2 4 . 0 5 6 2 9 . 5 56 4 3 . 0 L O N G . 130 2 9 . 5 128 5 4 . 0 129 1 2 . 0 131 1 9 . 5 130 4 3 . 0 130 5 3 . 0 130 3 9 130 3 7 . 0 S 1 0 2 4 8 . 2 6 4 7 . 3 8 48 . 13 5 9 . 18 4 6 . 13 4 6 . 4 8 4 6 . 46 4 8 . 0 1 T 1 0 j 1 . 8 6 3 . 3 5 3 . 2 6 0 . 33 2 . 56 2 . 7 2 2 . 82 2 . 32 A 1 2 0 3 1 3 . 38 14 . 54 1 4 . 7 3 1 5 . 2 8 14 . 6 9 1 6 . 5 3 1 5 . 24 1 6 . 6 1 F e 2 0 3 1 3 . 0 8 1 5 . 5 5 1 4 . 8 0 1 0 . 2 4 1 3 . 5 5 1 3 . 9 3 1 4 . 49 1 3 . 2 4 F e O 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 MnO 0 . 19 0 . 22 0 . 2 1 0 . 27 0 . 18 • 0 . 18 0 . 18 0 . 19 MgO 1 0 . 5 6 4 . 24 3 . 5 8 0 . 0 3 8 . 72 6 . 0 1 7 . 58 5 . 7 1 C a O 8 . 9 0 7 . 5 8 7 . 5 5 1 . 5 8 9 . 84 9 . 0 3 8 . 46 9 . 3 0 N a 2 0 2 . 6 7 4 . 7 1 5 . 0 9 7 . 7 9 3 . 15 3 . 8 6 3 . 35 3 . 4 3 K j O 0 . 74 1 .GO 1 . 7 0 5 . 2 8 0 . 78 0 . 9 4 1 . 01 0 . 8 6 P 2 ° 5 0 . 35 0 . 8 3 0 . 9 4 0 . 0 3 0 . 4 0 0 . 3 3 0 . 4 1 0 . 34 B a 2 3 2 . 0 9 1 5 . 0 9 7 6 . 0 0 . 0 2 7 9 . 0 3 1 2 . 0 2 9 7 . 0 4 5 3 . 0 Rb 14 . 0 2 3 . 0 2 3 . 0 107 . 0 1 1 . 0 1 6 . 0 15 . 0 1 4 . 0 T h 1 . 8 2 . 9 2 . 4 1 5 . 4 1 . 6 2 . 1 2 . 4 2 . 2 U 0 . 6 1 . 1 0 . 8 1 . 0 0 . 5 0 . 8 0 . 9 0 . 8 Nb 17 . 0 3 6 . 0 3 8 . 0 171 . 0 25 . 0 3 0 . 0 3 0 . 0 2 4 . 0 L a 17 . 8 3 0 . 9 3 2 . 6 1 2 8 . 5 23 . 5 2 8 . 5 3 0 . 5 24 . 0 C e 38 . 9 6 8 . 5 67 . 3 2 9 4 . 2 52 . 0 5 7 . 8 44 . 3 54 . 5 S r 4 0 6 . 0 4 3 7 . 0 4 3 5 . 0 0 . 1 5 8 1 . 0 6 8 9 . 0 6 8 7 . 0 6 4 1 . 0 N d 13 . 8 3 5 . 1 3 3 . 9 1 1 7 . 5 23 . 9 31 . 3 28 . 3 2 6 . 1 Sm 4 . 6 • 9 . 4 9 . 5 27 . 0 7 . 0 7 . 7 7 . 9 6 . 6 Z r 112 . 0 2 1 5 . 0 2 0 0 . 0 1 1 3 9 . 0 189 . 0 2 0 5 . 0 211 . 0 1 9 5 . 0 H f 2 . 9 4 . 6 4 . 7 2 2 . 8 5 . 3 4 . 9 3 . 6 4 . 4 E u 1 . 4 3 . 7 4 . 0 3 . 0 2 . 1 2 . 4 2 . 0 2 . 2 T b 0 . 5 1 . 2 1 . 0 N/A N/A N/A 0 . 8 N/A Y 2 6 . 0 3 6 . 0 3 9 . 0 1 1 6 . 0 29 . 0 3 0 . 0 29 . 0 2 9 . 0 Yb 1 . 5 2 . 4 2 . 4 8 . 9 2 . 4 2 . 3 1 . 8 2 . 3 L u 0 . 3 0 . 3 0 . 3 1 . 2 0 . 2 0 . 3 0 . 3 0 . 3 C o 4 9 . 0 4 0 . 0 34 . 0 2 . 0 53 . 0 5 0 . 0 2 3 6 . 0 46 . 0 C r 2 6 0 . 4 1 5 . 3 8 . 7 0 . 0 201 . 2 5 6 . 4 5 0 . 0 54 . 6 C u 5 9 . 0 44 . 0 44 . 0 1 1 . 0 34 . 0 22 . 0 37 . 0 23 . 0 N1 109 . 0 25 . 0 2 0 . 0 27 . 0 1 15 . 0 39 . 0 4 0 . 0 33 . 0 SC 23 . 5 2 3 . 1 2 2 . 5 0 . 1 24 . 8 2 1 . 7 19 . 5 24 . 0 V 87 196 . 0 . 1 8 5 . 0 1 8 0 . 0 3 . 0 2 4 2 . 0 2 1 2 . 0 2 2 5 . 0 2 1 3 . 0 S r | 6 0 . 7 0 3 7 0 . 7 0 3 3 0 . 7 0 3 1 0 . 7 0 7 0 0 . 7 0 3 4 0 . 7 0 3 5 N/A 0 . 7 0 3 8 K / R b 4 3 8 . 7 7 5 7 7 . 4 6 6 1 3 . 5 5 4 0 9 . 6 2 5 8 8 62 4 8 7 . 6 8 5 5 8 . 9 3 5 0 9 . 9 2 ( L a / Y b ) C H 7 . 9 6 8 . 6 6 9 . 2 0 9 . 73 6 . 46 8 . 46 1 1 . 5 6 6 . 8 7 ' L a / N b 1 . 0 5 0 . 8 6 0 . 8 6 0 . 75 0 . 9 4 0 . 9 5 1 . 0 2 1 . 0 0 M g ' 6 2 35 32 1 56 46 51 46 Dates and 7 . 2 + 0 . 8 2 2 0 y r s 2 2 0 y r s 0 . 0 2 + 0 . 0 1 3 . 0 4 ~ . 0 4 ' .04 ~ . 0 4 Ages (Ma). continued 1 64 BOWSER S P E C 1 S P E C 2 EDZ1 EDZ2 NEDZ1 NEDZ2 NEDZ3 S e r i e s A l k a l i n e A l k / T r a n s A l k a l i n e - A l k a l i n e A l k a l i n e A l k / T r a n s A l k a l i n e A l k a l i n e Name H a w a i i t e B a s a l t H a w a i I t e H a w a i i t e H a w a i I t e B a s a l t H a w a i i t e H a w a i i t e L A T . 56 54 57 1 7 . 5 ' 5 7 2 5 . 5 57 4 5 . 5 57 5 6 . 1 5 7 5 8 . 1 5 58 0 0 . 0 5 7 5 9 . 1 8 L O N G . 1 2 9 22 130 3 2 . 6 130 4 7 . 2 130 4 2 . 0 130 3 7 . 2 130 0 1 . 4 7 130 4 2 . 4 129 5 5 . 1 3 S 1 0 j 4 6 . 9 4 4 7 . 1 1 48 . 0 7 4 9 . 32 47 . 9 9 47 . 29 4 8 . 35 48 . 9 7 T 1 0 2 2 . 6 5 2 . 33 2 . 5 5 2 . 35 2 . 88 2 . 88 3 . 1 1 2 . 30 A 1 2 0 3 1 4 . 8 5 14 . 9 3 1 5 . 78 1 5 . 23 1 5 . 75 14 . 44 1 4 . 9 0 1 5 . 18 F e 2 0 3 1 3 . 9 4 1 3 . 9 5 1 3 . 0 0 12 . 72 1 3 . 19 1 3 . 59 1 3 . 0 0 1 3 . 0 5 F e O 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 MnO 0 . 19 0 . 18 0 . 21 0 . 18 0 . 2 0 0 . 15 0 . 18 0 . 13 Mgo 6 . 9 2 7 . 6 5 4 . 72 5 . 54 4 . 17 9 . 0 4 4 . 6 1 5 . 7 3 C a O 8 . 5 3 9 . 37 1 0 . 22 8 . 75 9 . 94 7 . 6 6 9 . 51 6 93 N a 2 0 3 . 8 0 3 . 01 3 . 89 3 . 88 3 . 6 9 3 . 16 4 . 42 5 . 19 K 2 0 1 . 5 9 0 . 88 1 . 01 1 . 5 0 1 . 3 0 1 . 33 1 . 25 1 . 78 P 2 ° S 0 . 6 1 0 . 61 0 . 56 0 . 54 0 . 91 0 . 4 5 0 . 67 0 . 7 2 B a 4 7 4 0 4 1 5 . 0 24 1 . 0 4 3 4 . 0 511 . 0 4 3 6 . 0 4 7 4 . 0 5 1 1 0 Rb 3 5 . 0 1 1 . 0 14 . 0 26 . 0 13 . 0 20 . 0 15 . 0 2 6 . 0 T h 4 . 3 1 . 7 1 8 3 . 5 2 . 4 3 . 0 2 3 3 . 4 U N/A 0 . 4 1 . 2 1 . 1 0 . 8 0 . 8 0 . 8 1 . 1 Nb 55 . 0 2 0 . 0 27 . 0 37 . 0 3 0 . 0 38 . 0 3 0 . O 4 5 . 0 L a 3 8 . 2 17 . 8 24 . 0 29 . 8 29 8 24 . 7 21 9 3 6 . 2 C e 9 0 . 0 35 . 4 6 2 . 4 57 . 3 48 . 0 43 . 5 5 0 . 4 9 0 . 6 ' S r 8 8 2 . 0 4 9 5 . 0 4 8 9 . 0 5 0 7 . 0 6 4 2 . 0 6 9 4 . 0 5 0 6 0 8 6 3 . 0 N d 3 0 . 0 18 . 4 3 0 . 1 28 . 8 3 0 . 1 28 . 0 2 0 . 6 3 8 . 6 Sm 1 1 . 0 6 . 0 7 . 3 6 . 9 8 . 2 4 . 8 6 . 2 8 . 1 Z r 3 0 2 . 0 140 . 0 2 0 4 . 0 2 0 8 . 0 181 . 0 2 3 5 . 0 186 . 0 262 . 0 H f N/A 2 . 9 4 . 8 5 . 0 3 2 5 3 3 . 9 5 . 7 E u 2 . 0 2 . 1 2 . 1 2 . 1 2 . 9 2 . 2 2 . 5 2 . 4 T b N/A 0 . 9 0 . 8 0 . 8 1 . 2 0 . 7 0 . 6 0 . 7 Y 34 . 0 25 . 0 34 . 0 29 . 0 31 . 0 21 . 0 25 0 1 9 . 0 Y b 3 . 1 1 . 6 2 . 2 2 . 0 2 . 0 0 . 9 2 . 2 1 . 0 L u 0 4 0 . 3 0 . 3 0 . 2 0 2 0 . 2 0 2 0 . 2 C o 46 . 0 44 0 36 . 0 44 . 0 33 . 0 53 . 0 39 . 0 4 2 . 0 C r 198 0 2 0 2 . 0 105 . 3 186 . 6 54 . 0 2 0 3 . 1 66 . 4 1 1 9 . 7 C u 4 9 . 0 4 8 . 0 45 . 0 5 0 . 0 5 0 . 0 46 . 0 37 . 0 4 3 . 0 N l 1 5 6 . 0 148 . 0 51 . 0 139 . 0 36 . 0 186 . 0 36 . 0 9 8 . 0 S c 2 0 . 2 24 . 7 25 . 9 21 . 2 22 . 1 15 . 7 26 . 3 1 1 . 8 V R 7 1 6 6 . 0 2 0 6 . 0 2 2 3 . 0 168 . 0 170 . 0 167 . 0 2 7 5 . 0 1 1 3 . 0 Sr%l 0 . 7 0 2 3 N/A N/A N/A N/A N/A N/A N/A K / R b 3 7 7 . 10 6 6 4 . 0 8 5 9 8 . 8 6 4 7 8 . 9 0 8 3 0 10 5 5 2 . 0 2 6 9 1 . 7 5 5 6 8 . 3 0 ( L a / Y b ) 8 . 2 1 7 . 4 6 7 . 39 9 . 8 4 9 . 8 3 17 . 4 1 6 . 7 1 23 . 8 0 L a / N b C H 0 . 6 9 0 . 8 9 0 . 89 0 . 8 1 0 . 9 9 0 . 6 5 0 . 7 3 0 . 8 0 M g ' 5 0 52 42 46 39 57 4 1 4 7 Dates and 1.6 + 0.3 7.8 ±0.3 ~ 3 5.9+0.9 0.62+0.4 5.7+0.2 0.43±0.15 4.9 + 0.2 Ages (Ma). c o n t i n u e d . . . . 165 NEDZ4 L E V E L D * L E V E L 1 L E V E L 2 * S A T L I N NATL IN S e r i e s A l k a l i n e A l k / T r a n s A l k a l 1 n e A l k a l I n e T h o l e l i t e A l k a l i n e Name H a w a i 1 t e B a s a 1 t H a w a 1 1 t e H a w a l i t e B a s a 1 t Hawa i i t e L A T . 5 8 0 1 . 8 58 1 9 . 7 58 2 8 . 0 58 2 8 . 9 59 1 9 . 0 59 4 5 . ( LONG - 130 0 3 . 7 2 131 4 0 . 0 131 2 6 . 9 131 2 6 . 2 133 4 2 . 7 5 133 2 0 . ( S 1 D 2 48 . 12 4 8 . 6 0 5 0 . 17 4 7 . 8 0 48 . 9 9 48 . 39 T 1 0 2 2 . 16 2 . 2 0 2 . 39 2 . 9 0 1 . 6 9 2 . 10 A 1 2 ° 3 1 5 . 0 0 1 5 . 6 0 15 48 1 5 . 4 0 1 4 . 6 7 14 . 32 F e 2 ° 3 1 3 . 3 1 2 . 6 0 1 1 . 94 2 . 4 0 13 32 1 1 . 36 F e O N/A 9 . 9 0 N/A 1 0 . 70 N/4 N/A MnO 0 . 17 0 . 20 0 . 16 0 . 20 0 . 18 0 . 15 MgO 6 . 9 3 6 . 0 0 5 . 8 7 6 . 0 0 7 . 8 5 8 . 0 4 C a O 7 . 7 0 1 0 . 2 0 8 . 0 1 9 . 10 8 . 9 5 8 . 29 N a 2 0 5 . 12 3 . 4 0 4 . 0 0 3 . 8 0 3 . 3 1 4 . 8 1 K 2 0 1 . 16 0 . 4 0 1 . 32 0 . 9 0 0 . 6 9 1 . 6 4 P 2 0 5 0 . 3 4 0 . 3 0 0 . 6 4 0 . 6 0 0 . 36 0 . 9 0 B a 3 4 6 . 0 174 . 0 5 1 9 0 2 9 2 . 0 258 . 0 582 . 0 Rb 1 5 . 0 3 . 0 1 7 . 0 1 2 . 0 1 0 . 0 28 . 0 T h 2 . 3 0 . 8 2 . 3 2 s. 7 2 . 0 4 . 4 U 0 . 7 0 . 3 0 . 9 0 . 6 0 . 5 1 . 5 Nb 31 . 0 1 2 . 0 28 . 0 32 . 0 1 7 . 0 5 1 . 0 L a 1 5 . 1 1 1 . 2 2 5 . 6 24 . 7 1 5 . 4 47 . 4 C e 3 8 . 1 1 5 . 1 5 6 . 9 4 5 . 8 4 0 . 2 93 9 S r 5 8 0 . 0 441 . 0 6 0 9 . 0 464 . 0 5 1 0 . 0 1 1 3 5 . 0 N d 2 6 . 7 14 . 5 2 8 . 7 23 . 6 2 0 . 1 43 . 5 Sm 4 . 4 4 . 6 8 . 7 8 . 0 4 . 3 9 . 3 Z r 189 . 0 1 0 6 . 0 195 . 0 185 . 0 92 . 0 178 . 0 H f 3 . 9 2 . 3. 4 . 4 4 . 6 2 . 6 3 . 6 E u 1 . 6 1 . 4 2 . 7 2 . 2 1 . 4 2 . 7 T b N/A 0 . 7 0 . 8 0 . 7 N/A 0 . 6 Y 1 9 . 0 2 0 . 0 2 5 . 0 3 0 . 0 2 0 . 0 24 . 0 Y b 1 7 2 . 0 1 . 6 2 . 2 1 . 1 1 . 3 L u 0 . 2 0 . 2 0 . 2 0 . 2 0 . 2 0 . 1 C o 4 9 . 0 N/A 5 4 . 0 N/A 5 0 . 0 8 9 . 0 C r 2 0 6 8 2 1 8 . 0 5 9 9 188 O 254 O 22G . 5 C u 4 5 . 0 6 1 . 0 4 9 . 0 153 . 0 56 . 0 52 0 N1 1 7 1 . 0 138 . 0 3 9 . 0 1 1 2 . 0 1 1 2 . 0 152 . 0 S c 1 8 . 6 2 4 . 2 1 8 . 1 27 . 1 2 1 . 3 1 7 . 0 V 87 1 7 5 . 0 N/A 157 . 0 N/A 1 7 0 . 0 1 6 5 . 0 S r 8 6 N/A 0 . 7 0 3 2 4 N/A 0 . 7 0 3 0 2 0 . 7 0 3 9 0 . 7 0 3 9 K/Rb 64 1 . 9 4 1 1 0 6 . 8 0 6 4 4 . 5 5 6 2 2 . 5 7 5 7 2 . 7 7 4 8 6 . 2 0 ( L a / Y b ) 5 . 9 5 3 . 8 3 1 0 . 6 1 7 . 58 9 . 24 24 . 48 L a / N b C 0 . 4 9 0 . 9 4 0 . 9 1 0 . 7 7 0 . 9 1 0 . 9 3 M g ' 51 47 49 45 54 58 Dates and 0 . 5 0 7 + 0 . 0 7 ~ 12 ~ 12 ~ 1 2 1 6 . 5 + 3 . 1 N/A * Major element and some trace element data from Hamilton (1981). N/A = not analyzed Ages (Ma) 7. ALERT BAY VOLCANIC BELT Three samples r e p r e s e n t i n g the A l e r t Bay V o l c a n i c B e l t were s e l e c t e d f o r a n a l y s i s ( F i g . 7.1). Two of the samples (ALERT1 and ALERT2) are b a s a l t i c i n composition ( S i 0 2 l e s s than 50 wt. % ) , and the remaining sample (ALERT3) i s a n d e s i t i c ( S i 0 2 = 61.15 wt. % ) . Most of the A l e r t Bay v o l c a n i c rocks were erupted approximately 3.5 ± 1 Ma ago (Table V I ) . They are a product of voicanism i n the a r c - t r e n c h gap, generated along the descending p l a t e edge (Armstrong et a l . , i n p r e s s ) . 7.1 MAJOR ELEMENT CHEMISTRY Most major element abundances i n b a s a l t i c samples ALERT1 and ALERT2 (Table VI) are t y p i c a l of the range of abundances from t h o l e i i t i c and and a l k a l i n e oceanic WPB ( B a s a l t i c Voicanism Study P r o j e c t , 1981). A 1 2 0 3 abundances are s l i g h t l y higher than 'average'. The Mg' number f o r ALERT1 i s 45, but f o r ALERT2 i t i s 62 i n d i c a t i n g t h a t t h i s l a t t e r sample i s more p r i m i t i v e . In c o n t r a s t the major element abundances i n a n d e s i t i c sample ALERT3 are more c h a r a c t e r i s t i c of a c a l c a l k a l i n e convergent margin a n d e s i t e , low T i 0 2 and F e 2 0 3 with h i g h A l 2 0 3 . T h i s sample has a Mg' number of 49. 166 167 F i g . 7.1. Sample l o c a t i o n map f o r the A l e r t Bay V o l c a n i c B e l t . A l l subsequent diagrams i n t h i s chapter use i d e n t i c a l symbols. 168 7.2 DISCRIMINANT DIAGRAMS 7.2.1 MAJOR ELEMENT CLASSIFICATIONS On t o t a l a l k a l i s vs. s i l i c a ALERT1 l i e s j u s t w i t h i n the a l k a l i n e f i e l d , ALERT2 l i e s on MacDonald's (1968) s u b a l k a l i n e - a l k a l i n e f i e l d boundary and ALERT3 l i e s w i t h i n the s u b a l k a l i n e f i e l d ( F i g . 7.2). Ol'-Ne'-Qz (not shown) c l a s s i f i e s a l l three samples as s u b a l k a l i n e . On AFM and FeO*/MgO vs. S i 0 2 diagrams ALERT1 l i e s w i t h i n the t h o l e i i t i c f i e l d , ALERT3 l i e s w i t h i n the c a l c a l k a l i n e f i e l d and ALERT2 l i e s on the boundaries between t h o l e i i t i c and c a l c a l k a l i n e f i e l d s ( F i g s . 7.3 and 7.4). A d d i t i o n a l A l e r t Bay Group b a s a l t s - a n d e s i t e s - d a c i t e s and r h y o l i t e s p l o t t e d on an AFM diagram i n d i c a t e that ALERT1 belongs to the t h o l e i i t i c / t r a n s i t i o n a l M u l l t r e n d , whereas ALERT2 and ALERT3 belong to the c a l c a l k a l i n e Cascade t r e n d (Armstrong et a l . , i n p r e s s ) . A l 2 0 3 vs. normative p l a g i o c l a s e (not shown) c l a s s i f i e s ALERT1 and ALERT2 as t h o l e i i t i c and ALERT3 as c a l c a l k a l i n e . On T i 0 2 - K 2 0 - P 2 0 5 ALERT1 l i e s w i t h i n the oceanic f i e l d and ALERT2 l i e s on the boundary between the oceanic and non-oceanic f i e l d s ( F i g . 7.5). On MnO-Ti0 2-P 20 5 both b a s a l t i c samples l i e w i t h i n the OIA f i e l d ( F i g . 7.6). ALERT 1 i s c l a s s i f i e d as convergent margin and ALERT2 as N-MORB on FeO*-MgO-Al 20 3 ( F i g . 7.7). 169 F i g . 7.2. T o t a l a l k a l i s vs. s i l i c a . S u b a l k a l i n e / a l k a l i n e boundary fom MacDonald (1968). F i g . 7.3. AFM diagram. T h o l e i i t i c / c a l c a l k a l i n e boundary from I r v i n e and Baragar (1971). Na20 + K 20 rlgO F i g . 7.4. FeO*/MgO vs. S i 0 2 . T h o l e i i t i c / c a l c a l k a l i n e boundary from M i y a s h i r o (1974). ALERT1 + ALERT2 A ALERT3 • SiO,  171 7.2.2 TRACE ELEMENT CLASSIFICATIONS On T i - Z r - Y , V vs. Ti/100 and T i / Y vs. Nb/Y both b a s a l t i c samples are c l a s s i f i e d as WPB ( F i g s . 7.8, 7.9 and 7.10 r e s p e c t i v e l y ) . On T i / C r vs. Ni ALERT3 l i e s w i t h i n the IAT f i e l d , and ALERT1 and ALERT2 l i e w i t h i n the TH MORB f i e l d ( F i g . 7.11). 7.2.3 TRACE AND REE CLASSIFICATIONS A l l three samples l i e w i t h i n the convergent margin f i e l d on Sm/Ce vs. Sr/Ce ( F i g . 7.12), but on Cr vs. Ce/Sr only ALERT3 i s u n e q u i v o c a l l y c l a s s i f i e d as convergent margin ( F i g . 7.13). On the l a t t e r diagram ALERT 1 l i e s w i t h i n the o v e r l a p p i n g ARC-MORB f i e l d s and ALERT2 l i e s w i t h i n the o v e r l a p p i n g MORB-WPB f i e l d s . On Cr vs. Y ALERT3 l i e s w i t h i n the convergent margin f i e l d and ALERT1 and ALERT2 l i e w i t h i n the ove r l a p p i n g ARC-MORB-WPB f i e l d s ( F i g . 7.14). A l l samples l i e w i t h i n the orogenic a n d e s i t e f i e l d on La vs. Ba, c l o s e to the boundary with the E-MORB (WPB) f i e l d ( F i g . 7.15), but on ( B a / L a ) C H vs. (La/Sm) C H a l l samples l i e w i t h i n the oceanic (WPB) f i e l d ( F i g . 7.16). ALERT3 l i e s j u s t w i t h i n the o v e r l a p p i n g ARC f i e l d . On La vs. Th ALERT1 and ALERT2 l i e w i t h i n the E-MORB (WPB) f i e l d with La/Th r a t i o s between 7 and 15 ( F i g . 7.17). ALERT3 has an La/Th r a t i o of 4.6 and Ti/100 172 173 F i g s . 7.11 and 7.12. T i / C r v s . Ni (above) and Sm/Ce vs. Sr/Ce (below). 1 000 1 00 1 0 0.01 0.1 Ce/Sr ALERT1 + ALERT2 A ALERT3 • 1 0 100 F i g s . 7.13 and 7.14. Cr v s . Ce/Sr (above) and Cr vs. Y (below). 175 F i g s . 7.15 and 7.16. La v s . Ba (above) and (Ba/La) vs. (La/Sm) r (below). 1 76 c l e a r l y l i e s w i t h i n the orogenic a n d e s i t e f i e l d . On La vs. Nb ALERT1 and ALERT2 have La/Nb r a t i o s of l e s s than 1 and consequently l i e w i t h i n the E-MORB (WPB) f i e l d ( F i g . 7.18). ALERT3 has an La/Nb r a t i o of 1.64 and l i e s w i t h i n the N-MORB f i e l d . On K 20/Yb vs. Ta*/Yb and Th/Yb vs. Ta*/Yb both b a s a l t samples l i e w i t h i n the o v e r l a p p i n g MORB-WPB f i e l d s and ALERT3 l i e s w i t h i n the ARC f i e l d ( F i g s . 7.19 and 7.20) . ALERT3 l i e s w i t h i n the convergent margin (CAB) f i e l d on Th-Hf/3-Ta* and ALERT1 and ALERT2 l i e w i t h i n the E-MORB- t h o l e i i t i c WPB f i e l d ( F i g . 7.21). 7.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) Bend p a t t e r n s from the three A l e r t Bay samples are shown on F i g . 7.22. ALERT1 and ALERT2 have v i r t u a l l y i d e n t i c a l l y shaped p a t t e r n s . They are s h a l l o w l y convex-up, 'peaking' at Nb, with a concave-up d i p from Sm to Eu. Both samples have a 'trough' at U, i n d i c a t i n g r e l a t i v e U d e p l e t i o n . When compared to the two p a t t e r n s d e s c r i b e d above the p a t t e r n from ALERT3 i s n o t i c e a b l y d i f f e r e n t , e s p e c i a l l y from Ba to T i . I t i s e n r i c h e d i n LIL r e l a t i v e to LREE, has a 'trough' at Nb and Sm and has a convex-up hump from Sm to T i . From Eu to Yb the p a t t e r n from ALERT3 i s i d e n t i c a l to the p a t t e r n s from ALERT1 and ALERT2. F i g s . 7.17 and 7.18. La v s . Th (above) and La vs. Nb (below). 1 78 100 10 J X3 O 1 H o. 1 I y ' .'*M O R B .*' 0.01 0.1 1 TaVYb 1 0 F i g . 7.19. K 20/Yb vs, Ta*/Yb. ALERT1 + ALERT2 A ALERT3 • 1 0 F i g . 7.20. Th/Yb v s. Ta*/Yb. Hf/3 Th 1 - i o . i H 0.0 1 V . "o i l Ta*/Yb F i g . 7.21. Th-Hf/3-Ta*. 1 o Ta* 1 79 1000 -, CO LU D - J < > Q III N CE O 100 H 10 J • ^Jr \ X r-i ALERT1 + ALERT2 A ALERT3 • V — i — ' — i — i — i — i — r — i — i — i — i — i — i i i i — i — i — Ba RbTh U K NbLa Ce SrNdSm Zr Hf Ti Eu Tb Y Yb Lu F 1 g . 7 . 2 2 . BEN d i a g r a m f o r s a m p l e s ALERT 1, ALERT2 and ALERT3 180 A l l p a t t e r n s d i s p l a y a s l i g h t p o s i t i v e Eu anomaly. 7.3 TRACE ELEMENT CHEMISTRY Trace and rare e a r t h element abundances f o r ALERT1 and ALERT2 (Table VI) l i e w i t h i n the range of abundances from WPB erupted at other l o c a t i o n s i n B r i t i s h Columbia (eg. S t i k i n e V o l c a n i c B e l t , C h i l c o t i n Group B a s a l t s and Anahim V o l c a n i c B e l t ( t h i s s t u d y ) ) . BEND p a t t e r n s a l s o have convex-up WPB-like shapes. La abundances are 76.5 and 50.6 times c h o n d r i t i c , Yb abundances are 10.9 and 8.6 times c h o n d r i t i c and ( L a / Y b ) C H r a t i o s are 7.1 and 5.96 f o r ALERT1 and ALERT2 r e s p e c t i v e l y . La/Nb r a t i o s of 0.86 and 0.83 and Rb/Nb r a t i o s of 0.69 and 0.75 are w i t h i n the range of r a t i o s c h a r a c t e r i s t i c of oceanic WPB (Thompson et a l . , 1983). R e l a t i v e to ALERT1 and ALERT2, ALERT3 has higher abundances of Rb lower abundances of Nb and REE and s i m i l a r to lower abundances of Sr, Zr and Hf. I t s La content i s 44.8 times c h o n d r i t i c , Yb content i s 5 times c h o n d r i t i c and ( L a / Y b ) C H r a t i o i s 8.99. I t has an La/Nb r a t i o of 1.64 and an Rb/Nb r a t i o of 2.67. These r a t i o s are t y p i c a l of a convergent margin b a s a l t or a w i t h i n p l a t e b a s a l t which has a s s i m i l a t e d c o n t i n e n t a l c r u s t , but i t must be remembered th a t ALERT3 i s an a n d e s i t e , and t h e r e f o r e these r a t i o d i s c r i m i n a n t s may not a p p l y . 181 7.3.1 TH AND U Th abundances i n ALERT1 and ALERT2 are 2.7 and 1.6 ppm r e s p e c t i v e l y , U abundances are 0.6 and 0.4 ppm and Th/U r a t i o s are 4.5 and 4.0. These are w i t h i n the range of abundances and r a t i o s from oceanic WPB. ALERT3 has higher abundances of both Th and U; Th = 3.2 ppm and U = 1.2 ppm, and a lower Th/U r a t i o ; Th/U = 2.7. High abundances of Th and U i n a s u b a l k a l i n e rock are more ' t y p i c a l ' i n samples from a convergent margin s e t t i n g . 7.3.2 TRANSITION ELEMENTS Abundances of Cr and Ni i n ALERT1 are lower than e q u i v a l e n t abundances i n ALERT2. T h i s r e f l e c t s ALERT2's more p r i m i t i v e ( l e s s f r a c t i o n a t e d ) nature. Sc contents are 24.9 and 22.3 ppm f o r ALERT1 and ALERT2 r e s p e c t i v e l y . ALERT3 has much lower abundances of both Cr and N i , i n d i c a t i n g a g r e a t e r amount of both o l i v i n e and pyroxene f r a c t i o n a t i o n d u r i n g i t s p e t r o g e n e s i s . I t s Sc content of 11 ppm p r o v i d e s a d d i t i o n a l evidence f o r the f r a c t i o n a t i o n of pyroxene. 7.4 ISOTOPIC DATA Sr i s o t p e r a t i o s range from 0.7031 to 0.7035, the lowest r a t i o belonging to ALERT3 (Table V I ) . These r a t i o s are lower than r a t i o s from most v o l c a n i c a r c s , but they are l i k e those from the G a r i b a l d i V o l c a n i c B e l t and are t y p i c a l of r a t i o s from WPB magmas (Zhou and Armstrong, 1982; Faure, 1 82 1977) . Oxygen i s o t o e a n a l y s i s done at the U n i v e r s i t y of A l b e r t a and repor t e d by Armstrong et a l . ( i n pr e s s ) i n d i c a t e rocks from the A l e r t Bay V o l c a n i c B e l t are e n r i c h e d in 0 1 8 compared to t y p i c a l mantle values ( A l e r t Bay average 0 1 8 = 7.1%; mantle 0 1 8 = 5 to 6 % ) . T h i s i s o t o p i c enrichment i s c i t e d as evidence f o r the a s s i m i l a t i o n of c r u s t a l m a t e r i a l . 7.5 DISCUSSION OF DISCRIMINATION DIAGRAMS On almost a l l of the major, t r a c e and rare e a r t h element d i s c r i m i n a t i o n diagrams b a s a l t i c samples ALERT1 and ALERT2 are c l a s s i f i e d as WPB (E-MORB) and a n d e s i t i c sample ALERT3 i s c l a s s i f i e d as convergent margin. D i s c r e p a n c i e s occur on MgO-FeO*-Al 20 3 ( F i g . 7.7), Sm/Ce vs. Sr/Ce ( F i g . 7.12), La vs. Ba ( F i g . 7.15), ( B a / L a ) C H vs. (La/Sm) C H ( F i g . 7.16) and La vs. Nb ( F i g . 7.18). On MgO-FeO*-Al 20 3 n e i t h e r of the b a s a l t s are c l a s s i f i e d as WPB because t h e i r abundances of A l 2 0 3 are high e r than ' t y p i c a l ' A l 2 0 3 abundances i n oceanic WPB (OI). Both b a s a l t samples l i e w i t h i n the ARC f i e l d on Sm/Ce vs. Sr/Ce. T h i s d i s a g r e e s with the WPB c l a s s i f i c a t i o n of most of the other diagrams, but as t h i s diagram does not have a separate f i e l d f o r WPB, the ARC c l a s s i f i c a t i o n should probably be d i s r e g a r d e d . On La vs. Ba a l l samples are c l a s s i f i e d as orogenic a n d e s i t e s , but on ( B a / L a ) ^ vs. (L a / S m ) C H a l l samples l i e w i t h i n the oceanic (WPB) f i e l d . T h i s i n d i c a t e s Ba abundance 183 has not been s u f f i c i e n t l y e n r i c h e d to c l a s s i f y any of these samples as ' t y p i c a l ' convergent margin b a s a l t or a n d e s i t e . La vs. Nb a l s o suggests the convergent m a r g i n - l i k e chemistry of ALERT3 i s not r e a l l y ' t y p i c a l ' of an an d e s i t e erupted at a convergent margin s e t t i n g . Although ALERT3 e x h i b i t s an Nb 'trough' on a BEND, which i s c h a r a c t e r i s t i c of convergent margin b a s a l t s and an d e s i t e s i t s Nb d e p l e t i o n i s not great enough f o r an orogenic a n d e s i t e c l a s s i f i c a t i o n on the diagram c i t e d above. T h i s i m p l i e s e i t h e r : ALERT3 magma came from a w i t h i n - p l a t e b a s a l t source which was contaminated with c o n t i n e n t a l c r u s t (Thompson et a l . , 1983), or ALERT3 magma i s a product of mixing WPB and ARC magmas. 7.6 SUMMARY The A l e r t Bay b a s a l t samples are c l a s s i f i e d as w i t h i n - p l a t e b a s a l t s , whereas the a n d e s i t i c sample i s c l a s s i f i e d as a convergent margin a n d e s i t e . Thus, the l i m i t e d data presented here c o n f i r m the o b s e r v a t i o n s and c o n c l u s i o n s of Armstrong et a l . ( i n p r e s s ) . The above authors recognized two d i f f e r e n t f r a c t i o n a t i o n t r e n d s : one f o l l o w i n g an almost a l k a l i n e , t h o l e i i t i c trend; e x p l a i n a b l e by shallow f r a c t i o n a t i o n of an anhydrous aluminous WPB (re p r e s e n t e d here by ALERT1), and the other f o l l o w i n g a convergent margin Cascade-type t r e n d ; e x p l a i n a b l e by e i t h e r f r a c t i o n a t i o n of a hydrous aluminous b a s a l t , a s s i m i l a t i o n of c r u s t a l m a t e r i a l or 184 mixing of c r u s t a l melt and primary b a s a l t magma (represented here by ALERT2 (low s i l i c a end member) and ALERT3 (more s i l i c e o u s member)). 185 TABLE VI. Alert Bay Volcanic Belt Major, trace and rare earth element abundances, Sr isotope ratios and K-Ar dates. A L E R T 1 A L E R T 2 A L E R T 3 S e r i e s T h / T r a n s C a l c a l k C a l c a l k Name B a s a 1 t B a s a l t A n d e s 1 t e L A T . SO 3 5 . 2 5 0 3 0 . 8 5 0 31 L O N G . 127 1 1 . 6 127 1 2 . 3 127 1 5 . 0 S t O j 4 9 . 1 1 4 9 . 8 6 61 . 15 T 1 0 2 2 . 8 9 2 . 15 1 . 14 * ' 2 ° 3 1 6 . 4 0 1 5 . 4 7 1 6 . 3 4 F e j O j 1 1 . 92 1 0 . 9 0 6 . 2 1 F e O N/A N/A N/A MnO 0 . 18 0 . 14 0 . 0 8 MgO 4 . 8 2 8 . 8 7 3 . 0 6 C a O 9 . 8 2 8 . 2 7 6 . 4 0 N a 2 0 3 . 38 3 0 6 4 . 1 4 K 2 0 0 . 9 8 0 87 1 32 P j O , 0 . 5 0 0 . 4 1 0 . 17 B a 4 5 3 . 0 2 5 7 . 0 2 5 5 . 0 Rb 2 0 . 0 1 5 . 0 24 . 0 T h 2 . 7 1 . 6 3 . 2 U 0 . 6 0 . 4 1 . 2 Nb 2 9 . 0 2 0 . 0 9 . 0 L a 25 . 1 1 6 . 6 14 . 7 C e 44 . 5 42 . 7 27 . 1 S r 5 1 4 . 0 4 4 1 . 0 4 3 1 . 0 N d 2 5 . 3 22 . 6 1 7 . 5 Sm 6 . 7 5 . 8 3 . 4 Z r 2 1 3 . 0 1 7 3 . 0 1 5 6 . 0 H f 4 . 8 3 . 4 3 . 5 E u 2 . 1 1 . 6 1 . 1 T b 1 . 1 N/A N/A Y 34 . 0 2 9 . 0 18 . 0 Yb 2 . 4 1 . 9 1 . 1 L u 0 . 3 0 . 3 0 . 2 C o 42 . 0 4 3 . 0 1 5 . 0 C r 9 0 . 2 155 . 0 24 . 0 C u 36 . 0 3 9 . 0 2 2 . 0 N1 5 8 . 0 8 5 . 0 26 0 S c 24 . 9 2 2 . 3 1 1 . 3 V 87 2 2 2 . 0 1 9 3 . 0 105 . 0 S r e e 0 . 7 0 3 5 0 . 7 0 3 4 0 . 7 0 3 1 N/A n o t a n a l y z e d K / R b 4 0 6 . 7 5 4 8 1 . 4 6 4 5 6 . 5 5 ( L a / Y b ) C H 7 . 1 0 5 . 9 6 8 . 9 9 L a / N b 0 . 8 6 0 . 8 3 1 . 6 4 M g ' 45 6 2 49 K / A r D A T E 7 ± 3 4 . 3 ± 0 . 4 3 . 0 ± 0 . 4 (Ma) 8. OFFSHORE BASALTS Eleven samples from the P a c i f i c Ocean s e a f l o o r were s e l e c t e d f o r a n a l y s i s ( F i g . 8.1). P a c i f i c p l a t e b a s a l t s are from Brown Bear and Cobb seamounts (2 samples from each) and Ex p l o r e r seamount (3 samples). The remaining four samples are from southern E x p l o r e r Ridge (1 sample), E x p l o r e r R i f t and E x p l o r e r Deep (1 sample each) and Paul Revere Ridge ( F r a c t u r e Zone) (1 sample). Most of the samples are probably l e s s than 1 Ma o l d , except the Paul Revere Ridge sample which may be as o l d as 4.5 Ma (Riddihough, 1980) and the E x p l o r e r seamount samples which are approximately 4 Ma o l d (R.L. Chase, p e r s . comm., 1985). 8.1 MAJOR ELEMENT CHEMISTRY B a s a l t s from E x p l o r e r seamount and EXRIFT have c h a r a c t e r i s t i c N-MORB major element chemistry (Table V I I ) , i . e . low S i 0 2 , K 20 and P 2 0 5 and high MgO and CaO (Melson et a l . , 1976). T i 0 2 abundances l i e w i t h i n the T i 0 2 abundance range from N-MORB ( C h r i s t i e and S i n t o n , 1981; Pearce, 1982; Sun et a l . , 1979). Mg' numbers f o r E x p l o r e r seamount samples range from 60 and 62 but EXRIFT has an Mg' number of 66. T h i s l a t t e r b a s a l t i s a p i c r i t e a c c o r d i n g to the c l a s s i f i c a t i o n of I r v i n e and Baragar (1971). B a s a l t s from the Brown Bear and Cobb seamounts have higher abundances of T i 0 2 , FeO*, K 20, Na 20 and P 2 0 5 and a s l i g h t l y lower MgO content than N-MORB (Table V I I ) . These 186 187 F i g . 8 . 1 . Sample l o c a t i o n map f o r the Ocean F l o o r B a s a l t S u i t e . Key to symbols below. EXMOUNT1 • COBB 1 V EXMOUNT2 • COBB2 • EXMOUNT3 0 SEXRIDGE + BRBEAR1 A PREVRDG X BRBEAR2 A EXRIFT 0 EXDEEP • 188 abundances are s i m i l a r to abundances from E-MORB (Sun et a l . , 1979). Mg' numbers range from 47 to 54 i n d i c a t i n g these b a s a l t s are more evolved than the E x p l o r e r Seamount and E x p l o r e r R i f t samples. B a s a l t s SEXRIDGE and EXDEEP have major element c h a r a c t e r i s t i c s of both N- and E-MORB; i . e . low t o t a l a l k a l i s and high MgO and CaO, but a l s o high K 20, T i 0 2 and P 2 0 5 (Table V I I ) . Mg' numbers are 58 and 57 r e s p e c t i v e l y . F o l l o w i n g the c l a s s i f i c a t i o n of Melson et a l . (1976), Cousens et a l . (1984) c l a s s i f y these b a s a l t s as low t i t a n i u m members of the FETI group, or MORB bo r d e r i n g on f e r r o b a s a l t . R e l a t i v e to N- or E-MORB PREVRDG has higher abundances of T i 0 2 , F e 2 0 3 , MnO, K 20 and P 2 0 5 , and lower abundances of A 1 2 0 3 , MgO and CaO (Table V I I ) . Mg' equals 36. These chemical c h a r a c t e r i s t i c s are t y p i c a l of extreme FETI b a s a l t s ( C h r i s t i e and Sinton, 1981), and are suggested by Cousens et a l . (1984) t o be evidence f o r a once a c t i v e , n o r t h e a s t e r l y p r o p a g a t i n g r i f t . 8.2 DISCRIMINATION DIAGRAMS 8.2.1 MAJOR ELEMENT CLASSIFICATIONS On t o t a l a l k a l i s v s . s i l i c a three samples are c l e a r l y s u b a l k a l i n e (SEXRIDGE, EXRIFT and EXDEEP) and the remaining e i g h t s i t a s t r i d e MacDonalds (1968) s u b a l k a l i n e / a l k a l i n e f i e l d boundary ( F i g . 8.2). 189 The Ol'-Ne'-Qz' diagram c l a s s i f i e s f i v e samples as a l k a l i n e (EXMOUNT2, EXMOUNT3, BRBEAR2, COBB 1 and COBB2) and the remaining s i x as s u b a l k a l i n e . On an AFM diagram a l l b a s a l t s except PREVRDG l i e w i t h i n the f i e l d of a b y s s a l t h o l e i i t e s o u t l i n e d by Mi y a s h i r o et a l . (1970) ( F i g . 8.3) and on FeO*/MgO vs. S i 0 2 ( F i g . 8.4) and A l 2 0 3 vs. normative p l a g i o c l a s e , a l l samples e x c l u d i n g EXMOUNT1, are c l a s s i f i e d as t h o l e i i t e s . Thus, the f i v e samples c l a s s i f i e d as a l k a l i n e on Ol'-Ne'-Qz are designated t r a n s i t i o n a l and w i l l be p l o t t e d with the s u b a l k a l i n e samples. EXMOUNT1 i s s u f f i c i e n t l y aluminous to l i e j u s t w i t h i n the c a l c a l k a l i n e f i e l d on A l 2 0 3 vs. normative p l a g i o c l a s e . A c a l c a l k a l i n e c l a s s i f i c a t i o n f o r an Ex p l o r e r seamount sample has a l s o been o b t a i n e d by Armstrong and Nixon (1980). On T i 0 2 - K 2 0 - P 2 0 5 , a l l samples l i e w i t h i n the oceanic f i e l d ( F i g . 8.5). On MnO-Ti0 2-P 20 5 COBB1, COBB2, BRBEAR2 and PREVRDG l i e a s t r i d e the MORB-OIT f i e l d boundary, BRBEAR1 and EXDEEP l i e w i t h i n the MORB f i e l d and samples from the Ex p l o r e r seamount (EXMOUNT1, EXMOUNT2 and EXMOUNT3) l i e a s t r i d e the MORB-IAT f i e l d boundary. ( F i g . 8.6). SEXRIDGE and EXRIFT l i e w i t h i n the IAT f i e l d . Samples from E x p l o r e r seamount plus sample EXRIFT c l e a r l y l i e w i t h i n the MORB f i e l d on MgO-FeO*-Al 20 3 ( F i g . 8.7). COBB 1 and COBB2 l i e w i t h i n the c o n t i n e n t a l 190 0.2 0.4 0.6 0.8 Na20 + K20 MgO T i 0 2 0.2 0.4 0.6 0.8 R 1 2 0 3 192 f i e l d , EXDEEP and BEBEAR1 p l o t around the t r i p l e p o i n t , BRBEAR2 l i e s j u s t w i t h i n the orogenic f i e l d and SEXRIDGE l i e s j u s t w i t h i n the OI f i e l d , near to the MORB f i e l d . PREVRDG l i e s f a r from the other samples, towards FeO*, w i t h i n the ocean i s l a n d f i e l d . 8.2.2 TRACE ELEMENT CLASSIFICATIONS A l l samples l i e w i t h i n the OFB-LKT-CAB f i e l d on T i - Z r - Y ( F i g . 8.8). and on T i - Z r - S r a l l samples except PREVRDG l i e w i t h i n the OFB f i e l d ( F i g . 8.9). PREVDG p l o t s away from Sr, j u s t o u t s i d e of the OFB f i e l d . On V vs. Ti/1000 ten samples have r a t i o s between 33 and 41 and p l o t w i t h i n the MORB f i e l d ( F i g . 8.10). The exce p t i o n i s PREVRDG which has a T i / V r a t i o of 53 and l i e s j u s t w i t h i n the WPB f i e l d . Samples from E x p l o r e r seamount p l u s EXRIFT have the lowest T i and V abundances and are t h e r e f o r e separated from the other seven samples. A l l samples l i e w i t h i n the o v e r l a p p i n g convergent margin-MORB f i e l d s on T i / Y vs. Nb/Y ( F i g . 8.11). E x p l o r e r seamount samples have the lowest T i / Y and Nb/Y r a t i o s and p l o t away from the other samples. SEXRIDGE s i t s a s t r i d e the boundary with the WPB f i e l d . On T i / C r vs. Ni a l l samples except COBB2 c l e a r l y l i e w i t h i n the TH MORB f i e l d ( F i g . 8.12). COBB2 has s l i g h t l y lower Ni and l i e s a s t r i d e the TH MORB-IAT f i e l d boundary. Ti /100 193 Ti/1000 1 9 4 1 ooo ̂ >- i— 1 00 0 0 1 I r 0 . 1 1 Nb/Y EXMOUNT1 D EXM0UNT2 • EXM0UNT3 0 BRBEARt A BRBEAR2 • EXDEEP • 1 0 COBB 1 V C0BB2 T SEXRIDGE + PREVRDG X EXRIFT 0 1 ooo H 1 0 0 0 F i g s . 8.11 and 8.12. Ti/Y vs. Nb/Y (above) and T i / C r vs. Ni (below). 195 8.2.3 TRACE AND REE CLASSIFICATIONS A l l samples p l o t w i t h i n the oceanic f i e l d on Sm/Ce vs. Sr/Ce ( F i g 8.13). On Cr vs. Ce/Sr BRBEAR and COBB samples p l u s SEXRIDGE and EXRIFT p l o t w i t h i n the o v e r l a p p i n g MORB-WPB f i e l d s , and Exmount samples p l u s EXDEEP p l o t adjacent to the MORB-convergent margin f i e l d boundary ( F i g . 8.14). PREVRDG has an unu s u a l l y h i g h Ce/Sr r a t i o and p l o t s o u t s i d e of a l l f i e l d s . On Cr vs. Y a l l samples l i e w i t h i n the MORB f i e l d ( F i g . 8.15). PREVRDG has a much higher Y abundance and p l o t s away from the other samples. On La vs. Ba a l l samples except PREVRDG have Ba/La r a t i o s between n e a r l y 4 and 11 and p l o t w i t h i n or c l o s e to the N-MORB f i e l d ( F i g . 8.16). PREVRDG has a Ba/La r a t i o of 1.2 and l i e s o u t s i d e of a l l f i e l d boundaries. On ( B a / L a ) C H vs. ( L a / S m ) C H a l l samples l i e w i t h i n or c l o s e to the ocean f i e l d , with (La/Sm) C H l e s s than 1.5 and ( B a / L a ) C H l e s s than 0.5 ( F i g . 8.17). BRBEAR1, BRBEAR2, COBB 1, COBB2 and EXDEEP have the h i g h e s t ( B a / L a ) C H r a t i o s and PREVRDG has the lowest ( B a / L a ) C H r a t i o . These s i x samples have the hig h e s t ( L a / S m ) C H r a t i o s . On La vs. Th EXMOUNT1 and EXMOUNT2 have La/Th r a t i o s g r e a t e r than 15 and l i e w i t h i n the N-MORB f i e l d ( F i g . 8.18). The nine remaining samples have La/Th r a t i o s between 7 and 13 and l i e w i t h i n the E-MORB f i e l d . 1 000 0.01 0.1 Ce/Sr F i g s . 8.13 and 8.14. Sm/Ce vs. Sr/Ce (above) and Cr vs. Ce/Sr (below). 197 E X M O U N T 1 • E X M O U N T 2 • E X M O U N T 3 0 BRBEAR1 A BRBEAR2 • E X D E E P • C O B B 1 V COBB2 • S E X R I D G E + P R E V R D G X E X R I F T 0 F i g . 8.15. Cr vs. Y. 198 F i g s . 8.16 and 8.17. La vs. Ba (above) and (Ba/La) vs. (La/Sm)_„ (below). 199 F i v e of these nine l i e w i t h i n the part which o v e r l a p s the orogenic a n d e s i t e f i e l d . On La vs. Nb a l l samples except EXMOUNT2 and EXMOUNT3 have La/Nb r a t i o s l e s s than 1 and l i e w i t h i n the E-MORB f i e l d ( F i g . 8.19). EXMOUNT2 and EXMOUNT3 have La/Nb r a t i o s of 1.2 and 1.3 r e s p e c t i v e l y and l i e j u s t w i t h i n the N-MORB f i e l d . On K 20/Yb vs. Ta*/Yb a l l samples l i e w i t h i n the MORB f i e l d ( F i g . 8.20). On Th/Yb vs. Ta*/Yb samples BRBEAR2, COBB 1 and EXDEEP l i e w i t h i n the o v e r l a p p i n g MORB-WPB f i e l d s ( F i g . 8.21). The remaining e i g h t samples l i e w i t h i n the MORB f i e l d . Samples l i e w i t h i n both the N- and E-MORB f i e l d s on Th-Hf/3-Ta* ( F i g . 8.22). E x p l o r e r seamount samples and EXRIFT l i e w i t h i n the N-MORB f i e l d and BRBEAR(s), COBB(s) and EXDEEP l i e w i t h i n the E-MORB f i e l d . SEXRIDGE p l o t s on the boundary l i n e between the N- and E-MORB f i e l d s , and PREVRDG l i e s c l o s e to the boundary l i n e , t h e r e f o r e t h e i r c l a s s i f i c a t i o n s are not c e r t a i n . 8.2.4 BULK EARTH NORMALIZED DIAGRAMS (BEND) Three BEND were p l o t t e d f o r ocean f l o o r data ( F i g . 8.23, 8.24 and 8.25). BEND p a t t e r n s on F i g . 8.23 are from E x p l o r e r Seamount. In ge n e r a l p a t t e r n s from these samples slope p o s i t i v e l y from Ba to Sm, s l o p e n e g a t i v e l y from Sm to Hf 200 F i g s . 8.18 and 8.19. La vs. Th (above) and La vs. Nb (below). 1 00 10 H O 1 H o. 1 201 Fig. 8.20. K20/Yb vs. Ta*/Yb. EXMOUNT1 • EXMOUNT2 • EXMOUNT3 0 BRBEAR1 A BRBEAR2 • EXDEEP • COBB 1 V COBB2 • SEXRIDGE + PREVRDG X EXRIFT 0 0 . 0 1 0.1 TaVYb 1 o Fig. 8.21. Th/Yb vs, Ta*/Yb. Hf/3 0 . 0 1 TaVYb F i g . 8.22. Th-Hf/3-Ta* Th Ta* 202 iooo V co UJ D —I < > Q UJ N 100 H EXMOUNT1 D EXM0UNT2 • EXM0UNT3 0 o 10 — ' — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i i Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu i g . 8 . 2 3 . BEN d i a g r a m f o r samples EXMOUNT1, EXM0UNT2 and EXM0UNT3 203 and have a convex-up hump fom Hf to Lu. EXMOUNT1 has a 'peak' at Rb. None of these p a t t e r n s have Eu anomalies. BEND p a t t e r n s on F i g . 8.24 are from Brown Bear and Cobb seamounts. P a t t e r n s have g r o s s l y convex-up shapes which 'peak' at Nb and have 'troughs' at Sr and Hf. From T i to Lu the p a t t e r n s are r e l a t i v e l y u n f r a c t i o n a t e d and have no Eu anomalies, d e s p i t e t h e i r Sr anomalies. In a d d i t i o n , Cobb p a t t e r n s have a 'trough' at K and BRBEAR1 and COBB2 are s l i g h t l y e n r i c h e d i n Ba r e l a t i v e to Rb. BEND p a t t e r n s from F i g . 8.25 are from Southern E x p l o r e r Ridge, Paul Revere Ridge, E x p l o r e r R i f t and E x p l o r e r Deep. The BEND p a t t e r n s from SEXRIDGE and PREVRDG are g r o s s l y s i m i l a r . Both are r e l a t i v e l y u n f r a c t i o n a t e d and both have 'troughs' at Sr, the 'trough' being e s p e c i a l l y n o t i c e a b l e i n the p a t t e r n from PREVRDG. PREVRDG has a s l i g h t 'trough' at K and a 'peak' at Th whereas SEXRIDGE has a 'peak' at Nb. EXRIFT has 'peaks' at Rb and Nb, but otherwise slopes p o s i t i v e l y from Ba to Nd and i s r e l a t i v e l y f l a t from Sm to Yb. EXDEEP has a p a t t e r n with a convex-up shape 'peaking' at Nb, and a 'trough' at Sr. T h i s l a t t e r p a t t e r n i s g r o s s l y s i m i l a r to p a t t e r n s from F i g . 8.24. None of these p a t t e r n s have Eu anomalies. 204 1000 -i BRBEAR1 A CO BRBEAR2 A [JJ COBB 1 v D 1 0 0 " C0BB2 T < > Q 111 1 — ' — i — i — i — i — i — i — i — i — r — i — i — i — i — i — i — i i i — i — Ba RbTh U K Nb La Ce Sr Nd Sm Zr Hf Ti Eu Tb Y Yb Lu F i g . ' 8 . 2 4 . BEN d i a g r a m f o r s a m p l e s BRBEAR1, BRBEAR2, COBB 1 and C0BB2 205 1000 - i CO m D < > Q UJ N CC O 2- 100 H SEXRIDGE + PREVRDG X EXRIFT 0 EXDEEP * 10 " i — i — i — i r - n 1 1—i 1 — i — i 1 — i — i — i — | — | — Ba RbTh U K Nb La Ce Sr NdSm Zr Hf Ti Eu Tb Y Yb Lu F i g . 8 . 2 5 . BEN d i a g r a m f o r samples SEXRIDGE. PREVRDG, EXRIFT and EXDEEP 206 8.3 TRACE ELEMENT CHEMISTRY In general the o v e r a l l abundances of t r a c e and rare e a r t h elements are lower than abundances i n samples from any of the other s u i t e s i n t h i s study. Trace element abundances and BEND p a t t e r n s f o r E x p l o r e r seamount samples and EXRIFT g r o s s l y resemble abundances i n N-MORB, but they have hi g h e r c o n c e n t r a t i o n s of Ba, Rb and Sr, average to higher abundances of Nb and Zr and lower abundances of Hf (Sun, 1980; Sun et a l . , 1979; Pearce, 1982; Pearce and Cann, 1973). Zr/Nb r a t i o s between 17.5 and 33 are lower than the average N-MORB r a t i o of 40 to 50 c a l c u l a t e d by. E r l a n k and Kable (1976) suggesting the mantle source region f o r these b a s a l t s i s l e s s d e p l e t e d than the source f o r most N-MORB. La abundances range from 6.1 to 11.9 times c h o n d r i t i c , Yb abundances are 10.4 to 14.5 times c h o n d r i t i c , ( L a / Y b ) C H = 0.58 to 0.81 and ( L a / C e ) C H = 0.72 to 0.99. These r a t i o s are w i t h i n the range of r a t i o s from N-MORB (Henderson, 1984). Samples from Brown Bear and Cobb seamounts and E x p l o r e r Deep have s i m i l a r to s l i g h t l y ' e n r i c h e d t r a c e and REE abundances r e l a t i v e to abundances in an 'average' E-MORB, and t h e i r BEND p a t t e r n s resemble E-MORB p a t t e r n s (Sun, 1980; Thompson et a l . , 1983; Sun et a l . , 1979; Pearce, 1982). La abundances l i e between 19.2 and 34.7 times c h o n d r i t i c , Yb ranges from 12.7 to 17.3 times c h o n d r i t i c , ( L a / Y b ) C H r a t i o s range from 1.53 to 2.40, ( L a / C e ) ^ H r a t i o s l i e between 0.95 to 1.16 and Zr/Nb r a t i o s l i e between 9.6 and 13.2. These 207 r a t i o s a l s o suggest an E-MORB source (Henderson, 1984; Pearce, 1982; E r l a n k and Kable, 1976). Rather than a plume augmented N-MORB source ( i . e . E-MORB) f o r EXDEEP, Cousens et a l . (1984) suggest small degrees of p a r t i a l m e l t i n g of the mantle source as the cause of high LIL and LREE abundances i n t h i s sample. The 8 7 S r / B 6 S r r a t i o s from t h i s area support t h i s e x p l a n a t i o n . R e l a t i v e to N-MORB, SEXRIDGE has higher abundances of a l l t r a c e elements except Sr. Abundances of LIL are lower than abundances i n E-MORB but Zr, Hf and HREE contents are higher (Pearce, 1982; Sun et a l . , 1979; Sun, 1980). The BEND pa t t e r n from t h i s sample does not resemble e i t h e r an N- or E-MORB p a t t e r n but has c h a r a c t e r i s t i c s of both. Cousens (1982) suggests i t s shape may be produced by mixing N- and E-MORB magmas, i . e . mixing of EXRIFT and EXDEEP magmas. SEXRIDGE has an La content of 14 times c h o n d r i t i c , Yb equal to 14.1 times c h o n d r i t i c , an ( L a / Y b ) C H r a t i o of 0.9 and an ( L a / C e ) C H r a t i o of 0.93. I t s Zr/Nb r a t i o equals 14.3 These r a t i o s l i e between r a t i o s from EXRIFT and EXDEEP, f u r t h e r support f o r magma mixing. Except f o r Ba and Sr (Ba = 21 ppm, Sr = 133 ppm) PREVRDG has the hi g h e s t t r a c e and REE c o n c e n t r a t i o n s of a l l samples i n t h i s s u i t e . La equals 55.2 times c h o n d r i t i c , Yb i s 35 times c h o n d r i t i c , ( L a / Y b ) C H equals 1.59 and ( L a / C e ) C H i s 1.06. Zr/Nb equals 14.7, s i m i l a r to Zr/Nb r a t i o s i n BRBEAR1 and SEXRIDGE. S c h i l l i n g et a l . (1976) suggest higher t r a c e and rare e a r t h element abundances i n propogating r i f t 208 segments are evidence f o r hotspot a c t i v i t y . 8.3.1 TH AND U Th abundances are 0.3 ppm or l e s s i n E x p l o r e r seamount samples and EXRIFT and between 0.6 and 1.0 ppm in Brown Bear and Cobb seamount samples and SEXRIDGE (Table V I I ) . These abundances are w i t h i n the range of N- and E-MORB r e s p e c t i v e l y ( B a s a l t i c Volcanism Study P r o j e c t , 1981). Abundance of Th i s 1.5 ppm in EXDEEP and 2.3 ppm in PREVRDG. U was not analyzed i n samples SEXRIDGE, PREVRDG, EXRIFT and EXDEEP but estimated abundances from BEND are 0.2, 0.6, l e s s than 0.1 and 0.4 ppm r e s p e c t i v e l y . U abundance i n the remaining seven samples ranges from l e s s than 0.1 to 0.4 ppm. These abundances are w i t h i n the range of N- and E-MORB from the P a c i f i c Ocean (Jochum et a l . , 1983). Th/U r a t i o s range from 2 to 4 and average 3. 8.3.2 TRANSITION ELEMENTS Cr abundances i n E x p l o r e r seamount samples, BRBEAR2 and PREVRDG are s l i g h t l y lower than an 'average' N-MORB, and Ni abundances are m a r g i n a l l y higher (Engel et a l . , 1965). Abundances of Cr and Ni i n BRBEAR1 and SEXRIDGE l i e w i t h i n the range from 'average' N-MORB. COBB 1, COBB2 and EXDEEP are d e p l e t e d i n Cr and Ni r e l a t i v e to both N and E-MORB. 209 EXRIFT has the hi g h e s t Cr and Ni abundances (Cr = 390 ppm, Ni = 270 ppm) r e f l e c t i n g i t s ( u n f r a c t i o n a t e d ) Mg' number of 66. Sc abundances range from 27.1 to 43.6 ppm and average 37 ppm. Th i s i s w i t h i n the range of MORB (Erlank and Kable, 1976; Pearce, 1982). Petrography by Cousens (1982) e s t a b l i s h e d o l i v i n e and p l a g i o c l a s e as the dominant phenocryst phases i n Ex p l o r e r b a s a l t s . Pyroxene phenocrysts occ u r r e d only r a r e l y . Therefore Ni c o n c e n t r a t i o n s are p r i m a r i l y c o n t r o l l e d by o l i v i n e f r a c t i o n a t i o n and Cr contents are presumably c o n t r o l l e d by f r a c t i o n a t i o n of a s s o c i a t e d C r - s p i n e l . 8.4 SR ISOTOPES Sr i s o t o p e r a t i o s were not a v a i l a b l e f o r samples from E x p l o r e r , Brown Bear or Cobb seamounts but Armstrong and Nixon (1980) report an 8 7 S r / 8 6 S r r a t i o of 0.70250 f o r an Ex p l o r e r seamount sample l o c a t e d at 49° 03 N and 130° 54 W, and Eaby et a l . (1984) r e p o r t 8 7 S r / 8 6 S r r a t i o s of 0.70251 and 0.7023 f o r Brown Bear and Cobb seamounts r e s p e c t i v e l y . Sr i s o t o p e r a t i o s from SEXRIDGE, PREVRDG and EXRIFT l i e between 0.70232 and 0.70254 (Table VII) and a sample from E x p l o r e r Deep analyzed by Cousens (1982) has an 8 7 S r / 8 6 S r r a t i o of 0.70252. These t i g h t l y c l u s t e r e d r a t i o s a l l l i e w i t h i n the range of r a t i o s from MORB (Hart, 1976) d e s p i t e the f a c t that E x p l o r e r , Brown Bear and Cobb are seamounts. 210 8.5 DISCUSSION OF DISCRIMINATION DIAGRAMS Ex p l o r e r seamount samples p l o t w i t h i n or c l o s e to the N-MORB f i e l d on a l l diagrams and do not have the chemical or i s o t o p i c c h a r a c t e r i s t i c s of WPB. T h i s i s c o n s i s t e n t with t h e i r BEND p a t t e r n shapes. Although a N-MORB seamount may seem unusual, B a t i z a (1980) suggests that most small volcanoes on young oceanic c r u s t are c h e m i c a l l y s i m i l a r to MORB. EXRIFT i s c l a s s i f i e d as N-MORB on a l l diagrams except MnO-Ti0 2-P 20 5 (IAT) ( F i g . 8.6), La vs. Th (E-MORB) ( F i g . 8.18) and La vs. Nb (E-MORB) ( F i g . 8.19). R e l a t i v e d e p l e t i o n i n P 2 0 5 ( P 2 0 5 = 0.8 wt. %) causes the IAT c l a s s i f i c a t i o n on the f i r s t diagram, whereas r e l a t i v e enrichment i n Th and Nb r e s p e c t i v e l y c l a s s i f y EXRIFT as E-MORB on the l a t t e r two diagrams. However, i t s BEND p a t t e r n i s more c h a r a c t e r i s t i c of N-MORB than of E-MORB. On most diagrams Brown Bear and Cobb seamount samples p l o t f a r from E x p l o r e r seamount samples and sample EXRIFT. They are c l a s s i f i e d as ocean f l o o r b a s a l t s or E-MORB on a l l diagrams except MgO-FeO*-Al 20 3 ( F i g . 8.7) and La vs. Ba ( F i g . 8.16). Higher FeO* and lower A l 2 0 3 and MgO abundances r e s u l t i n OI and ARC c l a s s i f i c a t i o n s on the former diagram, whereas r e l a t i v e l y low Ba abundances ( r e l a t i v e to E-MORB) r e s u l t i n an N-MORB c l a s s i f i c a t i o n on the l a t t e r diagram. These low Ba abundances are c l o s e to or below d e t e c t i o n l i m i t s and c l a s s i f i c a t i o n s based on Ba should be judged a c c o r d i n g l y . BEND p a t t e r n s c l a s s i f y these samples as E-MORB 21 1 ( F i g . 8.24). Brown Bear and Cobb seamounts have low Sr isotope r a t i o s , more c h a r a c t e r i s t i c of N-MORB, suuggesting that the seamounts are c o n s t r u c t e d of lavas from d e p l e t e d sources, r a t h e r than from an en r i c h e d mantle plume (Eaby et a l . , 1984). EXDEEP p l o t s near the Brown Bear and Cobb samples on a l l of the diagrams, and i s thus c l a s s i f i e d as E-MORB. I t s BEND p a t t e r n ( F i g . 8.25) confirms t h i s c l a s s i f i c a t i o n . SEXRIDGE l i e s w i t h i n the IAT f i e l d on MnO-Ti0 2-P 20 5 ( F i g . 8.6) because of a r e l a t i v e l y high MnO abundance (MnO = 0.21 wt. % ) . R e l a t i v e to N-MORB i t i s s l i g h t l y d e p l e t e d i n A l 2 0 3 and en r i c h e d i n FeO*, hence i t s OI c l a s s i f i c a t i o n on MgO-FeO*-Al 20 3 ( F i g . 8.7). On a l l other diagrams SEXRIDGE p l o t s w i t h i n the MORB f i e l d ; as N-MORB on La v s . Ba ( F i g . 8.16) and as E-MORB on La vs. Th and La vs. Nb ( F i g s . 8.18 and 8.19). On Th-Hf/3-Ta* ( F i g . 8.22) i t l i e s on the N- and E-MORB f i e l d boundary. These chemical c h a r a c t e r i s t i c s support the mixing h y p o t h e s i s suggested by t h i s samples BEND p a t t e r n and incompatible element r a t i o s . Sample PREVRDG p l o t s o u t s i d e of MORB f i e l d boundaries on many of the diagrams (MgO-FeO*-Al 20 3 ( F i g . 8.7), T i - Z r - S r ( F i g . 8.9), Cr vs. Ce/Sr ( F i g . 8.14) and La vs. Ba ( F i g . 8.16)). On Th-Hf/3-Ta* ( F i g . 8.22) i t p l o t s c l o s e to the boundary between N-MORB and E-MORB. I t s BEND p a t t e r n and l o c a t i o n on a l l diagrams except T i - Z r - S r , Cr v s . Ce/Sr and La vs. Ba suggest mixing of N- and E-MORB sources. The very low Sr content, evident on T i - Z r - S r , Cr vs. Ce/Sr and BEND 212 may be a product of extreme p l a g i o c l a s e f r a c t i o n a t i o n and low Ba abundance may be produced by seawater a l t e r a t i o n (Korringa and Noble, 1971; P h i l p o t t s et al.,1969). However Sr d e p l e t i o n by p l a g i o c l a s e f r a c t i o n a t i o n u s u a l l y has an a s s o c i a t e d negative Eu anomaly and seawater d e p l e t i o n of Ba should supply an accompanying i n c r e a s e i n R and Rb. As ne i t h e r of these accompanying geochemical c h a r a c t e r i s t i c s are observed both of these suggestions appear u n l i k e l y , implying t h i s anomalous chemistry i s i n h e r i t e d from the source. 8.6 SUMMARY In general o f f s h o r e b a s a l t samples are d i s t i n c t from a l l other samples i n t h i s study because of t h e i r low o v e r a l l abundances of tr a c e and rare e a r t h elements, and low 8 7 S r / 8 6 S r i s o t o p e r a t i o s . On a l l t e c t o n i c d i s c r i m i n a t i o n diagrams the samples l i e w i t h i n the MORB f i e l d . Diagrams which are able to separate N- from E-MORB (La vs. Ba, La vs. Th, La vs. Nb and Th-Hf/3-Ta*) d i s t i n g u i s h three groups of samples. E x p l o r e r seamount and Expl o r e r R i f t samples are c l a s s i f i e d as N-MORB, Cobb and Brown Bear Seamount and E x p l o r e r Deep samples are c l a s s i f i e d as E-MORB and Southern E x p l o r e r Ridge and Paul Revere Ridge samples are c l a s s i f i e d as a mixture of N- and E-MORB magmas. BEND p a t t e r n shapes confirm these c l a s s i f i c a t i o n s . 213 R e l a t i v e to the remainder of the s u i t e PREVRDG has higher abundances of T i 0 2 , F e 2 0 3 , MnO and P 2 0 5 and lower abundances of A l 2 0 3 , MgO and CaO. I t a l s o has much higher , abundances of a l l t r a c e and r a r e e a r t h elements, e x c l u d i n g Ba and Sr. The t r a c e and REE abundances g r o s s l y resemble those from an oceanic WPB, but Sr isotope r a t i o s and BEND p a t t e r n shape imply a MORB-like source. Extremely high F e 2 0 3 content and lower than 'average' abundance of MgO have been suggested by Cousens et a l . (1984) to be evidence f o r a once a c t i v e n o r t h e a s t e r l y d i r e c t e d propogating r i f t . 214 TABLE VII. OFFSHORE BASALTS Major, trace and rare earth element abundances, Sr isotope ratios and estimated ages. EXMOUNT11 EXM0UNT21 EXM0UNT31 BRBEAR 1 1 BRBEAR21 COBB l l C0BB2 1 S e r i e s T h o l e l 1 t e A 1 k/Trans A 1k/Trans Tho1e * i t e A 1k / T r a n s A 1k / T r a n s A 1 k / T r a n s Name Ba s a l t Basa1t B a s a l t Basa1t B a s a 1 t B a s a 1 t B a s a 1 t LAT . 49 04.0 49 04.0 49 04.0 46 05.7 4C 05.7 46 45.0 46 45.0 LONG. 130 56.0 130 56.0 130 5G.0 130 27.8 ''130 27 .'8 " 130 50.0 130 50.0 s i o 2 47.99 47 . 84 47 . 87 47 . 72 5O.09 48 . 57 48.72 T10 2 1 . 25 1 . 25 1 . 34 1 . 72 1 . 94 2 . 04 2 . 12 A l j 0 3 17.18 17.18 17 .08 15 . 77 15.72 15 . 33 14.75 F e 2 0 3 10. 70 10. 39 10.41 11.91 10. 46 12 . 66 13 . 48 FeO N/A N/A N/A N/A N/A N/A N/A MnO 0. 17 0. 17 0. 17 0. 19 0.16 0. 18 0. 18 MgO 8 .04 8.56 8.41 7 .05 5 . 74 6 . 54 5 . 96 CaO 1 1 . 62 1 1 .62 1 1 . 58 11.77 11.51 10. 50 10. 80 Na 20 2.80 2.81 2.91 2.78 3.71 3. 54 3.51 K 20 0. 16 0.08 0.12 0. 26 0 . 47 0. 35 0. 27 P 2 0 5 0. 10 0. 10 0.11 0. 19 0. 20 0. 25 0. 20 H 20 N/A N/A N/A 0.80 0.84 0. 30 1 . 34 Ba 24 .0 24 .0 13.0 64 .0 92 .0 94 .0 84.0 Rb 3.6 1 .5 2.0 3.0 5.0 6 .0 4.0 Th 0.2 0.2 0.3 0.6 0 9 1 .0 0.8 U 0. 1 < 0. 1* 0. 1 0.2 0.4 0 . 4 0. 3 Nb 4.0 3.0 3.0 9.0 12.0 13 .0 12.0 La 3.6 3.5 3.9 6.3 9 . 1 1 1 . 4 9 . 2 Ce 9.8 11.6 10.3 17.4 21.4 27 . 1 22 .9 Sr 155 .0 177 .0 189 .0 214.0 227 ,0 248 .0 232 .0 Nd 10. 5 9.7 8.6 12.4 15 . 7 19 . 1 16 8 Sm 3 . 1 3 . 2 3 . 4 4 . 1 5.0 5 .2 5.3 Zr 92 .0 89.0 99.0 1 19.0 134 .0 154 .0 144 .0 Hf 2 . 1 1 . 9 2.0 2.0 2 . 6 3 .6 2.7 Eu 1 . 1 1.0 1 . 1 1 . 3 1 . 5 1 . 5 1 . 5 Tb 0.7 • 0.8 O B 0.9 0.9 0 .9 0.9 V 29.0 29.0 30.0 36 .0 33 .0 38 .0 38 .0 Yb 3.0 3.0 3 . 2 2.8 3 . 1 3 . 2 3.8 Lu 0.3 0.3 0.4 0.3 0.5 0 . 4 0.5 Co 90.0 126 .0 99 . 0 59 .0 6 1.0 69 .0 54.0 Cr 223 . 7 211.0 2 10.7 225 . 0 175 . 7 120 . 8 95 .9 Cu 80.0 85 .0 91.0 47.0 6 1.0 50 .0 70.0 N1 160.0 153.0 142.0 80.0 134 .0 59 .0 47 . 0 Sc 38.2 36 . 6 35.5 39.5 43 . 6 4 1 8 42 . 7 V 87 213.O 2 16.0 219.0 283 . 0 330.0 300 .0 328 .0 Sre6 N/A N/A N/A N/A N/A N/A N/A K/Rb 368.93 442.72 498.06 719.42 780.29 484 22 560.32 ( L a / Y b ) C H 0.80 0. 77 0.81 1 . 53 1 . 93 2 . 40 1 .64 La/Nb 0.90 1 .15 1 . 30 0. 70 0.75 0 . 88 0. 77 Mg' 60 62 62 54 52 51 47 Age (Ma) 4 4 * Estimated from BEND 4 < 1 < 1 < 1 Continued. . 215 SEXRIDGE 2 PREVRDG 2 EXRIFT 2 EXDEEP 2 S e r i e s T h o l e i i t e T h o l e i i t e T h o l e i i t e T h o l e i i t e Name Basalt Basalt Basalt Basalt LAT. 49 55.2 50 00.42 50 13.9 50 05. 5 LONG. 130 10.8 129 31.5 130 15. 1 129 44. 5 SIOj 48 . 4 1 48 . 24 . . 46 . 03. 49.32 T I 0 2 1 . 61 3.53 .1 . 09 1 . 76 A1 20, 13. 48 10.69 15. 19 •15. 10 F e 2 ° 3 12 . 63 19.33 12 . 27 11.51 FeO N/A N/A N/A N/A MnO 0. 21 0. 30 0. 19 0. 19 MgO 8 . 81 5 . 44 12. 20 7.81 CaO 12 . 04 8 . 38 12 . 00 1 1 .43 Na 20 2 . 24 2.79 1 . 87 2 . 44 K 20 0. 19 0.53 0. 06 0. 45 P2°5 0'. 14 0. 39 0. 08 0.21 H 20 0. 22 1 . 10 0. 25 0.50 Ba 30 .0 21.0 8 .0 106 0 Rb 5 .0 10.0 3 .0 10.0 Th 0 .6 2 . 3 0 . 2 1 . 5 U 0 .2* 0 6* < 0 . 1 * 0.4* Nb 7 .0 19.0 4 .0 15.0 La 4 .6 18 . 1 2 .0 11.4 Ce 13 .0 44.8 7 .3 25.8 Sr 122 .0 133.0 144 .0 161 .0 Nd 9 .9 30. 7 6 .0 17.2 Sm 3 5 10.0 2 . 2 4.8 Zr 100 .0 280.0 70 .0 144 .0 Hf 3 . 1 7.6 2 .0 3.8 Eu 1 . 1 2.9 0 .8 1 . 4 Tb 0 . 8 2. 1 0 . 6 0.8 y 26 .0 65.0 20 .0 32 .0 Yb 3 . 1 7 . 7 2 . 3 3 . 2 Lu 0 . 4 1 . 1 0 . 3 0.4 Co 42 .0 42 0 52 .0 41.0 Cr 278 .0 108.9 390 . 2 76.2 Cu N/A N/A N/A N/A Ni 78 .0 147 .0 270 .0 63.0 Sc 36 .7 34 . 7 27 . 1 34 . 4 V 87 290 .0 400.0 183 .0 274 .0 S r 8 9 0.70254 0.70254 0.70232 N/A K/Rb 315 .44 439.95 166 .02 373.54 (La/Yb) 1 .00 1 . 59 0 . 58 2 . 39 La/Nb 0 .66 0.96 0 .50 0.76 Mg' 58 36 66 57 Age (Ma) < 1 4.5 < 1 < 1 M a j o r a n d some t r a c e e l e m e n t a b u n d a n c e s f r o m : ^ R . L . C h a s e ( p e r s . c o m m . , 1984) 2 8 . L . C o u s e n s ( 1 9 8 2 ) * E s t i m a t e d f r o m BEND N/A = n o t a n a l v z e d 9. SUMMARY OF DISCRIMINATION DIAGRAM DISCUSSIONS Major, t r a c e and rare e a r t h element t e c t o n i c d i s c r i m i n a t i o n diagrams a p p l i e d to data from Neogene and Quaternary b a s a l t s i n B r i t i s h Columbia and the adjacent P a c i f i c Ocean f l o o r c o r r e c t l y i d e n t i f y the t e c t o n i c s e t t i n g s of a l l s u i t e s except the G a r i b a l d i V o l c a n i c B e l t (Table V I I I ) . However the d i f f e r e n t WPB t e c t o n i c s e t t i n g s ( i . e . hotspot, r i f t , back-arc, plate-edge) cannot be d i s t i n g u i s h e d from each other as data from these WPB s u i t e s completely o v e r l a p . G a r i b a l d i B e l t b a s a l t s erupted i n a convergent margin s e t t i n g p l o t as WPB. T h i s i m p l i e s that geochemistry alone i s not always a v a l i d method f o r d i s t i n g u i s h i n g a n c i e n t t e c t o n i c s e t t i n g s . A n a l y s i s f o r Ta was u n s u c c e s f u l , but Nb/16 s u b s t i t u t e d f o r Ta produced a c c e p t a b l e r e s u l t s on a l l of the diagrams i n c o r p o r a t i n g Ta. The a l k a l i n e s e r i e s b a s a l t s from a l l t e c t o n i c s e t t i n g s can be d i s t i n g u i s h e d from the t h o l e i i t i c s e r i e s by t h e i r higher o v e r a l l abundances of t r a c e and rare e a r t h elements. Both N- and E-MORB are d i s t i n g u i s h e d from WPB and convergent margin b a s a l t s by t h e i r lower o v e r a l l abundances of t r a c e and rare e a r t h elements. T h i s chemical c h a r a c t e r i s t i c c l e a r l y separates them from other p o s s i b l e t e c t o n i c s e t t i n g s on almost a l l of the d i s c r i m i n a t i o n diagrams p l o t t e d . In a d d i t i o n , N-MORB are more d e p l e t e d i n the l a r g e low valency c a t i o n s (Ba, Rb, K and Sr) and Th and U than E-MORB so that t e c t o n i c d i s c r i m i n a t i o n diagrams using 216 TABLE VIII. CLASSIFICATION OF SAMPLE SUITES USING DISCRIMINATION DIAGRAMS Abbreviations used on the following data pages are l i s t e d below: N/A = not applicable OFB* = OFB plus CAB plus LKT and = overlap of data points onto two f i e l d s or = one f i e l d for two possible tectonic settings convergent margin setting ocean f l o o r s e tting within plate setting MORB OFB TH MORB WPB } 01 \ CB J Continued TABLE VIII (cont.) SUITE LIMITATIONS TECTONIC 1 SETTING T not for rocks with alk. >20% on AFM not for cont. thol. not for alkaline series N/A not for WPB not for CAB N/A Unfract. samples not for WPB GARIBALDI BELT ARC Non-oceanic WPB and ARC N-MORB and CB WPB and OFB* N/A WPB and MORB WPB TH MORB ARC COQUIHALLA COMPLEX ARC N/A ARC ARC CAB CAB N/A ARC or MORB I AT ARC CHILCOTIN BASALTS WPB (Back-arc?) Non-oceanic and Oceanic WPB and MORB and ARC N-MORB and CB and OI WPB and OFB* N/A WPB WPB and MORB or ARC TH MORB and IAT N/A ANAHIM VOLCANIC BELT WPB (Hotspot?) Non-oceanic and Oceanic WPB and MORB CB and OI WPB and OFB* N/A WPB and MORB WPB TH MORB and IAT N/A MASSET FORMATION ARC? WPB? (Hotspot?) N/A WPB and ARC N-MORB and ARC CAB CAB N/A MORB IAT ARC STIKINE VOLCANIC BELT WPB (Incipient Rift) Non-oceanic and Oceanic WPB and MORB CB and OI WPB N/A WPB WPB TH MORB and IAT N/A ALERT BAY VOLCANIC BELT WPB (Arc-trench gap) Non-Oceanic and Oceanic WPB N-MORB and ARC WPB N/A WPB WPB TH MORB and IAT ARC OFFSHORE BASALTS MORB Oceanic MORB and ARC N-MORB and CB and OI and ARC OFB* OFB MORB MORB or ARC TH MORB MORB Continued TABLE VIII (cont). SUITE TECTONIC SETTING GARIBALDI BELT ARC WPB and ARC WPB and ARC ARC and N-MORB Oceanic (WPB) E-MORB or WPB and N-MORB E-MORB or WPB and N-MORB and ARC WPB? WPB WPB and ARC COQUIHALLA COMPLEX ARC ARC ARC ARC ARC ARC ARC ARC ARC ARC CHILCOTIN BASALTS WPB (Back-arc?) WPB or MORB and/or ARC WPB and/or ARC ARC and WPB or E-MORB Oceanic (WPB) or ARC E-MORB or WPB and ARC WPB WPB? WPB and ARC WPB ANAHIM VOLCANIC BELT WPB (Hotspot?) WPB or MORB and/or ARC WPB or ARC or MORB ARC and N-MORB and E-MORB or WPB Oceanic (WPB) or ARC E-MORB or WPB and ARC E-MORB or WPB and N-MORB WPB? WPB WPB MASSET FORMATION ARC? WPB? (Hotspot?) ARC WPB or ARC ARC Oceanic (WPB) E-MORB or WPB and ARC N-MORB WPB? ARC ARC? STIKINE VOLCANIC BELT WPB (Incipient Rift) WPB and ARC WPB and/or ARC ARC and N-MORB and E-MORB or WPB Oc eanic (WPB) or ARC E-MORB or WPB and ARC E-MORB or WPB and N-MORB WPB WPB WPB ALERT BAY VOLCANIC BELT WPB (Arc-trench gap) WPB or MORB and/or ARC WPB or MORB and/or ARC ARC Oceanic (WPB) E-MORB or WPB and N-MORB E-MORB or WPB and N-MORB WPB and ARC WPB and ARC WPB and ARC OFFSHORE BASALTS MORB WPB or ARC or MORB ARC or MORB N-MORB Oceanic (MORB) E-MORB or WPB and N-MORB N-MORB and E-MORB or WPB MORB MORB N-MORB and E-MORB 220 these elements are e s p e c i a l l y e f f e c t i v e i n se p a r a t i n g these two MORB environments, e.g. La vs. Ba, La vs. Th, La vs. Nb and Th-Hf/3-Ta* (Sun et a l . , 1979; Wood, 1980; G i l l , 1981). WPB have higher abundances of a l l t r a c e and rare e a r t h elements than e i t h e r N- or E-MORB and g e n e r a l l y have lower abundances of Ba, Th, K and Sr and higher Nb and T i abundances than b a s a l t s from a convergent margin. These geochemical c h a r a c t e r i s t i c s r e a d i l y d i s t i n g u i s h WPB from N-MORB and convergent margin b a s a l t s on V vs. Ti/1000, T i / Y vs. Nb/Y, La vs. Ba, La vs. Th, La vs. Nb, K 20/Yb vs. Ta*/Yb, Th/Yb vs. Ta*/Yb and Th-Hf/3-Ta* ( G i l l , 1981; She r v a i s , 1982; Pearce 1982; Wood, 1980; Thompson et a l . , 1983 and 1984). D i s t i n c t i o n of WPB from E-MORB i s p o s s i b l e using V vs. Ti/1000, T i / Y vs. Nb/Y, K 20/Yb vs. Ta*/Yb, Th/Yb vs. Ta*/Yb and Th-Hf/3-Ta*. Some c o n t i n e n t a l t h o l e i i t i c WPB have elemental abundances resembling those i n a convergent margin b a s a l t and l i e w i t h i n the convergent margin f i e l d on most t e c t o n i c d i s c r i m i n a t i o n diagrams. Therefore samples i n the g e o l o g i c r e c o r d which are geochemically i d e n t i f i e d as convergent margin t h o l e i i t e s should be judged with t h i s i n mind. Convergent margin b a s a l t s are i d e n t i f i e d by an enrichment i n l a r g e low valency c a t i o n s r e l a t i v e to WPB, N- and E-MORB and a d e p l e t i o n i n Nb and T i r e l a t i v e to WPB (Pearce, 1982; Thompson et a l . , 1983 and 1984; Jakes and White, 1972; Kay, 1980; Sh e r v a i s , 1982; Hawkesworth and Powell, 1980). Most b a s a l t s from convergent margin s e t t i n g s 221 have La/Nb g r e a t e r than 2.0, whereas WPB have La/Nb r a t i o s which are l e s s than or equal to 1.0. Using t e c t o n i c d i s c r i m i n a t i o n diagrams, s e p a r a t i o n of convergent margin b a s a l t s from WPB i s best accomplished u s i n g V vs. Ti/1000, La vs. Ba, ( B a / L a ) ^ vs. (La/Sm) C H, La vs. Th, La vs. Nb, K 20/Yb vs. Ta*/Yb, Th/Yb vs. Ta*/Yb and Th-Hf/3-Ta*. Convergent margin b a s a l t s are d i s t i n g u i s h e d from both N- and E-MORB on most of the same diagrams, e x c l u d i n g T i / Y v s . Nb/Y, and i n c l u d i n g Sm/Ce vs. Sr/Ce and Cr vs. Ce/Sr. Table IX presents the s t u d i e d t e c t o n i c d i s c r i m i n a t i o n diagrams i n order of t h e i r o v e r a l l success at c l a s s i f y i n g t e c t o n i c s e t t i n g s . S u i t e s of b a s a l t i c samples are c l a s s i f i e d with g r e a t e r c e r t a i n t y than i n d i v i d u a l samples and r e l a t i v e l y u n f r a c t i o n a t e d and u n a l t e r e d samples are ob v i o u s l y p r e f e r r e d . C h a r a c t e r i s t i c BEND p a t t e r n shapes h e l p i d e n t i f y t e c t o n i c s e t t i n g s , and are a l s o u s e f u l f o r determining anomalous enrichments and/or d e p l e t i o n s i n i n d i v i d u a l samples r e l a t i v e to the remainder of the s u i t e . The f i r s t 8 diagrams l i s t e d i n Table IX were very to f a i r l y s u c c e s s f u l at s e p a r a t i n g convergent margin, ocean f l o o r and w i t h i n p l a t e b a s a l t s and r e q u i r e no f u r t h e r e x p l a n a t i o n s . However, the remaining 10 diagrams were not as s u c c e s s f u l , because of the v a r i o u s reasons l i s t e d below. Nb d e p l e t i o n s and enrichments which r e s u l t i n the m i s i d e n t i f i c a t i o n of samples on La vs. Nb are small and wi t h i n a n a l y t i c a l e r r o r of ' t y p i c a l ' Nb abundance. By p l a c i n g the N- and E-MORB f i e l d boundary at a La/Nb r a t i o of TABLE IX EFFICIENCY OF TECTONIC DISCRIMINATION DIAGRAMS * WPB CONVERGENT MARGIN (N-) MORB (E-) DISCRIMINANT DIAGRAM USED of s u i t e c o r r e c t l y Ident1fled % of other mlsIdent1fled of s u i t e c o r r e c t l y i d e n t 1 f l e d % of other mi s ident i f1ed of s u i t e c o r r e c t l y I d e n t i f i e d % of other m i s l d e n t l f l e d Th-Hf/3-Ta* (Ti-Zr-Y ( T i - Z r - S r TI/Y vs. Nb/Y Th/Yb vs. Ta*/Yb ( B a / L a ) C H v s . (La/Sm)^ H V vs. Ti/1000 La vs. Th La vs. Nb MnO-T10 2-P 20 5 T i / C r vs. Ni Sm/Ce vs Sr/Ce Cr vs . Y K 20/Yb vs. Ta»/Yb Cr vs. Ce/Sr FeO»-MgD-Al 20 3 La vs. Ba 98% 94% 98% 98% 91% 94% 89% 83% 85% 83% 74% 46% 50% 86% 13% 5% 0% 0% 0% 0% 0% 6% 0% 0% 0% 0% 0% 0% 23% 0% 88% 2% 100% 0% 100% 0% 100% 2% 80% 2% 100% 8% 0% 0% 83% 9% 80% 2% 100% 8% 100% 14% 100% 0% 100% 2 2% 100% 0% 100% 44% 100% 3% 100% 57% 100% 100% 100% 100% 100% 100% 100% 100% 100% 3% 12% 73% 100% 100% 100% 100% 100% 45% 100% 29% 100% G% 0% 0% 0% 0% 1 1% 100% 100% 10% 0% 0% 0% 0% 8% 12% o% OCEANIC NON-OCEANIC % of s u i t e c o r r e c t l y Ident1fled 100% % of other m i s i d e n t l f ied 27% of s u i t e c o r r e c t l y ident t f l e d 72% % of other mi s i d e n t 1 f l e d 0% * Diagrams are l i s t e d i n order of o v e r a l l success 223 1.2 i n s t e a d of 1, the percentage of m i s i d e n t i f i e d N-MORB samples would decrease from gre a t e r than 70% to l e s s than 20% and the percentage of c o r r e c t l y i d e n t i f i e d WPB samples would increase from 83% to 93%. MnO-Ti0 2-P 205r which uses major element oxides, i s the most s u c c e s s f u l major element diagram f o r d i s t i n g u i s h i n g MORB, WPB and convergent margin t e c t o n i c s e t t i n g s . Anomalously low P 2 0 5 abundances i n a few S t i k i n e , Anahim and o f f s h o r e samples are the primary cause of m i s i d e n t i f i c a t i o n and may be a r e s u l t of a p a t i t e removal. T i / C r vs. Ni was s u c c e s s f u l at s e p a r a t i n g u n f r a c t i o n a t e d convergent margin b a s a l t s from MORB pl u s WPB. If f r a c t i o n a t e d samples were i n c l u d e d t h i s diagram was l e s s s u c c e s s f u l , as many WPB p l o t t e d w i t h i n the convergent margin f i e l d because of low Ni abundance (almost c e r t a i n l y caused by o l i v i n e f r a c t i o n a t i o n ) . Sm/Ce vs. Sr/Ce does not c o n t a i n a f i e l d f o r WPB, but most WPB from t h i s study would have p l o t t e d w i t h i n the MORB f i e l d , suggesting t h i s diagram may be even more s u c c e s s f u l than T i / C r vs. Ni f o r s e p a r a t i n g convergent margin b a s a l t s from WPB plus MORB because Sm/Ce vs. Sr/Ce i s u n a f f e c t e d by o l i v i n e and/or c l i n o p y r o x e n e f r a c t i o n a t i o n . Low abundances of Y which a f f e c t c l a s s i f i c a t i o n s u s i n g Cr vs. Y are probably caused by the presence of one or more minor r e s i d u a l source or magma chamber phases which r e t a i n t h i s element (garnet?) (Pearce, 1982). F r a c t i o n a t i o n of pyroxene ± C r - s p i n e l a l s o i n f l u e n c e s a samples p o s i t i o n on 224 I t h i s diagram, but most u n f r a c t i o n a t e d samples are c o r r e c t l y i d e n t i f i e d . K 20/Yb vs. Ta*/Yb c o r r e c t l y i d e n t i f i e s only 46% of WPB samples because over 50% l i e between the WPB and convergent margin f i e l d boundaries. T h i s i s caused by an enrichment i n K 20. S i m i l a r i l y , the low success of Cr vs. Ce/Sr was caused by Sr enrichment, as w e l l as Cr d e p l e t i o n by pyroxene ± C r - s p i n e l f r a c t i o n a t i o n . E r u p t i o n through c o n t i n e n t a l c r u s t has been used by Do s t a l et a l . (1977), Jakes and White (1977) and G i l l (1981) to e x p l a i n the i n c r e a s e d abundances of Ba, Rb, Th, U, K and Sr i n c o n t i n e n t a l convergent margin magmas. R e s u l t s from t h i s study suggest that s i m i l a r i n c r e a s e s occur i n WPB magmas erupted through c o n t i n e n t a l c r u s t . T h i s i s evident on K 20/Yb vs. Ta*/Yb, Ce vs. Ce/Sr and La vs. Ba. FeO*-MgO-Al 20 3, intended f o r use i n c l a s s i f y i n g s u b a l k a l i n e b a s a l t s proved to be of l i t t l e v a l u e . (This study a l s o p l o t t e d the ' t r a n s i t i o n a l ' samples). Samples which on other diagrams were c l a s s i f i e d as WPB p l o t t e d i n both the CB ( c o n t i n e n t a l b a s a l t ) and OI (ocean i s l a n d ) f i e l d s , with 74% of the s t u d i e d samples l y i n g w i t h i n the OI f i e l d , and none of the ocean f l o o r samples p l o t t e d w i t h i n the E-MORB f i e l d d e s p i t e t h e i r E-MORB c l a s s i f i c a t i o n on La vs. Th, La vs. Nb and Th-Hf/3-Ta*. When a l l s u b a l k a l i n e samples were p l o t t e d together most of them c l u s t e r e d around the CB, OI, N-MORB t r i p l e j u n c t i o n so th a t i d e n t i f i c a t i o n of 225 t e c t o n i c s e t t i n g was im p o s s i b l e . O v e r a l l t h i s diagram was not s u c c e s s f u l f o r c l a s s i f y i n g the b a s a l t s s t u d i e d and should only be used i f these are the only major element oxides which have been analyzed, and i f l a r g e numbers of samples are being compared. La v s . Ba was the l e a s t s u c c e s s f u l t r a c e and rare e a r t h element t e c t o n i c d i s c r i m i n a t i o n diagram because most of the WPB samples p l o t t e d w i t h i n the convergent margin f i e l d . T h i s was caused by t h e i r anomalous enrichments i n Ba (mentioned above). T i 0 2 - K 2 0 - P 2 0 5 , which a l s o uses major element oxides, was 72% e f f e c t i v e i n s e p a r a t i n g non-oceanic from oceanic s u b a l k a l i n e b a s a l t s but as WPB, convergent margin b a s a l t s and MORB cannot be separated, t h i s diagram was not a s u c c e s s f u l d i s c r i m i n a t o r . T i / Y vs. Nb/Y, ( B a / L a ) C H vs. (La/Sm> C H, T i / C r vs. N i , Cr vs. Y and Cr vs. Ce/Sr appear to be s u c c e s s f u l f o r d i s t i n g u i s h i n g MORB, WPB and convergent margin b a s a l t t e c t o n i c environments (Table I X ) . However, they a l l c o n t a i n o v e r l a p p i n g f i e l d s , and consequently are only u s e f u l i f combined with some other i n d i c a t i o n of t e c t o n i c s e t t i n g . P o s i t i v e Eu anomalies occur i n BEND p a t t e r n s from a l l of the s u i t e s , and although Eu anomalies are important i n f r a c t i o n a t i o n s t u d i e s of evolved magmas they are of l i t t l e use f o r d i s t i n g u i s h i n g t e c t o n i c o r i g i n s . Eu anomalies are absent i n many BEND p a t t e r n s which have p o s i t i v e Sr anomalies; a f u r t h e r suggestion that e r u p t i o n through 226 c o n t i n e n t a l c r u s t , r a t h e r than p l a g i o c l a s e accumulation, causes the Sr enrichment observed i n some of the samples. 10. CONCLUSIONS E i g h t s u i t e s of b a s a l t i c rocks from B r i t i s h Columbia and i t s o f f s h o r e ocean f l o o r were d i s t i n g u i s h e d one from the other using eighteen t e c t o n i c d i s c r i m i n a t i o n diagrams and bulk e a r t h normalized diagrams (BEND). B a s a l t s from the ocean f l o o r were c l a s s i f i e d as N- and E-MORB, those from the C o q u i h a l l a Complex and the Masset Formation as ARC and the remainder were c l a s s i f i e d as WPB ( G a r i b a l d i B e l t , C h i l c o t i n B a s a l t s , Anahim V o l c a n i c B e l t , S t i k i n e V o l c a n i c B e l t , A l e r t Bay V o l c a n i c B e l t ) . Of a l l t e c t o n i c d i s c r i m i n a t i o n diagram s t u d i e d , none was abl e to separate the v a r i o u s w i t h i n p l a t e environments ( i . e . hotspot (Anahim B e l t ) , i n c i p i e n t r i f t ( S t i k i n e B e l t ) , back-arc ( C h i l c o t i n Group), plate-edge ( A l e r t Bay B e l t ) ) . The G a r i b a l d i B e l t b a s a l t s , i n a convergent margin s e t t i n g , were c o n s i s t e n t l y c l a s s i f i e d as WPB, suggesting that geochemical t e c t o n i c c l a s s i f i c a t i o n s of a n c i e n t b a s a l t s be a p p l i e d with c a u t i o n and supporting evidence, such as chemistry of a s s o c i a t e d m o r e - f r a c t i o n a t e d rocks, should be i n c l u d e d . Some w i t h i n p l a t e b a s a l t s erupted through c o n t i n e n t a l c r u s t have higher than 'average' abundances of Ba, Th, U, K and Sr. In most cases these ' c o n t i n e n t a l ' enrichments are not l a r g e enough to a f f e c t the o v e r a l l c l a s s i f i c a t i o n of a s u i t e on t e c t o n i c d i s c r i m i n a t i o n diagrams. Although REE abundances from INAA are important f o r q u a n t i t a t i v e models of w i t h i n - s u i t e f r a c t i o n a t i o n paths 227 228 (e.g. Eu anomalies, Yb abundances and and ( L a / Y b ) ^ r a t i o s ) most are not important for e s t a b l i s h i n g t e c t o n i c s e t t i n g . The o n l y exception i s La, used i n the r a t i o La/Nb. La/Nb r a t i o s l e s s than 1.2 c o r r e c t l y separate 93% of WPB, i n c l u d i n g E-MORB, from N-MORB (La/Nb of 1.2 to 2) and convergent margin (La/Nb > 2) b a s a l t s . Major and t r a c e element abundances from XRF a n a l y s i s are g e n e r a l l y s u f f i c i e n t f o r d i s t i n g u i s h i n g the t e c t o n i c e n v i ronment. I f only major element oxide abundances are a v a i l a b l e , t e c t o n i c s e t t i n g s can be determined f a i r l y s u c c e s s f u l l y u s i n g MnO-TiO 2-P 20 5. B e t t e r d i s c r i m i n a t i o n i s obtained u s i n g the p a i r e d T i - Z r - Y and T i - Z r - S r diagrams. T h i s p a i r of diagrams i s very s u c c e s s f u l f o r s e p a r a t i n g w i t h i n p l a t e from convergent margin from oceanic b a s a l t s , but N- and E-MORB are not sep a r a t e d one from the other. The most e f f e c t i v e diagram f o r d i s t i n g u i s h i n g b a s a l t s and more f r a c t i o n a t e d magmas of w i t h i n p l a t e , convergent margin, N-MORB and E-MORB i s Th-Hf/3-Ta. These t r a c e elements are from INAA, but acc e p t a b l e r e s u l t s were produced u s i n g the XRF element r a t i o s Nb/16 and Zr/39, s u b s t i t u t e d f o r Ta and Hf r e s p e c t i v e l y . No XRF s u b s t i t u t i o n was found f o r Th but i t may c o n v e n i e n t l y be determined v i a y c o u n t i n g . The l e a s t e f f e c t i v e t e c t o n i c d i s c r i m i n a n t diagrams are FeO*-MgO-Al 20 3 and La vs. Ba. Those using Cr and Ni ( T i / C r v s . N i , Cr vs. Ce/Sr and Cr vs. Y) are very s e n s i t i v e to 229 f r a c t i o n a t i o n , but i f p r o p e r l y a p p l i e d they are able to d i s t i n g u i s h convergent margin from MORB p l u s WPB b a s a l t s . REFERENCES Abbey, S., 1976, SY-2, SY-3 and MRG-1. 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Thompson, R.N., Morrison, M.A., Hendry, G.L. and Parry, S.J., 1984, An assesment of the r e l a t i v e r o l e s of c r u s t and mantle i n magma ge n e s i s : An elemental approach. P h i l o s o p h i c a l T r a n s a c t i o n s of the Royal S o c i e t y of London S e r i e s A, v. 310, p. 549-590. Thornton, C P . and T u t t l e , O.F., 1960, Chemistry of igneous 241 r o c k s : I. d i f f e r e n t i a t i o n index. American J o u r n a l of Science, v. 258, p. 664-684. van der Heyden, P., 1982, Tec t o n i c and s t r a t i g r a p h i c r e l a t i o n s between the Coast P l u t o n i c Complex and Intermontane B e l t , West C e n t r a l B r i t i s h Columbia. Unpublished M.Sc..thesis, Department of Geology, U n i v e r s i t y of B r i t i s h Columbia, Vancouver, Canada, 172 P- Wager, L.R. and Deer, W.A., 1939, The p e t r o l o g y of the Skaergaard i n t r u s i o n , Kangerdlugssuag, East Greenland. Meddl. om Gronland, v. 105, No. 4, p. 1-352. Weaver, B.C. and Tarney, J . , 1983, Chemistry of the su b - c o n t i n e n t a l mantle: i n f e r e n c e s from Archaean and P r o t e r o z o i c dykes and c o n t i n e n t a l f l o o d b a s a l t s . in C o n t i n e n t a l B a s a l t s and Mantle X e n o l i t h s . Hawkesworth, C.J. and Norry, M.J. (eds.), Shiva Press, p. 209-229. White, W.M. and Bryan, W.B., 1977, Sr Isotope, K, Rb, Cs, Sr, Ba and rare e a r t h geochemistry of b a s a l t s from the FAMOUS area. G e o l o g i c a l S o c i e t y of America B u l l e t i n , v. 88, p. 571-576. White, W.M. and P a t c h e t t , J . , 1984, Hf-Nd-Sr iso t o p e s and incompatible element abundances i n i s l a n d a r c s : i m p l i c a t i o n s f o r magma o r i g i n s and crust-mantle e v o l u t i o n . E a r t h and Planetary Science L e t t e r s , v. 67, p. 167-185. Wilson, M. and Davidson, J.P., 1984, The r e l a t i v e r o l e s of c r u s t and upper mantle in the gen e r a t i o n of oceanic i s l a n d arc magmas. P h i l o s o p h i c a l T r a n s a c t i o n s of the Royal S o c i e t y of London S e r i e s A, v. 310, p. 661-674. Wood, D.A., 1980, The a p p l i c a t i o n of a Th-Hf-Ta diagram t o problems of tectonomagmatic c l a s s i f i c a t i o n and to e s t a b l i s h i n g the nature of c r u s t a l contamination of b a s a l t i c lavas of the B r i t i s h T e r t i a r y v o l c a n i c p r o v i n c e . E a r t h and Planetary Science L e t t e r s , v. 50, p. 11-30. Wood, D.A., Joran, J.-L. and T r e u i l , M., 1979, A r e - a p p r a i s a l of the use of t r a c e elements to c l a s s i f y and d i s c r i m i n a t e between magma s e r i e s erupted i n d i f f e r e n t t e c t o n i c s e t t i n g s . E a r t h and P l a n e t a r y Science L e t t e r s , v. 45, p.326-336. Yoder, H.S. and T i l l e y , C.E., 1962, O r i g i n of b a s a l t i c magmas - an experimental study of n a t u r a l and s y n t h e t i c systems. J o u r n a l of Petrology, V. 3, p. 342-532. Yorath, C.J. and Chase, R.L., 1981, T e c t o n i c h i s t o r y of the 242 Queen C h a r l o t t e i s l a n d s and sdjacent sreas - a model. Canadian J o u r n a l of Earth S c i e n c e s , v. 18, p. 1717-1739. Yorath, C.J. and Hyndman, R.D., 1983, Subsidence and thermal h i s t o r y of Queen C h a r l o t t e b a s i n . Canadian J o u r n a l of E a r t h Sciences, v. 20, p. 135-159. Young, I., 1981, S t r u c t u r e of the western margin of the Queen C h a r l o t t e b a s i n . Unpublished M.Sc. t h e s i s , Department of Geology, U n i v e r s i t y of B r i t i s h Columbia, Vancouver, Canada, 380 p. Zhou, X. and Armstrong, R.L., 1982, Cenozoic v o l c a n i c rocks of eastern China; s e c u l a r and geographic trends i n chemistry and strontium i s o t o p i c composition. E a r t h and Panetary Science L e t t e r s , v. 58, p. 301-329. APPENDIX I SAMPLE SOURCES AND PREVIOUS ANALYSES On the following pages samples are l i s ted in the order they appear in the text. SAMPLE - sample name used in this study. ORIGINAL NUMBER - sample name used by the original col lector. FORM - form the sample was in when selected for this study. Whole rock - small rock fragments. Powder - powdered rock sample, no rock fragments. Pellet - pressed powder pellet used in previous XRF analysis. PREPARATION - method used to powder the rock samples for analysis: N/A - not known. W-Carb. - tungsten carbide ring m i l l . BICO - steel disc m i l l . Agate - Motor driven agate mortar. BCDM - Prepared by the B.C. Department of Mines. GSC - Prepared by the Geological Survey of Canada. COLLECTOR - individual who collected the sample in the f i e l d . PREVIOUS ANALYSES - previous analytical work. N/A - not known, or no previous analyses. Major Elements - a l l major element oxides in weight %. REFERENCE - reference (s) which include this sample. N/A - no published reference. 243 GARIBALDI AND PEMBERTON BELTS SAMPLE ORIGINAL NUMBER FORM PREPARATION COLLECTOR PREVIOUS ANALYSIS REFERENCE ELAHO RD-44084-VI Powder W-Carb. R. Anderson Major Elements, K-Ar d a t e , Sr I s o t o p e r a t i o Anderson, 1975 GARIBALD MG-74-36-4 Powder N/A N. Green Major Elements, Ba, C r , Cu, Nb, N i , Rb, S r , V, Y, Zn, Zr Green, 1981 CHEAK GV-7 Powder N/A D. F i e s l n g e r Major Elements F i e s i n g e r , 1975 N i c h o l l s e t a l . , 1982 MEAGER RD-4B1 Powder W-Carb. R. Anderson Major Elements, K-Ar d a t e , Sr i s o t o p e r a t i o Anderson, 1975 CAYLEY SE1501-79 Powder BICO, Agate J.G. Souther N/A N/A SALAL1 SALAL2 SALAL3 C5-5 Ml-12 M5-14 P e l l e t BICO, Agate R. Lawrence Major Elements, Ba, Cr, Nb, N i , Rb, S r , V, Y, Z r , Sr i s o t o p e r a t i o Lawrence, 1979 Lawrence e t a l . , 1984 SILVERA SILVERH SE77-1-1 SE77-1-7B Powder BICO, Agate J.G. Souther K-Ar d a t e , Sr i s o t o p e r a t i o N/A COQ251 COQ632 COQ61 251 632 61 P e l l e t N/A R. Berman Major Elements, Ba, Ce, Cr, Nb, Nd, N i , Rb, S r , V, Y, Z r , Sr i s o t o p e r a t i o Berman, 1979 Berman and Arm- s t r o n g , 1980 rO CHILCOTIN BASALTS SAMPLE ORIGINAL NUMBER FORM PREPARATION COLLECTOR PREVIOUS ANALYSES REFERENCE REDSTONE 93B Powder N/A T. Hamilton N/A N/A BULL CAN BC-6 Powder N/A M.L. Bevier Major Elements, Nb, Ni, Rb, Sr, Y, Zr, K-Ar date, Sr isotope r a t i o Bevier, 1982 Parrish, 1982 NAZKO Nazko Whole rock W-Carb. W.H. Mathews Major Elements, K-Ar date N/A QUESW WHM-76-1 Powder BICO, Agate W.H. Mathews Major Elements, K-Ar date, Sr isotope r a t i o N/A CARD CTM-76TD Powder GSC J.G. Souther K-Ar date, Sr isotope r a t i o N/A CAMEL DOG CK CA-1 DC-1 Powder N/A M.L. Bevier Major Elements, Nb, Ni, Rb, Sr, Y, Zr, K-Ar date, Sr isotope r a t i o Bevier, 1982 EDMUND Edmund Whole rock W-Carb. W.H. Mathews Major Elements, K-Ar date N/A DEADMAN DR-11 Powder N/A M.L. Bevier Major Elements, Nb, Ni, Rb, Sr, Y, Zr, K-Ar date, Sr isotope r a t i o Bevier, 1982 WOOD LK Wood Lk Whole rock W-Carb. W.H. Mathews Major Elements, K-Ar date N/A BLIZZARD Bli z z a r d Powder BICO, Agate R.L. Armstrong K-Ar date, Sr isotope r a t i o N/A it* ANAHIM VOLCANIC BELT SAMPLE ORIGINAL NUMBER FORM PREPARATION COLLECTOR PREVIOUS ANALYSES REFERENCE MASSET1 MASSET2 MR3 MR8 Pel l e t BICO, Agate I. Young K-Ar date, Sr isotope r a t i o Young, 1981 ARIS IS KITASU LAKE IS SE090265 SE050365 SE030865 Pe l l e t GSC J.G. Souther Sr isotope r a t i o N/A RAINBOW ANAHIM R25 AP15 Pe l l e t BICO, Agate M.L. Bevier Major Elements, Ba, Nb, Ni, Rb, Sr, K-Ar date, Sr isotope r a t i o Bevier, 1978 ITCHA1 IMV 76-11 Powder BICO, Agate J. Nicholls B. Proffet K-Ar date, Sr isotope r a t i o P r o f f e t , unfinished thesis ITCHA2 Itcha l i b Powder N/A T. Hamilton N/A N/A ALEX TD58CA6 Pe l l e t GSC H.W. Tipper Sr isotope r a t i o N/A QUESLK JSG 80-37 Whole rock W-Carb. J. Getsinger N/A N/A SPAN CK 118cAcB-l Powder GSC J.G. Souther Sr isotope r a t i o N/A WGRAYN TROPHY BCV-12 BCV-2 Powder N/A D. Fiesinger Major Elements, Sr isotope r a t i o Fiesinger, 1975 to STIKINE VOLCANIC BELT SAMPLE ORIGINAL NUMBER FORM PREPARATION COLLECTOR PREVIOUS ANALYSES REFERENCE PRINCER CD575 Powder BICO, Agate C. Dingee K-Ar date, Sr isotope r a t i o N/A AYNSHl AYNSH2 NR-6 NR-2B Powder N/A J. N i c h o l l s Sr isotope r a t i o N/A HOODOO SE1701-76 P e l l e t BICO, Agate J.G. Souther R.L.Armstrong K-Ar date, Sr isotope r a t i o N/A' BORDERLK ISKUT ISKUTW 11285M 11297M 11288M Powder BCDM E.W. Grove Sr isotope r a t i o Grove, 1974 MT DUNN Mt. Dunn Powder N/A T. Hamilton N/A N/A BOWSER GE1 Pe l l e t . BICO, Agate G. Eisbacher K-Ar date, Sr isotope r a t i o N/A SPECl SPEC2 EDZl EDZ2 SE1603-73 SE1504a-72 SE04076-76 ML0614-66 Powder BICO, Agate J.G. Souther K-Ar date Souther et a l . , 1984 NEDZl NEDZ 2 NEDZ3 NEDZ4 H81-4KAr H81-169 H81-8KAr H80-87F Powder BICO, Agate P.B. Read K-Ar date N/A LEVEL1 8/28-68/5815 Powder N/A T. Hamilton Major Elements Hamilton, 1981 LEVELD LEVEL2 KD-1 8/25-50/6397 Powder N/A T. Hamilton Major Elements, Ba, Cr, Cu, Nb, Ni, Rb, Sr, Th, U, Y Hamilton, 1981 NATLIN A- l Powder N/A J. N i c h o l l s Major Elements, Sr isotope r a t i o N i c h o l l s et a l . , 1982 SATLIN T75 215-1 Powder N/A T. Bultman N/A N/A ALERT BAY VOLCANIC BELT SAMPLE ORIGINAL NUMBER FORM PREPARATION COLLECTOR PREVIOUS ANALYSES REFERENCE ALERT1 ALERT2 ALERT3 69-7A1 69-31-D 69-31-Fl Powder BICO, Agate J. Muller Major Elements, Ba, Cr, Nb, Ni, Rb, Sr, V, Y, Zr, K-Ar date, Sr isotope r a t i o Armstrong et a l . , (in press) OFFSHORE BASALTS SAMPLE ORIGINAL NUMBER FORM PREPARATION COLLECTOR PREVIOUS ANALYSES REFERENCE EXMOUNT1 EXMOUNT2 EXM0UNT3 RLC-1 RLC-2 RLC-4 Whole rock W-Carb. R.L. Chase Major Elements, Ce, Cr, Nb, Nd, Ni, Rb, Sr, Th, Y, Zr N/A BRBEAR1 BRBEAR2 COBBl RLC-1155-1 RLC-1155-2 RLC-1152-360 Whole rock W-Carb. R.L. Chase Major Elements, Ba, Cr, Cu, Nb, Ni, Rb, Sr, V, Y, Zr N/A COBB 2 RLC-1152-500 Powder N/A R.L. Chase SEXRIDGE 77-14-36-X Powder Cr-steel ri n g m i l l R.L. Chase Major Elements, Ba, Ce, Co, Cr, Nb, Nd, Ni, Rb, Sc, Sr, V, Y, Zr, La, Sm, Eu, Tb, Yb, Lu, Sr isotope r a t i o Cousens, 1982 Cousens et a l . , 1984 PREVRDG EXRIFT EXDEEP 72-22-7-1 70-25-4-62G 70-25-17-1 Powder Cr-steel r i n g m i l l A.G. Thomlinson M it* CO APPENDIX II - NEUTRON ACTIVATION ANALYSIS Each sample was analyzed by instrumental neutron a c t i v a t i o n a n a l y s i s (INAA) to determine the content of s e l e c t e d r a r e e a r t h (La, Sm, Eu, Tb, Yb, Lu) and t r a c e (Th, Ta, Hf, Sc) elements. When an element i s bombarded by neutrons, whose f l u x i s expressed as the number of neutrons p a s s i n g through an area of 1 cm 2 d u r i n g one second, the neutrons are absorbed by a f r a c t i o n of the t a r g e t n u c l e i , the e f f i c i e n c y of capture being expressed as a capture c r o s s s e c t i o n f o r the atom of the element. T h i s i s expessed as: a* = a 0 * B * F, where a 0 = number of atoms a* = number of atoms absorbing neutrons B = the capture c r o s s s e c t i o n and F = the i n t e g r a t e d neutron f l u x ( f l u x * ti m e ) . The absorbed neutrons are h e l d by a b i n d i n g energy which has a value from about 7 . 5 to 8 . 8 MeV and t h i s e x t r a energy leaves the r e s u l t i n g i s o t o p e s i n an e x c i t e d s t a t e . D e - e x c i t a t i o n i s accomplished by an almost instantaneous emission of a gamma ray. The above process can be w r i t t e n as-the f o l l o w i n g e q u a t i o n : *X + i n -» A + J Y + 7 249 250 where A (the mass number) = number of protons p l u s neutrons, n i s the absorbed neutron and 7 i s the emitted gamma ray. Isotopes produced i n t h i s manner may be s t a b l e or u n s t a b l e . In some cases the f i r s t daughter product of a r a d i o a c t i v e i sotope i s a l s o unstable and w i l l undergo a f u r t h e r decay forming another daughter product and so on, u n t i l a s t a b l e n u c l i d e i s produced. The f i n a l s t a b l e n u c l i d e i s i n i t i a l l y i n an e x c i t e d s t a t e and subsequently emits gamma rays with c h a r a c t e r i s t i c e n e r g i e s u n t i l i t s ground s t a t e i s reached. R a d i o a c t i v e decay i n v o l v e s emission of one or more p a r t i c l e s . Each p a r t i c l e i s a s s o c i a t e d with a complimentary gamma ray with s p e c i f i c mean energy. T h i s means that each r a d i o a c t i v e isotope has i t s own c h a r a c t e r i s t i c gamma energy spectrum making i t p o s s i b l e to uni q u e l y d e t e c t the presence of that p a r t i c u l a r i s o t o p e . The amount of an element present i n a sample i s d i r e c t l y p r o p o r t i o n a l to gamma energy emitted. To determine the c o n c e n t r a t i o n of elements i n an i r r a d i a t e d unknown sample a standard with known c o n c e n t r a t i o n of elements i s s i m i l a r i l y i r r a d i a t e d and anal y z e d . The r a t i o of unknown to standard r a d i o a c t i v i t y , a f t e r any necessary c o r r e c t i o n s f o r r a d i o a c t i v e decay decay between counting times, i s used to c a l c u l a t e the c o n c e n t r a t i o n (Henderson and Pankhurst, 1984). Table X c o n t a i n s the l i s t of i s o t o p e s used, t h e i r c o r r e s p o n d i n g h a l f - l i v e s and the ene r g i e s of the photopeaks used f o r determining abundances of elements. TABLE X ELEMENT ISOTOPE DATA (Lederer and Shirley, 1978) ACTIVATION HALF-LIFE ENERGY OF 7-RAY PEAKS REACTION (hrs.) (keV) 1l]Eu-» ''IfEu 122736 122, 344, 1408 '?SHf-» 1 f ^Hf 101 7.6 133, 482 1|?La-» '§?La 40.2 487, 1596 1?^Lu-» M'Lu 1 58.88 208, 113 2?Sc-» \ ?Sc 201 1 .68 889 ' l l S i w 'liSm 46.7 103, 69 1 ?jTa-» 1?|Ta 2760 1121, 1221 1l|Tb-> '|§Tb 1728 879, 298 2|gTh-» 2 | i P a 648 312, 300 1 ?gYb-> 1 ? c 5 Y b 100.56 396, 282 252 SAMPLE IRRADIATION AND COUNTING TECHNIQUES 1.000 gm of a c c u r a t e l y weighed <80 mesh whole rock sample was p l a c e d i n a small p l a s t i c i r r a d i a t i o n v i a l and he a t - s e a l e d to prevent leakage. The sample v i a l s were then packed i n four l a y e r s i n a l a r g e r Nalgene b o t t l e , each l a y e r c o n t a i n i n g twelve to fourteen unknown samples and f i v e to s i x standards. A d d i t i o n a l standards as unknowns were i n c l u d e d i n the f i r s t b o t t l e i n order to check a n a l y t i c a l p r e c i s i o n and systematic e r r o r s . Each l a y e r contained at l e a s t : 1. a standard prepared by Chemex c a l l e d LIQUID 1 which was used to determine the c o n c e n t r a t i o n s of La, Eu, Sm, Tb, Yb and Lu. 2. Standard NIML f o r Th and Hf abundances (Abbey, 1983). 3. Chemex standard SC50 f o r Sc abundances. 4. Chemex standards TA2 or TA10 f o r c o n c e n t r a t i o n s of Ta. 5. SY2 (Abbey, 1983). Abundances of s e l e c t e d t r a c e and rare e a r t h elements i n these standards are l i s t e d i n Table XI. The b o t t l e s were sent to Washington State U n i v e r s i t y at Pullman, Washington where they were subjected to a neutron f l u x of 6.7 X 1 0 1 2 neutrons/cm 2/sec (±15%) f o r 20 minutes. Although there i s no measureable f l u x g r a d i e n t at the i r r a d i a t i o n l o c a t i o n the sample b o t t l e s were a l s o r o t a t e d d u r i n g i r r a d i a t i o n to ins u r e f l u x homogeneity. A f t e r i r r a d i a t i o n the b o t t l e was returned to NOVATRAK (a s u b s i d i a r y of Chemex Labs Ltd.) at TRIUMF, U.B.C. and allowed 253 TABLE X I ABUNDANCES OF SELECTED TRACE AND RARE FOR INAA EARTH ELEMENTS IN STANDARDS USED Abundances i n ppm L I Q 1 1 NIML 2 S Y 2 3 SC50 1 TA2 1 TA10 1 Th 65 380? Ta 245 122 La 200 85 Sm 50 15 Hf 190? 8? Eu 10 2.2 Tb 50 2.7 Yb 50 17 Lu 50 3? Sc 7? 50 Chemex p r e p a r e d s t a n d a r d NIML a l u j a v r i t e from South A f r i c a n Committee f o r C e r t i f i e d R e f e r e n c e M a t e r i a l s (Abbey, 1983) . SY2 a s y e n i t e from Canadian C e r t i f i e d R e f e r e n c e M a t e r i a l s P r o j e c t (Abbey, 1976; Abbey, 1983). ? = q u e s t i o n a b l e v a l u e 254 to c o o l f o r f i v e to seven days. The samples and standards were then unpacked from the l a r g e i r r a d i a t i o n b o t t l e s and t h e i r gamma ray emissions were measured u s i n g a c o a x i a l G e ( L i) d e t e c t o r (Ortec® 7040 s e r i e s ) . P ulses from the d e t e c t o r went v i a an a m p l i f i c a t i o n stage to a 4000 channel m u l t i c h a n n e l a n a l y z e r (Ortec® 7000 s e r i e s ) I t would have been advantageous to have a planar Ge(Li) or pure Ge d e t e c t o r r a t h e r than a c o a x i a l one to analyze f o r the elements Ta, Eu, Lu, Yb, Hf and Ce, as a plana r d e t e c t o r a l l o w s b e t t e r r e s o l u t i o n i n the energy range 50-350 keV (Potts et a l . , 1981; Henderson and Pankhurst, 1984). Most peaks i n t h i s energy range analyzed by the c o a x i a l d e t e c t o r had to be c o r r e c t e d f o r i n t e r f e r e n c e . With a p l a n a r d e t e c t o r the i n t e r f e r e n c e s would have been s m a l l e r and the f i n a l r e s u l t s more a c c u r a t e . Each sample was counted f o r 1000 seconds. 1 The rare e a r t h elements La, Sm, Yb, and Lu which have h a l f - l i v e s ranging from 40 to 159 hours were counted immediately a f t e r the i n i t i a l c o o l i n g p e r i o d . Analyses of the remaining elements (Th, Ta, Hf, Eu, Tb and Sc) were done a f t e r a f u r t h e r 4 to 5 week c o o l i n g p e r i o d . An attempt was made to determine Cs content i n each sample, but i t appeared that abundances of Cs were below the d e t e c t i o n l i m i t , as no Cs gamma ray emissions were recorded. 1 Samples BOWSER, COQ61, COQ632 and COQ251 were counted by NOVATRAK s t a f f . A l l others were counted by the author. 255 Gamma rays emitted by samples are d i s p l a y e d and recorded as photopeaks on an energy spectrum, the net area under the photopeak being p r o p o r t i o n a l to the f l u x of gamma rays emitted per u n i t time, which i n turn i s p r o p o r t i o n a l to the c o n c e n t r a t i o n of the parent n u c l i d e . Net area of photopeaks (the area of the peak above the background, NOT the t o t a l count above the b a s e l i n e ) ( C o v e l l , 1959) was c a l c u l a t e d u sing an EGG Ortec® m u l t i c h a n n e l a n a l y z e r . Whenever p o s s i b l e the net areas f o r two photopeaks of the same isotope were recorded and c o n c e n t r a t i o n s were c a l c u l a t e d s e p a r a t e l y f o r each photopeak. D i f f e r e n c e s i n c o n c e n t r a t i o n between peak p a i r s ranged from 0% to 10%. Only one useable photopeak was found f o r the elements Th, Ta, Tb, and Sc. Each photopeak net area i n the standards and samples was c o r r e c t e d f o r decay back to an a r b i t r a r y i n i t i a l time t 0 . The c o r r e c t i o n i s : e x ( t - t 0 ) N a = N a o w h e r e : X = l n 2 / h a l f - l i f e - t = time that counting of the sample began - t 0 = chosen i n i t i a l time - Na = measured net peak area - Na 0 = c a l c u l a t e d net peak area at t 0 When the net peak area f o r a l l of the photopeaks i n the 256 samples and standards have been c a l c u l a t e d back to an i n i t i a l time, t 0 , the c o n c e n t r a t i o n of elements i n the samples can be determined by the f o l l o w i n g e q u a t i o n : (Net Area) „ (Cone, of element) sam sam (Net A r e a ) s t a n d (Cone, of e l e m e n t ) s t a n d U abundances were determined by delayed neutron a c t i v a t i o n at the r e a c t o r s i t e i n Pullman, Washington. T h i s a n a l y s i s was performed by NOVATRAK s t a f f . INTERFERENCE OF PHOTOPEAKS I n t e r f e r e n c e of the Ta, Sm, Yb and Lu photopeaks by c o i n c i d e n t photopeaks of Sc, Pa p l u s Np, Pa and Np r e s p e c t i v e l y must be c o r r e c t e d b e f o r e abundances of Ta, Sm, Yb and Lu can be c a l c u l a t e d . Chemical s e p a r a t i o n to remove the i n t e r f e r r i n g element w i l l of course give the best r e s u l t s , but t h i s i s not always e f f i c i e n t . A q u i c k e r method i n v o l v e s i r r a d i a t i n g a pure form of the i n t e r f e r r i n g element and determining a r a t i o of the c o i n c i d e n t photopeak to another photopeak. T h i s r a t i o can then be a p p l i e d to a l l samples. As no pure forms of U and Th (hence Np and Pa) were a v a i l a b l e , an estimate of the c o r r e c t i o n r a t i o was c a l c u l a t e d from Lederer and S h i r l e y (1978) and Kennedy and Fowler (1983). These were used f o r the d u r a t i o n of the a n a l y s e s . A T a - f r e e Sc standard was i n c l u d e d i n each of the i r r a d i a t e d l a y e r s so that a c o r r e c t i o n r a t i o to apply to the Sc peak at 889 keV c o u l d be uni q u e l y determined f o r each l a y e r 257 TABLE XII TABLE OF INTERFERENCES * ISOTOPE ENERGY OF INTERFERRING PEAK MEASURED RATIO 1 7-RAY (keV) PHOTOPEAKS FOR CORRECTIONS AT ENERGY OF •T,\ Lu 208 2 3 9Np @ 210 278 keV 0.345 y\\ Sm 1 03 2 3 3Pa @ 104 312 keV 0.021 2 3 9 N p @ 106 106 keV 0.854 1 8.| Ta 1121 4 6 S c @ 1121 889 keV 0.802 0.805 0.797 0.795 0.795 0.794 0.798 0.794 0.781 0.791 0.793 0.789 1?§ Yb 396 2 3 3 P a @ 398 312 keV 0.032 1 A d i f f e r e n t r a t i o f o r Sc was determined f o r each l a y e r with an approximate e r r o r of ± 0.04. In the t a b l e the Sc r a t i o s are given i n order of b o t t l e s and l a y e r s , s t a r t i n g with b o t t l e 1 - l a y e r 1 and c o n t i n u i n g to b o t t l e 4 - l a y e r 3. I n t e r f e r r i n g photopeaks and corresponding peak(s) to measure for c o r r e c t i o n s compiled from Kennedy and Fowler (1983), Lederer and S h i r l e y (1983) and NOVATRAK data sheets. 258 of samples. This r a t i o ranged from 0.781 to 0.805 ± 0.04. The above i n f o r m a t i o n i s given i n Table X I I . ACCURACY and PRECISION According to Henderson and Pankhurst (1984) a n a l y t i c a l p r e c i s i o n of INAA at the l e v e l of REE c o n c e n t r a t i o n s found i n b a s a l t s w i l l be about 2-4% f o r the elements La, Ce, Nd, Sm, Eu, and Yb and 3-6% f o r Tb and and Lu, a l l at an accuracy of about 5%. A n a l y t i c a l p r e c i s i o n in t h i s study was based on r e p l i c a t e a n a l y s e s of standards NIML and SY2 as w e l l as i n t r a l a b geology standards P-1 and WP1, a l l of which were i n c l u d e d i n a l l of the i r r a d i a t i o n s . P r e c i s i o n of analyses i s ± 5% f o r Th, La, Hf and Sc; ± 7% f o r Sm; ± 10% f o r Ta, Eu, Tb and Yb; and ± 15% f o r Lu (Table XIV). Table XIII l i s t s the data used to c a l c u l a t e the above p r e c i s i o n s . As only one c a l c u l a t e d abundance was recorded f o r each of the other standards and unknowns (no r e p l i c a t e analyses were done) the above p r e c i s i o n s are assumed to apply to a l l of the samples a n a l y z e d . A n a l y t i c a l accuracy i s dependent on c a l i b r a t i o n of the s i n g l e or multi-element standards used i n c a l c u l a t i n g the c o n c e n t r a t i o n s of elements i n the unknowns. To c o n f i r m the c a l i b r a t i o n s numerous i n t e r l a b o r a t o r y rock standards of known c o n c e n t r a t i o n were analyzed as unknowns (Abbey, 1983; Flanagan, 1974; Flanagan, 1976; Kramar and P u c h e l t , 1982; Rozenberg and Z i l l i a c u s , 1980; S t e e l e et a l . , 1978; Gladney 259 and Goode, 1981; Govindaraju, 1984; A l i b e r t et a l . , 1983). C a l c u l a t e d c o n c e n t r a t i o n s vs. r e f e r e n c e c o n c e n t r a t i o n s were t a b u l a t e d (Table XV) and systematic e r r o r s in analyses were c a l c u l a t e d f o r each element, (Table XVI). Systematic e r r o r s were l e s s than the p r e c i s i o n f o r Th, Sm, Eu, Tb and Lu but were g r e a t e r than the p r e c i s i o n f o r Ta, La, Hf, Yb and Sc. Consequently, c a l c u l a t e d abundances of the l a t t e r elements were r e v i s e d by an amount equal to the sytematic e r r o r ; -16% fo r Ta, +14.5% fo r La, +8% f o r Hf, +12% f o r Yb and +19.5% fo r Sc . TABLE X I I I ( c o n t . ) PRECISION OF INAA BASED ON REPLICATE ANALYSES Abundances i n ppm LMPLE Th Ta La Sm Hf Eu Tb Yb Lu Sc Run Lay WP1 1 . 7 9 1 . 0 6 1 1 . 4 3.2 1.5 0.7 N/A 1 . 4 0.2 7.6 ! 2 WP1 2 . 6 8 1.44 1 1 . 9 3.2 2.1 0.7 N/A 1.3 0.2 7.8 1 2 WP1 2 . 3 9 1 . 3 1 . 1 1 . 6 3.1 2.2 0.6 N/A 1.3 0.2 7.6 1 2 WP1 2 . 0 4 0 . 9 8 1 1 . 1 3.1 2.1 0.6 N/A 1.5 0.2 7.8 1 2 WP1 2 . 3 4 N/D 1 1 . 2 3.0 1.8 0.6 N/A 1.2 0.2 7.8 1 2 WP1 2 . 4 6 N/D 11.4 3.2 1.9 0.6 N/A 1.3 0.2 8.0 1 2 WP1 2 . 1 8 0 . 1 2 1 1 . 3 3.3 2.6 0.7 N/A 1.4 0.2 7.6 1 3 WP1 1.73 N/D 1 0 . 7 3.1 2.1 0.8 N/A 1.2 0.2 7.5 1 3 WP1 2 . 1 6 N/D 1 1 . 5 3.1 2.6 0.6 0.3 1.4 0.2 7.5 2 1 WP1 2 . 3 8 0 . 5 6 1 1 . 6 3.1 2.8 0.7 0.3 1.3 0.2 7.3 2 2 WP1 2 . 2 2 N/D 1 1 . 3 3.0 2.8 0.7 0.4 1.2 0.2 7.7 2 3 WP1 2 . 2 5 1 . 5 9 1 0 . 3 3.1 2.5 1.0 1.0 1.0 0.2 7.9 3 1 Mean 2 . 2 2 0 . 5 9 1 1 . 2 3.1 2.3 0.7 0.5 1.3 0.2 7.7 l a 0.27 0.64 0 . 4 3 0 . 0 9 0.42 0 . 1 2 0 . 3 4 0 . 1 3 0.0 0 . 2 0 N/D = not d e t e c t e d N/A = not a n a l y z e d c o n t i n u e to cn o TABLE X I I I ( c o n t . ) PRECISION OF INAA BASED ON REPLICATE ANALYSES Abundances i n ppm SAMPLE Th Ta La Sm Hf P - l 3.3 4.3 10.7 2.6 2.2 P - l 3.9 1.1 10.4 2.8 2.8 P - l 3.6 1.2 10.7 2.7 2.8 P - l 3.7 2.1 10.6 2.7 3.0 P - l 3.8 0.4 10.3 2.6 3.0 P - l 3.7 0.1 10.0 2.9 2.9 P - l 3.8 N/D 10.9 2.9 3.0 P - l 3.7 N/D 10.4 2.5 3.3 Mean 3.7 1.15 10.5 2.7 2.9 l a 0.18 1.47 0.28 0.15 0.32 N/D = not d e t e c t e d N/A = not a n a l y z e d Eu Tb Yb Lu Sc Run La y e r 0.5 N/A 1.8 0.3 9.1 1 2 0.6 N/A 1.8 0.3 8.3 2 1 0.7 N/A 2.0 0.3 8.1 2 1 0.6 N/A 2.1 0.3 8.5 2 2 0.6 N/A 1.9 0.3 8.4 2 2 0.6 N/A 1.8 0.3 9.1 2 3 0.7 N/A 2.0 0.3 9.1 2 3 0.6 N/A 1.8 0.3 8.9 2 3 0.6 1.9 0.3 8.7 0.06 0.12 0.0 0.41 c o n t i n u e . CTl TABLE X I I I ( c o n t . ) PRECISION OF INAA BASED ON REPLICATE ANALYSES Abundances i n ppm [PLE Th Ta La Sm Hf Eu Tb Yb Lu Sc Run Layi SY2 362.6 N/D 65 15.0 N/A 1.6 N/A N/A N/A 5.4 1 1 SY2 365.8 N/D 65 16.3 6.6 2.2 N/A 19.3 N/A 5.1 1 2 SY2 366 N/D 72.1 16.6 6.9 2.0 N/A 13.6 3.0 5.3 1 3 SY2 380 N/D 73.2 15.4 7.2 2.3 2.5 16.9 2.1 5.4 2 1 SY2 385 N/D 70.3 15.3 7.3 2.3 3.0 15.1 1.9 5.2 2 2 SY2 386 N/D 73.9 18.1 7.6 2.5 2.5 14.2 3.1 5.6 2 3 SY2 374 N/D 76.4 17.5 6.9 2.1 3.0 13.5 3.0 5.7 2 4 SY2 399 N/D 64.2 15.6 7.3 2.3 2.8 15.3 2.2 5.8 3 1 SY2 364 N/D 68.1 15.4 7.2 2.4 3.0 15.2 3.0 5.8 4 1 SY2 373 N/D 65.7 15.0 7.9 2.1 3.3 16.1 2.7 7.5 4 2 SY2 366.5 N/D 73.0 16.8 8.3 2.6 3.4 17.1 2.3 7.6 4 3 Mean l a 374.7 11.6 69.7 16.1 4.3 1.1 7.3 2.2 2.9 15.6 0.5 0.27 0.33 1.79 2.6 0.46 5.8 0.87 N/D = not d e t e c t e d N/A = not a n a l y z e d c o n t i n u e to tn to TABLE X I I I PRECISION OF INAA BASED ON REPLICATE ANALYSES Abundances i n ppm WPLE Th Ta La Sm Hf Eu Tb Yb Lu Sc Run Lay> NIML STD 27.6 202 4.8 STD 1.2 N/D 3.6 0.4 0.2 1 1 NIML STD 25.0 201 5.3 STD 0.8 N/D 3.5 0.4 0.2 1 2 NIML STD 26.5 189 4.8 STD 1.0 N/D 2.5 0.5 0.2 1 3 NIML STD 26.1 201 4.6 STD 1.1 N/D 2.8 0.4 0.2 2 1 NIML STD 26.3 187 4.7 STD 0.9 N/D 3.6 0.4 0.1 2 2 NIML STD 26.3 192 4.5 STD 1.0 N/D 2.6 0.5 0.2 2 3 NIML STD 24.7 197 5.1 STD 0.9 N/D 2.2 0.5 0.2 2 4 NIML STD 27.7 177 5.6 STD 1.1 N/D 2.0 0.5 0.1 3 1 NIML STD 26.7 209 4.2 STD 1.0 N/D 2.7 0.4 0.3 1 1 NIML STD 21.9 206 4.8 STD 0.9 N/D 2.7 0.6 0.2 4 1 NIML STD 22.5 190 4.1 STD 1.0 N/D 3.2 0.4 0.3 4 2 NIML STD 21.3 210 4.8 STD 1.2 N/D 3.1 0.4 0.3 4 3 Mean 25.2 197 4.8 1.0 2.9 0.45 0.22 l a 2.2 9.9 0.42 0.12 0.5 0.07 0.06 N/D = not d e t e c t e d STD = sample used as a s t a n d a r d to tr. OJ TABLE XIV RELATIVE PRECISIONS BASED ON REPLICATE ANALYSES C o n c e n t r a t i o n and l a i n ppm P r e c i s i o n s 1 i n % Th Ta La Sm Hf Cone. l a P r e c . Cone. l a P r e c . Cone. l a P r e c . Cone. l a P r e c . Cone l a P r e c . NIML STD 25.2 2.2 8.7 197 9.9 5 4.8 0.4 8.7 STD SY2 374.7 11.6 3.1 N/D 69.7 4.3 6 16.1 1.1 6.8 7.3 0.5 6.8 WP1 2.2 0.3 13.6 ( 0 . 5 9 ) * ( 0 . 6 4 ) * ( 1 0 8 ) * 12.8 0.4 3.1 3.1 0.1 2.9 2.5 0.4 16 P - l 3.7 0.18 4.9 ( 1 . 1 5 ) * ( 1 . 4 7 ) * ( 1 2 8 ) * 12.0 0.3 2.5 2.7 0.2 5.5 3.1 0.3 10 R e l a t i v e ±5% o r 0.3 ppm ±10% o r 0.6 ppm ±5% o r 0.4 ppm ±7% o r 0.2 ppm ±5% o r 0 .4 ppm P r e c i s i o n Eu Tb Yb Lu Sc Cone. l a P r e c . Cone. l a P r e c . Cone l a P r e c . Cone. l a P r e c . Cone l a P r e c . NIML 1.0 0.1 12 N/D 2.9 0.5 17 0.45 0.07 15.5 0.22 0.06 27 SY2 2.2 0.3 12.3 2.9 0.3 11.4 15.6 1.8 11.5 2.6 0.5 17.7 5.8 0.9 15 WP1 0.7 0.1 17 0.5 0.3 68 1.5 0.1 6.6 0.2 0.0 ^ 2 5 9.2 0.2 2.2 P - l 0.6 0.1 10 N/D 2.1 0.1 4.8 0.3 0.0 ^ 1 7 10.4 0.4 3.8 R e l a t i v e ±10% o r 0.2 ppm ±10% o r 0.3 ppm ±10% o r 0.4ppm ±15% o r 0. lppm ±5% o r 0.1 ppm P r e c i s i o n N/A = not a n a l y z e d STD = Sample used as a s t a n d a r d N/D = below d e t e c t i o n l i m i t * = c o n t a m i n a t e d sample *These p r e c i s i o n s a r e c a l c u l a t e d from d a t a c o n t a i n e d i n t h e p r e v i o u s T a b l e s , (a/mean) X 100. TABLE XV TEST OF ANALYTICAL ACCURACY FOR INAA Abundances i n ppm SAMPLE Th Ta La Sm Hf Eu Tb Yb Lu Sc Run-- l a y e r NIMG Ref. 51.412.6 5 2 3 5.110.6 4 . 6 4 1 2 104±5 1 0 7 1 2 1511 15.4 5 10.910.5 1 2 ? 3 0.410.2 0.4? 3 N/A 14.511.5 14 3 1.8+0.1 2?3 0.410.1 0 . 5 i 2 1 -1 NIMS Ref. 1.210.3 0.9? 3 N/D 4.6+0.6 4 ? 2 1.310.2 1.212 0.410.3 0 . 3 1 2 N/D N/A N/D N/D 2.910.1 3 . 8 1 2 1 -1 SY3 Ref. 985+49 990 3 N/D 1226+61 1350 3 82.7+6 95 1 8.310.4 9 ? 3 16.211.6 14? 3 N/A N/D N/D 5.U0.3 7 ? 3 1--1 RGM-1 Ref. 13.610.7 1 5 ? 3 1.0+0.6 1.0 3 19.1+1 2 3 ? 3 4.010.3 4.3? 3 5.510.4 6.0? 3 0.510.2 0.7? 3 N/A 1.510.4 2.3 7 N/D 3.310.2 4.7 3 1 -3 QLO-l Ref. 5.410.3 4.8? 3 0.7+0.6 0.63 7 24.2+1.2 2 7 ? 3 5.210.4 5.1? 3 4.710.4 4.6? 3 1.310.2 1.5? 3 N/A 1.9+0.4 2.2 7 0.410.1 0.4 8 7.010.4 9 ? 3 1 -3 BHVO-l Ref. 1.110.3 1.0 3 1.010.6 l . l ? 3 13.9+0.7 1 7 ? 3 6.710.5 6.1 3 4.210.4 4.3 3 2.010.2 2.0 3 N/A 1.710.4 1.9 3 0.310.1 0.3 6 26.3+1.3 3 1 6 1 -3 GSP-1 Ref. 10915 105 3 1.610.6 l ? 3 155+8 1 9 1 i o 2812 2 6 . 8 ? 9 13.610.7 1 4 ? 3 2.210.2 2 . 2 1 0 N/A 1.6+0.4 1.9 3 0.210.1 0.2? 3 4.910.2 6.6 3 1 -3 STM-1 Ref. 29.3+1.5 3 1 ? 3 21.6+0.6 18? 3 145+7 1 4 6 1 1 1311 1 3 3 23.611.2 2 7 ? 3 3.010.3 3.7 3 N/A 3.710.4 4.3 3 0.510.1 0.7 8 0.410.1 0 . 5 1 1 1--3 N/D = not d e t e c t e d N/A = not a n a l y z e d ? = q u e s t i o n a b l e v a l u e c o n t i n u e d w tn tn TABLE XV (cont.) TEST OF ANALYTICAL ACCURACY FOR INAA Abundances i n ppm SAMPLE Th Ta La Sm Hf Eu Tb Yb Lu Sc BCR-1 6.9±0.3 1 •3±0.6 24±1 7.3±0.5 3 .810.4 2.110.2 0.710.3 3.410.3 0.510.1 29.411.5 Ref. 6.13 0.8?3 27 3 6.53 5 3 2.03 1.03 3.43 0.5?3 33 3 ARCHO-1 7.610.4 2 .6±0.6 38.5±2 9.9±0.7 9 .710.5 4.410.4 1.510.4 3.910.4 0.610.1 31.911.6 Ref. 7.310.14 1.184 45.810.64 9.834 11.1* 4.31^ 1.47?1* 4.210.l't 0.63?1* 28.934 NIML STD 25 .210.6 197±3 4.8 STD 1.0 N/D 2.910.1 0.4510.02 0.2210.02 Ref. 2 2 ? 3 200? 3 4.8 1 2 l ? 3 3.5 1 2 0.4? 1 2 0.27? 1 2 SY2 374.713.5 N/D 69.7±1.3 16.110.3 7 .310.2 2.2 2.910.1 15.610.6 2.610.1 5.810.3 Ref. 380? 3 85 1 15? 3 8? 3 2.21 2.71 17 3 3? 3 7? 3 R-L 4-2 4-3 n=12 n=ll R-L = Run-layer N/D = not detected N/A = not analyzed STD = sample used as a standard ? = questionable value 1 Abbey, 1976 2 Abbey, 1980 Abbey, 1983 Additon and S e l l , 1979 Ali b e r t et a l . , 1983 Flanagan, 1974 Flanagan, 1976 8 Gladney and Goode, 1981 9 Govindaraju, 1984 1 0 Kramar and Puchelt, 1982 1 1 Rozenberg and Z i l l i a c u s , 1980 Steele et a l . , 1978 12 M cn CTl ABUNDANCES FROM DUPLICATE ANALYSES (INAA) Abundances i n ppm La Sm Eu Tb Yb Lu Sc SEXRIDGE U. B.C. 4.6 3.5 1.1 0.8 3.1 0.4 36.7 S c h i l l i n g 4.6 3.7 1.30 0.79 3.1 0.43 43 PREVRDG U. B.C. 18.1 10.0 2.9 2.1 7.7 1.1 34.7 S c h i l l i n g 15.2 9.9 3.02 2.09 7.8 1.08 36 EXRIFT U. B.C. 2.0 2.2 0.8 0.6 2.3 0.3 27.1 S c h i l l i n g 1.9 2.5 1.01 0.61 2.4 0.34 31 EXDEEP U.B.C. 11.4 4.8 1.4 0.8 3.2 0.4 34.4 S c h i l l i n g 9.7 4.8 1.68 0.93 3.7 0.54 39 U.B.C. = INAA by t h e a u t h o r . S c h i l l i n g = INAA by J.G. S c h i l l i n g , p r e s e n t e d i n Cousens e t a l . , 1984. to cn TABLE XVI SYSTEMATIC ERROR IN INAA ANALYSES SAMPLE Th Ta La Sm Hf Eu Tb Yb Lu Sc NIMG -1%±5% +9.9%±5% -3%±5% -3%±7% -9%±5% 0%±15% N/A +4%±10% -10%±15% -20%±10% NIMS +33%±25% N/D -15%±13% +8%±15% N/D N/D N/A N/D N/D -24%±14% SY3 -0.5%±5% N/D -9%±5% -13%±7% -8%±8% +15%±10% N/A N/D N/D -27%±8% RGM-1 -9%±5% +0%±3% -17%±5% -7%+7% -8%±7% -28%±12% N/A -35%±13% N/D -42%±12% QLO-1 +13%±5% +11%±20% -10%±5% +2%+7% +2%±7% -13%±10% N/A -14%±10% 0%±10% -22%±6% BHVO-1 +10%±27% -9%±5% -18%±5% +10%±7% -2%±7% 0%±15% N/A -10%±10% 0%±10% -15%±5% GSP-1 +4%±5% +60%±20% -23%±5% +4%±7% -3%±5% 0%±10% N/A -16%±10% 0%±20% -26%±8% STM-1 -5%±5% +20%±10% -0.7%±5% 0%±7% -13%±5% -19%±15% N/A -14%±10% -28%±5% -25%±10% BCR-1 +13%±5% +62%±15% -11%±5% +12%±7% -24%±15% +5%±12% -30%±20% 0%±10% 0%±20% -11%±5% ARCHO-1 +4%±5% +54%±20% -1.9%±5% +0.7%±7% -14%±5% +2%±10% +2%±15% -7%±10% -5%±16% -10%±5% NIML STD +14%±2% -18%±1.5% 0%±7% STD 0%±10% N/D -17%±3% +13%±4% -19%±9% SY2 -0.2%±1% N/D -18%±1.8% +7%±2% -9%±3% 0%±10% +7%±3% -8%±4% -13%±4% -17%±5% MEAN +2.8% +33% -13% +1.7% -9% -4% +6% -12% -6% -21.5% WGTD. MEAN +1.4% +16.3% -14.4% +2.4% -8.3% -1.5% +3% -12.2% -6.2% -19.4% let UNCERTAINTY ±3.8% ±5.9% ±3.6% ±6.0% ±5.7% ±11.4% ±15.0% ±7.4% ±7.8% +7.1% OF WGTD. MEAN N/D = not determined N/A = not a n a l y z e d STD = sample used as a st a n d a r d to CTl CO 269 NOVATRAK ANALYSES Samples BOWSER, COQ251, COQ632 and COQ61 were analyzed by NOVATRAK. A l l four samples have two to three times the Yb content of other samples and samples BOWSER and C0Q61 e x h i b i t a s i m i l a r enrichment i n Th. None of the samples analyzed by the author are en r i c h e d to the same extent, suggesting the enrichment i s a product of NOVATRAK a n a l y s i s . T h e r e f o r e these abundances were not recorded. To p l o t BEND p a t t e r n s f o r these samples an estimated Yb content was c a l c u l a t e d u s i n g the r a t i o Y/Yb = 13, the average r a t i o from a l l other samples. ELEMENT ABUNDANCES IN STANDARDS WP1 AND P-1 I n t r a l a b standards P-1 and WP1 were a n a l y z e d numerous times throughout the study p e r i o d to e s t a b l i s h them as secondary standards. Although major element oxide abundances had been p r e v i o u s l y determined no p r i o r a n a l y s e s had determined abundances of Th, Ta, La, Sm, Hf, Eu, Tb, Yb, Lu and Sc. C a l c u l a t e d abundances from t h i s study are recorded i n Table 4 and r e v i s e d abundances are l i s t e d i n Table XVII. TABLE XVII ELEMENT ABUNDANCES I N INTRALAB STANDARDS WPl and P - l STANDARDS ELEMENT WPl P - l Eu 0.7± 0.1 0.6± 0.1 Hf 2.5± 0.1 3.1± 0.1 La 12.8± 0.1 12.0± 0.1 Lu 0.2± 0.1 0.3± 0.1 Sc 9.2± 0.1 10.4 ± 0.1 Sm 3.1± 0.1 2.7 ± 0.1 Tb 0.5± 0.1 N/D Th 2.2± 0.1 3.7 ± 0.1 Yb 1.5± 0.1 2.1± 0.1 Abundances i n ppm N/D = not d e t e c t e d APPENDIX III - MAJOR AND TRACE ELEMENT ANALYSIS BY XRF PREPARATION FOR ANALYSIS Nearly a l l of the samples s e l e c t e d f o r a n a l y s i s had been crushed and powdered during previous, s t u d i e s . The remainder were small whole rock fragments which were powdered to approximately 200 mesh by g r i n d i n g them f i r s t i n a tungsten c a r b i d e r i n g m i l l and then i n an agate mortar. A l l powdered samples were subsequently made i n t o p e l l e t s as d e s c r i b e d i n the U.B.C. XRF l a b i n s t r u c t i o n sheets. P e l l e t p r e p a r a t i o n was done by the author. MAJOR ELEMENT ANALYSIS Major element oxide c o n c e n t r a t i o n s were determined by X-ray f l o u r e s e n c e spectroscopy on an automated Phillips® spectrometer, using the pressed powder method of van der Heyden (1982). T h i s a n a l y s i s was performed by B. Cousens i n the department of Oceanography at the U n i v e r s i t y of B r i t i s h Columbia. Analyses f o r H 20 and C0 2 were not performed. The method and o p e r a t i n g c o n d i t i o n s as w e l l as a complete d e s c r i p t i o n of the computer program used i n data r e d u c t i o n are c o n t a i n e d i n van der Heyden (1982). Included i n the sample set were four standards analyzed as unknowns and f o u r t e e n samples f o r which major element abundances had p r e v i o u s l y been determined. Estimated p r e c i s i o n s were c a l c u l a t e d from these d u p l i c a t e analyses by 271 272 f i n d i n g the mean range (w) and d i v i d i n g t h i s number by a constant ( d n ) (Davies, 1961). These estimated p r e c i s i o n s are l i s t e d i n Table XVIII, along with % mean d e v i a t i o n s from the recommended values f o r standards used i n c o n s t r u c t i n g the working curves (Abbey, 1983). TRACE ELEMENT ANALYSIS Con c e n t r a t i o n s of Ba, Rb, Nb, Ce, Sr, Nd, Zr, Y, Co, Cr, Cu, Ni and V were determined by XRF analyses of pressed powder p e l l e t s . These p e l l e t s were the same as those used f o r major element oxide d e t e r m i n a t i o n s . A l l of the above elements, except Ce and Nd, were analyzed by B. Cousens of U.B.C. Ce and Nd analyses were done by the author at the department of G e o l o g i c a l S c i e n c e s , U.B.C. Raw data was reduced u s i n g a computer program w r i t t e n by Berman (1979) and m o d i f i e d by B. Cousens (pers. comm.). Included with the unknown samples were f i v e standards and s i x t e e n samples i n which abundances of a l l or some of the t r a c e elements had been p r e v i o u s l y determined. Table XIX l i s t s 1a e r r o r s on the analyses of standards used to c r e a t e the working curves, as w e l l as a n a l y t i c a l p r e c i s i o n estimates based on d u p l i c a t e a n a l y s e s . P r e c i s i o n f o r Ba i s poor due to low c o u n t i n g i n t e n s i t i e s . 273 TABLE XVIII PRECISION OF MAJOR ELEMENT ANALYSES MAJOR ELEMENTS: % mean d e v i a t i o n from working curves c o n s t r u c t e d using the recommended valu e s f o r the same standards (Abbey, 1983). Estimated p r e c i s i o n s are from d u p l i c a t e analyses of unknown samples. % MEAN ESTIMATED PRECISION DEVIATION S i 0 2 1% 1.7% T i 0 2 2.5% 2.5% A1 20 3 3.7% 3.5% F e 2 0 3 2% 2.8% MnO 1% 10% MgO 1.3% 9.5% CaO 2.8% 2.7% Na 20 4.0% 8.7% K 20 4.1% 5% P 2 0 5 10.4% 10.0% On the f o l l o w i n g pages a r e : 1. Computed major element abundances i n the analyzed standards which were used to c a l c u l a t e % mean d e v i a t i o n , and 2. Abundances from d u p l i c a t e a n a l y s e s . FINAL DATA FOR STANDARDS USED IN CONSTRUCTION OF WORKING CURVES FOR MAJOR ELEMENT ANALYSIS STANDARDS IDENT SI AL FE MG CA NA K TI MN P H20 C02 TOTAL BHVO-1 49. 81 14 . 64 12. 05 7 . 18 11 .21 2. 44 0 .46 2 .61 0. . 16 0. 21 0 .20 0. .04 lOI . 01 FINAL VALUE 49. 31 14. 49 11 . 93 7 . 11 11 . 10 2. 42 0 .46 2 .58 0 . 16 0. 21 0 .20 0. .04 NORM. VALUE 49. 90 13. 70 12. 10 7 .20 1 1 .40 2. 30 0 .53 2. .70 0. . 17 0. .28 0 .20 0. 04 100. .52 RECCOM. VALUE -0. 59 0. 79 -0. 17 -0 .09 -0 .30 0. 12 -0 .07 -0. . 12 -0. .01 -0. 07 0 .0 0. .0 NORM.-RECC. BCR-1 54. 34 13. 61 13. 16 3 .48 7 .03 3. 45 1 68 2. 23 0 . 18 0. ,37 0 .67 0 .02 100. .23 FINAL VALUE 54 . 22 13. 58 13. 13 3. .47 7 .01 3. 44 1 .67 2. 23 0. . 18 0. ,37 0 .67 0. 02 NORM. VALUE 54. 53 13. 72 13. 44 3. .48 6 .97 3. 30 1 .70 2. .26 0, . IS 0. ,36 0 .67 0. .02 100. .63 RECCOM. VALUE -0. 31 -0. 14 -0. 31 -O .01 0 .04 0. 14 -0 .03 -0. .03 0, .00 0. 01 0 .0 O. 0 NORM.-RECC. MRG-1 39. 61 8. 24 18. 01 13 .54 14 .94 0. 31 0 . 17 3. .73 0 . 17 0. 06 0 98 1 . OO 100. .77 FINAL VALUE 39. 31 8. 18 17. 87 13 .44 14 .83 0. 30 O. . 17 3. .70 0 . 17 0. 06 0 .98 1 . .00 NORM. VALUE 39. 32 8. 50 17. 85 13 49 14 .77 0. 71 0. . IB 3. 69 0. 17 0. 06 0. .98 1 . CO ICO. 72 RECCOM. VALUE -o. 01 -o. 32 0. 02 -o .05 0 .06 -0. 41 -0 .01 0 01 0. .00 0. 00 0. .0 0. .0 NORM.-RECC. OB-1 53. 01 14 . 92 9. 12 7. ,50 9 08 2. 60 1 .47 1 . 37 0 . 15 0. 28 1. .01 0. . 18 ICO. 70 FINAL VALUE 52. 64 14. 81 9. 06 7 .45 9 .02 2. 58 1 .46 1 . 36 0. . 15 0 28 1 .01 0. . 18 NORM. VALUE 52. 60 14. 62 9. 05 7 .76 9 .35 2. 79 1 .42 1 . 34 0 15 0. .26 1 .01 0. 18 100. .53 RECCOM. VALUE 0. 04 0. 19 0. 01 -0. ,31 -0. ,33 -0. 21 0. ,04 0. 02 0. oo 0. 02 0. .0 0. 0 NORM.-RECC. W-1 52. 06 15. 48 10. 93 6 .74 10 .92 2. 20 0 .65 1 . 08 0. 17 0. 18 0 .53 0. 06 101. 00 FINAL VALUE 51 . 55 15. 33 10. 82 6 ,67 10. 81 2. 18 0. ,65 1 . 07 0. . 17 0. 18 0. 53 0. ,06 NORM. VALUE 52 . 72 15. 02 11 . 10 6 .63 10 .98 2. 15 O .64 1 . 07 0. . 17 0. . 14 0. 53 0. 06 101. .21 RECCOM. VALUE -1 . 17 0. 31 -0. 28 O. .04 -0 . 17 O. 03 0. .01 -0. OO -0. CO 0. 04 0. ,0 0. 0 NORM.-RECC. AGV-1 59. 88 15. 82 7. 20 1 .88 5 .35 4. 26 2 92 1. , 14 0. , 10 0. 50 0. .78 0. 02 99. 83 FINAL VALUE 59. 98 15. 84 7. 21 1 .88 5 .36 4. 26 2. 92 1. 14 0. , 10 0. 50 0. ,78 0. 02 NORM. VALUE 59. 61 17 . 19 6. 82 1 52 4. 94 4. 34 2 92 1. 06 0. 10 0. 51 0 ,78 0. 02 99. 81 RECCOM. VALUE 0. .37 - 1 , 35 0. 39 0 .36 0 .42 -0. 08 0 .00 0, .08 -0. .00 -0. 01 0, .0 0. 0 NORM.-RECC. ABUNDANCES FROM DUPLICATE ANALYSES ESTIMATE OF ANALYTICAL PRECISION XRF MAJOR ELEMENTS Major element oxides in wt. %. SAMPLE S i 0 2 T i 0 2 A1 20 3 F e 2 0 3 MnO MgO CaO Na 20 K 20 P 2 ° 5 NBS688 47 79 1.19 17.99 10.61 0.17 7.54 12.35 2.02 0.19 0.15 Ref. 1 48. 4 1.17 17.36 10.35 0.167 8.4 12.17 2.15 0.187 0.134 NIML 53 82 0.49 14.72 10.02 (1.03) 0.43 3.35 (10.80) 5.31 0.04 Ref. 1 52 4 0.48 13.64 9.75 (0.77) 0.28 3.22 (8.37) 5.51 0.06 NIMC 73 79 0.12 13.28 2.46 0.02 0.07 1.05 3.63 5.58 0.01 Ref. 1 75 70 0.09 12.08 1.74 0.02 0.06 0.78 3.36 4.99 0.01 SY3 59 16 0.13 12.28 6.67 0.37 3.38 8.63 4.48 4.30 0.60 Ref. 1 59 68 0.15 11.80 5.66 0.32 2.67 8.26 4.15 4.20 0.54 COQ61 57 75 0.83 15.38 8.05 0.14 6.11 6.42 2.96 2.16 0.21 Ref . 2 58 51 0.82 16.22 7.91 0.15 4.30 6.51 3.08 2.27 0.22 COQ251 53 53 1.02 16.38 8.89 0.19 6.75 9.70 2.26 0.96 0.31 Ref. 2 53 98 1.01 17.74 8.87 0.18 4.40 9.60 2.89 1.04 0.28 COQ632 55 40 1.02 16.34 8.38 0.15 5.47 8.12 3.08 1.67 0.37 Ref. 2 54 58 1.03 16.98 9.63 0.15 4.58 8.02 3.17 1.61 0.28 ( ) These numbers were not used in the c a l c u l a t i o n of estimated precisions. cont inue to -J MAJOR c o n t . S i 0 2 WOOD LK. R e f . 4 48.19 46.40 EDMUND R e f . 4 50.55 48.79 NAZKO R e f . 4 51.24 49.50 V8M Ref. 3 50.59 50.86 12-2 R e f . 3 (43.27) (37.55) 27-22 Ref. 3 45.92 45.05 35-19b Ref. 3 44.41 42.81 DOG CK Ref. 5 51.25 50.65 BULL CAN Ref. 5 49.71 49.67 CAMEL Ref. 5 51.89 51.94 DEADMAN Ref. 5 48.41 49.11 T i 0 2 A 1 2 0 3 2.66 16.01 2.67 15.13 1.53 15.64 1.66 14.94 1.84 15.07 1.85 14.27 0.89 15.22 0.87 15.38 0.13 12.62 0.17 12.05 0.79 15.20 0.76 15.57 0.96 15.11 0.91 15.39 1.93 14.69 1.92 14.67 1.35 15.58 1.28 15.58 1.93 15.25 1.94 16.13 1.90 14.62 1.98 14.98 Abbey, 1983; 2 Berman, B e v i e r , 1982 F e 2 0 3 MnO MgO CaO Na 20 K 20 P2O5 13.65 13.95 0.18 0.16 4.60 4.21 7.60 7.31 4.93 4.79 1.38 1.20 0.80 0.58 11.78 12.10 0.16 0.17 6.28 7.34 8.95 8.61 4.03 3.97 0.67 0.55 0.42 0.24 12.12 12.26 0.16 0.17 6.82 8.14 8.46 8.34 3.38 3.36 0.62 0.53 0.30 0.21 12.50 12.58 (0.25) (0.09) 7.66 6.99 8.61 7.95 2.69 3.16 1.26 1.17 0.33 0.25 (14.45) (12.74) 0.23 0.14 (18.76) (23.67) (10.15) (8.41) 0.27 0.56 0.10 0.11 0.11 0.03 11.99 12.01 0.21 0.16 11.64 11.99 12.92 12.62 0.94 1.60 0.34 0.35 0.05 0.05 14.64 14.73 0.23 0.15 10.83 10.95 12.46 12.00 1.11 1.79 0.20 0.21 0.05 0.06 12.82 12.77 0.16 0.16 6.70 8.28 8.47 8.58 3.27 3.15 0.57 0.65 0.14 0.22 13.20 13.00 0.17 0.17 7.42 8.32 8.56 8.88 3.42 3.46 0.41 0.38 0.17 0.14 11.04 11.06 0.14 0.14 6.02 6.38 8.51 9.50 (4.25) (2.69) 0.81 0.82 0.15 0.30 (13.84) (12.14) 0.18 0.16 9.81 9.34 (7.54) (9.48) 2.19 2.40 1.04 1.05 0.34 0.34 ; I s a c h s e n , 1984; W. H. Mathews ( p e r s . comm.); to cn 277 T A B L E X I X P R E C I S I O N O F T R A C E E L E M E N T A N A L Y S E S TRACE ELEMENTS: Approximate 1a s c a t t e r of standards about working curves as generated by Berman (1979) program. Abundances i n standards are from Abbey (1983). Estimated p r e c i s i o n s are from d u p l i c a t e analyses of samples. APPROX. 1a ESTIMATED PRECISION ERRORS Ba 50 ppm 26.1 ppm Rb 1 ppm 2.3 ppm Nb 3 ppm 1.9 ppm Ce 10 ppm N/D* Sr 4 ppm 6.6 ppm Nd 5 ppm N/D* Zr 2 ppm 8.5 ppm Y 2 ppm 2.2 ppm Co 1 4 ppm 5.7 ppm Cr 1 9 ppm 10.2 ppm Cu 1 6 ppm 11.3 ppm Ni 5 ppm 4.8 ppm V 4 ppm 8.4 ppm 1 Estimated p r e c i s i o n s f o r Co, Cr, and Cu are based on r e l a t i v e l y few d u p l i c a t e a n a l y s e s . * N/D=not determined On the f o l l o w i n g pages a r e : 1. Computed t r a c e element abundance i n the analyzed standards which were used to c a l c u l a t e 1a, and 2. Abundances from d u p l i c a t e a n a l y s e s . TRACE ELEMENT REGRESSION ANALYSIS - MINOR BASALT DATA BATCH 1 NUMBER OF STANDARDS 3 13 *******+*******************************+*************#*****•***•**#**•******#•******************* BA SLOPE= 5 .8234 I N T E R C E P T 3 - 4 5 . 2 6 7 8 R 3 0 .99929 AVG. D E V I A T I O N 3 38 .01 STAN. D E V . 3 4 9 . 6 4 6 STANDARD ERROR IN S L O P E 3 0 . 0827 STANDARD ERROR IN I N T E R C E P T 3 1 .0189 STANDARD PPM CALCULATED DIFFERENCE BHVO 135 .00 191 . 10 56 . 10 BCR- 1 6 8 0 . 0 0 713 . 73 33 . 73 UB- 1 4 9 0 . 0 0 553 .08 63 .08 W- 1 160 .00 175 .85 15 . 85 AGV- 1 1200.00 1 157 .21 - 4 2 . 7 9 S Y - 3 4 3 0 . 0 0 358 .99 - 7 1 . 0 1 NIM-L 4 5 0 . 0 0 431 .61 - 18 .39 D T S - 1 5 . 0 0 -33 84 - 3 8 . 8 4 MGMICA 4 0 0 0 . 0 0 4002 29 2 . 29 REJECTED STANDARDS ARE: ( 0 . 0 ) CO S L O P E 3 0 . 2 9 7 0 INTERCEPT 3 0 . 2420 R= 0 .99535 AVG. O E V I A T I O N 3 3 .52 STAN. D E V . 3 4 . 3 7 4 STANDARD ERROR IN S L O P E 3 0 . 0096 STANDARD ERROR IN I N T E R C E P T 3 0 . 1 2 15 STANDARD PPM CALCULATED DIFFERENCE BCR- 1 36 .00 38 06 2 .06 MRG-1 86 00 88 31 2 .31 J B - 1 39 .00 37 . 33 -1 .67 W- 1 47 .00 41 16 - 5 . 8 4 AGV- 1 16 .00 20 91 4 .91 S Y - 3 12 .00 10 91 - 1 .09 NIM-L 8 00 9 34 1 . 34 DTS- 1 135 .00 129 48 - 5 . 5 2 P C C - 1 1 10 .00 115. 49 5 . 4 9 FEMICA 20 00 14 . 77 - 5 . 2 3 MGMICA 20 .00 23 . 23 3 . 2 3 REJECTED STANDARDS ARE: OLO-1 ( 15 BHVO ( -8 75) 78) tO - J CO SLOPE* 0 . 2 7 2 9 I N T E R C E P T * - 2 5 . 7 1 9 2 R = 0 . 9 9 9 9 6 AVG. DEVIATION* 6 . 5 3 STAN. DEV STANDARD ERROR IN SL0PE= 0 . 0 0 1 0 STANDARD ERROR IN INTERCEPT* 0 . 0 3 9 6 STANDARD BHVO BCR-1 W- 1 AGV- 1 N IM-L OLO- 1 P C C - 1 MGMICA PPM 3 0 0 . 0 0 1 5 . 0 0 1 1 5 . 0 0 1 0 . 0 0 10.OO 4 . 0 0 2 8 0 0 . 0 0 1 0 0 . 0 0 CALCULATED 2 8 9 . 9 8 20 . 72 124.46 - 3 . 6 2 18 .04 1 .54 2 8 0 0 . 4 1 102 .47 DIFFERENCE - 1 0 . 0 2 5 . 7 2 9 . 4 6 - 1 3 . 6 2 8 .04 - 2 . 4 6 0 . 4 1 2 . 4 7 REJECTED STANDARDS ARE: S V - 3 J B - 1 ( - 3 3 . 6 2 ) 1 9 . 4 9 ) ***************** *********************** SLOPE* 1 .1973 INTERCEPT* - 1 . 0 4 2 5 R* 0 . 9 9 5 2 9 AVG. DEVIATION* 3 67 STAN. DEV STANDARD ERROR IN SLOPE* 0 . 0 5 2 1 STANDARD ERROR IN INTERCEPT = 0 . 3 4 5 6 STANDARD BHVO J B - 1 W- 1 S Y - 3 0 L 0 - 1 P C C - 1 FEMICA PPM 1 4 0 . 0 0 56 . 0 0 1 1 0 . 0 0 16.OO 27 . 0 0 8 . 0 0 4 . 0 0 CALCULATED 132 .32 64 .41 1 1 4 . 3 0 1 5 . 9 9 2 7 . 12 4 . 7 9 2 . 0 7 DIFFERENCE - 7 . 6 8 8 . 4 1 4 . 3 0 - 0 . 0 1 0 . 12 - 3 . 2 1 - 1 . 9 3 REJECTED STANDARDS ARE: AGV- 1 BCR -1 1 3 . 6 4 ) 1 1 . 2 7 ) *************** ********* ******** continue NB S L O P E * 2 .3422 INTERCEPT* 3 .3493 STANDARD ERROR IN SLOPE = 0 . 0 2 8 6 R= 0 . 9 9 9 6 3 AVG. DEVIATION* STANDARD ERROR IN INTERCEPT* 2 .00 O 1500 STAN. DEV. 2 . 908 STANDARD PPM BHVO 19 .00 BCR-1 19 .00 MRG-1 2 0 . 0 0 AGV-1 16 .00 OLO-1 10 .00 FEMICA 2 7 0 . 0 0 MGMICA 120 .00 REJECTED STANDARDS ARE: W-1 ( CALCULATED 20 .26 14.67 21 .14 16.04 13.53 271 .03 117.33 6 . 6 8 ) DIFFERENCE 1 . 26 -4 . 33 1 . 14 0 0 4 3 . 5 3 1 .03 -2 .67 ********************* ************* ******* ******* NI S L O P E * 0 . 5 4 3 9 I N T E R C E P T * - 1 1 . 9 3 3 8 0 .99998 AVG. DEVIATION* 4 .02 STAN. D E V . * 5 .428 1 IN S L O P E * 0 . 0 0 1 3 STANDARD ERROR IN INTERCEPT* STANDARD PPM CALCULATED DIFFERENCE BHVO 120 .00 114.65 -5 . 35 BCR-1 10 .00 17 .99 7 .99 MRG- 1 195 .00 189.91 - 5 . 0 9 J B - 1 135 .00 128.39 - 6 . 6 1 W-1 7 6 . 0 0 7 6 . 0 0 0 . 0 0 AGV-1 15 .00 13.99 - 1 .01 NIM-L 11 .00 17 .07 6 .07 OLO-1 6 .00 9.11 3.11 PCC-1 2 4 0 0 . 0 0 2400.91 0 .91 0 . 0 3 3 6 REJECTED STANDARDS ARE: DTS-1 ( 4 6 . 2 0 ) ************** ************** ************ ********** cont inue. CO o RB SLOPE= 5 . 7 2 4 9 INTERCEPT = 0 .3191 R = 0 .99961 AVG. DEVIATION* 0 .58 STAN. DEV.= 0 . 8 1 0 STANDARD ERROR IN S L O P E * 0 .0716 STANDARD ERROR IN INTERCEPT* 0 .1844 STANDARD PPM CALCULATED DIFFERENC BHVO 10.00 9 .04 - 0 . 9 6 BCR- 1 47 .00 48 .04 1 .04 MRG-1 8 .00 7 .85 - O . 15 J B - 1 4 1 .00 41.21 0 .21 W- 1 21 .00 21 .78 0 . 7 8 AGV-1 6 7 . 0 0 6 6 . 8 5 0 . 15 OLO-1 74 .00 73 .24 - 0 . 7 6 E REJECTED STANDARDS A R E : DTS-1 ( 9 . 4 1 ) * + * * * * * * * * * * * * * * * * * * * * • * • * * * * * * * * * * * * * • * * + * * * * * * # * * * • • • * * * * • * » » + * * * * * • • • • * * * * • * * * • • * * * * * * + * * * • * * • • SR S L O P E * 69 .5064 INTERCEPT* 1.3856 R= 0 .99991 AVG. DEVIATION* 2 . 6 0 STAN. D E V . * 3 .787 STANDARD ERROR IN S L O P E * 0 . 4 2 4 0 STANDARD ERROR IN INTERCEPT = 0 .7788 STANDARO PPM CALCULATED DIFFERENCE BCR- 1 3 3 0 . 0 0 3 2 7 . 6 0 - 2 . 4 0 J B - 1 4 4 0 . 0 0 446 .23 6 . 2 3 W-1 190 .00 188.95 - 1.05 • AGV-1 6 6 0 . 0 0 6 5 7 . 1 6 - 2 . 8 4 PCC-1 1 .00 1 . 13 0 . 13 FEMICA 5 . 0 0 2 . 19 - 2 . 8 1 MGMICA 2 5 . 0 0 27 .74 2 . 74 REJECTED STANDARDS A R E : BHVO ( - 2 9 . 0 9 ) MRG-1 ( 9 . 8 4 ) + * * * * * * * * * * * * * * + * * * * * * * * * * * * * * * * * * * * + * • * • + + + + * * * * * * * * * + * + + • * * • * • + » • * + * * * * * * * * * * + * * * • * * * + * + * * • * + • * « continue CO V S L O P E 3 2 . 6 3 0 9 I N T E R C E P T 3 - 1 2 . 1 5 1 1 R 3 0 . 9 9 9 6 6 A V G . D E V I A T I O N 3 3 . 4 3 S T A N . D E V . 3 4 . 2 5 2 S T A N D A R D ERROR I N S L O P E 3 0 . 0 3 0 7 STANDARD ERROR I N I N T E R C E P T 3 0 . 2 4 7 2 STANDARD P P M C A L C U L A T E D D I F F E R E N C E B C R - 1 4 2 0 . 0 0 4 2 1 . 7 7 1 . 7 7 ' J B - 1 2 1 0 . 0 0 2 1 4 5 2 4 . 5 2 W- 1 2 6 0 . 0 0 2 5 5 . 5 7 - 4 . 4 3 A G V - 1 1 2 5 . 0 0 1 2 0 . 2 7 - 4 . 7 3 S Y - 3 5 1 . 0 0 4 8 . 17 - 2 . 8 3 D T S - 1 1 1 . 0 0 14 . 3 6 3 . 3 6 P C C - 1 2 9 . 0 0 3 1 . 3 4 2 . 3 4 R E J E C T E D S T A N D A R D S A R E : M R G - 1 ( 3 3 . 7 0 ) BHVO ( 1 8 . 5 0 ) O L O - 1 ( 9 . 5 7 ) •A************************************* ********************************************************** S L O P E 3 3 . 2 1 9 8 I N T E R C E P T 3 3 . 7 6 6 7 R= 0 . 9 9 9 9 7 A V G . D E V I A T I O N 3 1 . 3 9 S T A N . D E V . 3 2 . 1 7 1 S T A N D A R D ERROR I N S L O P E 3 0 . 0 1 0 6 STANDARD ERROR I N I N T E R C E P T 3 0 . 0 6 5 5 STANDARO P P M C A L C U L A T E D D I F F E R E N C E BHVO 27 . 0 0 2 9 . 4 6 2 . 4 6 B C R - 1 4 0 . 0 0 3 7 . 0 7 - 2 . 9 3 M R G - 1 1 6 . 0 0 1 5 . 5 9 - 0 . 4 1 J B - 1 2 6 . 0 0 2 4 . 4 6 - 1 . 5 4 A G V - 1 1 9 . 0 0 21 . 2 0 2 . 2 0 S Y - 3 7 4 0 . 0 0 7 4 0 . 0 4 0 . 0 4 O L O - 1 24 . 0 0 2 4 . 17 0 . 17 R E J E C T E D S T A N D A R D S A R E : ( 0 . 0 ) cont inue. to CD S L O P E * 2 1 . 3 8 0 4 I N T E R C E P T * 7 . 4 G B G R= 0 . 9 9 9 9 8 A V G . D E V I A T I O N S T A N D A R D ERROR I N S L O P E * 0 . O G O O STANDARD ERROR I N I N T E R C E P T * STANDARD BCR - 1 M R G - 1 A G V - 1 D T S - 1 P C C - 1 F E M I C A MGMICA P P M 1 8 5 . 0 0 105 . 0 0 2 3 0 . 0 0 1 0 . O O G . 0 0 8 0 0 . 0 0 2 0 . 0 0 C A L C U L A T E D 1 8 5 . 3 8 1 0 5 . 5 2 2 3 1 . 7 1 6 . 6 . 7 9 9 . 3 5 2 0 . 7 9 . 3 9 . 8 6 D I F F E R E N C E O . 3 8 O . 1 . - 3 . O . . 5 2 7 1 6 1 . 8 6 - 0 . 6 5 O . 7 9 R E J E C T E D S T A N D A R D S A R E : O L O - 1 J B - 1 BHVO W- 1 4 7 . 7 9 ) - 1 3 . 0 6 ) - 1 0 . 4 2 ) • 1 1 . 7 0 ) 1 . 2 2 S T A N . D E V . * 1 . 9 3 5 O . 1 7 7 0 ro CO to ABUNDANCES FROM DUPLICATE ANALYSES ESTIMATE OF ANALYTICAL PRECISION XRF TRACE ELEMENTS Abundances i n ppm SAMPLE Ba Rb Nb Sr Y Co Cr Cu N i V Zr NIML 355 195 (767) (4419) 20 2 (0) (76) 6 85 (10557) Ref. 450 190 (960) (4600) 25? 8? (10?) (13) 11 81 (11000) NIMD 0 0 3 3 4 194 (3209) 2 "(2701) 45 20 R e f . 5 10? N/R N/R 3? N/R 208 (2900) 10 (2040) 40 20? NIMG 82 340 59 11 144 5 (0) 3 6 2 287 R e f . 5 120? 325 53 10 147 4? (12) 12 8? 2? 300 SY3 388 (127) 136 (141) 748 13 0 (3) (88) 49 (252) Ref. 430 (208) 130 (306) 740 12 10 (16) (ID 51 (320) NBS688 180 2 6 170 22 42 (85) 81 145 (216) 60 Ref. 20.0 1.9 N/R 169 N/R 50 (330) 96 150 (250) N/R COQ61 842 54 6 479 28 * 65 * 12 191 149 Ref. 873 53 7 480 28 64 9 197 156 COQ251 576 21 5 605 23 * 39 * 27 241 95 Ref. 589 21 5 578 26 50 23 241 107 COQ632 646 42 6 500 28 * 4 * 12 213 120 Ref. 668 44 7 512 30 22 13 225 132 V8M 525 41 6 447 27 * * * 50 276 54 Ref. 534 36 4.1 420 25 54 267 65 12-2 1 3 2 49 10 * * * (316) 144 12 Ref. 13 1.72 3.4 46.2 4.6 (281) 143 22. »o co c o n t i n u e TRACE c o n t . SAMPLE Ba Rb Nb Sr Y 27-22 92 5 3 374 15 Ref. 86 5.1 1.9 353 13 35-19b 106 4 3 216 24 R e f . 4 72 3 3.1 211 22 35-17a (26) 3 2 (541) 4 R e f . 4 (75) 4.9 2.4 (665) 2.7 34-3b 290 36 7 394 16 R e f . 4 294 35 7.8 403 15 EXMOUNT1 * 4 4 (155) 29 Ref. 3 3.6 1.8 (181) 26.9 EXM0UNT2 * 1 3 177 29 Ref. 3 1.9 3 177 26.5 EXM0UNT3 * 2 3 189 30 Ref. 3 1.7 2 189 26.2 BRBEAR1 64 3 9 214 36 Ref. 3 50 2 6 208 32 BRBEAR2 92 5 12 227 33 Ref. 3 51 9 8 '235 34 COBB1 94 6 13 248 38 Ref. 3 40 3 9 248 32 COBB 2 84 4 12 232 38 Ref. 3 29 2 8 226 38 N/R = s t a n d a r d has no r e f e r e n c e d v a l u e * = sample was not a n a l y z e d p r e v i o u s l y ? = q u e s t i o n a b l e v a l u e Cr Cu N i V Zr * * 65 300 17 56 324 30 * * 221 295 25 211 307 38 * , * 23 (80) 4 26 (130) 21 * * 98 276 57 101 272 73 262 * 160 * 92 275.7 150.9 87 261 * 153 * 89 275.6 143.9 85 263 * 142 * 99 280.9 134.5 97 * 47 90 283 119 59 80 256 111 (176) 61 55 (330) 134 (238) 70 49 (269) 128 (118) 50 59 300 154 (271) 64 57 274 140 105 70 (47) (328) 144 110 82 (28) (276) 133 1Abbey, 1983 2Berman, 1979 3R.L. Chase ( p e r s . comm.) 4 I s a c h s e n , 1984 5 S t e e l e e t a l . , 1978 APPENDIX IV - TA CONTAMINATION New INAA Ta data p l o t t e d on d i s c r i m i n a t i o n diagrams showed both enormous enrichment and great s c a t t e r in Ta r e l a t i v e to abundances in the samples which were used to d e f i n e t e c t o n i c f i e l d s . (Wood, 1980; Wood et a l . , 1979; Pearce, 1979). T h i s suggested e i t h e r : the mantle source region beneath B.C. i s e n r i c h e d i n Ta and heterogeneous, a n a l y s i s f o r Ta was done i n c o r r e c t l y , or the samples had been contaminated with Ta d u r i n g p r e p a r a t i o n . Mantle enrichment i n Ta would l i k e l y be accompanied by enrichments i n other incompatible elements, but as these 'other' enrichments are not observed i t i s presumed that the mantle beneath B.C. i s not e n r i c h e d i n Ta. P r e c i s i o n of the Ta a n a l y s i s f o r r e f e r e n c e standards i s ± 10%, implying that the a n a l y t i c a l technique was not at f a u l t , but i n i n t r a l a b standards P-1 and WP1 the a n a l y t i c a l s c a t t e r i s l a r g e r than ± 100%. T h i s h i n t e d that sample contamination d u r i n g p r e p a r a t i o n was the most probable cause of the enrichment and v a r i a t i o n . Most of the samples had been powdered f o r a n a l y s i s i n p r e v i o u s s t u d i e s and incomplete records were kept concerning the equipment used i n t h e i r p r e p a r a t i o n (whether BICO d i s c m i l l and/or agate mortar, or s t e e l r i n g m i l l , or tungsten c a r b i d e r i n g m i l l ) . The samples prepared s p e c i f i c a l l y f o r t h i s 286 287 study were a l l crushed i n a tungsten-carbide r i n g m i l l and they a l l have anomalously high Ta abundances (see Table XX), s u g g e s t i n g i t was the tungsten-carbide which contaminated the sample.. In a d d i t i o n , Wood et a l . have (1979) have s t r e s s e d that p r e p a r a t i o n i n a tungsten c a r b i d e s h a t t e r box was a major source of Ta contamination and should be avoided. To c o n f i r m t h i s suggested source of contamination, s i l i c a sand was a c i d washed and crushed i n the same tungsten-carbide r i n g m i l l and the r e s u l t i n g powder was analyzed by XRF. As suspected a peak co r r e s p o n d i n g to tens of ppm of Ta was present, which c o u l d only be there as a r e s u l t of contamination (C.J. Hickson and S.J. J u r a s , i n p r e p a r a t i o n ) . Therefore i n order to use Ta d i s c r i m i n a t i o n diagrams a s u b s t i t u t i o n or c o r r e c t i o n must be made. Sienko and Plane (1957) and Parker and F l e i s c h e r (1968) note t h a t Nb and Ta are a p a i r of elements which have s i m i l a r i o n i c r a d i i (Nb=0.69 A; Ta=0.68 A), i d e n t i c a l valence s t a t e s , are v e r y incompatible, and always occur together i n m i n e r a l s . They s u b s t i t u t e f o r T i i n c l i n o p y r o x e n e , hornblende, Mg-Fe mica, t i t a n o m a g n e t i t e and sphene. Abundances and r a t i o s of Nb and Ta o c c u r r i n g i n v a r i o u s rock types were compiled by Parker and F l e i s c h e r (1968). Average abundances of Nb:Ta i n s u b a l k a l i n e c o n t i n e n t a l gabbros and b a s a l t s were r e p o r t e d as 17 ppm and 1 ppm r e s p e c t i v e l y whereas g r a n i t e s , quartz monzonites and g r a n o d i o r i t e s averaged 12 ppm Nb and 1.3 ppm Ta. In the a l k a l i n e e q u i v a l e n t s of the above rock types the Nb and Ta abundances i n c r e a s e d by 288 approximately f i v e times, however the Nb/Ta r a t i o s ranged from 10 to 15 independent of the rock s e r i e s . More r e c e n t l y Wood (1980) and G i l l (1981) r e p o r t the average Nb/Ta r a t i o equal to 16. A c o m p i l a t i o n of recent analyses of Nb and Ta i n some igneous rock standards i s presented i n Table XXI. Nb c o n c e n t r a t i o n s range from a low of 9.4 ppm i n RGM-1, a r h y o l i t e , to 380 ppm i n SG-1A, an a l b i t i z e d g r a n i t e , and Ta c o n c e n t r a t i o n s range from 0.50 ppm i n W-1, a diabase, to 26 ppm i n SG-1A, the a l b i t i z e d g r a n i t e standard. However Nb/Ta r a t i o s show a much c l o s e r agreement ranging from 9.4 to 23.75 and averaging 15.1. Table XXII records s i m i l a r data f o r average Lewisian g n e i s s e s , g r a n u l i t e x e n o l i t h s and b a s a l t s from the I s l e of Skye, I c e l a n d and the Emporer seamount (Wood, 1980). Although the contents of Nb and Ta are g e n e r a l l y much l e s s in the L e w i s i an rocks than i n the b a s a l t s the Nb/Ta r a t i o s are s i m i l a r , averaging 15.6, with a range from 11.3 to 20. The average Nb/Ta r a t i o f o r a l l b a s a l t i c samples l i s t e d i n Tables XXI and XXII i s 15.8. Approximately 50% of the Nb/Ta r a t i o s in the analyzed rocks from t h i s study do not l i e w i t h i n the range of r a t i o s d e f i n e d by the standards but abundances of Nb are s i m i l a r to r e p o r t e d Nb abundances in b a s a l t s , c o n f i r m i n g the probable contamination with Ta. With Nb/16 s u b s t i t u t e d f o r c a l c u l a t e d Ta i n the Ta-bearing d i s c r i m i n a n t diagrams, a l l of the data p o i n t s p l o t t e d w i t h i n the a p p r o p r i a t e t e c t o n i c f i e l d s . ( This 289 s u b s t i t u t i o n f o r Ta i s denoted by Ta* elsewhere i n the t h e s i s ) . The use of Nb i n d i s c r i m i n a n t diagrams which i n v o l v e Ta i s acce p t a b l e p r o v i d e d that the c o n c e n t r a t i o n s of Nb are 1 ppm or g r e a t e r (Wood et a l . , 1979). 290 TABLE XX CALCULATED Nb AND Ta ABUNDANCES IN ANALYZED BASALTIC SAMPLES * SAMPLE Nb (ppm) Ta (ppm) Nb/Ta ARIS IS 1 5 N/D > 15 KITASU 57 5 11.4 LAKE IS 23 82 0.3 RAINBOW 25 1 25 ANAHIM 33 2 16.5 ITCHA1 2 45 4 11.3 ITCHA2 61 3 20.3 ALEX 20 N/D > 20 QUES LK 21 3 7 SPAN CK 42 3 1 4 WGRAYN 22 4 5.5 TROPHY 16 1 16 MASSET1 1 4 2 7 MASSET2 1 5 1 1 5 SATLIN 1 2 N/D > 12 PRINCER 1 7 4 4.3 AYNSH1 41 2 20.5 AYNSH2 38 4 9.5 ISKUTW 30 N/D > 30 BORDERLK 25 5 5 MT. DUNN 30 3 10 ISKUT 24 1 24 HOODOO3 171 9 19 BOWSER 55 1 55 SPEC 1 20 N/D > 20 SPEC2 27 N/D > 27 EDZ1 37 2 18.5 EDZ2 30 1 30 NEDZ 1 38 3 12.7 NEDZ 2 30 2 15 NEDZ 3 45 5 9 NEDZ 4 31 4 7.8 LEVEL 1 28 1 28 LEVELD 1 2 N/D > 12 LEVEL2 32 2 1 6 NATLIN 51 4 12.8 * = Methods of p r e p a r a t i o n i n Appendix 1 N/D = not d e t e c t e d 2 Mugearite 3 P e r a l k a l i n e TABLE XX (cont.) SAMPLE Nb (ppm) Ta (ppm) Nb/Ta CHEAK 1 0 1 1 0 GARIBALD 9 7 1 .3 CAYLEY 1 6 1 6 ELAHO 1 2 N/D > 12 MEAGER 1 5 1 3 1 .2 SALAL1 25 2 12.5 SALAL2 21 1 21 SALAL3 27 2 13.5 SILVERA 1 20 3 6.7 SILVERH 23 4 5.8 COQ251 5 8 0.6 COQ61 6 1 6 COQ632 6 3 2 BLIZZARD 29 5 5.8 CARD 1 9 2 9.5 WOOD LK. 37 7 5.3 DEADMAN 22 5 4.4 REDSTONE 1 8 6 3 BULLCAN 6 6 1 DOGCK 1 2 1 1 2 CAMEL 9 5 1 .8 EDMUND 3 5 0.6 NAZKO 1 3 2 6.5 QUESW 23 2 11.5 ALERT1 1 9 5 1 .8 ALERT2 20 1 20 ALERT3 29 N/D > 29 BRBEAR1 9 5 1 .8 BRBEAR2 1 2 N/D > 12 COBB 1 1 3 4 3.3 COBB2 1 2 N/D > 12 EXMOUNT1 4 1 4 EXMOUNT2 3 2 1 .5 EXMOUNT3 3 4 0.75 SEXRIDGE 7 • 13 0.5 PREVRDG 19 9 2.1 EXDEEP 1 5 1 5 1 EXRIFT 4 7 0.6 N/D = not de t e c t e d 1 Andesite TABLE XX (cont.) (VANCOUVER ISLAND) SAMPLE Nb (ppm) Ta (ppm) Nb/Ta M598 10 3 3.3 M600 4 19 0.3 M605 8 10 0.8 M606 4.4 2 2.2 K609 1 2 1 7 0.7 K61 3 1 0 6 1 .7 K61 4 1 1 8 1 .4 K61 5 1 1 3 3.7 B61 8 5 N/D > 5 B61 9 1 7 4 1 .8 B620 7 N/D > 7 B621 7 N/D > 7 S630 7 4 1 .8 S631 1 5 4 1 .3 S632 1 3 18 0.7 79-H-39 29 1 2 2.4 79H-1OA1 10 1 .38 7.25 SICKER1 25 2 12.5 SICKER3 6 3 2 10-1265 4 N/D > 4 R-1 36 5 1 5 683422 5 7 N/D > 7 683241 5 8 N/D > 8 682132 1 9 1 9 GMIC#4S 7 1 7 34-3b 7.8 6 1 .3 WCT-3 7.6 4 1 .9 15-12a 3.4 4 0.8 35-l9b 3.1 9 0.3 1 2-2 3.4 2 1 .7 27-22" 1 .9 N/D > 1 .9 V8M 4 7 0.6 V8F 1 4 N/D > 4 I I P 5 7.1 6 1 .2 N/D = not detected 1 A n d e s i t e 4 Ankaramite 5 D i o r i t e 6 G r a n o d i o r i t e 293 TABLE XXI ABUNDANCES OF Nb AND Ta IN STANDARDS (Abbey, 1983) SAMPLE ROCK TYPE Nb (ppm) Ta (ppm) Nb/T, BHVO-1 Ba s a l t 1 9 1.1? 17.3 BCR-1 B a s a l t 1 9? 0.8? 23.8 BE-N B a s a l t 100 5.5? 18.2 W-1 Diabase 9.5 0.50 19 AGV-1 Andesite 1 6? 1 .4? 11.4 G-1 Gr a n i t e 24 1 .5 16.0 G-2 Gr a n i t e 1 3? 0.8? 16.3 NIM-G Gr a n i t e 53 4.5? 11.8 SG-1A A l b i t i z e d G r a n i t e 380 26 14.6 QLO-1 Quartz L a t i t e 10.5? 0.9? 11.7 STM-1 Syeni t e 270? 1 8? 15.0 RGM-1 R h y o l i t e 9.4? 1 .0? 9.4 qu e s t i o n a b l e value 294 TABLE XXII ABUNDANCES OF Nb AND Ta IN TERRESTRIAL ROCKS (Wood, 1980) SAMPLE ROCK TYPE Nb (ppm) Ta(ppm) Nb/T, LEWISIAN 2 4 Basic Gneisses 2 0.1 20 LEWISIAN 3 Basic Gneiss 2 0.12 16.7 LESOTHO G r a n u l i t e X e n o l i t h s 5 0.3 16.7 SKYE 1 A l k a l i B a s a l t 9 0.80 11.3 SKYE2 Hawai i t e 30 2.04 14.7 EMPORER Hawai i t e 29 2.01 14.4 ICELAND 1 Th. B a s a l t 1 1 0.76 14.5 ICELAND 2 S h i e l d t h o l e i i t e 2 0.12 16.7

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