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The Coquihalla volcanic complex, Southernwestern British Columbia Berman, Robert G. 1979

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THE COQUIHALLA VOLCANIC COMPLEX, SOOTHWESTEEN EEITISH COLUMBIA by ROBEET G- BEEMAN B. A., Amherst College, 1975 SUBMITTED IN PAETIAL FULFILLMENT REQUIEEMENTS FOE THE DEGBEE OF MASTEE OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of Geological Sciences We accept t h i s thesis as conforming to the required standard THE UNIVEESITY OF BBITISH COLUMEIA June, 1979 THESIS THE © Eobert G. Berman, 1979 I n 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 o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e 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 a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . r, . x Geological Sciences D e p a r t m e n t o f _ The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 July 6 , 1979 D a t e :  C o q u i h a l l a M o u n t a i n v i e w e d f r o m H i d d e n C r e e k . A d i o r i t e s t o c k f o r m s t h e c o r e o f t h e m o u n t a i n , a n d c u t s a n o l d e r a n d e s i t e i n t r u -s i v e w h i c h f o r m s t h e l e d g e i n t h e f o r e g r o u n d . A n a n d e s i t e dome o c c u r s o n t h e l e f t s i d e o f t h e p h o t o g r a p h . i ABSTRACT The Coguihalla Volcanic Complex consists of c a l c - a l k a l i n e acid to intermediate extrusive and intrusive recks which have an areal extent of roughly 30 km2, near Hope, B r i t i s h Columbia. The oldest and most voluminous members of the complex are r h y c l i t i c p y r o c l a s t i c rocks (variably welded l i t h i c - c r y s t a l l a p i l l i t u f f , v i t r i c t u f f , and c r y s t a l - l i t h i c l a p i l l i t u f f ) , that have an overall thickness of approximately 1600 m. Later igneous a c t i v i t y produced numerous andesite to dacite domes, dykes, and s i l l s - A l a t e stage d i o r i t e to guartz-diorite stock forms the core of Coguihalla Mountain. Most p y r o c l a s t i c rocks rest unconformably en the Jurassic to Cretaceous Eagle pluton. Monolithologic avalanche breccias formed i n the southern portion of the map area, where pyroclastic recks were deposited against a f a u l t scarp with u p l i f t e d Lower Cretaceous Pasayten Group recks. In the southeastern part of the area, monolithologic avalanche breccias formed in response to t i l t i n g and u p l i f t of the underlying Eagle pluton as the basin subsided. A l l tuffaceous rocks are characterized by v i t r o c l a s t i c textures, and contain phenocrysts of plagicclase (An 40-20), b i o t i t e , quartz, and minor potassium feldspar and titanomagnetite. Andesites are porphyritic with phenocrysts of plagioclase (An 76-30), c a l c i c augite, magnesic- to tschermakitic hornblende, and titanomagnetite. Glomeroporphyritic c l o t s consist of plagioclase, aluminous augite, and titancmagnetite. Porphyritic dacites contain phenocrysts of plagioclase(An 60-35), hornblende, titanomagnetite, and minor apatite. The d i o r i t e i i stock consists of orthopyroxene^ clinopyroxene, plagioclase, titanomagnetite, and ilmenite, with i n t e r s t i t i a l quartz and potassium feldspar. Three K-Ar dates average 21.4±0.7 Ma, and are concordant with a Eb-Sr isochron (22.3±4 Ma with i n i t i a l 8 7 S r / 8 6 S r = 0.70370±0.00008) based on seven whole rock sauries which span the entire compositional range of the suite. These re s u l t s indicate that the Coguihalla Volcanic Complex i s coeval with c a l c - a l k a l i n e centres i n the Pemberton Volcanic Belt. The whole rock compositions of members of the Ccguihalla Volcanic Complex show a range in s i l i c a contents frcm 54 to 76 weight per cent ( v o l a t i l e - f r e e ) . In r e l a t i o n to increasing s i l i c a content, chemical variations within the suite are characterized by enrichment of K 20, Na 20, Eb, and Nb, and depletion i n A l 2 0 3 , T i 0 2 / MgO, MnO, CaO, P2°5» N i, V, and Sr.. The elements Ba, Ce, Nd, and Zr show enrichment throughout most of the su i t e , but depletion i n the most f e l s i c members. Interpretation of chemical variations of whole recks and constituent phenocrysts suggests that the chemical d i v e r s i t y of the suite i s governed by 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 . The r e s u l t s of quantitative major and trace element modelling indicate that 1) hornblende dacites can be derived from basaltic-andesites by 50% c r y s t a l l i z a t i o n of a mixture of plagioclase, hornblende, clinopyroxene, titanomagnetite, and apatite, and 2) rh y o l i t e s can be derived from dacites by roughly 45% c r y s t a l l i z a t i o n of a mixture of plagioclase, hornblende, b i o t i t e , titanomagnetite, and apatite. Basaltic andesite compositions are consistent vith I l l derivation from b a s a l t i c l i q u i d s (modified by o l i v i n e fractionation) that are produced by p a r t i a l melting of hydrous mantle p e r i d o t i t e above the subducted Juan de Fuca plate. i v TABLE OF CONTENTS ABSTEACT i TABLE OF CONTENTS . .... ...................... i v LIST OF TABLES ^ . . . . . . . . . 1 . . •---- v i i TABLE OF FIGDEES AND PLATES ....... v i i i ACKNOWLEDGEMENTS ..... . . ... ... x i Introduction 1 Location And Access .... ................................. . 1 i Previous Work ....................... . i . . . . . . . . . . . . . . . . . . 1 Objectives ............... 3 Eegional Geology . . . . --.,. ............................... 3 Tectonic Setting .................................. 4 Geology of the Coquihalla Volcanic Complex 7 Stratigraphy ..» .. 7 Extrusive Bocks . ....... 7 Intrusive Bocks 12 Breccia Fans and Sheets .............................. 17 Source of Ash Flow Eruptions 20 Structural Belations .<,....«. 21 Alterat i o n ....... ;.... ................ ....... .. -. .. 22 Age . .. . 23 Geological History 24 General Chemistry and Eegional Correlation .............. 26 Tectonic Implications 29 Petrclogy and Geochemistry 32 Petrography .................... i 32 Intrusive Bocks .................................. 32 Extrusive Bocks ....................................... 38 Alteration Assemblages .............................. . 42 Mineral Chemistry „ 44 Pyroxene .-. 44 Hornblende ................................ 48 Plagioclase .......................................... 48 Bi o t i t e ....................... 52 Iron-Titanium Oxides .................................. 52 Discussion 56 Geochemistry 57 C l a s s i f i c a t i o n 57 Comparison with Cascade Calc-alkaline Suites 58 Discussion .................... ... .................... 60 Petrogenesis .................. .... ....... 67 Major Element Model 71 Trace Element Model 77 Discussion E5 Andesite Genesis 87 Conclusions ........... ^ ................................. 89 References 91 Appendix I: Whole-Rock Anal y t i c a l Data ..................... 103 Appendix I I : Representative Mineral Analyses „ . 1 1 0 A: Pyroxene Analyses 111 B: Hornblende Analyses .................................113 C: Plagioclase Analyses 114 D: B i o t i t e Analyses .................................... 115 E: Magnetite Analyses . 116 F: Ilmenite Analyses 117 G: Analyses of Secondary Minerals ........................118 v i Appendix I I I : Compilation of Mineral/Liquid Distribution C o e f f i c i e n t s 119 Appendix IV: Contributions to Laboratory A n a l y t i c a l Techniques 128 A: Operating Conditions For Trace Element Analysis By X-ray Fluorescence Spectrometry ....................... 129 B: Trace Element Reduction Program 111 C: Determination of Total Water and Carbon Dioxide ..... 150 D: Determination of Ferrous Iron 156 Appendix V: Computer Programs 159 A: Mass Absorption Computation ......................... 160 Bi Whole-rock Tabulation Program 162 C: Whole-rock Elot Program 164 D: Mineral Tabulation Program ........................... 167 E: Mineral Plot Program . . 170 v i i LIST OF TABLES Table 1: Potassium-Argon Analytical Data -................. 23 Table 2: Strontium Isotopic Data .......................... 25 Table 3: Representative Modal Analyses 33 Table 4: Major Element Model—Easaltic-andesite to Dacite . 75 Table 5: Major Element Model—Dacite to Ehyolite .............. 76 Table 6: Trace Element Modelling Results 81 Table 7: Operating Conditions for XEF Analysis of Cr-V .....135 Table 8: Operating Conditions for XRF Analysis of Ba .......136 Table 9: Operating Conditions for XEF Analysis of Ni ......137 Table 10: Operating Conditions for XEF Analysis of Nb-Zr-Y-Sr-Eb 138 Table 11: Operating Conditions for XRF Analysis c-f Ce-Nd ..139 Table 12: Concentrations and Mass Absorption C o e f f i -cients for Standard Bocks ...140 v i i i TABLE OF FIGURES AND PLATES Figures Frontispiece: Coquihalla Mountain Figure 1: Location map 2 Figure 2: Tectonic setting of southwestern B r i t i s h Columbia . 5 Figure 3: D i f f e r e n t i a l weathering of flattened tumice ..... 9 Figure 4: Bedding planes in l a p i l l i t u f f s ................. 9 Figure 5: Trough cross-bedding in l a p i l l i t u f f s 11 Figure 6: F y r o c l a s i t i c breccia ............................ 11 Figure 7: Andesite dome . ............................. 14 Figure 8: Radiating columnar joints i n a i d e s i t e dome ...... 14 Figure 9: Hornblende dacite dome .......................... 16 Figure 10: Avalanche breccia composed of Pasayten Group c l a s t s 18 Figure 11: Avalanche breccia north of Coquihalla Mountain . 18 Figure 12: Q'-Ol'-Ne* projection for Coquihalla Volcanic Complex and Pemberton Volcanic Belt rocks .............. 27 Figure 13: AFM diagram for Coquihalla Volcanic Complex and Pemberton Volcanic Belt rocks 28 Figure 14: Sieve-textured plagioclase phenocryst ........... 34 Figure 15: Fiamme structure i n densely-welded t u f f ......... 34 Figure 16: Lithophysae In pneumatolytically a l t e r e d . t u f f s . 40 Figure 17: D e v i t r i f i c a t i o n i n pumice fragment cf v i t r i c t u f f s . . i . . 40 Figure 18: Saussuritized plagioclase phenocryst ........... 43 Figure 19: Formation of s e r i c i t e i n plagioclase phenocryst 43 Figure 20: Vug minerals i n hornblende dacite .............. 45 i x Figure 21: P a r t i a l sphenitization of titanomagnetite phenocryst ......... 46 Figure 22: Formation of sphene and r u t i l e from titano-magnetite phenocryst 46 Figure 23: Triangular An-Ab-Or diagram showing Coguihalla Volcanic Complex feldspar compositions , 49 Figure 24a: Triangular diagram showing normative (An+Ab)-Or-Q compositions of Coguihalla Volcanic Complex whole-rock s .................................................. 51 Figure 24b: Triangular diagram shewing normative Ab-Or-Q compositions of Coguihalla Volcanic Complex whole-rocks 51 Figure 25: Triangular diagram showing compositions of Coguihalla Volcanic Complex titanomagnetites and ilmenites .........................~ 53 Figure 26: Normative plagioclase versus colour index c l a s s i f i c a t i o n diagram 59 Figure 27: Harker diagrams for A l 2 0 3 , FeO, and CaO ........ 61 Figure 28: Harker diagrams f o r HgO, Na20, and K 20 ......... 62 Figure 29: Harker diagrams for T i 0 2 # P2°5» an<* K n 0 63 Figure 30: Harker diagrams for Cr, Ni, Nb, and Y .......... 64 Figure 31: Harker diagrams for V, Zr, Rb, and Sr 65 Figure 32: Harker diagrams for Nd, Ce, and Ba 66 Figure 33: Calculated trace element correlation for p a r t i a l melting and f r a c t i o a n a l c r y s t a l l i z a t i o n processes 70 Figure 34: Correlation between Eb and Nb 72 Figure 35: Correlation of Ce, Nd, Zr, and Ba with Bb Concentration 86 Figure 36: Apparatus for determination of HO and CO 151 X Plates Plate I: Geology of the Coguihalla Volcanic Complex .................^4La.^J6—p-©c]fre.t.), Plate II: Sample L o c a l i t y Map (.back—po'ck'e'f)~""™ Platte I I I : Cross-sections of the Coguihalla Volcanic Complex ................. (ba^te-^tj^reT)"' x i ACKNOWLEDGEMENTS I wish to thank R.L. Armstrong for supervision of a l l stages of t h i s project, providing invaluable help in my f i e l d work, and f o r discussions and suggestions for the improvement of the f i n a l manuscript and maps. I am also grateful to D.J. Whitford for helpful discussions and c r i t i c a l reading of t h i s thesis. In addition, I wish to express my appreciation to Jane leroux for her patient assistance with my f i e l d work, L.C. Pigage for many b e n e f i c i a l discussions and f o r his assistance i n operation of computer programs for reduction of microprobe analyses and petrogenetic modelling, G.T. Nixcn for stimulating discussions and assuming the burden of improving major element a n a l y t i c a l procedures, K. Scott for helping with strontium isotopic measurements, J. Harakal f o r performing argon analyses, and f i n a l l y J. Knight for a s s i s t i n g with operation of the electron microprobe. I am also grateful to E.H- Perkins for making available several sophisticated pl o t t i n g programs. National Research Council of Canada Grant A-8841 to R.L. Armstrong provided funding for t h i s project. 1 Introduction Location and Access The Coquihalla Volcanic Complex l i e s approximately 3 2 km northeast of Hope and 32 km west of Princeton, B r i t i s h Columbia (Figure 1); the centre of the area i s at longitude 121°03' and lat i t u d e 49°32'. Access to most of the area i s via a shepherd's t r a i l (Plate I) that branches from the Jim Kelly Creek logging road, which starts at the mile 14 mark of the Tulameen River Road, southwest of the town of Tulameen. The northwestern portion of the area can be approached from the Coquihalla River road, approximately 35 km northeast of Hope. Previous Work Cairnes (19 24) named and described the rocks comprising the Coquihalla Volcanic Complex.. His map (1:63,360) shows an undifferentiated volcanic series which rests unconformably on a l l surrounding country rocks. He estimated a maximum thickness of 4500 feet (1370 m) for the volcanic rocks, and described them as consisting of widespread p y r o c l a s t i c recks and r h y c l i t e flows, lesser amounts of b a s a l t i c flows, numerous dykes, and a large d i o r i t e intrusion forming the core of Coquihalla Mountain. His interpretation that b a s a l t i c rocks are the oldest members and pyroclastic rocks the youngest members of the complex i s not supported by the present study. On the basis of s t r u c t u r a l evidence, he estimated that the volcanic complex was of Miocene age. 3 Objectives The present investigation was designed as a f i e l d and laboratory study of the Coguihalla Volcanic Complex. The objectives of the study were: 1) to map the rocks comprising the Coguihalla Volcanic Complex, 2) to determine th e i r age using iso t o p i c techniques, 3) to determine t h e i r mineralogical and chemical c h a r a c t e r i s t i c s , 4) to correlate the Coguihalla Volcanic Complex with other volcanic centres, and relate t h i s volcanism to the Cenozoic tectonic s e t t i n g of southwestern B r i t i s h Columbia, and f i n a l l y 5) to determine the genetic relationships between members of the Complex and to evaluate relevant petrogenetic models. Regional Geology The Coguihalla Volcanic Complex occurs i n the northern part of the Cascade Mountains, near the physiographic boundaries with the Coast Mountains on the west and the I n t e r i o r Plateau on the east. This boundary roughly corresponds to the tectonic d i v i s i o n between the Coast Plutonic Complex and the intermcntane Belt. The volcanic complex i s i n contact with the Jurassic-Cretaceous Eagle granodiorite on a l l sides except on the south where i t i s i n contact with the Lower Cretaceous Pasayten Group. The Eagle i s a large pluton of coarse grained, equigranular granodiorite to d i o r i t e with a variably developed northwesterly trending f o l i a t i o n (Monger, 1969). The Pasayten Group unconfprmably overlies the Eagle pluton (Mcnger, 1969), and consists of 8000 feet (2440 m) of non-marine conglomerate, sandstone, and p e l i t e (Cairnes, 1924). 4 East of the mapped area the Eagle pluton intrudes Upper T r i a s s i c greenstones of the Nicola Group, composed of altered submarine flows and flow breccias, with intercalated shales and limestones- Mafic to intermediate rocks are more abundant than rh y o l i t e and chemical data for Nicola volcanics indicate that both alkaline and sub-alkaline members are present (Souther, 1977} . The western boundary of the Eagle plutcn i s formed by the Pasayten Fault, along which considerable v e r t i c a l and right l a t e r a l movement i s i n f e r r e d (Coates, 1974). The f a u l t appears to have been inactive since mid-Cretaceous time (Staatz et a l . , 1971). C l a s t i c rocks of the Lower Cretaceous Jackass Mountain Group are i n contact with the Eagle pluton along this f a u l t , but elsewhere l i e unconformably on the Eagle pluton (Coates, 1974). On the west side of the Coquihalla Eiver, g r a n i t i c and granodioritic rocks of the Oligocene Needle Peak Pluton intrude the Eagle and Jackass Mountain Group rocks. Tectonic Setting The present tectonic setting of southwestern B r i t i s h Columbia and the geographic and temporal d i s t r i b u t i o n of late Cenozoic volcanic centres i s depicted i n Figure 2. North of la t i t u d e 50°N, the r i g h t l a t e r a l Queen Charlotte Fault separates the North American plate from the P a c i f i c plate; south of 50°N, a subduction zone forms the boundary between the North American plate and the Juan de Fuca plate. This subducticn zone appears to be presently active on the basis of evidence reviewed by Eiddihough and Hyndman (1976). The Juan de Fuca-Pacific plate F I G U R E 2: P r e s e n t p l a t e t e c t o n i c s e t t i n g o f s o u t h w e s t e r n B r i t i s h C o l u m b i a , s h o w i n g e x t e n t o f P e m b e r t o n V o l c a n i c B e l t ( s q u a r e s ) , G a r i b a l d i V o l c a n i c B e l t ( t r i a n g l e s ) , A n a h i m V o l c a n i c B e l t ( c i r c l e s ) , A l e r t B a y V o l c a n i c B e l t ( s t a r s ) , a n d o l d e s t K - A r a g e s i n Ma. S t i p l e d a r e a s h o w s t h e e x t e n t o f M i o c e n e p l a t e a u l a v a s ( S o u t h e r , 1 9 7 7 ) . 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 de F u c a p l a t e , N A P - N o r t h A m e r i c a n p l a t e , B P - b r o o k s P e n i n s u l a , 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 , S f z - S o v a n c o f r a c t u r e z o n e . D o t t e d l i n e i s p o s s i b l e E P - J d F P b o u n d a r y . 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 j ^ L . , 1 9 7 9 . 6 boundary i s a spreading ridge system (Barr and Chase, 1974) . Subduction of the Juan de Fuca plate beneath North America has produced arc and back-arc volcanism (Souther, 1977) „ Calc-alkaline volcanism i s observable as the Pleistocene to Becent Garibaldi Volcanic Belt and the Miocene Pembertcn Volcanic B e l t . Alkaline Miocene and younger plateau and valley lavas occur i n a t y p i c a l back-arc setting. 7 Geology of the Coquihalla Volcanic Complex Stratigraphy The Coquihalla Volcanic Complex covers approximately 30 square km, and i s exposed at elevations between 840 and 2160 m (2750-7100 f e e t ) . Outcrop i s excellent above 1500-1700 m; below t h i s l e v e l , dense vegetation makes detailed mapping impossible. Mapping was done on 1:15000 a e r i a l photographs, and the f i n a l map was compiled on a 1:15000 enlargement of National Topographic Series Map No. 92H/11. The geology of the Coguihalla Volcanic Complex i s presented in.Pla^e I. The Coquihalla Volcanic Complex consists of acid to intermediate extrusive and intrusive rocks which l i e unccnformably on, and i n f a u l t contact with, Eagle granodiorite and Pasayten Group rocks. F i e l d work was confined to mapping the volcanic rocks up to the contacts with surrounding rocks; a l l contacts on Plate I that separate pre-Miocene rocks are taken from Cairnes (1924) and Monger (1969) r Igneous rocks have been divided into eight map units based on mineralogical and textural properties. Avalanche breccias and minor amounts of e p i c l a s t i c conglomerate and sandstone are also present. Extrusive Rocks Tuffaceous p y r o c l a s t i c rocks represent the oldest members of the complex. A l l display v i t r o c l a s t i c textures, are of r h y o l i t i c composition, and contain phenocrysts of plagioclase, b i o t i t e , quartz, and minor potassium feldspar and magnetite. 8 Textural variations allow their subdivision i n t o three map units, which, with l o c a l exceptions, are conformable with stratigraphic horizons. Contacts between these subdivisions are generally gradational. The terminology used i n the following f i e l d descriptions i s consistent with that of Smith (1960a; 1960b), Fisher (1966), and Gary, et a l . (1972) . Moderately- to densely-welded, l i t h i c - c r y s t a l l a p i l l i t u f f s (Mtl) comprise the oldest p y r o c l a s t i c unit, and have a t o t a l thickness of roughly 550 m (1800 f e e t ) . These rocks generally form massive, l i t t l e - f r a c t u r e d outcrops more resistant to weathering than other p y r o c l a s t i c units, and range i n colour from l i g h t grey to l i g h t brownish grey; darker colours are correlated with greater degrees of welding. They are composed of 20^50% g r a n i t i c xenoliths, l e s s than 5% mudstone c l a s t s , 10-15% pumice fragments, and 15-30% phenocrysts set in v i t r o c l a s t i c matrices that show pronounced development of coarse-granular (0.05-0.13 mm) d e v i t r i f i c a t i o n products. Xenoliths average 1-2 cm i n size but occasionally are up to 15 cm; pumice fragments up to 4 cm i n length are not uncommon. F o l i a t i o n i s well displayed by the alignment of flattened pumice fragments which in many places are d i f f e r e n t i a l l y weathered out of the rock matrix (Figure 3). Vapour phase c r y s t a l l i z a t i o n of a l k a l i feldspar and guartz i s common within t h i s unit and a d i s t i n c t i v e pneumatolytic a l t e r a t i o n zone i s shown on Plate I. Moderately-welded to densely-welded v i t r i c t u f f s (Mtv) crop out on the two ridges above the Coguihalla River Valley, and have a t o t a l thickness of roughly 120 m (400 f e e t ) . Densely-F I G U R E 3: D i f f e r e n t i a l w e a t h e r i n g o f f l a t t e n e d p u m i c e f r a g m e n t s i n m o d e r a t e l y - w e l d e d t u f f . F I G U R E 4 : M o d e r a t e l y - w e l d e d l a p i l l i t u f f . F r a c t u r e s a r e p a r a l l e l t o b e d d i n g . 10 welded v a r i e t i e s are grey to dark grey i n colour, while moderately-welded v a r i e t i e s are grey to pinkish grey- These rocks are characterized by less than 5% g r a n i t i c xenoliths and 5-15% phenocrysts i n v i t r i c matrices composed of d e v i t r i f i e d ash and pumice fragments up to 4 cm i n length. Minor interbedded rheoignimbrites display prominent flow banding and contain pumice fragments up to 3 cm i n size-Non-welded to moderately-welded c r y s t a l - l i t h i e l a p i l l i t u f f s (Mt), approximately 915 m (3000 feet) th i c k , represent the youngest pyroclastic unit. They display mottled appearances with xenoliths, feldspar, quartz, and b i o t i t e phenocrysts set i n l i g h t greenish grey ash matrices. These rocks commonly weather along bedding planes into i r r e g u l a r planar sheets (Figure 4) . This unit i s composed of 10-30% plutonic quartz and feldspar xenocrysts and xenoliths of predominantly g r a n i t i c composition ranging i n size up to 20 cm; phenocrysts comprise 15-40% of these rocks. Matrices consist of variably d e v i t r i f i e d glass shards and pumice fragments which show only s l i g h t deformation and f l a t t e n i n g . Well-sorted, f i n e grained ash f a l l t u f f forms t h i n , discontinuous lenses near the top of t h i s unit. Several outcrops display trough cross bedding (Figure 5) i n structures approximately 3 m wide. These structures appear to be related to scouring and deposition by successive surges of ash-laden gas. Interpretation of lamination di r e c t i o n s suggests a source f o r these deposits which was located just north of Coquihalla Mountain. Throughout the entire ash flow succession, there.is a conspicuous absence of features suggestive of cooling breaks F I G U R E 6: P y r o c l a s t i c b r e c c i a w i t h s m a l l , a n g u l a r c l a s t s a n d l a r g e , r o u n d e d c l a s t s . 12 between i n d i v i d u a l ash flows; possible exceptions are the occurrence of several topographic steps within the oldest pyroclastic unit, which probably r e f l e c t varying degrees of welding. The lack of any regular bedding within a 300 m section of this unit exposed above the Coquihalla Eiver Valley i s consistent with descriptions of intracaldera ash flows (Elston et a l . , 1976) . A discontinuous explosion breccia (Mvbr) crops out at an elevation of approximately 1830 m (6000 f e e t ) , and i s best exposed on the divide-forming ridge (Figure 6). This unit ranges from 15-45 m (50-100 feet) i n thickness, and i s composed of 75-80% g r a n i t i c c l a s t s set i n a coarse g r i t matrix of angular quartz and feldspar c r y s t a l s and a small amount of v i t r o c l a s t i c material. Clast sizes average 5-10 cm but c l a s t s up to 30 cm are common; most are highly angular although larger sizes tend tc be rounded. Bedding within t h i s unit i s defined by sharp changes i n proportions of c l a s t s and matrix i n adjacent layers. In several places t h i s breccia l i e s above a thin (up to 20 cm) sandstone (Ms), which suggests that i t represents the product of a vent clearing eruption a f t e r a short i n t e r v a l of volcanic quiescence. Intrusive Rocks Flow-banded r h y o l i t e (Mr) at the base of Coquihalla Mountain consists of phenocrysts and xenocrysts of quartz and feldspar i n a cr y p t o c r y s t a l l i n e matrix. Steep inward-dipping flow banding on the north side of Coquihalla Mountain, and almost horizontal flow banding on the east side, suggests that t h i s unit represents the remnant of a r h y o l i t e dome that was 13 l a t e r intruded by the Coguihalla Mountain d i o r i t e stock-One other intrusive rhyolite (Mr) occurs near the northernmost boundary of the area- I t i s characterized by a fresh glassy matrix with up to 15% g r a n i t i c xenoliths, and phenocrysts of feldspar, b i o t i t e , and quartz. Igneous rocks of intermediate-mafic composition crcp oct at elevations above 1650 m (5400 f e e t ) . Although columnar j o i n t i n g i n one dacite unit i s suggestive of the colonnade and entatlature c h a r a c t e r i s t i c of extrusive lavas, no features i n d i c a t i v e of flow tops or bottoms have been found. For t h i s reason, a l l intermediate-mafic rocks are considered to be i n t r u s i v e . Pyroxene (Map) and hornblende (Mah) andesites form dykes, s i l l s , and domes which are greatly more resistant to erosion than surrounding p y r o c l a s t i c rocks. These rocks are dark greenish grey to greyish black, and are a l l characterized by porphyritic textures, while matrices range frcff h o l c c r y s t a l l i n e to aphanitic. Phenocrysts are plagioclase, pyroxene, hornblende, and magnetite. Dykes are commonly 5-10 m thick, pinch and swell along s t r i k e , and have steep contacts with 60-85° dips- Columnar j o i n t s perpendicular to contacts are commonly well developed, and flow banding defined by the alignment of feldspar and mafic phenocrysts i s p a r a l l e l to contacts. Andesite domes up to 0.5 km i n diameter are invariably surrounded by large talus aprons (Figure 7 ) , and show well developed columnar j o i n t i n g that forms ra d i a t i n g patterns near contacts with surrounding rocks (Figure 8 ) . Heterogeneity within 14 F I G U R E 7: H o r n b l e n d e a n d e s i t e dome e x p o s e d o n r i d g e n o r t h e a s t o f C o q u i h a l l a M o u n t a i n . D i a m e t e r o f dome i s a p p r o x i m a t e l y 0.35 km. F I G U R E 8: R a d i a t i n g c o l u m n a r j o i n t s i n h o r n b l e n d e a n d e s i t e dome s h o w n i n F i g . 7. 1 5 i i n d i v i d u a l domes i s reflected by contrasts i n phenocryst proportions and chemical composition. Although these variations are usually s l i g h t and unrelated to regular zonation, the large dome east of Coguihalla Mountain i s unique in that i t s core i s composed of h o l o c r y s t a l l i n e pyroxene andesite whereas the r e s t of the dome consists of more f e l s i c , fine grained hornblende andesite. Hornblende dacite (Md) i s much less abundant than andesite, and occurs as dykes and domes (Figure 9 ) . These rocks are l i g h t grey to greenish-grey i n hand specimen, are porphyritic, and contain phenocrysts of plagioclase, hornblende, magnetite, and occasionally apatite. A d i o r i t e to guartz d i o r i t e stock (Mcq) forms the core of Coquihalla Mountain (frontispiece) and crosscuts an e a r l i e r r h y o l i t e dome and andesite dyke. The stock i s coarse grained and composed of plagioclase, two pyroxenes, iron-titanium oxides, and lesser amounts of i n t e r s t i t i a l quartz and potassium feldspar. Zonation within the intrusion i s pronounced, especially in the southern portion of the body, where the i n t r u s i v e rock grades from guartz d i o r i t e at the contact to d i o r i t e near the peak of Coguihalla Mountain. The most mafic portion of the intrusion l i e s on the north side of Coquihalla Mountain. Flow banding near the contacts of the stock dip steeply inward and generally p a r a l l e l the orientation of major fractures within the d i o r i t e . Relative ages of the i n t r u s i v e rocks of the Coguihalla Volcanic Complex are d i f f i c u l t to ascertain because of the general lack of crosscutting r e l a t i o n s . Coquihalla Mountain F I G U R E 9: H o r n b l e n d e d a c i t e dome, o f dome i s a p p r o x i m a t e l y 0.75 km. D i a m e t e r 1 7 stock probably represents a l a t e stage intrusion as i t cuts an andesite dyke s i m i l a r to other large andesite intrusives i n the area, although several th i n andesite dykes crosscut the northern portion of the stock. In comparison to andesite domes, the coarser grain size of the stock suggests that i t c r y s t a l l i z e d at a l a t e r time, under a thicker accumulation of py r o c l a s t i c rocks. The i r r e g u l a r , d u c t i l y deformed contacts of the pyroxene andesite dyke which cuts the northern part of the stock indicate that this dyke was intruded before the stock had completely s o l i d i f i e d . Breccia Fans and Sheets Contacts of the volcanic rocks with surrounding rocks along the southern and southeastern boundaries are characterized by the presence of f a u l t s marked by the occurrence of d i s t i n c t i v e monolithologic avalanche breccias (Mbr). To the southwest, volcanic rocks contact Pasayten Group sediments along a f a u l t (Jim Kelly Creek fault) that dips northeast at approximately 85°; p r e f e r e n t i a l erosion of py r o c l a s t i c rocks along t h i s f a u l t has produced a steep scarp above Unknown Creek.. V e r t i c a l displacement i s unknown and the rel a t i o n s h i p of th i s f a u l t with the Pasayten Fault i n the Coquihalla River Valley has not been investigated. A d i s t i n c t i v e , ledge-forming breccia appears to have formed through large scale avalanching from the u p l i f t e d block southwest of the f a u l t . The breccia i s characterized by pccrly sorted, angular c l a s t s of Pasayten sediments up to 2 m in s i z e , set i n a matrix of clay and fine grained shale c l a s t s (Figure F I G U R E 10: A v a l a n c h e P a s a y t e n G r o u p c l a s t s W i d t h o f p h o t o g r a p h i s b r e c c i a c o m p o s e d o f up t o 1 m e t r e a c r o s s , a p p r o x i m a t e l y 5 m e t r e s . F I G U R E 11 : P a s a y t . e n a v a l a n c h e b r e c c i a f o r m i n g p r o m i n e n t l e d g e o n t h e n o r t h s i d e o f C o q u i h a l l a M o u n t a i n . L e d g e i s r o u g h l y 30 m e t r e s t h i c k . 19 10). Granitic rocks are less than 5% of the c l a s t s i n t h i s unit. This breccia sheet i s approximately 30 m thick, crops out on the north (Figure 11) and southwest sides of Coquihalla Mountain, and i s cut by l a t e r andesitic dykes and Coquihalla Mountain stock. It appears to thin and pinch out north of Coquihalla Mountain. The absence of thi s unit on the northwest side of Coquihalla Mountain suggests that a topographic high, near the present s i t e of the mountain, may have existed at the time of deposition. This topographic high may be related to the vent area of the ash flow t u f f s . The occurrence of a 10 m thick sandstone and conglomerate lens at the same elevation but farther to the northwest, implies that deposition of t h i s breccia took place during an hiatus i n volcanic eruptions. A small breccia fan i s exposed i n cross section at an elevation of 1800 m (5900 feet) just north of the Jim Kelly Creek f a u l t trace on the ridge southwest of Coquihalla Mountain. This outcrop i s l i t h o l o g i c a l l y s i m i l a r to that described above, but generally displays a more heterogenous mixture of fin e and coarse grained sedimentary rock c l a s t s . Thin c l a s t i c dykes consisting of sand cut the breccia, and probably formed as a re s u l t of the entrapment of f l u i d - r i c h sediments beneath the rapidly deposited breccia. At the top of the ridge the f a u l t i s buried by ash flows, which appear to have f i l l e d and overflowed the fault-bounded basin, and now res t unconformably on Pasayten Group rocks. A s i m i l a r Pasayten c l a s t breccia occurs east of the divide on the north side of Jim Kelly Creek. Alignment of occasional r e c t i l i n e a r andesite c l a s t s within t h i s unit suggests 20 northwesterly dips of 20-25 degrees. This breccia grades l a t e r a l l y to the north and s t r a t i g r a p h i c a l l y upwards into a breccia characterized by the dominance of Eagle granodiorite c l a s t s over Pasayten c l a s t s . The formation of t h i s breccia i s related to l o c a l i z e d t i l t i n g of the underlying Eagle granodiorite so that the unconformity i s rotated from t y p i c a l 25-30°, up to 700 westward dips. This . unit i s s i m i l a r to monolithologic breccias described by Lambert (1974) at Bennett Lake, B.C., and consists of angular c l a s t s up to 30 cm i n size set in a coarse-grit matrix of fragmented quartz and feldspar grains with minor clay material. Bedding i s t y p i c a l l y absent, but i n several areas, rough alignment of c l a s t s and large scale l i t h o l o g i c layering indicate dips up to 70° west. Occasional blocks of Eagle up to 20 m across occur with l i t t l e intervening matrix. Pyroclastic rocks that dip approximately 45° west unconformably o v e r l i e the western boundary of t h i s breccia. The implication of these overlapping relationships of breccias, pyroclastic rocks, and f a u l t s i s that basin subsidence was rapid, and contemporaneous with f a u l t i n g , t i l t i n g of the basal unconformity, and b a s i n - f i l l i n g volcanism. Source of Ash Flow Eruptions F i e l d r e lations i n the Coquihalla Volcanic Complex are s i m i l a r to those described i n "trap-door" type cauldrons, but there i s no evidence for ash flow eruption along the basin-bounding f a u l t . S i m i l a r i t y of Coquihalla ash flew seguences with intracaldera ash flows (Elston et a l ^ , 1976) i s interpreted as ind i c a t i n g close proximity to the source area and confinement of 21 ash flows within a basin formed i n part by subsidence along f a u l t s i n the southern part of the map area. The lack of sorting and large c l a s t size in the pyroclastic breccia north and east of Coguihalla Mountain support the i n t e r p r e t a t i o n that associated ash flows are near the source of eruptions. The r e l a t i v e l y small volume of ash flow material preserved in the Coguihalla Volcanic Complex (50 km3) suggests that the source for these eruptions was a central vent (Smith, 1960a). Although a source vent was not i d e n t i f i e d i n the f i e l d , several l i n e s of reasoning indicate that i t may have been located near the present-day s i t e of Coguihalla Mountain. The absence of the Pasayten-clast avalanche breccia unit on the northwest side of Coquihalla Mountain.suggests that a topographic high, possibly a source vent, was present at the time of breccia deposition. The pinching out of a d i s t i n c t i v e ledge-forming ash flow sheet to the northwest, and the location of v i t r i c t u f f units only on ridges west of Coquihalla Mountain, are both consistent with a source area located near Coquihalla Mountain, and cross-bedding i n ash flow deposits also indicates a s i m i l a r source location. The late-stage i n t r u s i o n of the Coquihalla Mountain stock might have been guided by preexisting fracture and conduit systems related to the vent area formed during e a r l i e r pyroclastic eruptions. Structural Relations Except i n the southern part of the map area, p y r o c l a s t i c rocks rest nonconformably on the Eagle granodiorite. Contacts along the eastern side of the area dip gently to the west at 2 2 angles less than 30°; along the north and west sides of the area, contacts dip inward at steeper angles up to 45°. Deformation of rocks within the Coquihalla Volcanic Complex i s s l i g h t i n comparison to that i n surrounding recks of the map area. Bedding s t r i k e s conform to the regional north-northwest trend and dips range up to 45°, but rarely exceed 30°. Bedding attitudes within pyroclastic rocks are l o c a l l y quite variable, r e f l e c t i n g the influence of o r i g i n a l topography on ash flow deposition. On a larger scale, bedding attitudes define two folds with northerly-trending axes (Plate I ) . a l t e r a t i o n Alteration of members of the Coquihalla Volcanic Complex i s quite variable and i s predominantly fracture controlled. High concentrations of secondary i r o n , v i s i b l e as brownish s t a i n s , occur around dykes on the north side of Coquihalla Mountain, and along the Jim Kelly Creek f a u l t trace separating volcanic from Pasayten Group rocks. A l t e r a t i o n of andesites and dacites most commonly involves the variable s a u s s u r i t i z a t i c n of plagioclase phenocrysts, c h l o r i t i z a t i o n of mafic phenocrysts, and the development of c a l c i t e and s e r i c i t e i n matrices. The degree of a l t e r a t i o n can range from negligible to pronounced over a distance of several metres. Alteration i s most evident i n areas characterized by multiple crosscutting i n t r u s i v e relations. Alte r a t i o n of pyroclastic rocks consists predominantly i n iron oxide coatings on matrix material, occasional a l b i t i z a t i o n of feldspar phenocrysts, and i r o n leaching leading to the formation of green b i o t i t e . 23 TABLE Potassium-Argon A n a l y t i c a l Data No". 1 Rock type Analysi s % K 2 4 0 A r * 3 l£Ar* Age {Ma) 4 *°Ar (total) 318 d i o r i t e 164 hb dacite 173 v i t r i c t u f f whole rock 1.89±.01 1. 676 0.560 22. 7±0. 8 hornblende 0.348±.002 0.272 0.197 20.0±0.9 b i o t i t e 5.70±.015 4.780 0.463 21.4±0.7 1 Sample l o c a l i t i e s : 318 (49°32 ,N /121°03 ,W), 164 (49°33'N,121 o03'W), 173 (49°34 ,N,121004'W) 2 Potassium analyses by K. Scott by atomic absorption; errors are deviation from mean value of duplicate analyses 3 Argon analyses by J. Harakal using MS10 mass spectrometer; Ar* refers to radiogenic argon; a l l values x 10 - 6 cm 3 g _ l S1E * Constants used i n c a l c u l a t i o n (Steiger and Jager, 1977): *£= 5.81 x 10-io/yr x «= 4. 962 x 10-»°/yr * O K / K = 1.167 x 10-2 atom?S errors are one standard deviation Age The sample locations of rocks used for i s o t c p i c determinations are shown in Plate I I . Results of three potassium-argon determinations are presented i n Table 1. The three samples give the same age within the estimated error of the technique. The average age of the three samples i s 21.4±0.7 Ma. Strontium i s o t o p i c compositions were determined f c r seven whole rock samples that span the compositional range d i o r i t e -andesite-dacite-rhyolite. Results are presented i n Table I I . An isochron can be f i t within the a n a l y t i c a l error of a l l points, 24 and t h i s gives an age of 22.4±0.6 Ma, with an i n i t i a l 8 7 S r / 8 6 S r ra t i o of 0.7037. Ages determined from both isotopic systems are i n good agreement and indicate that the Coguihalla Volcanic Complex i s of early Miocene age. Geological History Three cross sections are presented i n plate I I I , which offer a visual summary of s t r u c t u r a l r e l a t i o n s and i n t r t s i v e body shapes. Eruption of voluminous ash flows on a pre-Miocene e r c s i c n a l surface may have been i n i t i a t e d by tensicnal forces causing movement along the southern boundary f a u l t , or ac t i v a t i o n of th i s f a u l t may have taken place i n response to emptying of a shallow magma chamber by early ash flow eruptions. Accumulation of p y r o c l a s t i c rocks was greatest along t h i s f a u l t i n the southwestern part of the area, and the weight of p y r o c l a s t i c rocks may have accelerated t i l t i n g of the Eagle granodiorite unconformity that forms the southeastern boundary of the area. Concomitant with f a u l t i n g , t i l t i n g , and subsidence, avalanche breccias p e r i o d i c a l l y formed on oyersteepened exposures of Pasayten and Eagle rocks." After the accumulation of nearly a thousand metres of p y r o c l a s t i c material, a period of volcanic guiescence ensued, during which l o c a l i z e d , conglomerate and sandstone, and the large sheet of Pasayten breccia were deposited. Ash flow eruptions then resumed u n t i l another short break i n volcanic a c t i v i t y , marked by the occurrence of thin sandstone lenses. Then vent clearing eruptions produced the 25 TABLE 2j_ Strontium Isotopic Data No- i S i 0 2 2 Rb2 S r 2 Rb/Sr? 3 7 S r / 8 6 S r * 251 54.2 20.. 5 578 0.-03 5±1.0% 0.7036+0.00014 318 57. 1 55.3 489 C. 113±0.5% C.7039±0-00012 192 67. 0 62. 2 490 0. 127±0. 1% 0.7039±0.C0014 240 67.0 81.4 369 0. 221±0.9% 0. 7039±0. 00015. 319 71.8 87.8 184 0. 478±0.9% 0.7041±0.GC017 173 73.8 83. 8 120 0. 700±0-6% 0.7044+0.00015 712 77. 1 91.8 95.3 0. 964±0.7% 0.7046±O.OCC09 Calculated Isochron Date 5 22.3 ± 4Ma with i n i t i a l 8 7 S R / 8 6 S R = 0.70370 ± 0.00008 Sample l o c a l i t i e s : 251 (49°32'N, 121°03'W) , 318 (49°32 IN,121°03 ,W) , 192 (49 0 3 3 ' N, 121002' W) , 240 (49° 33' N, 12 1° 03 * W) , 319(49° 32'N,121°03' W) 1 7 3 ( 4 9 0 34'N, 121004"W) , 712(49°34'N #121°04'W) SiO 2/ Eb, and Sr determined by X-ray fluorescence; S i 0 2 i n wt. %, v o l a t i l e - f r e e ; Rb, Sr i n parts per m i l l i o n Errors represent deviations from mean of r e p l i c a t e analyses of Rb and Sr Sr r a t i o s normalized to a value of 0.71022 f o r NES Standard Sr 987 Errors i n measured 8 7 S r / 8 6 S r are one sigma Isochron calculated using computer program described by Mclntyre et a l . (1966), using A= 1.42 x l O - ^ V y r p y r o c l a s t i c breccia on the ridge north and east of Coguihalla 26 Mountain. Movement along the Jim Kelly Creek f a u l t ceased, and subsequent ash flows f i l l e d and overflowed that edge of the basin. F i n a l l y numerous andesite and dacite hypalyssal i n t r u s i v e s were emplaced. Coguihalla Mountain stock i s probably related to a f i n a l d i a p i r i c r i s e of fresh magma which c r y s t a l l i z e d under the blanket of previously-formed volcanic rocks. A few steeply dipping dykes postdate the stock. C i r c u l a t i o n of f l u i d s along fractures concentrated around intr u s i v e contacts produced lo c a l i z e d low-grade a l t e r a t i o n . . Post-Miocene u p l i f t t i l t e d and warped the volcanic rocks. Erosion removed what may have been extensive volcanic cover from the surrounding area, and uncovered the d i o r i t e stock of Coquihalla Mountain. General Chemistry and Regional Correlation Twenty-six whole-rock analyses were performed by X-ray fluorescence spectrometry. A n a l y t i c a l techniques and r e s u l t s are presented i n Appendix I. Figure 12 i s a normative Q'-Ol'-Ne' diagram which shows that a l l rocks are d i s t i n c t l y subalkaline according to the c l a s s i f i c a t i o n scheme of Irvine and Baragar (1971). The trend of whole-rock analyses on an AFM diagram (Figure 13) i s c l e a r l y calc-alJtaline, and the rocks plot i n the f i e l d of orogenic volcanics on an Mg0-Al203-FeO diagram (Pearce et a l . , 1977). Also plotted in Figures 13 and 14 are available analyses of rocks which form the Pemberton Volcanic Belt (Figure 2). Analyses of the Chilliwack Batholith, Mt. Barr b a t h o l i t h , and 01 01 ,0px vOpx / / \ N / / / A \ / v ' ' / c v + \ \  + \ \ + \. \ t ++- + \ Ne 1 Ab F I G U R E 1 2 : . O l ' - N e ' - Q ' b a s a l t r i a n g l e o f t h e C p x - 0 1 - N e - Q t e t r a h e d r o n , p r o j e c t e d f r o m C p x . The h e a v y l i n e s s e p a r a t e t h e f i e l d s o f a l k a l i n e a n d s u b a l k a l i n e r o c k s ( I r v i n e a n d B a r a g a r , 1 9 7 1 ) . S y m b o l s :-:+ - C o q u i h a l l a V o l c a n i c C o m p l e x , o t h e r s y m b o l s f o r t h e P e m b e r t o n V o l c a n i c B e l t : Q - Mt B a t h o l i t h , A ~ C h i l l i w a c k B a t h o l i t h , Q' X - W i l l i a m s B a r r P e a k S t o c k , F F A M F I G U R E 1 3 : AFM d i a g r a m w i t h c u r v e s e p a r a t i n g t h e f i e l d s o f t h o l e i i t i c a n d c a l c - a l k a l . l n e r o c k s ( I r v i n e a n d B a r a g a r , 1 9 7 1 ) . A = Na 0 + K 0, F = FeO + 0 . 89 9,8 F e ^ , M=MgO, a l l i n w e i g h t p e r c e n t . S y m b o l s a s i n F i g . 1 2 . tS3 0 0 29 Williams Peak Stock (from Richards, 1971) c l e a r l y plot i n the same f i e l d as rocks of the Coquihalla Volcanic Complex. This s i m i l a r i t y i n chemistry and age warrants consideration of the Coquihalla Volcanic Complex as a member of the Pemberton Volcanic Belt, and suggests that the Coquihalla Volcanic Complex represents the hypabyssal and volcanic equivalent of the plutons that comprise the southern portion of the Pemberton Volcanic Belt.. The apparent differences appear to be related to depth of erosion. Tectonic Implications In recent years, the association of c a l c - a l k a l i n e suites with areas of subduction along continental margins and i s l a n d arcs has been c l e a r l y demonstrated (cf. Wyllie, 1973) . In B r i t i s h Columbia, subduction of the Juan de Fuca plate and Explorer subplate has given r i s e to the 2 Ma to present Garibaldi Volcanic Belt (Green, 1977; Bevier et a l . , 1979), and Souther (1977) has suggested that the ori g i n of the Pemberton Volcanic Belt i s s i m i l a r l y related to Juan de Fuca plate subduction i n the Miocene. The trend of both volcanic b e l t s i s roughly p a r a l l e l , with the Pemberton Belt l y i n g approximately 75 km east of the Garibaldi Belt. This displacement of the Garibaldi Belt to the west could be accounted for by: 1) greater subduction rates during the Miocene with associated depression of isotherms along the subducted slab, resulting i n magma genesis at greater depths further from the active trench, 30 2) decrease in the width of the Juan de Fuca plate from Miocene to the present, so that Miocene subduction involved a cooler oceanic plate and consequent greater isotherm depression as above, or 3) accretion of sediments and/or oceanic crust onto the trench wall, sc that the position of the active trench s h i f t e d west with time (Dickinson, 1973). The observed greater K2<D contents of members of the Coguihalla Volcanic Complex as compared with rocks of the Garibaldi Volcanic Belt lend support to either Of the f i r s t two models (Hatherton and Dickinson, 1969). Calculations of Juan de Fuca plate spreading rates based on magnetic anomalies west of the Juan de Fuca ridge (Pitman III et a l . , 1S74) , indicate an average spreading rate (half-rate) of 3.2 cu per year for the period from 32-9.5 Ma. Comparison with calculations of Riddihough (1977) indicates that t h i s rate i s s l i g h t l y less than spreading rates from 9.5-4.5 Ma, and equal to or s l i g h t l y greater than spreading rates from 4.5 Ma to the present. It appears, then, that spreading rates of the Juan de Fuca ridge were not s i g n i f i c a n t l y d i f f e r e n t i n the Miocene, but models 1 and 2 are also c r i t i c a l l y dependent on Pacific-North American plate interactions over the time period i n guestion. Riddihough (1977) assumed constant r e l a t i v e motion f o r the l a s t 10 m i l l i o n years i n his modelling of plate interactions i n southwestern B.C., and calc u l a t i o n s based on global tectonic models appear to indicate that present directions of motion are applicable for the l a s t 20 mi l l i o n years (Minster et a l . , 1S74; Clague and Jarrard, 1973).. From studies on the Gulf of 31 C a l i f o r n i a , however, Larson (1972) i n f e r r e d that North American-Pacific plate i n t e r a c t i o n involved a 20° more westerly component pr i o r to 10 Ma. Unt i l such discrepancies are resolved, c a l c u l a t i o n s of North America-Pacific plate, and hence Juan de Fuca-North America plate interactions remain highly speculative f o r the time period from Miocene to the present-32 Petrology and Geochemistry Petrography The following descriptions summarize the petrographic features of rocks of the Coquihalla Volcanic Complex, and are based on a study of more than 150 thin sections. Representative modal analyses are presented in Table 3. Intrusive Rocks Pyroxene andesites are characterized by porphyritic textures with phenocrysts of plagioclase, clincpyroxene, and magnetite representing 35-60% of the rocks. Matrices are composed of fine grained aggregates of plagioclase l a t h s , anhedral clinopyroxene and magnetite, and glass. One andesite which forms the core of a large dome has a h o l o c r y s t a l l i n e matrix of the same mineralogy, with a d d i t i o n a l minor amounts of i n t e r s t i t i a l quartz and potassium feldspar. Plagioclase comprises between 45-65% of the phenocryst mode, and ranges i n siz e up to 3 mm. Most grains are subhedral to euhedral, contain inclusions of magnetite and minor apatite, and show pronounced compositional zonation. Normal zcning ranging from An 76 to An 35 i s most prevalent; o s c i l l a t o r y zoning, when present, i s confined to the outer sections of cr y s t a l s and probably r e f l e c t s fluctuations i n water pressure during the l a t t e r stages of phenocryst growth- Many phenocrysts display sieve textures s i m i l a r to those reported by Wise (1969) and Green (1977), in which ovoid cores riddled with glass •33 TABLE 3:. Represent ative Modal Analyses cf Coquihalla Volcanic Complex Igneous Rocks Phenocrysts No. Rock Type PI Cpx Opx Hb Bi Mt Q Ksp Ap Gndms 632 . d i o r i t e 62. 9 7.6 18. o - — 5.8 3.0 3.0 — — 251 prx andesite 6 1. 8 29. 3 - - 8.8 - - - 43. 1 61 prx andesite 55. 5 36. 1 - - - 8. 4 - - - 60. 9 252 hb andesite 6 1. 9 22.6 - 5.5 - 10.0 - - - 60. 0 4 hb andesite 64. 2 22. 3 - 4.3 - 13. 1 - 0. 9 56. 9 283 hb cacite 52. 9 8.0 35.8 - 11.3 - - 0. 4 60.7 192 hb dacite 65. 3 - - 23.5 - 10.1 - - 1. 2 67. 2 173 v i t r i c tuff 83. 6 — - - 15. 1 1.4 - - - 93- 0 712 v i t r i c t u f f 76. 1 - - 2.2 4.3 4.4 13. 0 - - 9 4. 2 Modal analyses based on over 600 points counted Phenocryst modes recalculated to 100% inclusions are enclosed by c l e a r , generally euhedral rims (Figure 14). Resorption zones are interpreted as forming through decreases in li g u i d u s temperatures related to pressure drops (Vance, 1S65) ; short i n t e r v a l s of c r y s t a l l i z a t i o n then followed prior to eruption. Plagioclase microphenocrysts shew l i t t l e zonation, and t h e i r compositions range from An 75 to An 35. Clinopyroxene represents 25-40% of the phenccryst mode of pyroxene andesites. Crystals have an average s i z e of 0.25 mm, but range up to 3 mm in length. Phenocrysts generally display a 34 F I G U R E 14: S i e v e - t e x t u r e d p l a g i o c l a s e p h e n o c r y s t i n p y r o x e n e a n d e s i t e . I n c l u s i o n s a r e g l a s s , c l i n o -p y r o x e n e , a n d t i t a n o m a g n e t i t e . N o t e i n c l u s i o n - f r e e r i m . W i d t h o f p h o t o m i c r o g r a p h i s 2.9 mm. F I G U R E 1 5 : F l a t t e n e d p u m i c e f r a g m e n t i n d e n s e l y -w e l d e d v i t r i c t u f f , s h o w i n g w e l l - d e v e l o p e d f i a m m e s t r u c t u r e . W i d t h o f p h o t o m i c r o g r a p h i s 2.9 mm. 35 combination of subhedral to euhedral faces and larger phenocrysts show moderate compositional zonation from Mg-rich cores to Fe-rich rims- Tiny rounded inclusions of magnetite and rarely ilmenite, and small laths of plagioclase are common. Anhedral magnetite, commonly with pronounced embayments, occurs up to 0.5 mm i n s i z e , and comprises 5-10% of the phenocryst mode. Magnetite inclusions i n plagioclase and pyroxene are i n d i c a t i v e of i t s early c r y s t a l l i z a t i o n . Apatite and zircon are scarce accessory minerals which form tiny prismatic inclusions in plagioclase. Glomeroporphyritic c l o t s up to 5 mm across are present i n most pyroxene andesites and consist of aggregates of clincpyroxene, plagioclase, and magnetite, with an average grain size of 0.1-0.25 mm. Grain boundaries within c l o t s are anhedral to subhedral, but euhedral c r y s t a l faces commonly protrude into the matrices. Plagioclase compositions are generally le s s anorthite-rich than phenocryst cores; pyroxene compositions show a marked increase in Al and T i substitution over phenocrysts. Hornblende andesites are characterized by si m i l a r textures and mineralogy as pyroxene andesites, with the addition of 1-10% hornblende to the phenocryst mode. Hornblende ranges i n length up to 2.5 mm, and generally displays subhedral c r y s t a l s invariably rimmed by oxides thought to have formed by oxidation during or subsequent to eruption. Hornblende phenocrysts contain inclusions of plagioclase, magnetite, and apatite; plagioclase phenocrysts rarely contain t i n y , subhedral hornblende inclusions. Glomeroporphyritic c l o t s i n hornblende andesites are 36 mineralogically and t e x t u r a l l y i d e n t i c a l with those i n pyroxene andesites-Hornblende dacites are porphyritic with 30-40% phenocrysts i n fine grained matrices composed of feldspar, Fe-Ti oxides, minor mafic minerals, and glass. Modally dominant plagioclase phenocrysts up to 4 mm i n size show les s pronounced zonation than andesitic plagioclase; compositions range from An 60 to An 35. Microphenocrysts have compositions s i m i l a r to phenocryst rims. Hornblende phenocrysts and c h l o r i t e pseudomorphs afte r hornblende up to 5 mm i n length, represent 15-35% of the phenocryst mode, and display euhedral to s l i g h t l y rounded c r y s t a l faces. Oxide reaction rims are le s s common than i n hornblende andesites and several dacites contain hornblende phenocrysts which show no signs of oxide development,. Anhedral to subhedral inclusions of plagioclase are common. Clinopyroxene microphenocrysts have an average si z e of 0-2 mm,, and represent less than 10% of the phenocryst mode. Crystals are euhedral and show no zonation. Magnetite, representing approximately 10% of the phenocryst mode, occurs as anhedral to subhedral phenocrysts and microphenocrysts up to 1 mm i n s i z e . Smaller subhedral grains occur as inclusions i n hornblende, and less commonly i n plagioclase. Subhedral to euhedral apatite i s more common than i n andesites, ranges i n length up to 0.3 mm, and generally occurs as inclusions i n plagioclase- Minor zircon needles also occur within plagioclase phenocrysts. 37 Gloraeroporphyritic c l o t s are rare in dacites and textures are i n d i c a t i v e of disequilibrium between the c l o t minerals and matrix- Mineral qrains i n contact with the matrix are rounded and embayed, and vermicular blebs of glass commonly occur at grain boundaries within the c l o t s . Op to 35% hornblende i s present i n these c l o t s , and t h e i r compositions are i d e n t i c a l to those of phenocrysts in dacites and andesites. Coquihalla Mountain stock i s composed of medium grained two-pyroxene d i o r i t e to orthopyroxene-biotite guartz d i o r i t e ; f e l s i c rocks occur on the southwestern side of Coguihalla peak. Bocks within the stock vary considerably i n grain s i z e but exhibit similar textures. Most d i o r i t e s display euhedral to s l i g h t l y rounded plagioclase up to 3mm i n s i z e , set i n an eguigranular matrix of pyroxene and plagioclase ranging i n s i z e from 0.3-0.5 mm. Less commonly, the matrix grain size i s 0.1-0.2 mm. A c h i l l zone along the southern contact of the stock has an average grain size of 0.05-0.15 mm, with plagioclase grains ra r e l y exceeding 0.5 mm. Pyroxenes are anhedral to subhedral with i r r e g u l a r , s l i g h t l y embayed boundaries. Abundant minute inclusions of magnetite and ilmenite, form wormlike blebs i n many places. In f e l s i c rocks pyroxenes are generally rimmed by b i o t i t e . P o i k i l i t i c plagioclase grains enclose pyroxenes and show pronounced zonation (An 75-30), both normal and o s c i l l a t o r y - In many phenocrysts, rounded cores containing abundant glass, oxide, and pyroxene incl u s i o n s have inclusion-free subhedral to euhedral rims. Smaller plagioclase laths i n the matrix are unzoned. 38 Quartz and potassium feldspar form i n t e r s t i t i a l l y to plagioclase and pyroxene-.In more f e l s i c rocks, the develotment of graphic texture i s common. Extrusive Rocks The petrography of the three p y r o c l a s t i c units are discussed separately, although s i m i l a r i t i e s , especially i n phenocryst populations and i n welding textures, do exist between the units. C h a r a c t e r i s t i c textures and compositions are presented for each group as a whole ; l o c a l i z e d exceptions were observed but not mapped i n the f i e l d . In general there i s a decrease in the degree of welding and amount of vapour phase c r y s t a l l i z a t i o n progressing s t r a t i g r a p h i c a l l y upwards; these variations are interpreted as r e s u l t i n g from gradual decreases in the temperature of py r o c l a s t i c extrusives over the period of r h y o l i t i c volcanism. Terminology used to describe welding and c r y s t a l l i z a t i o n textures conforms to that presented by Smith (1960b) and reviewed by Lambert (1974, pp. 20-35). l i t h i c - c r y s t a l l a p i l l i t u f f s are moderately- to densely-welded and consist of 30-50% v i t r o c l a s t i c matrix composed of d e v i t r i f i e d , comminuted glass and pumice fragments up to 4 cm i n length. Length to width r a t i o s of pumice fragments range from 2.5:1 up to 15:1, and average 6:1. Many large pumice fragments are collapsed to the point of displaying l i t t l e or no vesicular structure, show signs of deformation e s p e c i a l l y where moulded around c r y s t a l or l i t h i c fragments, have variably developed fiamme structure (Figure 15), and are aligned i n subparallel 39 fashion so as to impart a well-defined e u t a x i t i c f o l i a t i o n . D e v i t r i f i c a t i o n i s coarse-granular to granophyric, and commonly s p h e r u l i t i c . Vapour phase c r y s t a l l i z a t i o n , r e s u l t i n g i n aggregates of feldspar and guartz or tridymite, i s evident i n many rocks, but i s most pronounced.in a t h i n pneumatclytically altered zone shown on Plate I. In some places e u t a x i t i c f o l i a t i o n s are occasionally deflected around lithcphysae {Figure 16), indicating that vapour phase c r y s t a l l i z a t i o n may have preceded welding or that the c a v i t i e s expanded a f t e r welding. Ehenocrysts up to 1. 5 mm across comprise 15-30% of these rocks and consist predominantly of subhedral to euhedral plagioclase, with lesser amounts of anhedral guartz, euhedral b i o t i t e , and orthoclase. Skeletal plagioclase grains are common, and show variable degrees of a l b i t i z a t i o n . L i t h i c fragments are predominantly g r a n i t i c i n composition, and comprise 20-50% of these rocks.. Glast si z e ranges up to 10 cm, and averages about 5-6 mm; c l a s t outlines range from s l i g h t l y rounded to sharply i r r e g u l a r . V i t r i c t u f f s are moderately- to densely-welded and composed of more than 80% v i t r o c l a s t i c matrix consisting of d e v i t r i f i e d glass shards and flattened pumice fragments that are up to 4 cm in length. D e v i t r i f i c a t i o n i s generally fine-granular i n texture, but larger glass shards commonly display d i s t i n c t i v e spherulites with coarse-granular guartz rims surrounding remnant glass cores or fine grained intergrowths of guartz and feldspar. In some rocks, larger collapsed pumice fragments exhibit concentric ring structures suggestive of i n c i p i e n t d e v i t r i f i c a t i o n (Figure 17), and prominent p e r l i t i c fractures. 40 F I G U R E 16: V a p o u r p h a s e c r y s t a l l i z a t i o n o f a l k a l i f e l d s p a r a n d q u a r t z i n p n e u m a t o l y t i c a l l y a l t e r e d z o n e o f l a p i l l i t u f f s . N o t e d e f l e c t i o n o f e u t a x i t i c f o l i a t i o n a r o u n d c a v i t y . W i d t h o f p h o t o m i c r o g r a p h i s 2.9 mm. F I G U R E 1 7 : C o n c e n t r i c r i n g s t r u c t u r e s i n d i c a t i v e o f i n c i p i e n t d e v i t r i f i c a t i o n i n d e n s e l y - w e l d e d v i t r i c t u f f . W i d t h o f p h o t o m i c r o g r a p h i s 1.9 mm. 41 In densely-welded rocks, the outlines of pumice fragments can be recognized only i n crossed polarized l i g h t , because of t h e i r tendency to produce coarser grained d e v i t r i f i c a t i o n products-Length to width ra t i o s of pumice fragments are sim i l a r to those described above. Vapour phase c r y s t a l l i z a t i o n has not been recognized in rocks of thi s unit. Phenocrysts represent 5-15% of v i t r i c t u f f s , and l i t h i c fragments comprise less than 5% of these rocks,. Phenocrysts are predominantly subhedral, fragmented plagioclase (An 20-30), with small amounts of,quartz, euhedral b i o t i t e , and minor orthcclase and magnetite. Small inclusions of apatite i n plagioclase, and zircon, apatite, and r u t i l e i n b i o t i t e phenocrysts are common. L i t h i c fragments are g r a n i t i c , with composite grains of guartz and feldspar, and quartz xenocrysts being most common. Fragments are commonly less than 1 mm across, but do occur cp to 2,5 cm; most display i r r e g u l a r , fractured outlines with l i t t l e or no rounding. Non-welded to moderately-welded c r y s t a l - l i t h i c l a p i l l i t u f f s consist of 35-60% ash matrix, which, i n plane polarized l i g h t , varies i n colour from dark yellowish orange to dark reddish brown; dark colours are probably due to the dissemination of fin e grained iron oxide throughout the matrix. D e v i t r i f i c a t i o n i n these rocks i s fi n e r grained than i n the lower ash flow units. Non-matrix components i n these rocks consist of up to 40% pumice fragments, 10-30% l i t h i c fragments, and 15-40% phenocrysts. Pumice fragments up to 0.5 mm i n length generally display o r i g i n a l vesicular textures, with no fl a t t e n i n g of 42 vesicles i n non-welded v a r i e t i e s , and s l i g h t f l a t t e n i n g of vesicles i n moderately-welded rocks. Length to width r a t i o s range from 1.5:1 to 6:1, and average 2.5:1.. D e v i t r i f i c a t i o n of pumice fragments i s f i n e - to medium-granular. Phenocrysts display the same form and mineralogy as v i t r i c t u f f s , with the exception of greater percentages of b i o t i t e i n c r y s t a l - l i t h i c t u f f s . L i t h i c fragments average 0.3 to 0.6 mm across, but commonly range up to 10 cm. Smaller fragments are angular i n shape, whereas larger c l a s t s are commonly rounded. G r a n i t i c c l a s t s and xenocrysts of guartz and feldspar predominate over mudstone and fine grained volcanic c l a s t s . A l t e r a t i o n Assemblages As discussed above, a l t e r a t i o n appears to be largely fracture controlled with dramatic variations i n the extent of a l t e r a t i o n being evident i n rocks only metres apart. Metamorphic assemblages are lew-grade, and the formation of c h l o r i t e from pyroxene and hornblende i s most common. Saussuritization i s freguently displayed i n andesites and dacites, but i s rare in r h y o l i t i c rocks. Plagioclase phenocrysts are more susceptible to th i s a l t e r a t i o n process than groundmass plagioclase, and display mats of stubby epidote c r y s t a l s within patchy intergrowths of c a l c i t e , c h l o r i t e , and s e r i c i t e (Figure 18). Plagioclase phenocrysts in andesites and d i o r i t e s also display an unusual a l t e r a t i o n .involving the formation of s e r i c i t e in a p a r t i c u l a r plagioclase zone which, i n most places, F I G U R E 1 8 : S a u s s u r i t i z a t i o n o f p l a g i o c l a s e p h e n o c r y s t i n a n d e s i t e . H i g h b i r e f r i n g e n t m i n e r a l s a r e p r e d o m i n a n t l y e p i d o t e , w i t h m i n o r c a l c i t e . W i d t h o f p h o t o m i c r o g r a p h i s 1.9 mm. F I G U R E 1 9 : S e r i c i t e c o n f i n e d t o a p a r t i c u l a r p l a g i o c l a s e z o n e i n p y r o x e n e a n d e s i t e . N o t e u n a l t e r e d c o r e a n d r i m . W i d t h o f p h o t o m i c r o -g r a p h i s 2.9 mm. 44 i s contained within an outer unaltered rim (Figure 19) . Vugs i n andesites and dacites are fringed with fibrous c h l o r i t e and f i l l e d with guartz, epidote, or prehnite (Figure 20)- P a r t i a l sphenitization of titanomagnetite phenocrysts i s evident i n one dacite (Figure 21). Where t h i s reaction has gene to completion, r u t i l e c r y s t a l s surround secondary sphene and outline the o r i g i n a l magnetite c r y s t a l shape (Figure 22). Compositions of secondary minerals are l i s t e d i n Appendix Il g ; the high iron content of prehnite probably accounts for i t s unusually low 2V, between 20-30°. Mineral Chemistry A l l mineral analyses were performed on the electron microprobe; a n a l y t i c a l procedures are described in Appendix I I . Pyroxene Representative analyses are presented i n Appendix I l a . End members and f e r r i c i r o n contents were calculated by the procedure of Cawthorne and Collerson (1974). Andesites and dacites contain c a l c i c augites, while d i o r i t e s of Coquihalla stock contain hypersthene i n addition to c a l c i c augite. Normal zonation in both pyroxenes i s s l i g h t , and primarily involves substitution of Fe for Mg. The most s t r i k i n g chemical variations appear between phenocrysts and pyroxenes i n andesite c r y s t a l c l o t s . The l a t t e r contain up to 4.63 % A l 2 0 3 , 1.09% T i 0 2 , and 6.51% calcium-tschermak's molecule. On a plot of A l ^ 1 versus A l I V , c l o t pyroxenes define a d i s t i n c t h i g h - A l I V group considered to be F I G U R E 2 0 : V u g i n h o r n b l e n d e d a c i t e f r i n g e d w i t h c h l o r i t e ( b l a c k ) , a n d f i l l e d w i t h p r e h n i t e ( h i g h a n d a n o m a l o u s b i r e f r i n g e n c e ) a n d e p i d o t e ( l e f t s i d e o f p h o t o m i c r o g r a p h ) . W i d t h o f p h o t o m i c r o g r a p h i s 2.9 mm. 4 6 F I G U R E 2 1 : P a r t i a l s p h e n i t i z a t i o n o f t i t a n o -m a g n e t i t e p h e n o c r y s t i n h o r n b l e n d e d a c i t e . N o t e r o d l i k e a p a t i t e m i c r o p h e n o c r y s t s . W i d t h o f m i c r o p h o t o g r a p h i s 0.75 mm. F I G U R E 2 2 ; R u t i l e c r y s t a l s s u r r o u n d s e c o n d a r y s p h e n e , a n d o u t l i n e t h e o r i g i n a l s h a p e o f a t i t a n o m a g n e t i t e p h e n o c r y s t i n h o r n b l e n d e d a c i t e . W i d t h o f m i c r o p h o t o g r a p h i s 0.75 mm. 47 representative of high pressures of c r y s t a l l i z a t i o n (Aoki and Kushiro, 1968)- Alternately, high Al content of c l o t pyroxenes may indicate c r y s t a l l i z a t i o n prior to plagioclase; phenocrysts c r y s t a l l i z i n g a f t e r plagioclase w i l l display lower Al contents due to incorporation of Al into the plagioclase c r y s t a l structure (Barberi et a l . , 1971). Subtitutuion of T i for Al i n the pyroxene structure (Verhoogen, 1962) causes these elements to vary sympathetically. The absence of orthopyroxene from andesites and dacites may be related to c r y s t a l l i z a t i o n at lower pressures than the d i o r i t e stock, as experimental studies (cf. Bultitude and Green, 1968; 1971) indicate that orthopyroxene s t a b i l i t y i s favoured by high pressures under hydrous conditions. Experimental results of Eggler (1972) on a Paricutin andesite suggest, however, that water content may be the more important factor i n c o n t r o l l i n g orthopyroxene s t a b i l i t y ; orthopyroxene was found to be the liquidus phase at a l l values of X R Q , but increasing X H Q moved the appearance of clinopyroxene closer to the liquidus. These res u l t s are poorly understood at the present time, for experimental runs by Green (1972) on similar natural compositions produced no orthopyroxene at or near the liquidus. C r y s t a l l i z a t i o n temperatures calculated by the method of Wood and Banno (1973) from coexisting pyroxenes i n Coguihalla stock indicate a range from 1050° to 1170° Celsius. 48 Hornblende Representative analyses are presented i n Appendix l i b . F e r r i c i r o n contents were calculated by charge balance considerations summarized in Appendix Vd. Amphiboles are si m i l a r in composition to those reported from other c a l c - a l k a l i n e suites (Green, 1977) and from experimental studies of natural andesites (Green, 1972). Lower Al contents than hornblende produced in experimental runs at 9-10 kb (Green and Ringwood, 1968) suggest that Coquihalla hornblendes c r y s t a l l i z e d below these values. Coquihalla Volcanic Complex hornblendes straddle the boundary between the f i e l d s of magnesio-hornblende and tschermakitic hornblende (Leake, 1978). Compositional zonation i s s l i g h t i n large phenocrysts (rims enriched in Fe r e l a t i v e to Mg) and non-existent i n microphenocrysts. Hornblende 'i • compositions from a l l dacites and andesites are s u r p r i s i n g l y uniform, and they plot as a single c l u s t e r with respect to Ca, Mg, Fe contents. The only systematic v a r i a t i o n appears to be a decrease in Al and Na+K with increasing s i l i c a content of the host rocks. i Plagioclase Representative analyses of phenocryst, microphenocryst, and groundmass feldspars are presented i n Appendix l i e , and plotted in Figure 23. Although phenocryst zonation produces considerable overlap, there i s a systematic decrease i n anorthite content through the series diorite-andesite (An 76-30) , dacite (An 60-35), and r h y o l i t e (An 40-20).. These compositional variations An F I & U R E 2 3 : F e l d s p a r p h e n o c r y s t a n d m i c r o p h e n o c r y s t c o m p o s i t i o n s i n t e r m s o f mo 1 . % e n d - m e m b e r s . S y m b o l s : • d i o r i t e , A p y r o x e n e a n d e s i t e , V h o r n b l e n d e a n d e -s i t e , Q d a c i t e , r h y o l i t e . 50 seem to r e f l e c t decreasing temperatures of c r y s t a l l i z a t i o n throughout the series. Attempts to calculate e q u i l i b r a t i o n temperatures u t i l i z i n g the plagioclase thermometer of Kudo and Weill (1970), as modified by Mathez (1973), proved unsuccessful due to problems in obtaining consistent microprobe analyses of groundmass compositions. Potassium r i c h feldspars occur as sparse euhedral phenocrysts i n some r h y o l i t e s , and as i n t e r s t i t i a l grains i n Coquihalla Mountain d i o r i t e s . The greater amount of s o l i d solution towards a l b i t e of the l a t t e r feldspars are i n d i c a t i v e of higher temperatures of c r y s t a l l i z a t i o n than r h y o l i t e phenocrysts. Ehyolite phenocrysts, however, display less s o l i d solution (Or 84) than expected f o r potassium feldspar i n equilibrium with plagioclase of An 20-40 composition (Carmichael et a l - , 1974; Tuttle and Bowen, 1958), and they may have undergone subsolidus r e e q u i l i b r a t i o n . The normative whole reck components (An+Ab)-Or-Q and Afc-Or-Q of Coquihalla Volcanic Complex rocks are recalculated to 100% and plotted i n Figures 24a and 24b. The important role of plagioclase c r y s t a l l i z a t i o n i n the evolution of these rocks i s displayed i n the whole-rock trends d i r e c t l y away from the plagioclase apex (Figure 24a) . The most f e l s i c of the r h y o l i t e s plotted i n Figure 24b plots very near to the experimentally determined ternary minimum for the system Ab-Or-Q at water pressures of 1000 bars (Tuttle and Bowen, 1958). The occurrence of sparse quartz phenocrysts i n th i s rock indicates that the quartz-feldspar f i e l d boundary was A n + A b F I G U R E 2 4 a : N o r m a t i v e w h o l e - r o c k c o m p o s i t i o n s i n t e r m s o f ( A n + A b ) - O r - Q t r i a n g u l a r d i a g r a m , a s i n F i g . 2 3 . Q F I G U R E 2 4 b : N o r m a t i v e w h o l e - r o c k c o m p o s i t i o n s p l o t t e d i n t e r m s o f A b - O r - Q t r i a n g u l a r d i a g r a m . S o l i d c i r c l e s w i t h n u m b e r s s h o w t h e p o s i t i o n s o f t e r n a r y m i n i m a f o r d i f f e r e n t v a l u e s o f p H ^ O C k b ) , t a k e n f r o m T u t t l e a n d B o w e n ( 1 9 5 8 ) . S y m b o l s a s i n F i g . 2 3 . O r p l o t t e d S ymb o 1 s 52 reached. Comparison of water pressure with water content for t h i s system (Tuttle and Bouen, 1958) allows the magmatic water content for t h i s r h y o l i t e to be estimated at 3-4 weight per cent- low normative orthoclase contents of two of the plotted r h y o l i t e s are probably related to s i g n i f i c a n t amounts of b i o t i t e f r a c t i o n a t i o n as discussed i n a l a t e r section. B i o t i t e Representative analyses are presented i n Appendix li d . . Coquihalla Volcanic Complex b i o t i t e s display higher Fe/(Fe+Mg) ra t i o s than phenocrysts i n Garibaldi andesites, and they contain up to 1.25% BaO. Phenocrysts are unzoned, but show increasing Fe/(Fe+Mg) r a t i o s with increasing s i l i c a content of host rocks. E i o t i t e s in Coquihalla stock have l e s s Al and more Si than those i n r h y o l i t e s . The composition of b i o t i t e s i n g r a n i t i c xenoliths d i f f e r markedly from the volcanic b i o t i t e s , having higher Fe/(Fe+Mg) r a t i o s and lower T i contents. Iron-Titanium Oxides Representative analyses of titanomagnetites and ilmenites are presented i n Appendix l i e and I l f , and plotted in Figure 25,. Titanomagnetite i s a ubiquitous phenocryst, microphenocryst, and groundmass phase i n a l l Coquihalla Volcanic Ccnplex rocks. The occurrence of ilmenite i s limited to phenocrysts and microphenocrysts in the most mafic d i o r i t e of Coquihalla stock, sparse inclusions i n andesitic pyroxenes, occasional microphenocrysts in dacites, and rare inclusions i n r h y o l i t i c plagioclase. The modal prevalence of titanomagnetite ever T i 0 2 F I G U R E 2 5 : C o m p o s i t i o n s o f t i t a n o m a g n e t i t e a n d i l m e n i t e p h e n o c r y s t s a n d m i c r o p h e n o c r y s t s , p l o t t e d i n t e r m s o f T i O , F e O , a n d F e ^ . S y m b o l s a s i n F i g . 2 3 . 54 ilmenite probably r e f l e c t s complex interactions of factors such as titanium a v a i l a b i l i t y , s i l i c a a c t i v i t y , and oxygen fugacity (Haggerty, 1976). Most titanomagnetite grains are o p t i c a l l y and compositibnally homogenous; hematization of rims i s common. Ilmenite inclusions i n pyroxene or plagioclase show no signs of alt e r a t i o n or exsolution; in a few rocks, grcundmass grains exhibit i r r e g u l a r patches of hematite probably related to post-c r y s t a l l i z a t i o n oxidation. Titanomagnetites contain up to 3.96% A l 2 0 3 , 1.37% V 2 ° 3 * a n ^ 2.89% MnO. Al and V decrease, and Mn increases with increasing s i l i c a content of host rocks. Ilmenites contain up to 10.56% MnO as th e i r main minor element impurity. Coquihalla Volcanic Complex ilmenites are higher in MnO than these reported from other c a l c - a l k a l i n e suites (Carmichael, 1967; Green, 1977) and resemble ilmenites from peralkaline suites i n t h i s respect (Haggerty, 1976). The general lack of coexisting titanomagnetite and ilmenite i n Coguihalla Volcanic Complex rocks prevents determination of unique temperature, oxygen fugacity conditions using the experimental r e s u l t s of Buddington and Lindsley (1964). One andesite with coexisting spinel and rhombohedral phases gives a res u l t of les s than 600°C with f0 2; less than 10— 2 3 atmospheres. Although the recasting of microprobe analyses into end member components follows the procedures of Buddington and Lindsley as modified f o r minor elements by Anderson (1968), and takes into account attempts by Mazullo et a l . . (1975) to c a l i b r a t e t h i s thermometer for MnO-rich oxides, t h i s calculated temperature and 55 oxygen fugacity appear much too low when compared to other c a l c -a l k aline suites ( G i l l , 1978).. This inconsistency probably derives from the incompatibility of applying the pure 3 component experimental r e s u l t s to natural systems containing up to 1C weight per cent MnO i n ilmenite; p o s t - c r y s t a l l i z a t i o n oxidation would also contribute to low temperature results. Coexisting groundmass oxides i n one d i o r i t e of Coquihalla stock y i e l d a solidus temperature of 640°C and f 0 2 equal to 10-16 atmospheres. This temperature i s lower than experimentally determined water-saturated s p l i d i of si m i l a r compositions (Robertson and Wyllie, 1971), and perhaps r e f l e c t s re-e q u i l i b r a t i o n under slow cooling conditions. Oxygen fug a c i t i e s determined from coexisting oxides show that most orogenic andesites c r y s t a l l i z e d under f 0 2 conditions p a r a l l e l to but approximately one log unit above the Ni-NiO buffer ( G i l l ,1978). Carmichael (1967) has shewn that estimated ±02 for c a l c - a l k a l i n e suites show systematic variations depending on the phenocryst assemblages i n equilibrium with oxide minerals. Olivine-bearing rocks plot along the QFM buffer, orthopyroxene-bearing rocks f a l l along the Ni-NiO buffer, and b i o t i t e - and hornblende-bearing rocks f a l l above the Ni-NiO buffer. Oxygen f u g a c i t i e s tend to remain constant (Green, 1977) or increase s l i g h t l y (Carmichael, 1967) with increasing a c i d i t y of host rocks. Ulvospinel contents of titanomagnetites show continuous decreases with increasing s i l i c a content of host locks, although titanomagnetites of Coguihalla stock are displaced to lower ulvospinel contents. This systematic decrease can be accounted 56 for by st e a d i l y decreasing temperatures of c r y s t a l l i z a t i o n throughout the suite. Assuming oxygen f u g a c i t i e s along the Ni-NiO buffer for pyroxene andesites, and s l i g h t l y above i t for amphibole- and biotite-bearing dacites and r h y o l i t e s , temperature estimates vary from 925°C f o r andesites to 675°C for r h y o l i t e s . Lower ulvospinel contents of d i o r i t e s suggest c r y s t a l l i z a t i o n at lower temperatures under conditions of higher pH20, although, as mentioned above, subsolidus r e e g u i l i b r a t i o n may have taken place. Discussion Comparison of c r y s t a l l i z a t i o n seguences i n Coquihalla Volcanic Complex rocks with those produced in experimental studies of natural andesites allows some estimation of various intensive parameters involved in the formation of t h i s suite of rocks. Direct comparisons are subject to uncertainties insofar as oxide phases were found to have c r y s t a l l i z e d well below the experimental l i q u i d i of Green (1972), Eggler (1972), and Eggler and Burnham (1973), while oxides are early forming phases i n a l l Coquihalla Volcanic Complex rocks. Green's runs were a l l unbuffered, and the l a t t e r two experiments were run at the QFM and Ni-NiO buffers. S t a b i l i z a t i o n of oxide phases with respect to s i l i c a t e s by higher oxygen fugacities (Eggler and Burnham, 1973; Hamilton et a l . , 1964) suggests that the magmas i c r y s t a l l i z e d at oxygen fu g a c i t i e s above the Ni-NiO buffer, and lends more c r e d i b i l i t y to the temperature estimates discussed above. I t i s important to note that early c r y s t a l l i z a t i o n of Coquihalla Volcanic Complex oxides, and oxides i n other c a l c -57 al k a l i n e suites (Carmichael, 1967) i s inconsistent with the arguments of Eggler and Burnham (1973) that oxygen f u g a c i t i e s w i l l not be s u f f i c i e n t l y high to cause the appearance of oxides on the l i g u i d i of c a l c - a l k a l i n e magmas. Addition of water to andesite l i g u i d s causes pronounced depression of liquidus temperatures. Comparison of experimental r e s u l t s of Eggler (1972) and Green (1972) with pyroxene eg u i l i b r a t i o n temperatures i n d i o r i t e s of Coguihalla stock, suggests that the natural magmas contained 1-5% water at upper c r u s t a l pressures. C r y s t a l l i z a t i o n of orthopyroxene before plagioclase i n these rocks also indicates water contents i n d i o r i t e magmas greater than 2 weight per cent (Eggler, 1S72). Eeversal of t h i s c r y s t a l l i z a t i o n seguence i n andesites suggests that these magmas contained less water, and supports the higher oxide mineral e g u i l i b r a t i o n temperatures i n andesites as compared to d i o r i t e s . Geochemistry Whole-rock analyses of members of the Coguihalla Volcanic Complex are presented i n Appendix I. A n a l y t i c a l procedures for major elements are discussed in Appendix I, and procedures for trace element analyses are presented i n Appendix IV. C l a s s i f i c a t i o n The c a l c - a l k a l i n e rocks of the Coquihalla Volcanic Complex have been subdivided according to the c l a s s i f i c a t i o n system proposed by Irvine and Baragar (1971), with modifications based on the terminology of Wise (1969),, This system of c l a s s i f i c a t i o n 5 8 u t i l i z e s major element and normative compositions, calculated on a v o l a t i l e - f r e e basis, to subdivide the Coguihalla Volcanic Complex rocks into 4 groups: b a s a l t i c andesite, andesite, dacite, and r h y o l i t e . Figure 2 6 i s a plot of normative plagioclase content versus normative colour index and shows the c l a s s i f i c a t i o n l i n e s of Irvine and Baragar which delineate t h e i r f i e l d s of basalt, andesite, dacite, and rhyolite- The compositions of the two rocks ( 6 3 2 and 2 5 1 ) which f a l l well within the basalt f i e l d are termed 'basaltic andesite* i n t h i s study due to t h e i r lack of modal or normative o l i v i n e , and t h e i r petrographic s i m i l a r i t y to other andesites within the s u i t e . Rocks which f a l l on the dividing l i n e are grouped with the andesites. The rock ( 2 8 3 ) which f a l l s at the f e l s i c end of the andesite f i e l d has teen c l a s s i f i e d with the dacites due to i t s high s i l i c a ( 6 4 wt. % ) , d i f f e r e n t i a t i o n index ( 6 8 ) , and normative quartz ( 1 7 . 5 ) , and i t s petrographic s i m i l a r i t y to other dacites i n the suite. Comparison with Cascade Calc-alkaline Suites Andesites of the Coguihalla Volcanic Complex are similar to c a l c - a l k a l i n e suites i n western North America and worldwide, i n that they are quartz-normative, have an average s i l i c a content of 5 9 wt. %, and show Mg/(Mg+Fe) r a t i o s l e s s than 0 . 5 5 . Coguihalla Volcanic Complex andesites are s i m i l a r to Cascade andesites i n exh i b i t i n g i n i t i a l 8 7 S r / 8 6 S r r a t i o s of 0 . 7 0 3 7 , as compared to an average value of 0 . 7 0 3 7 f o r Cascade lavas ( C h u r c h and T i l t o n , 1 9 7 3 ) . Coguihalla Volcanic Complex andesites can be c l a s s i f i e d as UO 30 20 A n / ( A r i + A b ) 10 o F I G U R E 2 6 : N o r m a t i v e p l a g i o c l a s e ( 1 O O A n / ( A n + A b + 5 / 3 N e ) ) v e r s u s n o r m a t i v e c o l o u r i n d e x ( E O l + O p x + C p x + H m + I l m ) , w i t h t h e c l a s s i f i c a t i o n l i n e s o f I r v i n e a n d B a r a g a r ( 1 9 7 1 ) . S y m b o l s a s i n F i g . 2 3 ; X a l t e r e d r o c k s . 60 •average K20* andesites (Gunn, 1974) with K 20 contents d i s t i n c t l y higher than those f o r Cascade or Garibaldi andesites. In addition, Coquihalla Volcanic Complex rocks are enriched i n Ba and Eb, and depleted i n Ni and Cr r e l a t i v e to Cascade and Garibaldi lavas. Sr contents are s i m i l a r to those of Cascade volcanics but less than those of Garibaldi lavas. Discussion Members of the Coquihalla Volcanic Complex display a range in s i l i c a contents (volatile-free) from 54 to 76 weight per cent. The compositional hiatuses around a s i l i c a content of 67% are thought to be related to a sampling bias towards andesitic and r h y o l i t i c rocks. Chemical variat i o n s within the suite (Figures 27-32) are characterized by enrichment of K 20, Na 20, Rb, and Nb i n r e l a t i o n to increasing s i l i c a , and depletion of T i 0 2 , A l 2 0 3 , MgO, FeO, MnO, CaO, P 20 5 , C r » V ' a n d S r> T n e elements Ea, Ce, Nd, and Zr a l l show enrichment throughout most of the su i t e , and depletion i n the most f e l s i c members of the s u i t e . In order to estimate the effect of a l t e r a t i o n processes on whole rock compositions, four rocks, which showed pronounced development of secondary minerals, were analyzed and plotted with other •unaltered* rocks in Figures 30 to 35. The nain e f f e c t of a l t e r a t i o n i s an increase i n H20 and C0 2. The Harker diagrams (Figures 27-32) were constructed on a v o l a t i l e - f r e e basis, and they indicate that altered rocks plot s l i g h t l y outside the main f i e l d of compositional variation for the elements Na, K, Ca, Mn, Ba, and Sr- The N a 2 0 - s i l i c a diagram i s 61 1 9 1 8 H m 1 7 S 1 6 H ^ 1 5 i n • 1 3 • _ J • v • X + + + 5 0 ° 1 0 UJ o CE 8 H 6 il 2 0 5 5 6 0 6 5 7 0 7 5 o X + + + + 8 0 5 0 1 0 5 5 -zr 6 0 6 5 _ i _ 7 0 _ 1 _ 7 5 8 0 o CE 8 -6 -14 = 2 -0 • w X 5 0 5 5 6 0 6 5 S I 0 2 7 0 7 5 8 0 FIGURE 2 7: Harker v a r i a t i o n diagrams. Values i n weight p e r c e n t , v o l a t i l e - f r e e . Symbols as i n F i g . 26. —1 I I A O A no o X + +  + i i i r~~ 5 5 6 0 6 5 7 0 7 5 " 1 : i ! I I X • BA v + + i i i j —r 5 5 6 0 6 5 7 0 7 5 + + 5 5 6 0 6 5 7 0 15 S I 0 2 FIGURE 28: Harker v a r i a t i o n diagrams. Values i n weight p e r c e n t , v o l a t i l e - f r e e . Symbols as i n F i g . 26. 63 1 . 1 . fM 0 . So->- 0 . 0 . 0 . 0 . 0 . i n ° 0 . a. 0 8 6 H U 2 5 0 0 . 0 . 3 H 2 1 0 5 0 0 . 3 A O V X 5 5 5 5 _ L 44- +. 6 0 6 5 7 0 _1_ 7 5 _ L & v v A ^ P V ° o X + 4+ + 4-6 0 6 5 __L 7 0 _ J _ 7 5 8 0 8 0 o z 0 . 2 0 . 1 0 . 0 5 0 x 5 5 6 0 6 5 S I 0 2 T 7 0 7 5 8 0 FIGURE 29: Harker v a r i a t i o n diagrams. Values i n weight p e r c e n t , v o l a t i l e - f r e e . Symbols as i n F i g . 26. 3 6 H X 3 2 H 2 4 H 2 0 H 1 6 A xa 2 8 q • o 5 0 5 5 6 0 6 5 7 0 7 5 8 0 9c „ • O • A A V X ^ W ^ A X O + + 5 0 5 5 6 0 6 5 7 0 * 7 5 8 0 D 4 xA^ b„ ^ v T + O X + + + 5 0 5 5 e T 6 5 ~ 7 0 ~ 7s 8 0 1 • % ^ ^ • A + J_' • 5 0 5 5 6 0 6 5 ~ 7 0 7 5 8 0 S I 0 2 FIGURE 30: Harker v a r i a t i o n diagrams. Oxide v a l u e s i n weight p e r c e n t , v o l a t i l e - f r e e . T race element v a l u e s i n p a r t s per m i l l i o n . Symbols as i n F i g . 26. / 65 ^ 600 ^ 500 H ~ 400 o 300 £ 200 <° 100 50 100 _ 90-H ~ Z R —' o 60 - 50 co no ^ 2 0 H 10 50 x • o X 55 60 _ J _ 65 70 75 • ° X A ^ D V V D C 3 > X + 55 60 65 70 75 80 80 _ 240 -^ 220 -~ 200 -z 180 -o 160 -<-> m o -^ 120 100 80 - i 50 240 = " § 200 = - 1 6 0 -S 120E oE 8 0 40 0 50 X A D w x • o + + 55 60 65 70 75 x r 55 60 65 S I02 70 75 FIGURE 31: Harker v a r i a t i o n diagrams. Oxide v a l u e s i n weight p e r c e n t , v o l a t i l e - f r e e . T r a c e element: v a l u e s i n p a r t s per m i l l i o n . Symbols as i n F i g . 26, 80 80 66 1 6 0 0 -i x 1 4 0 0 2 1 2 0 0 = £ 1 0 0 0 = £ 8 0 0 -6 0 0 -5 0 U J {_> 1 0 0 -^ 8 0 -6 0 -4 0 2 0 H 5 0 50 3 : 4 5 -=» 4 0 -£ 3 5 ->- 3 0 -Q 2 5 -£ 2 0 - i z 1 5 1 0 50 x V v n V 0 x x • X o + + + + 55 6 0 65 7 0 _ J _ 7 5 X 5 5 6 0 6 5 7 0 7 5 4AY v n ^ o 5 5 6 0 6 5 S I 0 2 I 7 0 7 5 8 0 80 8 0 FIGURE 32: Harker v a r i a t i o n diagrams. Oxide v a l u e s i n weight p e r c e n t , v o l a t i l e - f r e e . Trace element v a l u e s i n p a r t s per m i l l i o n . Symbols as i n F i g . 26. 67 the only plot i n which s i g n i f i c a n t scatter appears among non-altered rocks. Depletion of Na 20 in some Coquihalla Volcanic Complex r h y o l i t e s could be due to a l k a l i leaching of glasses (Lipman, 1965), but these variations are not accompanied by changes i n Rb concentrations, which i s generally regarded to be mobile during hydrothermal a l t e r a t i o n (Chikhaoui et a l . , 1S78). Moreover, the depletion of Na 0 i s accompanied by decreases i n Ce, Nd, Ba, and Zr, and the l a t t e r element i s considered to be highly immobile during metamorphism (Smith and Smith, 1976; Winchester and Floyd, 1977). In view of the small amount of scatter i n chemical variation diagrams, and the small compositional e f f e c t s on highly altered rocks, the chemical variations exhibited by members of the Coguihalla Volcanic Complex are reqarded as r e f l e c t i n q the primary igneous history of these rocks. A model to account for the late-stage depletion of the above-mentioned elements i s proposed below. Petroqenesis Models proposed for the genesis of s i l i c i c members of c a l c -a l kaline suites (dacites and rhyolites) f a l l i nto three groups: a) upper c r u s t a l anatexis (Ewart and Stipp, 1968; Ewart et a l . , 1971) , b) low pressure 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 andesitic l i q u i d s (Nicholls, 1971; Ewart et a l . , 1973; Lambert et a l . , 1974) , and c) p a r t i a l melting of quartz e c l o g i t i c upper mantle (Wilkinson, 1971) . 68 A genetic rel a t i o n s h i p between members of the Coquihalla Volcanic Complex i s suggested by r e l a t i v e l y smooth chemical variations and strontium is o t o p i c uniformity within the sui t e . Systematic variations of modal abundances, and the c o r r e l a t i o n of . whole rock chemistry with constituent feldspar and titanomagnetite compositions, suggest that c r y s t a l fractionation played a dominant role i n generating the petrological d i v e r s i t y within the Coquihalla Volcanic Complex. Although p a r t i a l melting of an i s o t o p i c a l l y uniform source could also account for t h i s d i v e r s i t y , arguments based on trace element constraints severely l i m i t the a p p l i c a b i l i t y of t h i s model. The trace element d i s t r i b u t i o n patterns within a suite of igneous rocks can be used to discriminate between the eff e c t s of p a r t i a l melting 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 as discussed by Ferrara and T r e u i l (1974). The trace element d i s t r i b u t i o n produced by 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 i s governed by the Eayleigh f r a c t i o n a t i o n law (Arth, 1976): Equ. 1.1 Cz/C? = F<D.+1> 1 ' ' where C± i s the concentration of i i n the remaining l i q u i d C° i s the concentration of i i n the o r i g i n a l l i q u i d F i s the fraction of l i q u i d remaining D± i s the bulk s o l i d / l i q u i d d i s t r i b u t i o n c o e f f i c i e n t , defined as Equ. 1.2 D. = x. k. . where x. i s the fr a c t i o n of mineral j i n the cumulate k.. i s the s o l i d / l i q u i d d i s t r i b u t i o n c o e f f i c i e n t for mineral j and element . i For equilibrium p a r t i a l melting, the trace element 69 d i s t r i b u t i o n i s governed by the following r e l a t i o n (Shaw, ,1S70): Equ. 1.3 c j /C° = 1/(D.+ F(1 - D) ) where C°. i s the i n i t i a l concentration of i i n the s o l i d i i s the concentration of i i n the l i q u i d formed F i s the fr a c t i o n of melting D. i s the bulk d i s t r i b u t i o n c o e f f i c i e n t defined in x egu. 1.2 Elements for which the bulk d i s t r i b u t i o n c o e f f i c i e n t , D, i s close to zero are concentrated i n the l i g u i d and have been c a l l e d •hygromagmatophile* (Ferrara and T r e u i l , 1974). Eguations 1.1 and 1.3 are si m p l i f i e d f o r hygromagmatophile elements, and and both reduce to: Egu. 1.4 /C° = 1/F It can be seen from equ. 1.4 that the amount of l i g u i d , F, can be estimated from the concentration r a t i o of two related rocks, and that plots of the va r i a t i o n of two hygromagmatophile elements w i l l produce l i n e a r correlations f o r suites of rocks derived by either p a r t i a l melting or 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 . The two processes can be distinguished, however, on plots i l l u s t r a t i n g the.variation of two trace elements which have s l i g h t l y d i f f e r e n t degrees of p r o c l i v i t y f or the l i g u i d phase. Equations 1.1 and 1.3 were used to calculate the d i s t r i b u t i o n of two trace elements with d i f f e r e n t , but constant values of D, as a function of F; i t can be seen from Figure 33 that the p a r t i a l melting process causes a much greater departure from l i n e a r i t y i n trace element patterns than c r y s t a l f r a c t i o n a t i o n processes i f the two elements have s l i g h t l y d i f f e r e n t bulk d i s t r i b u t i o n c o e f f i c i e n t values, even i f neither element i s F I G U R E 33: T h e c a l c u l a t e d c o r r e l a t i o n c u r v e s o f two t r a c e e l e m e n t s a n d w i t h d i f f e r e n t b u l k d i s t r i b u t i o n c o e f -f i c i e n t s d u r i n g p a r t i a l m e l t i n g (PM) a n 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 ( F C ) p r o c e s s e s . N u m b e r s i n d i c a t e t h e f r a c t i o n o f m e l t r e m a i n i n g 'or f o r m e d . 71 hygromagmatophile. I t should be noted that calculated trace element d i s t r i b u t i o n s for other types of p a r t i a l melting processes produce s i m i l a r patterns to those shown i n Figure 33 for the equilibrium case. Of the trace elements analyzed ' in Coguihalla Volcanic Complex rocks, Zr, Nd, Ce, and Nb are commonly considered, as hyqromagmatophile (Ferrara and T r e u i l , 1974; Allegre et a1., 1977). The only elements, however, which increase i n concentration throughout the Coquihalla Volcanic Complex sequence andesite to r h y o l i t e are Eb and Nb, and t h e i r enrichment rates indicate that bulk d i s t r i b u t i o n c o e f f i c i e n t s are s i g n i f i c a n t l y greater than zero. The c o r r e l a t i o n of these two elements (Figure 34) closely matches the calculated 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 curve i n Figure 33, and implies that the volcanic suite has been generated by c r y s t a l f r a c t i o n a t i o n processes- In order for a p a r t i a l melting process to produce t h i s nearly-linear pattern, d i s t r i b u t i o n c o e f f i c i e n t s for fit and Nb would have to be almost equal; t h i s i s inconsistent with steadily increasing Rb/Nb r a t i o s observed i n Coquihalla Volcanic Complex rocks. In addition to the above argument,.it would be d i f f i c u l t to account for the depletion of Ce, Nd, Ba, and Zr i n some rhyoli t e s by p a r t i a l melting of mantle of upper c r v s t a l material, i n which bulk d i s t r i b u t i o n c o e f f i c i e n t s for these elements are nearly zero. NIOBIUM cn co »J co CD o CO <^ 3 H 3 CL o cr c o 3 H-w Cfi O o-CO tn uin • • H- H 3 3* 3 ft) >*i H-o O 00 o cr . Si w c fD ON D* <; Co n> a M Co CO < i-i o H h-1 fD O M CO (D 3 rt H- H-n O 3 o o o 3 •o (—' fD 3 X bi i-i o O c 3 • a CD 73 Major Element Model In order to quantitatively t e s t the 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 model, solutions were sought tc least squares mass balance equations which te s t whether the major element composition of a rock can be mathematically derived from that of another rock by subtraction of the compositions of phenocrysts observed i n these rocks. Solutions by algorithms of Wright and Doherty (1970) or Bryan et a l . , (1969) seem inappropriate i n that no allowance i s made for a n a l y t i c a l error i n microprobe analyses of mineral phases. A program written by Albarede and Provost (1977) was used i n t h i s study and a l l mineral and whcle-rock analyses were assigned standard deviations egual to 2% of the concentrations of each element present. Modelling of the spectrum of Coquihalla Volcanic Complex compositions was divided into two steps: b a s a l t i c andesite-d i o r i t e to dacite, and dacite to r h y o l i t e . This d i v i s i o n i s a r t i f i c i a l i n that the fr a c t i o n a t i o n process i s envisioned to be continuous. Different phenocryst populations between andesites and rh y o l i t e s , however, make, i t reasonable to formulate the modelling i n t h i s manner. A l l members of the Coquihalla Volcanic Complex are porphyritic or h o l o c r y s t a l l i n e , and i t i s net known whether phenocrysts represent cumulate phases or whether they c r y s t a l l i z e d from d i f f e r e n t i a t e d l i q u i d s . In order to minimize the effects of t h i s uncertainty, averages of two whole rock compositions were used for the basaltic-andesite and dacite compositional stages. A crystal-poor v i t r i c t u f f was used for the rhyolite end member. Mineral compositions were taken from 74 microprobe analyses of phenocrysts i n the modelled rocks and i n rocks similar to them, except for the apatite analysis which was taken from Green (1977). Results of each step of the' model are presented i n Tables 4 and 5. Both f i t t i n g steps produced adjusted mineral and whole rock compositions i n which a l l residuals were less than the assumed 2% errors. Major element modelling indicates that: A) hornblende dacites can be derived from basaltic-andesites by roughly 5055 c r y s t a l l i z a t i o n of a mixture of plagioclase (Any5), hornblende, clinopyroxene, titanomagnetite, and apatite, b) r h y o l i t e s can be derived from hornblende dacites by 30-40% c r y s t a l l i z a t i o n of a mixture of plagioclase (An 42) , hornblende, b i o t i t e , magnetite, and apatite, and c) the guantity of r h y o l i t i c magmas produced by 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 basaltic-andesite l i g u i d s w i l l be roughly egual to 25-30% of the original.magma volume. It should be noted that results of t h i s modelling procedure are not' overly s e n s i t i v e to p a r t i c u l a r mineral or whole rock compositions; f i t t i n g of other whole rock pairs similar to the average compositions shown i n Tables 4 and 5 generally produces res u l t s within two standard deviations of the calculated c o e f f i c i e n t s shown i n these tables. Modal abundances of phenocrysts in Coguihalla Volcanic Complex rocks (Table 3) are generally compatible with the mineralogical proportions of the calculated cumulates. Recent experimental work by Kushiro (1978) indicates that a l l fr a c t i o n a t i n g phases are more dense than hydrous andesitic 75 MAJOE ELEMENT MODEL: STEP 1— EAS ALTIC ANDESITE TO DACI1E Ap Hb P I Mt Cpx Dacite Mean 0.004 C.128 Sigma 0.001 0.028 Mineral % 0.82 26.35 Fraction cf l i g u i d remaining 0.204 0.C38 0.0 15 0.003 42.20 7.80 0.511 0.111 0.511 0.025 0. 020 22. 84 I n i t i a l Compositions Ap Hb P I Mt Cpx Dacite Andesite Si 0.0 4 5 . 20 4 9 . 17 0. 0 7 5 0 . 3 8 6 5 . 6 3 5 4.. 54 T i 0.0 2 . 6 3 0. 07 8. 19 1.09 0.58 1. 03 Al c. c 9. 40 3 2 . 29 3.08 4. 51 1 6 . 6 9 17. 44 Fe 0.0 1 2 . 46 0. 40 88 . 59 9. 12 4,. 40 8. 36 Mg 0.0 14 . 54 0. 06 0. 16 1 4 . 9 3 1.77 4. 51 Ca 5 4 . 0 0 1 1 . 5 2 1 5 . 95 0.01 2 0 . 16 3.51 8. 80 Na 0.0 2.19 2. 55 0.02 0.32 4.39 2. 99 K 0.0 0. 49 0. 16 0.0 0.0 2- 38 1. 33 P 4 0 . 0 0 0.0 0. C 0.0 0.0 0. 23 0. 28 Mn 0.0 0. 36 0- 04 0. 80 0.24 0. 12 0. 17 Absolute Residuals 1 Ap Hb P I Mt Cpx Dacite Andes i t e S i 0 . 0 0 0 0 . 0 2 2 0. 042 0 . 0 0 0 0 . 0 2 4 Cw 186 - 0 . 2 5 3 Ti 0. 0 0 0 0 . 0 1 5 0. 002 0 . 0 2 8 0. 0 0 4 0 . 0 1 1 - 0 . 0 3 6 Al - 0 . 0 0 0 - 0 . 0 1 5 - 0 . 2 4 3 - 0 . 00 1 - 0 . 0 0 4 - 0 . 1 7 1 0. 36 5 Fe -o.oco - 0 . 0 1 8 - 0 . 0 0 0 - 0 . 2 3 7 - 0 . C 0 9 - 0 . 0 1 2 0. 0 6 9 Mg - 0 . 0 0 0 - 0 . 0 6 3 - 0 . 0 0 0 - 0 . 0 0 0 - 0 . 0 5 8 - 0 . 0 0 8 0. 0 6 2 Ca 0 . 0 1 6 0. 0 2 7 0. 081 0 . 0 0 0 0.. 0 6 8 0 . 0 1 4 - 0 . 1 3 2 Na 0 . 0 0 0 0 . 0 0 5 0. 0C9 0 . 0 0 0 0.C01 0. 0 5 4 - 0 . 0 5 8 K - 0 . 0 0 0 - 0 . 0 0 1 - 0 . 0 0 1 -0,. 00 0 - 0 . 0 0 0 - 0 . 0 1 3 0. 0 1 2 P - 0 . 0 1 2 - 0 . 0 0 0 - 0 . 0 0 0 - 0 . 0 0 0 - 0 . 0 0 0 - 0 . 0 0 1 0. 0 0 3 Mn 0 . 0 0 0 0 . 0 0 0 0. 0 0 0 0.00 0 0. 0 0 0 0. 0 0 1 - 0 . 0 0 2 Reduced Residuals 2 AP Hb P I Mt Cpx Dacite Andesite Si 0. 0 0 0 0. 0 2 4 0- 0 4 2 0 . 0 0 0 0 . 0 2 3 0. 140 - 0 . 2 2 8 Ti 0 . 0 0 2 0. 2 0 4 0. CS7 0 . 1 5 3 0. 102 0 . 3 5 6 - 0 . 89 6 Al - 0 . 0 0 0 - 0 . 0 7 1 -o,. 36 5 - 0 . 0 0 8 -0.. 0 3 3 -C. 4 8 5 0. 9 8 9 Fe - 0 . 0 0 0 - 0 . C 6 7 - 0 . 011 - 0 . 1 3 2 - 0 . 0 4 4 - 0 . 1 0 8 0. 36 6 Mg - 0 . 0 0 0 - 0 . 2 0 3 - 0 . 0 2 2 - 0 . 0 0 4 -0,. 181 ^ 0 . 1 4 5 c. 5 6 5 Ca 0 . 0 1 5 0. 110 0. 2 3 8 0 . 0 0 3 0 . 1 6 1 0. 158 - 0 . 6 7 2 Na 0 . 0 0 1 0. 0 7 4 0. 132 0.0C7 0 . 0 2 7 0 . 5 0 1 - 0 . 7 2 7 K - 0 . 0 0 0 - 0 . 0 22 - 0 . 0 2 7 - 0 . 0 0 4 - 0 . 0 1 3 - C . 199- 0. 2 6 8 P - C . 0 1 5 - 0 . 0 1 2 - 0 . 0 1 9 - 0 . 0 0 3 - 0 . 0 1 0 - 0 . 0 5 8 0. 118 Mn 0. 0 0 0 0 . 0 1 0 0. 0 1 3 0. 0 0 4 0. 008 0. 0 3 4 - 0 . 0 7 0 1 2 Difference between i n i t i a l and f i n a l , adjusted comtcsiticrs Absolute residuals divided by error (2%) of analyses : 76 5_i HA JOB ELEMENT MODELj. STEP 2 — EACITE TO RHYOLITE Ap Hb Pl Mt Bi Rhyolite Mean 0.005 0.074 0.281 0.028 0.024 0.567 Sigma 0.C01 0.017 . 0.C24 0.001 0.015 0.031 Mineral % 1. 18 17.46 66.67 6.71 7.98 Fraction of l i g u i d remaining 0.567 I n i t i a l Compostions Ap Hb Pl Mt Bi Dacite Rhyolite Si 0.0 43. 62 58. 23 0.31 38.62 77.02 65. 63 Ti 0.0 2.93 0. 10 5. 35 4. 07 0.14 0. 58 Al 0. 0 11.11 26.79 2. 10 14.. 55 12.23 16. 69 Fe 0. 0 11.76 0. 12 89.90 13.75 0. 84 4. 40 Mg 0.0 14. 80 0.03 0. 6 7 16.15 C. 14 1. 77 Ca 54. 0C 11. C5 7.56 0. 14 0.10 0.68 3. 51 Na 0.0 2. 50 7. 23 0. 08 0.75 3.79 4. 39 K 0. C 0. 35 0.21 0.C8 7.01 3. 80 2. 38 P 40. 00 0.0 0.0 0.0 0.0 0.04 0. 23 Mn 0.0 0.31 0.0 0.90 0.55 0.05 0. 12 Absolute Residuals 1 Ap Hb Pl Mt Bi Dacite Rhyolite Si -0.000 -0.023 -0. 158 -0.000 -0.008 -0.553 0. 71 1 T i 0.000 0.011 0.003 0. 012 0.009 0. 007 -0. 025 Al -o.oco -0.007 -0.142 -0. coc -0.005 -0.075 0. 20 4 Fe -0.000 -0.005 -0.000 -0.099 -0.003 -0. 00 1 0. 012 Mg -0. ceo -0.C54 -0.001 -0.000 -0.029 -0.002 0. 023 Ca 0.049 0.035 0.067 o.ooc 0.000 0.005 -0. 067 Na 0. 000 0. 000 0.002 o.ooc 0,. 000 0.001 -0. 002 K 0. 000 0.001 0.002 0.000 C.011 0. 067 -0. 058 P -0.037 -0.000 -0.001 -0.000 -0.000 -0.003 0. 007 Mn -0.000 -0.002 -0.004 -0.001 -0.001 -0.009 0. 018 Reduced Residuals 2 Ap Hb Pl Mt Bi Dacite Rhyolite Si -0.000 -0.026 -0. 133 -0.00 0 -0.011 -0.354 0. 534 T i 0. 003 0. 146 0. 156 0.091 0. 086 0.326 -0. 7S7 Al -c.oco -0.C29 -0.255 -0.003 -0.017 -0. 263 0. 57 8 Fe -0.000 -0.020 -0.007 -0.055 -0.011 -0.022 0. 115 Mg -0.001 -0. 171 -0.043 -0.007 -0.085. -0. 095 0. 407 Ca 0.045 0. 145 0. 394 0.005 0. 006 0. 156 -0. 737 Na 0. 000 0.001 0.010 0.000 0.000 0.012 -0. 023 K 0.001 0.025 0.1 C87 0.008 0.069 0. 695 -0. 863 P -0.045 -0.016 -0.062 -0.. 0 06 -0.007 -C. 130 0. 27 1 Mn -0.004 -0.C70 -0.205 -0.039 -0.038 -0.434 0. 816 1 Difference between i n i t i a l and f i n a l , adjusted compositions 2 Absolute residuals divided by error (2%) of analyses 77 l i q u i d s . The observation that plagioclase occurs i n s l i g h t l y greater amounts than predicted by these cal c u l a t i o n s may be related to the lower density, and hence slower s e t t l i n g rates of plagioclase, as compared to other fra c t i o n a t i n g phases. Experimental studies by Green (1972) and Eggler (1974) on natural and synthetic andesitic compositions demonstrate the f e a s i b i l i t y of t h i s proposed fractionation model. I t should be noted that the lack of precise stratigraphic control between r h y o l i t e s and intermediate vclcanics i n the f i e l d , and the use of average intermediate compositions do not necessarily imply derivation of a l l igneous rocks i n stages, from a single, stagnant, fra c t i o n a t i n g magma chamber. Coquihalla Volcanic Complex r h y o l i t e s and dacites appear to be derived by c r y s t a l f r a c t i o n a t i o n of andesitic magmas, but the actual process may involve more than one magma chamber, or periodic replenishment of a single magma chamber by mafic melts. Trace element model Serious d i f f i c u l t i e s are presented i n the use of trace elements to test the consistency of the r e s u l t s of major element modelling. The problem of whether analyzed rocks represent true l i q u i d s can be circumvented only with completely aphyric recks. Errors related to analysis of a rock composed of cumulate phases and l i g u i d are small for elements with d i s t r i b u t i o n c o e f f i c i e n t s (D) near zero, but quite considerable for elements with large D values (Allegre et a l . , 1977). The greatest problem in quantitative treatment of trace element d i s t r i b u t i o n s i s the uncertainty i n , and wide range of 78 values for mineral/liguid d i s t r i b u t i o n c o e f f i c i e n t s (Jc). A large percentage of determinations of k values on analyses of phenocryst-matrix pairs i n natural rocks. D i s t r i b u t i o n c o e f f i c i e n t s determined i n t h i s manner . i m p l i c i t l y assume bulk equilibrium between mineral and l i q u i d , and can give r i s e to spurious r e s u l t s when applied to Rayleigh f r a c t i o n a t i o n models. Ana l y t i c a l r e s u l t s of Philpotts and Schnetzler (1970) c l e a r l y show phenocryst zcnation with respect to trace elements, and k values calculated from zoned minerals i n their study show differences up to an order of magnitude. As pointed out by Albarede and Bottinga (1972) , apparent d i s t r i b u t i o n c o e f f i c i e n t s calculated from zoned minerals w i l l be higher than equilibrium values i f k > 1, and lower than equilibrium values i f k < 1. In recognition of t h i s problem, Z i e l i n s k i (1S75) has modelled trace element abundances using a bulk equilibrium fr a c t i o n a t i o n equation. Although t h i s presents an i n t e r n a l l y consistent approach, r e s u l t s are probably inappropriate for application to natural systems where Rayleigh-type processes appear to be active. In addition to the problem of selecting appropriate k values, recent experimental studies (reviewed by Irving, 1S78) demonstrate that k values vary considerably with intensive parameters such as composition of mineral and melt, temperature, and oxygen fugacity. Increases in k values with decreasing temperature and increasing s i l i c a content of melts appear to r e f l e c t the increasing polymerization and Si/0 bond r a t i o s i n the melt structure (Irving, 1978). Discrepancies between apparent and experimental k values can i n part be resolved by 79 more rigorous d e f i n i t i o n of d i s t r i b u t i o n c o e f f i c i e n t s i n terms of proposed equilibrium exchange reactions incorporating a c t i v i t y estimates of melt components ( i . e . k values for Ni i n o l i v i n e , Leeman and Lindstrom, 1S78). at the present time, however very much more experimental work i s necessary to extend th i s technigue to other trace elements and the ccmmcn minetals in volcanic rocks. In addition, the e f f e c t of water content of melts on d i s t r i b u t i o n c o e f f i c i e n t values i s i n need of experimental investigation. In view of the above g u a l i f i c a t i o n s , . i t makes l i t t l e sense to calculate trace element d i s t r i b u t i o n s using best estimates for k values. Graphical technigues can be used to calculate bulk d i s t r i b u t i o n c o e f f i c i e n t s for suites of rocks (Allegre et _al., 1977; Duchesne, 1978), and mineral percentages can be calculated i f k values for i n d i v i d u a l minerals are chosen. The approach taken i n this study i s an inversion of t h i s l a s t procedure, i n that k values are calculated from the mineral percentages given by major element modelling. Rewriting equation 1.1 as: Equ. 1.5 D = In (C */C°)/ln(F) +1 , i t can be seen that the bulk d i s t r i b u t i o n . c o e f f i c i e n t for any trace element can be calculated from the concentration r a t i o of whole rock pairs, combined with values of F derived from the major element model. Values f o r mineral d i s t r i b u t i o n c o e f f i c i e n t s can then be computed u t i l i z i n g the mineral fractions from the major element model (equation 1.2). Consistency of the trace element model, can be .judged, by comparing these calculated k values with the ranges of values 80 quoted i n the l i t e r a t u r e (Appendix I I I ) . A major benefit of t h i s approach i s that calculated d i s t r i b u t i o n c o e f f i c i e n t s may provide valuable suqqestions f o r further investiqation by experimental techniques-It should be noted that trace element modelling of t h i s nature can be formulated such that solutions can be obtained by leas t sguares f i t t i n g akin to the major element procedure. This approach has recently met with some success i n guantitative modelling of batch p a r t i a l melting processes (Minster and Allegre, 1978). Attempts to solve the problem i n t h i s manner, however, led to non-converging solutions due to the large errors associated with k values for many minerals. The results of the trace element modelling are presented i n Table 6. Modelling was again divided into two steps using the trace element concentrations of the same rocks used i n the major element models. Bulk d i s t r i b u t i o n c o e f f i c i e n t s were calculated in the manner described above. For each element, one mineral/liquid d i s t r i b u t i o n c o e f f i c i e n t was calculated (indicated by an asterisk i n Table 6) from the bulk d i s t r i b u t i o n c o e f f i c i e n t a f t e r other minerals, with mere constrained k values, were assigned values taken from the l i t e r a t u r e (Appendix I I I ) . This procedure i s somewhat ar b i t r a r y and calculated k values can vary dramatically depending on the values chosen. Assumptions made i n assigning k values, and re s u l t s of these cal c u l a t i o n s are discussed below f o r each element. 81 TABLE 6l TEACE ELEMENT MODELLING RESULTS STEP 1: BASALTIC ANDESITE TC EACITE D Cpx Hb Plag Mt Ap Cr 3. 80 3.0 5.0 — 23* — V 2. 53 2.8 4.0 . - 10.7* — Ni 3.01 2. 5 2.9 - 21-4* -Sr 1- 16 0. 12 0.46 2.4* - 1. 0 Ba 0. 19 - 0.42 .19* - -Rb 0- 07 - 0.19* .05 . - -Nd 0,. 6 2 0. 2 0.5 0.08 - 49.9* Ce 0.30 0. 1 0.3 0.09 19.6* STEP 2: DACITE TO RHYOLITE D Bio Hb Plag Mt Ap Cr 3.05 7 5 24. 2* V 4. 55 9.3* 4 - 46. 5* — Ni 2. 25 3.7 2.9 - 21.7* -Sr 3. 86 0.4 0.46 5.6* - 1 Ea 1.13 10. 2* 0.42 0.35 • - . -Rb 0.26 2.4* 0.19 0.05 - -Nd . 1.93 0.34 0.5 6.12 - 147* Ce 1.9 8 0. 3 2 0.3 0.2 153* * Indicates calculated value - Indicates d i s t r i b u t i o n c o e f f i c i e n t value close to zero Chromium Step 1.1 Experimental work demonstrates that k (cpx) decreases with decreasing fO as Cr changes from +3 to +2 valence state (Schreiber and Haskin, 1976). The Table 6 value i s adjusted to a higher value to account for the higher s i l i c a content and lower temperatures of c r y s t a l l i z a t i o n i n Coguihalla Volcanic Complex rocks as compared with the study ci t e d - No experimental data are available on k(hb); the Table 6 value i s calculated from the average hb/cpx concentration r a t i o for Cr i n Coguihalla Volcanic Complex phenocryts, analyzed by microprobe,. The calculated k.(mt) 82 value (23) f a l l s well within the range (1-58) found from studies of natural phenocryst-matrix pairs (Appendix I I I ) . Step 2: K (hb) i s taken from the re s u l t s of step 1. No experimental work has been carried out on k ( b i o t i t e ) , and the Table 6 value i s taken from calculations by Leeman (1976). The calculated k(mt) value (24) i s s i m i l a r to that of step 1. Vanadium Step, 1_1 K(cpx) decreases with increasing fo (Lindstrom, 1976) and the Table 6 value i s taken from t h i s study. K (hb) i s taken frcm the average hb/cpx concentration r a t i o for V i n Coguihalla Volcanic Complex phenocrysts. The calculated k(mt) value (11) agrees well with experimentally determined values at oxygen fug a c i t i e s just above the QFM buffer (Lindstrom, 1976). Step 2\_ Microprobe analyses of coexisting b i o t i t e and magnetite i n Coguihalla Volcanic Complex rocks indicate that k(mt) i s roughly f i v e times k ( b i o t i t e ) . The calculated k (mt) value (46) i s within the range of values (24-63) calculated i n natural systems; the higher value than calculated i n step 1 may r e f l e c t a re a l variation of k (mt) with increasing s i l i c a content and lower temperature. The k (biotite) i s much lower than that calculated by Andriambolclcna et a l . , (1975) for natural rocks. Nickel Step K (cpx) and k(hb) are taken from the experimental results of Mysen (1978) which indicate that variations * i t h temperature and pressure are s l i g h t . The calculated k(mt) value (21) i s si m i l a r to values determined experimentally (Leeman, 1974; Lindstrom, 1976) and i n natural systems. Step 2|_ No experimental data are available of k (biotite) and 83 the Table 6 value i s taken from calculations of Leeman (1S76). The calculated k(mt) value(22) i s s i m i l a r to results of step 1. Strontium Step 1: K (cpx) i s taken from the average value of experimental work by Sun et a l . , (1974) and Shimizu (1S74) . K(hb) i s taken as an average value frott studies on natural systems by Schnetzler and Philpotts (1970) and Ewart and Taylor (1969). K (apatite) i s adopted from ca l c u l a t i o n s by Sun and Hanson (1976). The calculated k (plag) value (2.6) agrees with estimates calculated f o r An-rich plagioclase (Kcrringa and Noble, 1971), and with experimental re s u l t s of Drake and Weill (1975) f o r temperatures between 1100-1200°C. Step 2z_ K (biotite) i s taken from the average value for phenocrysts i n dacites and r h y o l i t e s (Philpotts and Schnetzler, 1970). The calculated k(plag) value (5.4) i s consistent with the results of Korringa and Noble (1971) for intermediate-composition plagiocase, and with Drake and Weill's (1975) experimental results when extrapolated to temperatures estimated for c r y s t a l l i z a t i o n of Coguihalla Volcanic Complex r h y o l i t e s . Barium Step 2± K(cpx) i s taken from the experimental work of Shimizu (1974). K (hb) i s taken as the average value of G r i f f i n and Murthy (1969) and Leeman (1S76). The calculated k(plag) value (0.19) i s s i m i l a r to experimental r e s u l t s of Drake and Weill (1975), and i s consistent with r e s u l t s f o r natural systems. Step 2: K(plag) i s taken from the lower temperature values of Drake and Weill (1975) and from the calculated values of 84 Korringa and Noble (1971) for intermediate composition plagioclase. The calculated k(biotite) value(10) i s s i m i l a r to natural phenocryst values determined by Schnetzler and P h i l p c t t s (1970). Rubidium Step. J2 K(plag) i s taken from the experimental work of McKay and Weill (1976; 1977), and k (cpx) from the results of Shimizu (1974) and Hart and Brooks (1974). The calculated k (hb) value (0.19) i s within the range of values determined from natural phenocrysts. Step 2.1. Using k(hb) of step 1, the calculated k (biotite) value (2.4) agrees well with natural phenocryst r e s u l t s of Higuchi and Nagasawa (1969). . Neodymiam Step 1.1 K (Plag) i s taken from the experimental re s u l t s of Drake and Weill (1975) and W e i l l and McKay (1975),.. K (cpx) and k(hb) are taken from the experimental work of Frey (in Irving, 1978). The calculated k (apatite) value (50) i s within the range of values detrmined by Nagasawa (1970) on natural phenocryst-matrix pairs. Step 2: K(plag) i s taken from the lower temperature experimental r e s u l t s of Drake and Weill (1975), and i i e i l l and McKay (1975). No experimental data are avail a b l e on k(biotite) and the Table 6 value i s that of Schnetzler and P h i l p c t t s (197C) . The calculated k (apatite) value (147) i s higher than any estimates i n the l i t e r a t u r e , and may> i n part, r e f l e c t increasing s i l i c a content and lower temperatures of the melt. The presence of zircon inclusions i n r h y o l i t i c b i o t i t e s would 85 lower the calculated value for k(apatite) . Cerium Step Jz Sources of data are the same as used for neodymium cal c u l a t i o n s . The calculated k (apatite) value (20) i s s i m i l a r to re s u l t s on natural systems, but i s inconsistently low when compared to the r a t i o of apatite d i s t r i b u t i o n c o e f f i c i e n t s for Ce and Nd (Nagasawa, 1970; Nagasawa and Schnetzler, 1971). Step 2-L T n e calculated k (apatite) value (153) i s s i m i l a r to that for Nd, but higher than values found for natural phenocrysts. Discussion The general agreement of calculated d i s t r i b u t i o n c o e f f i c i e n t s (Table 6) with reported ranges of values found i n the l i t e r a t u r e (Appendix III) o f f e r s excellent support for the proposed d i f f e r e n t i a t i o n model. Discrepancies i n the trace element model for the rare earth elements may r e f l e c t sampling problems, where apatite phenocrysts in dacites could be considered as culmulate phases. The problem i s compounded in r h y o l i t e s where rocks with higher modal percentages of apatite show much greater concentrations of Ce and Nd. If Eb content i s used as an indicator for degree of d i f f e r e n t i a t i o n (from equation 1-1), i t i s evident that Ce and Nd increase steadily i n abundance u n t i l a sharp decrease i s encountered i n the most d i f f e r e n t i a t e d r h y o l i t e s (Figure 35). Similar trends are recorded for Zr and Ba, and lead to the conclusion that the depletion of these elements marks a point of increased fr a c t i o n a t i o n of b i o t i t e , with conccnitant removal of 86 160<H 3. mooH = 1 2 0 0 £ 1 0 0 0 H m 800 H 600 _ 240 -= 220 -2 200 -z 1 8 0 -o 1 6 0 -<-> mo -°= 120 -~ 100 80 10 az U J o 100 90 -80 -70 -60 -50 -40 -30 -20 -20 I 10 20 x 3 2 -2 2 8 J 24 Q 20 £ l 6 H Z 1 2 H V a • 30 i T 40 50 60 70 _ J _ • • v • 30 40 _i_ 50 60 _ J _ 70 80 90 _ 1 L A A V • • A v° I i i i j 1 r 10 20 30 40 50 60 70 R U B I D I U M 80 90 FIGURE 35: The c o r r e l a t i o n s of r u b i d i u m w i t h barium, z i r c o n i u m , cerium, and neodymium i n C o q u i h a l l a V o l c a n i c Complex r o c k s . Symbols as i n F i g . 26. 1 00 80 90 100 100 100 87 the abundant zircon, apatite, and r u t i l e inclusions observed i n r h y o l i t i c b i o t i t e s . Similar decreases i n Zr content of rh y o l i t e s in New Zealand have been interpreted i n an analogous fashion (Ewart et a l . , 1968) . I t i s intere s t i n g to note that the two rhy o l i t e samples which show the greatest range of Ce, Nd, Zr, and Ba concentrations are only separated s t r a t i g r a p h i c a l l y by approximately 75 m. The enriched sample (173) has roughly 15% b i o t i t e phenocrysts while the depleted sample (712) has less than 5%. The lower st r a t i g r a p h i c position of the depleted sample suggests that eruptions tapped a zoned magma chamber i n which b i o t i t e had accumulated i n lower l e v e l s , leaving residual l i g u i d s markedly depleted i n c h a r a c t e r i s t i c trace elements. Andesite Genesis In recent years many dif f e r e n t processes have been proposed to account for the petrogenesis of ca l c - a l k a l i n e andesite associated with subduction zones. These processes include p a r t i a l melting of e c l o g i t i c oceanic crust (Green and Eingwccd, 1968), p a r t i a l melting of hydrous mantle p e r i d o t i t e (Kushiro, 1974; Mysen and Boettcher, 1975a; 1975b), 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 b a s a l t i c magmas (Green and Eingwocd, 1967; Osborn, 1969; Cawthorne and O'Hara, 1976), and mixing of bas a l t i c and r h y o l i t i c magmas (Eichelberger, 1978). The chemistry of Coguihalla Volcanic Complex rocks can be used to evaluate the roles of these various processes. Mixing of b a s a l t i c magma with upper c r u s t a l material i s unlikely in view of the uniform Sr isotopes within the volcanic 88 su i t e , and the lack of observed c r u s t a l xenoliths i n Coquihalla Volcanic Complex andesites. Mixing of b a s a l t i c and r h y c l i t i c magmas i s not supported by the general lack of diseguilibrium phenocryst assemblages and reversed zoned phenocrysts, and the nonlinearity of whcle-rock compositional va r i a t i o n s . The uniform yttrium contents of Coguihalla Volcanic Complex andesites argues against t h e i r derivation by p a r t i a l melting of e c l o c i t i c oceanic crust, as the high d i s t r i b u t i o n c o e f f i c i e n t of garnet f o r Y would be re f l e c t e d in variatio n s i n Y content of rocks formed by di f f e r e n t degrees of p a r t i a l melting- In addition, l i q u i d s produced by meltinq of high Na/K e c l o g i t i c oceanic crust would be expected to show higher Na/K r a t i o s than those observed in Coguihalla Volcanic Complex rocks (Whitford, et a l . , 1979) . The low Mg/(Mg+Fe) r a t i o s of Coguihalla Volcanic Ccuplex andesites, and low Cr and Ni contents are incompatible with equilibrium of these rocks with mantle p e r i d o t i t e (Rceder and Emslie, 1970; Nicholls and Whitford, 1976). Experimental data of Nich c l l s and Ringwood (1973) show, however, that t h c l e i i t i c l i q u i d s produced by hydrous p a r t i a l melting of p e r i d o t i t i c assemblages at depths of 60-100 km, w i l l undergo pronounced o l i v i n e fractionation as they ascend through the mantle and lower crust. Such high pressure accumulation of o l i v i n e , plus clinopyroxene or chrome-spinel can account s a t i s f a c t o r i l y for the low Mg/(Mg+Fe) r a t i o s , and low Ni and Cr contents of Coguihalla Volcanic Complex b a s a l t i c andesites. Subsequent i, residence in high l e v e l magma chambers would allow fr a c t i o n a t i o n of the low pressure phases involved i n generating the chemical 89 spectrum through dacites and r h y o l i t e s . Couclusigns The chemical c h a r a c t e r i s t i c s of Coguihalla Volcanic Complex andesites are consistent with derivation through high pressure modification of parental b a s a l t i c magmas. The association of the Coguihalla Volcanic Complex with subduction of the Juan de luca plate, and andesites i n general with zones of lithospheric subduction, implies a genetic r e l a t i o n s h i p such as outlined by Green (1977) or Mysen (1978b). Generation of dacites and rhy o l i t e s by low pressure fra c t i o n a t i o n of andesitic l i g u i d s i s supported by guantitative major and trace element modelling, as well as the resu l t s of experimental studies. This low pressure f r a c t i o n a t i o n implies long term residence of magmas i n the upper crust, and may be a conseguence of the increased v i s c o s i t y of andesitic l i g u i d s as they r i s e through the crust (Kushiro, 1978). . The observed stratigraphic sequence of the Coquihalla Volcanic Complex suggest a model i n which tapping of the upper, di f f e r e n t i a t e d portion of a high l e v e l magma chamber occurs, producing voluminous ash flow eruptions which tend to decrease i n temperature with time. Periodic replenishment of the magma chamber with mantle-derived andesitic l i q u i d s maintains si m i l a r d i f f e r e n t i a t i o n paths throughout the period of explosive volcanism. 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The technigue for analysis and data reduction of major elements i s presented by Nixon (1979). Technigues for trace element analysis, and reduction program procedures are presented i n Appendix IVa and IVb. Total water and carbon dioxide contents were determined on an apparatus designed after Hutchinson (1974), and the a n a l y t i c a l procedures are discussed i n Appendix IVc. Ferrous iron concentrations were determined by wet chemical methods outlined in Appendix IVd. Major element analyses are presented on the following pages f o r twenty-six samples (locations shown on Plate II) of the Coquihalla Volcanic Complex. These analyses have been recalculated to 100%, but the reported sums are for the o r i g i n a l XRF analyses. Trace element concentrations are reported i n parts per m i l l i o n . Normative compositions were calculated on a v o l a t i l e - f r e e basis, after the ferrous iron content of a l l recks had been adjusted by the procedure of Le Maitre (1976), i n order to normalize the suite of rocks to oxidation states more representative of th e i r o r i g i n a l compositions. The normative 104 c a l c i t e contents reported are taken from separate norm calculations done on a vo l a t i l e - i n c l u d e d basis. 105 APPENDIX I: WHOLE-BOCK ANALYSES -PYROXENE ANDESITE- ,—HORNBLENDE ANDESITE-251 61 380 252 * 30 SI0 2 52. 10 57.32 56.44 54.48 55-. 19 TI02 0. 98 0.80 0;.S8 1.04 0.86 AL203 17. 12 15.89 16.89 17.25 17.24 FE2C3 4.72 3.62 4^62 4.90 5.0 8 FEO 3. 46 3.72 2.81 3.28 2.31 MNO 0. 17 0* 15 0* 15 0.15 0.15 MGO 4.25 4.21 3.27 3.08 3*51 CAO 9.26 6.38 6. 48 7.76 7.71 NA20 2.79 3.C2 3.69 3.00 3.05 K20 1.00 2. 22 1.7 4 1.32 1.41 P20 5 C.27 0.22 0.30 0.27 0.27 CC2 2.79 0. 15 0.35 1.06 0.35 H20 1.10 2.32 2.25 2.37 2.86 SUM 99,. 16 100.31 98.80 99.17 100.40 TEACE ELEMENT CHEMISTRY NI 23 9 8 10 14 CB 50 64 11 13 21 V 241 197 195 218 166 SB 578 480 579 572 592 EB 21 53 37 15 31 EA 589 873 906 672 691 ZR 107 156 150 126 125 Y 26 28 29 28 28 NB 5 7 7 6 6 CE 29 48 52 22 41 ND 16 29 29 19 21 NOEMATIVE COMPOSITION Q 8. 66 11.10 9.56 10.53 10.25 OE 6. 21 13.53 10.61 ,8.18 8.68 AB 26. 32 27.98 34. 19 28.26 28.52 AN 32.82 23.99 25. 17 31. 17 30.40 DI 10. 88 5.76 4.63 5. 90 6.08 EN 7.31 9.76 7.60 6.93 7.90 FS 0. 61 2.83 2.66 3.31 3.04 MT 5. 18 3.42 3.46 3.61 3.29 IL 1. 43 1.15 1.41 1.52 1.25 AP C.59 0.47 0.71 0.59 0.59 C 0.0 0.0 0. 0 0.0 0.0 CC 7. 17 0.39 0.91 2.7 8 0.92 D.I,. 41.18 52.61 54. 36 46.97 47.45 APPENDIX I.: (CONT.) HOBNBLENDE ANDESITE-66 38 171 4 635 SI0 2 57.73 56.86 56.01 59.4 8 59.95 TI0 2 0.86 0.91 0.95 0.83 0.78 AL203 17. 11 16. 93 16.85 17.22 16.93 FE203 4.39 4. 42 1. 34 4.23 6.03 FEO 2. 58 2.87 0.0 1.7^ 0.0 MNO 0. 14 0. 12 Oi 13 0. 13 0^ 15 MGO 3. 12 2.63 2.96 2.36 2.42 CAO 6. 15 6. 20 6. 51 5.85 5.11 NA20 2.87 2.41 3.30 3.08 3.89 K20 1. 74 2.30 1.80 2.29 2.36 P20 5 0. 24 0.29 0.29 0.25 0.29 CG2 0.64 1,. 55 0.71 0.6 0 0.06 H20 2.42 2.50 3. 15 1.95 2.03 SUM 100.85 99.26 100.04 100.41 99.55 TEACE ELEMENT CHEMISTEY NI 10 11 7 9 6 CE 12 14 11 11 • 8 V 172 170 173 137 115 SE 57 5 555 506 568 572 EB 46 51 38 50 59 BA 831 1040 833 863 1089 ZE 145 161 165 166 164 Y 28 29 31 30 29 NB 8 8 7 7 • 8 CE 41 41 . 61 50 56 ND 24 21 27 i 24 28 NOBMATIVE COMPOSITION • C 15i03 15.67 11.30 15.74 13.04 OE 10.73 14.40 11.16 14^02 14.29 AB 26.89 22i93 31,i0 9 28.66 35.81 AN 29.92 30.30 27.13 27^36 22.32 DI 0.23 0. 13 3. 82 0.82 1.39 EN 8.90 7.65 7.20 6.45 6.33 FS 3i32 3. 47 2.84 2.32 2.0 8 MT 3. 21 3.41 3.43 2.87 3.00 I L 1.25 1.34 1. 39 1.20 1.11 AP 0.52 0.69 0.64 0.54 0.6 2 C 0. 0 0.0 0.0 0.0 0.0 cc 1.68 4.07 1.87 1.56 0. 16 D.I,. 52. 64 53.00 53. 55 58.43 63.14 APPENDIX I: (CONT.) -COQUIHALLA MOUNTAIN -STOCK 632 311 318 366 310 SI0 2 54. 58 56.49 56.82 59.60 61.66 TI02 1*03 0.96 0. 95 0.81 0-78 AL203 16.98 17.44 17.4 3 16.73 16.93 FE203 4.00 4. 31 2*26 3.41 3.3 6 FEO 5.07 3.71 6.64 3.46 2.31 MNO 0. 15 0. 17 0* 15 0.16 0. 16 MGO 4. 58 3.54 3.05 3.19 2.00 CAO 8.0 2 6. 66 6.33 6.02 4.78 NA20 3. 17 4.C4 3.72 3.24 4.51 K20 1.61 1.67 1.97 2.02 1.96 P20 5 0.28 0.29 0.24 0.23 0.25 C02 0. 06 0.08 0. 12 0.03 0 . 1 6 H20 0. 47 0.64 0.32 1.09 1. 15 SUM 100.20 98.73 99.67 99.44 100.31 TEACE ELEMENT CHEMISTEY NI 13 11 13 10 8 CE 22 18 37 23 9 V 225 167 181 154 121 SE 512 566 489 454 511 EB 44 37 55 56 48 EA 66 8 823 685 785 1001 ZE 132 142 152 158 168 Y 30 30 30 31 28 NB 7 6 8 9 8 CE 34 36 35 53 58 ND 22 19 23 22 26 NOEMATIVE COMPOSITION Q 5. 45 6.28 7*81 13.64 13.38 OE 9.63 9.S6 11.78 12.17 11.74 AB 28. 80 36.60 33* 82 29.68 41.07 AN 27.68 24.75 25.36 25.65 20.45 DI 8. 59 5.35 3. 88 ' 2.63 1.56 EN 9.88 8.07 7.34 8.10 5.09 FS 4. 68 3.94 4.72 3.87 2.69 MT 3.24 3.09 3.43 2.61 2.38 IL 1. 45 1.35 1.34 1.15 1.10 AP 0. 59 0.61 0*51 0.49 0.53 C 0.0 0.0 0.0 0.0 0.0 cc 0. 15 0.20 0.31 0.08 0.41 D,I. 43. 88 52.84 53. 4 1 55.49 66.20 108 APPENDIX I i (CONT.) HORNBLENDE ALTERED —-ALTERED ANDESITE— DACITE DACITE 296 253 59 283 192 240 SI02 57. 40 54.09 55.01 63.29 65.52 65.89 TI0 2 0.80 0.86 1.03 0.58 0.56 0. 60 AL2C3 16.90 16.64 16.89 16.65 16.13 16.99 FE203 3.63 3.16 4.48 2. 13 2.61 1. 58 FEO 2. 93 4.00 3. 46 2.78 1.60 1.56 MNO 0. 14 0.18 0.20 0.12 0, 12 0. 09 MGO 3.34 3. 17 3-4 8 2.05 1.44 C.85 CAO 5.65 5.44 4.68 4.21 2.68 2.60 NA20 3. 12 3-05 4. 40 4. 13 4.48 4.62 K20 1.78 2.35 2.07 2.19 2.48 3.39 E205 0. 22 0. 26 0.32 0.29 0.21 0. 16 CO 2 1.35 3.41 1.00 0.09 0.47 0. 10 H20 2.71 3. 39 2.96 1.49 1.67 1.58 SUM 99.96 99.29 99.73 t 100.70 99.47 99.85 TRACE ELEMENT CHEMISTRY NI 11 10 9 4 5 5 CR 20 10 11 4 7 3 V 157 187 193 99 68 33 SR 531 345 467 488 490 369 RB 48 51 43 58 62 81 BA 650 737 998 1085 1076 1280 ZR 167 127 160 171 184 239 Y 31 27 31 29 27 37 NB 7 6 8 9 9 10 CE 61 41 52 48 52 102 ND 27 20 24 25 29 43 NORMATIVE COMPOSITION .< . • Q 13. 99 10.09 5.50 17.40 20^91 18. 25 OR 11. 04 15,00 12^71 13. 18 15.00 20.32 AB 29.41 29.59 41 .08 37.77 41.19 42. 09 AN 27. 93 26.77 21; 03 19.35 12*21 12.03 DI 0.0 0.45 0^75 0^0 0.0 0.0 EN 9.68 9. 29 9.70 5.77 4.07 2.38 FS 3. 10 3.41 3.12 2.24 1. 18 0. 45 MT 3. 10 3. 50 3U91 2.27 2.27 1.76 IL 1. 17 1.29 1.49 0.82 0.80 0.85 AP 0. 48 0. 59 0.70 0.62 0.45 0.34 C 0. 11 0.0 0.0 0.58 1.91 1 a 5 2 cc 3.52 8.90 2. 60 0.23 1.21 0.26 D-I. 54.44 . 54.69 59.29 68.35 77. 11 80.66 APPENDIX I:_ (CONT.) RHYOLITE 319 112 26 712 173 SI0 2 71. 10 72.82 73.92 75.53 72.87 TI02 0.37 0. 27 0.31 0.14 0.27 AL203 15.58 15.32 13.90 12.97 13.46 FE2C3 1. 12 0.64 0.80 0,91 0.68 FEO 1. 29 0.81 0.92 0;. 0 1.51 MNO 0. 11 0.06 0.0 8 0.05 0,07 MGO 0.66 0.57 0.59 0. 14 0.31 CAO 1.22 0.50 0.27 0.67 0,24 NA20 4.49 4.96 4.75 3.72 5.64 K20 3.06 2, 21 2. 37 3.80 3.71 P20 5 0. 06 0.04 0. 07 0.04 0.03 C02 0. 10 0. 15 0. 17 0.21 0. 13 H20 0.84 1.69 1.85 1.72 1.12 SDM 99.76 99.96 99.80 100.56 99.56 TRACE ELEMENT CHEMISTRY NI 8 5 5 2 7 CR 13 7 5 2 23 V 37 20 21 11 11 SR 184 243 175 95 120 RB 88 61 55 92 84 BA 1033 i2 i g 1247 1006 1593 ZR 160 156 168 79 203 Y 30 17 23 28 26 NB 12 9 9 12 11 CE 55 54 62 29 89 ND 27 25 23 16 29 NORMATIVE COMPOSITION Q 27.72 31.65 33.9 7 36.04 23,29 OR 18.29 13.28 14.34 23.15 22.09 AB 40.79 45. 31 43. 68 34.44 51.03 AN 5.73 2.26 0.90 3.16 0.46 DI 0. 0 0.0 0.0 0.0 0.44 EN 1.84 1.60 1.67 0.40 0.69 FS 0,4 9 0. 22 0. 27 0.15 0.20 MT 1.38 0.83 1.01 0.55 1.35 IL 0, 52 0.38 0.4 4 0.20 0.38 AP 0. 13 0.09 0.15 0.09 0.06 C 3. 10 4.39 3. 57 1.82 0.0 CC 0.26 0.39 0.44 0.55 0.33 D.I. 86. 81 90.24 91.99 93.63 96.42 110 APPENDIX II I MICROPROBE MINERAL ANALYSES A l l mineral analyses were performed by an ARI-SEMQ electron microprobe- The accelerating voltage was 15 KV, the specimen current 50 nannoamperes, and a beam width of 10-20 microns was generally used. Most analyses were reduced using the correction procedures of Bence and Albee (1968) and Albee and Ray (1S70) ; analyses which include vanadium were reduced by c l a s s i c a l correction procedures using the EMPADE VII computer program of Rucklidge and Gasparrini (1969) . A combination of natural and synthetic minerals were used as standards. Formula bases, f e r r i c iron contents, and end-member compositions were calculated using the MINTABLE program discussed i n Appendix Vd, This program u t i l i z e s the reduction procedures of Cawthorne and Collerson (1974) f o r pyroxenes, Anderson (1968) and Carmichael (1967) for i r o n - titanium oxides, and Eapike et a l . (1974) for amphiboles. Mineral analyses are presented on the following pages, and elements which were not determined i n particular analyses are indicated by dashes ( — ) - . • . APPENDIX IIA: PYEOXENE ANALYSES' 111 PYROXENE . HORNBLENDE DIORITE —ANDESITE ANDESITE — 632 318 251 251 252 252 SI02 52-02 52. 64 50.38 5 2.41 50-22 50. 13 TI02 C- 16 0. 29 1.09 0.56 0.73 0. 71 AL2C3 0.53 0. 99 4. 51 1-75 4.63 2. 88 CR203 — — — — — 0. 03 V2 03 — : — — — 0. C7 NIO — — — — — 0. 0 FEO 9. 60 10,. 61 9.12 7.95 6.88 8.14 MNO 0.34 0. 47 0.2 4 0.49 0.28 0. 29 MGO 14. 25 14. 08 14. 93 16.04 14.66 14. S6 CAO 22.93 20. 91 20.16 20.21 22.66 21. 59 BAO 0.07 0.0 0.06 0.0 0.12 0. 0 NA20 C.28 0. 39 0.32 0.36 0.3 2 0. 38 K2C 0.02 0. 0 0.0 0.02 0.04 0. 0 SUM 100.20 100.38 100.81 99.79 100.54 99. 18 FORMULA EASED ON 6 OXYGENS SI 1.9550 1.9677 1.8614 1.9442 1.8 57 4 1 . 8870 Al IV 0.0235 0.0323 0. 1386 0.0558 0.1426 0 . 1130 TI 0.0C45 0.0082 C.0303 0.0156 0.0203 0 .0201 AL VI 0.0 0.0114 0.C57 8 0.0207 0.C592 0 .0148 CR — — • — — — 0 .0009 V — — — — — 0 .0021 NI — • — — — 0 .0 J7E2 + 0.3017 0.33 17 0.2818 0.2466 -0.2128 0 . 2563 FE3 + 0.0080 0.00 10 0.0 0.. 0 0.0 0 .0 MN 0.0109 C.0150 C.0C76 0.0155 0.0C88 0 .0093 MG 0.7982 0.7845 0.8222 0. 8869 0.8C82 0 . 63S4 CA 0.9233 0.8375 C.7981 0.8033 0.8980 0 .8708 BA 0.0010 0.0 0.0009 0. 0 0.0017 0 -0 NA C.0204 C.0283 0.0229 0.0259 0.0229 0 . 0277 K 0.0010 0.0 0.0 0.0009 0.0019 0 .0 CA 45.39 42. 54 41.79 41.14 46.58 44. 07 MG 39. 24 39.85 4 3.06 45.43 41.92 42. 48 IE 15.37 17. 61 15.15 13.43 11.50 13.44 XY 2. 06 2.02 2.02 2.02 2. 03 2. 04 Z 1.98 2.00 2.00 2.00 2.00 2. 00 MOLE PERCENT END MEMBERS JD 1.39 2.69 2.33 2.64 2.57 2.66 AC 0.77 0. 09 0.0 0.0 0.0 0. 0 I EC ATS 0. 0 0. 0 0.0 0.0 0.0 C. 14 TICATS 0. 44 0. 80 2.96 1. 54 1-96 1. 93 CATS 0.0 0.0 5.48 0.91 6.51 2. 87 WO 44. 27 40-81 34. 83 38.33 39-17 39.34 EN 38. 46 38.60 40.23 43.67 39.C7 40. 30 FS 14.68 17. 01 14. 16 12. 91 1C.71 12.75 112 APPENDIX IIA: (CONTINUED) -HORNBLENDE ANDESIT E — DACITE -—DIORITE 252 635 004 283 318 632 SI02 52. 16 52-, 54 50. .93 52. 13 51. .72 51. . 47 TI02 0. . 16 0. , 47 0. .65 0. 29 0. .44 0. , 33 A12 03 0.81 1. 45 2. . 52 1,. 07 1. .04 0. . 86 CR203 0. .01 — — 0. 01 — — V203 0. ,0 — — 0. 08 — - — NIO 0, .0 — — • 0. 01 — . — FEO 8. 83 7. 66 8. , 37 8,-43 24, .49 21. , 77 MNO 0. .68 0. .56 0. .36 0. 65 0. .73 0. 62 MGO 14. 59 15. ,44 15. .35 14. 93 20. .26 22. . 68 CAO 2 1. 97 21. , 44 21. .77 21- 95 1. .95 2. 07 BAO 0. 0 0. 10 0. ,04 0. 0 0. .0 0. 0 NA20 0. .30 0. ,36 0. ,30 0-36 0. .01 0. 02 K20 0. 02 0. 05 0. ,05 0. 0 0. .0 0. , 02 SUM 99. .53 100.07 100. .34 99. 91 100. ,64 99. 84 FORMULA EASED ON 6 OXYGENS SI 1.9614 - 1.95C3 1.8963 1.9496 1.9475 .1.9332 AL IV 0.0359 0.0497 0.1037 0-0472 0.0462 0.C381 TI 0. 0045 0.0131 0.0182 0.0082 0.0125 0.0093 AL VI 0.0 0.0137 0.0069 0. 0 0.0 0.0 CR 0.0003 — • — C.C003 — — V 0.0 — . — 0.0024 — — NI 0.0 — — 0.0003 • — — FE2 + 0.2777 0.2378 0. 2606 0.2637 0.7712 0.6838 FE3 + O.C 0.0 0.0 0.0 0.0 0.0 MN 0.0218 0.0177 0.0114 0.. 0207 0.0234 0.0199 MG 0.8178 0.8543 0.8519 0.8323 1.137 1 1.2697 CA 0.8852 0.8527 0.8685 0.8796 0.0787 0.0833 BA O.C 0.0015 C.0006 0.0 0.0 0.0 NA 0.0219 0. 0259 0.0217 0.0261 0-0007 0.0015 K • 0.0010 0.0024 0.0024 0.0 0.0 0.CO 10 CA 44.20 43- 45 43. 59 4 4.06 3-91 4. 05 MG 40.84 43.53 42.76 41.69 56.56 61.74 FE 14. 96 13,. 02 13.65 14-25 39.53 34.21 XY 2.03 2. 02 2.04 2.03 2.02 2. 07 Z 2.00 2. 00 2-00 2.00 1-99 1.9 7 MOLE PERCENT END MEMBERS JD 2. , 22 2.92 2. .36 2. 53 0. .07 0.23 AC 0, .0 0. , 0 0. .0 0. 0 0. .0 0. 0 FECATS 0. .01 0. , 0 0. .0 0,. 13 0. .0 0. , 0 TICATS C. .44 1. .29 1. .75 0. 79 1. .22 0. ,90 CATS 0. , 20 0. . 37 2. .38 0. 23 1. .01 0.. 82 HO 42. .75 41. , 00 39. .60 42. 11 2. .75 3. 15 EN 39. , 80 41. . 90 40. , 86 40. 40 55. ,8S 61. , G6 FS 14. .58 12. .53 13. .05 13. 80 39. ;06 33. 84 113 APPENDIX I I B : HORNBLENDE ANALYSES HORNBLENDE ANDESITE -HORNBLENDE DACITE-252 252 635 004 283 283 164 SI02 41.26 43.0 6 43. 64 45. 20 45.20 43.95 43.62 TIC 2 3.32 3. 07 3, 22 2. 64 2.64 2.81 3.07 AL203 10.63 11.C4 9.7C 8.55 9.40 9.27 11.11 CR203 — ' 0.01 — — 0.02 0.01 — • • V203 — 0.11 — — 0.14 0. 10 . — NIO — 0.01 — — - 0.01 0.0 --FEO 12.37 11.71 11.92 1 1.78 12.46 12. 10 11.76 MNO 0.36 0. 23 0. 40 0. 44 0.36 0.36 0.31 MGO 15.09 14.59 14.63 15.23 14.54 14.40 14.80 CAO 11.26 11.17 11.04 11. 54 11.52 11.13 11.45 BAO 0. 16 — 0. 18 0.05 — •. — 0.0 NA20 2.54 2.47 2. 40 2. 22 2- 19 2. 24 2.50 K20 0.44 0.42 0. 54 0.50 0.49 0.45 0.47 SOM 97.43 97. 89 97. 67 98. 15 98. 97 96. £2 99.09 FORM OLA BASED ON 23 OXYGENS SI 6.1494 6.3172 6.4358 6.6103 6.5645 6.5249 6.3237 AL I V 1.8506 1.6828 1.5642 1.3897 1.4355 1.4751 1.6763 TI 0.3721 0,3387 0.3571 0.2903 0.2883 0.3137 0.3347 AL VI 0.0167 0.2262 0.1218 0.C841 0.1735 0.147C 0.2221 CR — 0.0012 -- ~ 0,0023 0.0012 V — 0.0129 — — r 0.0163 0.C119 NI — 0.0012 — — 0.0012 0.0 FE2+ 1.2885 1.4367 1.4702 1.4408 1.5134 1.5024 1.4258 FE3+ 0.2534 0.0 0.0 0.0 0.0 0.0 0.0 MG 3.3523 3.1905 3.2159 3.3199 3.1475 3.1866 3.1981 < MN 0.0458 0.0288 0.0503 0.0549 0-0446 C.0456 0.0383 CA 1.7981 1.7558 1.7444 1.8083 1.7926 1.77C4 1.7785 NA 0.0 0.0080 0.0402 0.0017 0.0203 0.0212 0.0024 BA 0. 0093 — 0.01C4 0.0029 — — 0.0 NA 0.7340 0.6946 0.6461 0.6278 0.5964 0.6236 0.7003 K C.0837 C.0786 0.1016 0.0933 0.0908 0.0852 0.0869 CA 27.73 27.38 26.92 27,30 27.59 27.22 27.61 MG 51.70 49.76 49.62 50.12 48.44 48.99 49.65 FE 20.58 22.86 23,46 22.58 23.98 23.80 22.73 Z 8.00 8.00 8.00 8.00 8.00 8.00 8.00 Y 5.06 5.00 5.00 5.00 5.00 5.00 5.00 X 2.06 2.00 2.00 2.00 2.00 2.00 2.00 W 0.83 0,77 0.76 0.72 0.69 0.71 0,79 A P P E N D I X I I C : F E L D S P A R A N A L Y S E S P Y R O X E N E H O R N B L E N D E D I O R I T E — A N D E S I T E — A N D E S I T E D A C I T E 6 3 2 3 1 0 3 1 0 2 5 1 0 6 1 2 5 2 1 6 4 1 9 2 S I O - 2 5 3 . 0 0 5 0 . 4 5 6 0 . 5 0 4 9 . 1 7 5 5 . 0 9 5 4 . 1 0 4 9 . 1 9 5 0 . 2 3 T I 0 2 0 . 1 1 0 . 0 2 0 . 0 4 0 . 0 7 0 . 0 9 0 . 0 7 0 . 0 5 0 . 1 0 A L 2 0 3 . 2 0 . 7 1 3 0 . 4 1 2 3 . 0 0 3 2 . 2 9 2 7 . 9 0 2 7 . 7 2 3 2 . 3 2 2 6 . 7 9 F E O ' 0 . 4 3 . 0 . 5 1 0 . 2 1 0 . 4 0 0 . 4 5 0 . 4 4 0 . 3 1 0 - 1 2 M N O 0 . 0 0 0 . 0 1 0 . 0 2 0 . 0 4 0 . 0 0 0 . 0 0 0 . 0 0 0 . 0 0 MG 0 . 0 . 0 4 ' 0 . 0 1 0 . 0 2 0 . 0 6 0 . 0 0 •• 0 . 0 7 0 . 0 4 0 . 0 3 C A O . I V . 7 7 1 4 . 3 6 6 . 6 9 1 5 . 0 5 1 0 . 3 0 1 0 . 0 0 1 5 . 6 0 7 . 5 6 B A O 0 . 1 0 — -- -- 0 . 0 0 • 0 . 0 1 N A 2 0 . 4 . 8 8 3 . 4 6 7 . 0 0 2 . 5 5 5 . 4 5 5 . 4 5 2 . 7 1 7 . 2 3 K 2 0 •> 0 . 3 7 0 . 1 2 0 . 4 3 0 . 1 6 0 . 5 0 0 . 2 4 0 . 1 2 0 . 2 1 S U M 9 0 . 5 2 9 9 . 3 5 9 9 . 6 7 1 0 0 . 6 9 9 9 . 8 6 9 9 . 1 3 1 0 0 . 4 2 1 0 0 . 2 8 F O R M U L A B A S E D O N 0 O X Y G E N S S T 2 . 4 2 4 1 2 . 3 2 0 1 2 . 7 1 0 2 2 . 2 3 9 4 2 . 4 9 3 6 2 . 4 7 6 1 2 . 2 4 3 3 2 . 5 9 7 2 A L 1 . 5 4 7 0 1 . 6 4 0 3 . 1 . 2 6 0 0 1 . 7 3 3 3 1 . 4 0 0 4 1 . 4 9 3 1 1 . 7 3 7 2 1 . 4 0 0 3 T I • 0 . 0 0 3 0 0 . 0 0 0 7 0 . 0 0 1 3 0 . 0 0 2 4 0 . 0 0 3 1 0 . 0 0 2 4 0 . 0 0 1 7 0 . 0 0 3 4 I ' E 0 . 0 1 6 4 0 . 0 1 9 6 0 . 0 0 7 9 0 . 0 1 5 2 0 . 0 1 7 0 0 . 0 1 6 0 0 . 0 1 1 0 0 . 0 0 4 5 M N 0 . 0 0 0 0 0 . 0 0 0 4 0 . 0 0 0 0 0 . 0 0 1 6 0 . 0 0 0 0 0 . 0 0 3 1 0 . 0 0 0 0 0 . 0 0 0 0 fIG 0 . 0 0 2 7 0 . 0 0 0 7 0 . 0 0 1 3 0 . 0 0 4 1 0 . 0 0 0 0 0 . 0 0 4 0 0 . 0 0 2 7 0 . 0 0 2 0 C A . 0 , 5 7 5 9 0 . 7 0 7 6 0 . 3 2 1 1 0 . 7 7 0 3 0 . 5 0 3 4 0 . 5 2 0 8 0 . 7 6 6 2 0 . 3 6 1 3 H A 0 . 0 0 1 0 -- — — 0 . 0 0 1 4 -- 0 . 0 Q 0 2 N A 0 . 4 3 2 1 0 . 3 0 0 5 0 . 6 0 4 4 0 . 2 2 5 2 0 . 4 7 0 3 0 . 4 0 2 9 0 . 2 3 9 6 0 . 6 2 5 2 K • 0 . , 0 2 1 6 0 . 0 0 7 0 0 . 0 2 4 6 0 . 0 0 9 3 0 . 0 2 0 9 0 . 0 1 4 0 0 . 0 0 7 0 0 . 0 1 1 9 X Y 1 . 0 5 4 3 1 . 0 4 4 5 1 . 0 4 1 4 1 . 0 3 6 1 1 . 0 3 0 7 1 . 0 5 4 3 1 . 0 2 9 1 V . 0 0 0 5 7 3 . 9 7 1 1 3 . 9 6 0 4 3 . 9 7 1 1 . 3 . 9 7 2 7 3 . 9 0 2 0 3 . 9 6 9 2 3 . 9 0 0 6 4 . 0 0 5 5 A M 55. 9 4 6 9 . 1 6 3 1 . 1 7 7 6 . 0 5 4 9 . 0 1 5 1 . 5 6 7 5 . 6 5 3 6 . 1 0 A B 4 1 . 9 7 3 0 . 1 5 6 6 . 4 4 2 2 . 2 3 4 7 . 3 3 4 7 . . 0 0 2 3 . 6 6 6 2 . 6 2 on 2 . 0 9 0 . 6 9 2 . 3 9 0 . 9 2 2 . 0 6 1 . 3 6 0 . 6 9 1 . 2 0 R H Y O L I T E D I O R I T E 173 7 12. 22J 632 6 1. 50 62. 50 71. 60 66. 39 0. 07 0. 05 0. 25 0. 04 23. 60 2 2 . 96 14.99 10. 00 0. 31 0. 26 0. 19 0.4 7 0. 07 0. 06 0. 09 0. 02 0. 04 0. 04 0.04 0. 00 5. 64 5. 24 0.36 0. 79 0. 15 0. 25 0. 32 0. 30 0. 01 0. 31 1. 24 2. 62 0. 57 0. 71 11.44 10. 07 9 9 . 96 100.30 100.60 99. 66 . 74 19 2 .7745 3 . 1939 3 . 0077 . 24 01 1 .2013 0 . 7072 1 . 0081 . 0023 0 . 00 17 0 . 0004 0 .0014 .0116 0 . 0097 0 .007 1 0 . 0 1 7 0 . 00 27 0 . 0 023 0 . 0034 0 . 0000 . 0027 0 . 0026 0 . 0027 0. 0000 . 2694 0 .24 92 0 .0172 0 . 0 303 . 00 26 0 . 00 43 0 . 0056 0 .0067 - 6924 0 .7152 0 .1071 0 . 230 1 . 0324 0 . 04 02 0 . 6503 0 . 5020 . 01 61 1 . 02 53 0 .8017 0 . 0771 . 9020 3 . 9757 3 .90 11 4 .0 150 27. 10 24. 81 2. 22 4. 51 6 9. 64 7 1 . 19 13. U3 2 7..06 3. 26 ' 4- 00 83.9 5 6 0. 4 3 115 APPENDIX IID:.BIOTITE ANALYSES DIOEITE • RHYOLITE GRANITE 3 10 173 173 712 223 180 183 SI02 39.76 38. 62 38.06 36.78 36. 68 36.76 35.35 TI02 4.56 4.07 4.03 4.04 4.36 4. 19 3. 39 AL203 11.90 14.55 13.96 . 13.81 13. S7 13.84 15. 58 CR203 — — 0.0 — — — — V203 — — 0. 12 — — — ' — NIO — — C.01 — — — • — FEO 9. 57 13. 75 13. 57 17.66 16.58 15.33 20.70 MNO 0. 26 0.55 C.31 0.58 C.60 0. 57 0. 49 MG 0 18. 96 16. 15 16. 11 13.62 14. C8 14. OS 9.23 CAO 0.C8 0. 10 0,03 0.11 0. 10 0. 10 0. 08 BAO 0. 62 1.25 — 0. 53 0.85 0.71 0. 68 NA20 0. 23 0.75 0.80 C.72 C.7C 0. 55 0. 24 K20 9.64 7.01 7. 86 8.70 8.64 8.70 9.-32 SUM 95. 58 96.80 94.86 96.55 96.56 94.86_ 95. 06 FORMULA j BASED ON 22 OXYGENS SI 5 .808 1 5.6297 5.6400 5.5350 5.5041 5 .5763 5. 50 16 AL IV 2 .0488 2. 3703 2.3600 2.4495 2.47C7 2 .4237 2.4984 TI C -5CC9 0.4462 0.4491 0.4572 0.4920 0 .4777 0-. 39 68 AL VI Q .0 0. 1295 0.0782 0.0 O.C 0 .0495 0.3594 CR — — 0.0 — — — — V — - — 0.0143 — — — — NI — — 0.0012 — — — — FE2 + 1 . 1692 1.6763 1.6817 2.2226 2.0807 1 .9438 2. 6942 MN 0 .0324 0.0684 0.0392 0.0745 0.0768 0 .0737 0.C651 MG 4 . 1283 3.5091 3.5584 3.0551 3.1493 3 .1842 2. 1411 CA 0 .0125 C.0156 0.0048 0.0177 0.0161 0 .0162 0.0133 BA 0 .0355 0.0714 — 0.0312 0.0500 0 .0422 0.0415 NA c .0651 C.2120 0.2299 0.2101 C.2037 0 . 16 17 0. C724 K 1 .7964 1. 3036 1.4858 1.6702 1.6539 1 .6826 1.6503 Z 7.86 8.CO 8.CO 7.98 7. 97 8. 00 8. 00 Y 5. 83 5.70 5.74 5.81 5.80 5. 68 5.30 X 1.91 1.60 1.72 1.93 1.92 1. 90 1. 98 APPENDIX H E : • MAGNETITE ANALYSES PYROXENE HORNBLENDE DIORITE —ANDESITE- —ANDESITE- CACHE RHYOLITE 632 3 18 310 251 061 252 252 283 192 173 17 3 712 SI02 1. 20 0. 14 0. 29 0. 45 0.29 0. 4 1 0. 25 0. 6 5 0.07 0.31 0. 15 0. 62 TI02 3-75 3.12 2. 53 17. 62 11-85 14. 57 13. 44 8. 16 8. 19 6. 29 5-82 5. 22 AL2 03 i . 13 1. 5.2 0. 72 0. 53 2. 04 3.54 3-3 2 1. 20 3.08 1.78 1.62 1. 75 CR203 0. 07 — — - - — — 0. 03 0. 0 3 — — 0.0 --V203 0. 0 — — -- — — 1. 36 1.10 — — 0. 62 -NIO 0. 0 — -- -- — — 0. 0 0- 02 — — 0.03 -FEO 85. 52 87- 58 89. 56 77. 06 78.71 75. 24 75. 89 82- 47 83-50 8 1.90 81.98 80. 1 1 MNO 0. 24 0. 25 0. 46 1. 07 0. 59 0-00 0- 68 0. 15 0.80 2.27 1.49 2. 89 MGO 0. 03 0.09 0. 14 0. 14 0.05 0. 13 0. 09 0. 05 0. 16 0. 67 0.88 0. 1 1 CAO 0. 03 0- 05 0.09 0. 07 0. 34 0. 17 0. 06 0. 14 0. 0 1 0. 14 0.0 0. 21 0 AO 0. 0 0. 0 0- 17 0. 1 1 0.0 0. 24 0. 0 0. 0 0.02 0. 18 0.0 0. 23 NA20 0. 0 0. 0 , 0. 09 0. 02 0.03 0.06 0. 0 0. 03 0.04 0.08 0-02 0. 05 K20 0. 0 0.01 0. 08 0. 03 0. 0 4 0. 06 0. 02 0. 03 0.02 0.08 0.0 1 0. 08 SUM 91. 97 92. 76 94. 13 97. 10 93-9 4 95. 30 95. 14 94. 03 95.89 93-70 92.62 91. 27 RECALCULATED ON ULVOSPIHEI BASIS — PROCEDURE OF ANDERSON ( 196 8) FEO 33. 00 34.04 32. 95 46. 32 41.61 44. 90 44 . 80 38- 83 39.0 0 34. 00 34 . 14 32- 26 FE203 57. 39 59. 50 62.91 34. 16 41.23 33.72 34. 56 40. 50 48. 57 53.24 53.16 53. 18 SUM 97. 72 98. 72 100. 44 100. 52 90.07 90. 68 98. 60 90. 89 100.76 99. 04 97.95 96. 60 %USP 11. 55 9.49 7. 44 50. 17 36. 49 46.34 43. 74 25. 16 25.2 1 17.34 17.6 1 14. 03 RECALCULATED ON ULVOSPINEL BASIS — PROCEDU RE OF CARMICHAEL (1967) FEO 35. 79 34. 26 33. 47 47. 07 42.07 45.63 45- 19 39- 88 39.9 1 34. 55 34.40 33. 32 FE203 55. 26 59.26 6 2. 3 4 3 3. 33 40-72 32. 9 1 34. 1 1 47. 34 48. 44 52.63 52-88 5 2-0 1 SUM 97. 51 98. 70 100.38 100. 44 98.02 98. 60 98. 56 98. 77 100.75 98.90 97.9 2 96. 48 % U S P 15. 62 9. 57 8. 33 51. 32 35. 17 42-69 39. 01 2 5.92 23. 1 5 19-13 17.38 17. 77 117 APPENDIX IIF: ILMENITE ANALYSES HORNBLENDE DIOEITE ANDESITE DACITE REYOLITE 632 632 SI02 0.0 0.40 TI02 45.14 43.76 AL2C3 0.03 0.0 CR20 3 V203 NIO FEO 53.58 51,46 MNO 1.72 1.15 MGO 0. 07 0. 13 CAO 0.05 • 0.05 BAO 0.32 NA20 0.01 0.0 K20 0. 03 0.0 SOM 100.95 96.95 252 283 180 2. 57 0.21 ' 0. 28 50.88 51.08 33.34 0. 10 0.0 0.19 — 0.01 — • — 0, 47 — — 0.03 39.0 1 35. 98 57.33 6.62 10.56 1.14 0.16 0. 24 1.03 0.28 0.02 0. 11 0. 40 0.0 0. 26 0.05 0.0 0.03 0.08 0.0 0.08 100.15 98.60 93.79 RECALCULATED EY PSOCEDUEE OF ANDERSON ( 1968) IEO 38.50 37.88 38.17 34.71 26.72 FE203 16.76 15, 09 0.94 1.41 34.02 SUM 102.63 98.46 100.24 98.74 97.20 XFE-203 • 16. 46 15. 20 1. 45 3-06 36,82 RECALCULATED BY PROCEDURE OF CARMICHAEI(1967) FEC 38.69 38.36 39.01 35.42 27.44, FE203 16.55 14.56 0.0 0.62 33.22 SUM 102.61 98.41 100.15 98.66 97.12 SSFE'203 15. 49 14. 12 0. 15 1.09 33.00 APPENDIX IIG: ANALYSES OF SECONDARY MINERALS PREHNITE EPI DOTE SPHENE MUSCOVI' 1 2" 3 4 5 SIC2 42. 57 37.53 33. 53 30.09 44.77 TI02 0. C7 0. 02 0.11 29.40 0.09 AL2C3 20. 81 23.96 33.66 6. 93 27.40 FEO 4.46 10.95 8.94 0.-58 6.73 MNO 0. 12 0.24 0. 28 0.01 0.21 MGO C. C4 0. 04 0.04 0.02 5.29 CAO 26. 79 23.46 20. 03 29.09 0. 80 BAO — — — 0.02 0.49 NA20 0.05 0.0 0. 0 0.02 0.39 K20 0. 03 0.0 0.02 0-01 8.06 SUM 94.94 96. 21 96. 61 96. 17 94.23 FORMULA BASES SI 6.6041 3.2095 2. 79 49 4.0563 6.7843 TI C.0C86 0.0015 0.0067 2.9803 0.0101 AL 3.8053 2.4152 3. 3060 1.1011 4.8937 FE . 0.5780 0.7832 0.6233 0.0650 0.8532 MN 0.0160 0.0177 0.0198 0.0013 0. 0264 MG 0.0C97 0.0046 0.0049 0.0048 1. 1959 CA 4.4529 2. 1499 1.7888 4.2004 0. 1302 BA — — 0.0009 0.0288 NA 0.0141 0.0 0.0 0.0091 0. 1147 K 0.C061 0.0 0.0022 0.0014 1. 5573 1 vug f i l l i n g in hornblende dacite (164) ; 24 oxygens 2,3 vug f i l l i n g in hornblende dacite (164) ; 13 oxygens 4 titanomagnetite a l t e r a t i o n product in.hornblende dacite (240); 20 oxygens 5 plagioclase a l t e r a t i o n product i n pyroxene andesite (251) ; 24 oxygens 119 APPENDIX IVj. COMPILATION OF MINEBAL/LIQUID DISTRIBUTION COEFFICIENTS OF CIINCPYROXENE, HORNBLENDE, PLAGIOCLASE, BIOTITE, APATITE, JND ZIRCON FOR THE ELEMENTS CHROMIUM^ VANADIUM, NICKEL^ STEC NT IU K f BARIUM^. RUBIDIUM, NEODYMIUM, AND CERIUM 120 CHBQMIUH Beference Clino£l£oxene 2.6* lindstrom and W e i l l , 1978 2.5-3.7* Schreiber and Haskin, 1976 0.3-32 10 Hornblende Ewart et al.,1973 Leeman, 1976 Bemarks Di-Ab-An; 1290°C Fo-An-Di; 1350°C; 1 atra; k dec with dec f02 b a s a l t i c andesite to dacite; k dec inc Fe/(Fe + Mg) of cpx estimated from range cf experimental and natural data 23-36 12 Magnetite 100-620* 27-58 9-26 1-58 B i o t i t e G i l l , 1978 Leeman, 1976 Lindstrom, 1976 Ewart et a l . , 1973 Leeman, 1978 G i l l , 1978 andesite tc dacite c a l c u l a t e d from hb/cpx and c p x / l i g u i d r a t i o s a l k a l i c basalt; 1111-1168°C, 1 atm f02=10~* to 10-iz atm andesite to dacite calculated frcm Bayleigh model of l a s a l t s andesite to dacite 12.6±ft..8 .Higuchi and Nagasawa, 1969 17 Andriambololona et al.,1975 7 Leeman, 1976 dacite dacite c a l c u l a t e d from uica/ctx and c p x / l i g u i d r a t i o s * i n d i c a t e s to experimentally determined values • i n c ' = 'increases 'dec* = 'decreases' 121 VANADIUM D Reference Clinopyrcxene 0.03-10* Lindstrom, 1976 0.8-2 , Ewart et a l . , 1973 Hornblende 18-45 G i l l , 1978 Magnetite 0-67* 24-63 4.9-17 B i o t i t e 50 Remarks Lindstrom, 1976 Ewart et a l . , 1973 Leeman, 1978 Andriambololona et al.,1975 basalt; 1125-1315°C; 1 atm; k dec with i n c f02 andesite to dacite andesite to dacite basalt; 1112-1135°C; 1 atm; k dec with i nc ftv? andesite to dacite c a l c u l a t e d frcm Kayleigh model of t a s a l t s dacite 122 NICKEL D Reference Clinopyroxene 2.2-4.4* Hakli and Wright, 1967 1.5-11.7* Lindstrom ana W e i l l , 1978 2.55* Mysen, 1978a 2.0 Leeman, 1976 3.5-£ G i l l , 1978 Hornblende 2.9* Mysen,1978a 3.7 leeman, 1976 7-8 G i l l , 1978 Magnetite 12.2-19.4* Leeman, 1974 20-77* Lindstrom, 1976 4-19 G i l l , 1978 B i o t i t e Bemarks Makaopuhi basalt; 1050-1160°C; 1 atn k dec with i n c T°C Ab-An-Di;1150-1350°C;1 atm k dec with, inc T°C Ab (45) An (45)Fo (7) Q (3) ; 1025°C; 20 kbs. estimate from experimental and n a t u r a l data andesite An(41) Afc(41)Fo(16)Q(2) ; 1000°C;.15 kb c a l c u l a t e d frcm hb/cpx and c p x / l i g u i d r a t i o s andesite to dacite p i c r i t i c t h o l e i t e ; 1300-1252°C;1 atm a l k a l i c basalt;1111-1168°C; f0 2=10-* to 10-* 3 atm andesite to dac i t e 13 3-7 Andriambololona et al.,1975 Leeman, 1976 andesite c a l c u l a t e d from mica/cpx and cpx / l i q u i d r a t i o s 123 STBON TIDM Reference Remarks Clincpyrqsene 0.06-0.08* Shimizu, 1974 Di{50) Ab(25)An(25) ; 1 100-1200°C; 15-30kb; fO 2=10-8 to 10-* atm 0.18-0.3* Sun et a l . , 1974 basalt; 1110-1140°C; 1 atm 0.07-0.11 Hart and Brooks, 1974 ankaramite, b a s a l t i c andesite 0.12-0.43- P h i l p o t t s and Schnetzler, 1970 basalt-zoned phenocrysts 0.01-0.06 " andesite 0.52 " rhyodacite 0.11 Onuma et al.,1968 0.12 Sun and Hanson, 1976 megacryst i n basalt Hornblende 0.31 G r i f f i n and Hurthy, 1969 basalt 0.2-0.5 Ewart and Taylor, 1969 andesite to r h y c l i t e 0.55-C.64 P h i l p o t t s and Schnetzler, 1970 b a s a l t 0.19 " andesite Pla g i o c l a s e 1. 5-2-2* 1. 2-3.3* 1. 4-2. 8 1.3- 1.8 2.8 2.4- 4.5 1.5-7 1. 4-1.8 1.9-2.6 2.6 4.6 2.0-3.9 2.3 Sun et a l . , 1974 Drake and W e i l l , 1975 Schnetzler and P h i l p o t t s , 1970 II II Dudas et a l . , 197 1 Korringa and Noble,1971 Ewart et al.,1973 Sun and Hanson,1976 Duchesne,1978 Duchesne and Demaiffe,1978 basalt; 1110-1140°C; 1 atm t h o l e i t e , a n d e s i t e ; 1150-1400°C; 1 atm; k inc with dec T°C basalt andesite dacite dacite k i n c from An (90) to An (30) An (84-88) i n b a s a l t i c andesite An (80-85) i n dacite An (85) i n r h y c l i t e basalt k i n c frcm An (50) to An (31) An (47) i n j o t u n i t e B i o t i t e 0.08 P h i l p o t t s and Schnetzler,1970 basalt 0.12 » dacite 0.67 " rhyodacite Apatite 0. 41 1.5 Duchesne,1978 Sun and Hanson, 1976 c a l c u l a t e d from anorthosite basalt 124 BARIUM D Reference Clinopyroxene <0.01* Shimizu,1974 <0.01 <0.01 0.03-0-05 0.01-0.39 0.13 0.01-C.04 0.03 Hornblende 0. 45 0.42-0.73 0. 10 0.4 Hart and Brooks,1974 Onuma et al.,1968 Schnetzler~and Philpotts, 1968 P h i l p o t t s and Schnetzler,1970 II II Sun and Hanson,1976 G r i f f i n and Murthy,1969 P h i l p o t t s and Schnetzler,1970 II Leeman,1976 Sun and Hanson,1976 0.32 Pla g i o c l a s e 0.2-C.7* Drake and Weill,1975 0.15-0.59 0.05-0;24 0.36 0. 1 6-0.42 0.34-1.43 0.12-0.17 0.11-0.17 0. 16 1.47 0.39 B i o t i t e 9.7+1.3 1.09 6.36 15.3 P h i l p o t t s and Schnetzler,1970 Korringa and Noble,1971 Dudas et al.,1971 Ewart et al.,1973 Sun and Hanson,1976 Duchesne and Demaiffe,1978 Higuchi and Nagasawa,1969 P h i l p o t t s and Schnetzler,1970 II it Remarks Di (50) Ab (25) An (25) ; 1100-1200°C; 15-20 kb ankaramite and b a s a l t i c andesite a l k a l i - c l i v i n e basalt b a s a l t basalt - zoned phenocryst rhyodacite andesite basalt negacryst basalt basalt andesite c a l c u l a t e d from hb/cpx and c p x / l i g u i d r a t i o s k a e r s u t i t e negacryst i n basalt natural t h o l e i t e , andesite 1150-1400°C; 1 atm; k i nc with dec T basalt andesite dacite k i n c from An (90) to An (30) dacite b a s a l t i c andesite to andesite dacite r h y o l i t e basalt An (47) i n j o t u n i t e dacite phlogopite i n ba s a l t b i o t i t e i n dacite b i o t i t e i n rhyodacite 125 BUBIDIOM B e f e r e n c e Clinopyroxene Shimizu,1974 Hart and Brooks,1974 P h i l p o t t s and Schnetzler,1970 II <0.01* <0.01 0.02-0-26 0.03 0.01-0.04 Hornblende 0.27 G r i f f i n and Murthy,1969 0.01 Kagasawa and Schnetzler,1971 0.41-0.43 Schnetzler and Philpotts,1970 0.05 " 0-4 Leeman, 1976 Plagioclase 0.02* McKay and Weill,1976 0.08* McKay and Weill,1977 0.12-0.25 0.03-0.19 0. 06-0.49 0. 05 0.12-0.25 B i o t i t e Duchesne,1978 P h i l p o t t s and Schnetzler,1970 Dudas et al.,1971 Sun and Hanson,1976 Duchesne and Demaiffe,1978 Bemarks Di(50) Ab(25)An(25) ; 1100-1200°C; 15-30 kb ankarauite and b a s a l t i c andesite ba s a l t rhyodacite b a s a l t i c andesite basalt dacite basalt andesite c a l c u l a t e d frcm amph/cpx and c p x / l i g u i d r a t i o s s y n t h e t i c lunar basalt; 1200°C; 1 atm sy n t h e t i c low-K basalt; 1240°C;1 atm k i n c frcm An (50) to At (31) andesite dacite basalt k i n c frcm An{50) to An (20) 2.24±.47 3.06 3.26 0.94 3.0 Higuchi and Nagasawa,1969 Ph i l p o t t s and Schnetzler,1970 Leeman, 1976 dacite phonolite dacite rhyodacite c a l c u l a t e d from mica/cpx and c p x / l i g u i d r a t i o s 126 NEODYMIOM Reference Clinopyroxene 0.21-0.24* Grutzeck et al.,1974 0.35* 26-0.32 17-0.18 07-0.65 1. 28 0.94 0.38 Tanaka and Nishizawa,1975 Schnetzler and Philpotts,1968 Schnetzler and Philpctts,1970 Nagasawa and Schnetzler,1971 Sun and Hanson,1976 Remarks Abr-An-Di; 1265°C ; 1 atm basalt; 1200°C ; 20 kb basalt b a s a l t andesite rhyodacite dacite basalt Hornblende 0.5* Frey (in Irving,1978) 0.16 Schnetzler and Philpotts,1968 0.19 Schnetzler and Philpotts,1970 1-4.25 Nagasawa and Schnetzler,1971 0.85-3,2 1 Sun and Hanson,1976 Plagi o c l a s e 0.04-0.C6* W e i l l and HcKay,1975 0.08-0.13* Drake and Weill,1975 0.04 0.11 0.02-O.C7 0.02-0.2 0. 17 0. 14-0.29 0. 17 B i o t i t e Higuchi and Nagasawa,1969 Schnetzler and Philpotts,1968 Schnetzler and Philpotts,1970 Dudas et al.,1971 Sun and Hanson,1976 t h o l e i t e ; 1000°C ; 5 kb bas a l t andesite dacite basalt. s y n t h e t i c lunar b a s a l t ; 1200-1340°C ; k dec with dec T t h o l e i t e , andesite, and Ab-An-Di 1150-14'00°C ; 1 atm; k inc with dec T basalt basalt basalt • andesite dacite dacite basalt 0.03 0.04 0.34 Apatite 27.4-81.' 21 1.4-16 Schnetzler and Philpotts,1970 II Nagasawa,1970 Nagasawa and Schnetzler,1971 Sun and Hanson,1976 basalt dacite rhyodacite dacite dacite c a l c u l a t e d f o r basalt Zircon 2-6.5 Nagasawa,1970 dacite CERIUM Reference Bemarks Clinopyroxene 0.1-0.12* Grutzeck et al.,1974 0.2* Tanaka and Nishizawa,1975 0.3* Mysen,1978c 0.17 Onuma et al..1968 0.12-0.18 Schnetzler and philpotts,1968 0-36 Nagasawa and Schnetzler,1971 0.08-0.1 Schnetzler and Philpotts,1970 0.04-C.51 » 0.65 » 0. 1 Leeman,1976 0.18 Sun and Hanson,1976 same conditions as for Nd same conditions as f o r Nd ba s a l t ; 950°C ;20 kb a l k a l i - c l i v i n e basalt b a s a l t dacite basalt andesite rhyodacite estimated from experimental and n a t u r a l data basalt Hornblende 0.3* - F r e y ( i n Irving,1978) 0.04* Mysen,1978c 0.12 Schnetzler and Philpotts,1968 0.34 Higuchi and Nagasawa,1969 0.09 Schnetzler and Philpotts,1970 0.49-1.98 Sun and Hanson,1976 0.43-1-77 Nagasawa ana Schnetzler,1971 0., 2 Leeman, 1976 t h o l e i t e ; 1000°C ; 5 kb An (41) Ab (41) 3?o (16) Q (2) ; 1000°C ; 15 kb basalt basalt andesite basalt aacite estimate from experimental and n a t u r a l data Plagioclase 0.C7-0.14* Drake and Weill,1S75 0.05-0.07* Weill and McKay,1975 0.09 Higuchi and Nagasawa,1969 0.02-0.11 Schnetzler and Philpotts,1970 0.C8-C.3 " 0.24 " 0.16-0.4 Dudas et al.,1971 0.22 Sun and Hanson,1976 0.1 Leeman,1976 same conditions as f o r Nd same conditions as f o r Nd basalt basalt andesite dacite dacite basalt estimate frcm experimental and natural data B i o t i t e 0.32 0.03 0.04 0.23 Higuchi and Nagasawa,1969 Schnetzler and Philpotts,1970 dacite basalt dacite rhyodacite Apatite 18-52.5 Nagasawa,1970 16.6 Nagasawa and Schnetzler,1971 1.1-12 Sun and Hanson,1976 aacite aacite calculated f o r basalt Zircon 2-3-7.4 Nagasawa,1970 dacite 128 i l l l J M X IV: COJSTHIBOTIOSS TO LABORATORY AjyULj^KAL TECHN.IQDES 129 APPENDIX IVA: OPERATING CONDITIONS FOR TRACE JIEMENT ANALYSIS BY X-RAY FLUORESCENCE SPECTROMETRY Tables 7-11 l i s t the operating conditions f o r the analysis of f i v e sets of trace elements: chromium-vanadium, barium, n i c k e l , niobium-zirconium-yttrium-strontium-rubidium, and cerium-neodymium. These trace elements are run i n the above groups due to the proximity of two theta positions, and the prescence of some interferences between elements of a given group. The following procedure should be followed i n setting up the X-ray fluorescence spectrometer for analysis of any set of trace elements (for an e x p l i c i t description of general analysis procedures, the reader i s referred to the XRF Guidebook): — Turn water supply to machine on (red l i g h t on) — Turn main power on — Wait several minutes for machine to • c l i c k * on — Slowly turn Kv d i a l up to desired setting — Slowly turn Ma d i a l up to desired setting — Check argon flow i f the flow proportional counter i s to be used; regulator on argon tank=10 lb/inch; flow gauge i n XRF=6-7 — Wait at least one hour for machine to warm up — Set a l l machine parameters to values l i s t e d i n operating condition tables — Using standards or correction p e l l e t s with high concentrations of the elements of i n t e r e s t , do 2% scans to determine lower l e v e l and window settings; these settings can change markedly from day to day — Using the same high concentration samples, determine peak 130 positions by counting for 10 seconds at two theta i n t e r v a l s of .01°; repeat t h i s procedure u n t i l consistent peak positions are located — From these peak positions, subtract or add the values l i s t e d i n the tables of operating conditions i n order to determine the two theta positions of a l l background measurements — Run two theta scans on several standards and unknowns i n order to check for correct positioning of peak and background measurements — Proceed with analyses, bracketing a l l runs on unknowns between runs on the group of standard recks selected for c a l i b r a t i o n The following sections discuss modifications i n the operating conditions set.up by Matters (1975), Chromium-Vanadium These two elements need to be analyzed together due to the interference of CrK a (2. 2896A°) by VKg (2,. 2843A°) ra d i a t i o n . In addition VK (2.503A0 i s interfered with by T i K e (2.5138A°) radiat i o n . Vanadium (1000 ppm V)- and titanium (Ti02 -B) -spiked correction p e l l e t s are run to evaluate these interference e f f e c t s . These elements are analyzed using the molybdenum tube set at 60 Kv and 40 Ma. Although WLa radiation (1,476A°) i s closer to the absorption edge of Cr (2.07) than McKa (.709A°), the lower power (50 Kv and 40 Ma) of the tungsten tube gives lower i n t e n s i t i e s than the molybdenum tube. Both the flow proportional and s c i n t i l l a t i o n counters are 131 used for t h i s series of elements as the s c i n t i l l a t i o n counter alone yields very low i n t e n s i t i e s - Using both counters and the fine collimator, resolution between the vanadium an titanium peaks i s poor; the two peak positions must by determined using each correction p e l l e t in turn. Although correction factors are quite large, excellent regression l i n e s for vanadium are achieved with t h i s method. Unfortunately, the molybdenum tube (and the tungsten tube) appear to have minor amounts of chromium alloyed with the metal of the tube casing, and large chromium peaks are produced on blank samples. This leads to regression l i n e s with large negative intercepts (over -100), and low peak/background r a t i o s . For t h i s reason, an aluminum f i l t e r i s use to block out most of this primary Cr r a d i a t i o n . The chromium peak and backgrounds on both sides are measured using t h i s f i l t e r and the coarse collimator; the vanadium peak, titanium peak, and background for these peaks are measured without this f i l t e r and with the f i n e collimator. The vanadium correction p e l l e t should be run on a l l peak and background positions; the titanium correction p e l l e t need be run on only the vanadium and titanium peaks and the associated background. The background positions around the chromium peak have been chosen so as to avoid large barium and cerium peaks; care should be taken to check background positions from two theta scans run on rocks with high concentrations of these elements. The lower l e v e l and window settings f o r Cr, V, and T i are a l l s i m i l a r and should be set by running 2% scans on PCC or DTS 132 for Cr, and the appropriate correction p e l l e t f o r V and T. These settings should be extended at least 10-15% cn both sides i n order to avoid d r a s t i c reductions i n count rate that can occur due to small voltage s h i f t s with time. I t i s recommended that ultramafic rocks be used with caution in c a l i b r a t i o n l i n e s (for n i c k e l , too) , as there are large discrepancies in the quoted concentrations from d i f f e r e n t sources (cf. Abbey, 1977 and Flanagan, 1973). In addition, c a l i b r a t i o n l i n e s weighted by the high concentrations of ultramafic standards w i l l lead to overestimaticn of the concentrations of normal (1-400 ppm) rocks. Barium Barium i s analyzed using the chromium tube as i t s L a absorption edge (2.36A°) l i e s just to the long wavelength side of CrK a radiation (2.29A°). The TiO^-B p e l l e t i s run i n order to c a l i b r a t e the interference of TiKg with BaL a . Use of the flow proportional counter and the f i n e collimator y i e l d good i n t e n s i t i e s and acceptable resolution between the two peaks. Only one background position need be run as backgrounds are f l a t across the two peak positions. Mickel Nickel i s analyzed using a molybdenum target (,711A°) and settings of 60 Kv and 40 Ma. I n t e n s i t i e s are better than with the tungsten tube (50Kv and 40Ma), even though tungsten radiation (1.476A°) i s closer to the K absorption edge cf Ni (1.488A°). I f ni c k e l i s analyzed at the same tine as zinc and 133 copper, however, the chromium tube should be used as the MoK and WL peaks i n t e r f e r e with the Zn peak and background measurements around i t . The flow proportional and s c i n t i l l a t i o n counters are used together as i n t e n s i t i e s with the s c i n t i l l a t i o n counter alone are unacceptably low. The aluminum f i l t e r i s used to reduce primary n i c k e l radiation (due to a ni c k e l a l l o y i n the target) to an acceptable l e v e l . Nicbium-Zirconium-Yittrium-Strontium-Bubidium These elements are analyzed using the tungsten tube because MoK i n t e r f e r e s with the niobium peak. Interferences of BbK on YK and SrK c on ZrK are calibrated by running the strontium and rubidium-spiked p e l l e t (Bb+Sr i n s i l i c i c and boric acid) on a l l peak and background positions. Intensities on most rock samples are great enough that counting times on peak need be no greater than f o r t y seconds. The background position between the niobium and zirconium peaks can be ignored as i t i s distorted i n most sample due to the prescence of the ThL^ peak. The Zr and Y peak positions should be located using rocks which have high concentrations of these elements and low concentrations of Sr and Bb (due to the interferences discussed above). i Cerium-Necdymium ' These elements are analyzed using the molybdenum tube at settings of 60Kv and 40Ma. Use of the flow proportional and s c i n t i l l a t i o n counters y i e l d optimum i n t e n s i t i e s , and resolution 134 between the overlapping t a i l s of both peaks i s adeguate. A cerium-spiked p e l l e t (Cerium i n s i l i c i c + b o r i c acid) i s run to c a l i b r a t e the interference on NdKa . At present no supply of neodymium has been located; i d e a l l y , a neodymium-spiked p e l l e t should be run to ca l i b r a t e the interference on CeL„ . X i J J L ^ l l O E Z ' E A l I N f l CONDITIONS FOR CHROMI U V AN ADIUM Peak,Bkd # Counting P o s i t i o n s Two . Theta Angles Count Times Target (Kv-Ma) Cr y s t a l Counter (Vo-ltage) Gain C o l l insa tor F i l t e r Lower Level-Window Counts on AGV Regression Equation Standard Deviation Composition Range bkd - 1 pk - 1 bkd Cr C r - 2 . 20 6 9 . 3 5 '4 0 1 0 0 Molybdenum Tube.. ( 6 0 - 4 0 ) LIF ( 2 0 0 ) FPC ( 8 . 6 )+Sc ( 1 0 . 8 ) 128 Coarse Aluminum F i l t e r • ;  1 0 0 - 2 4 0 0 2 4 4 2 7 6 0 6 2 4 . 2 x - 1 4 . 1 3 1 . 7 9 6 - 5 3 ,hkd-2 bkd - 3 bkd bkd C r * 1 . 5 0 V - 1 . 8 6 4 0 40 pk - 2 pk - 3 V T i 7 6 . 0 6 7 7 . 2 1 100 4 0 Fine r-No F i l t e r 5 4 5 8 1 8 0 9 2 2 0 6 3 2 7 5 8 8 1 0 8.7X + 9 . 6 ' 5 . 6 " 5 - 4 1 0 1 3 6 IABLE 0.1 OPEEATING CONDITIONS FOR BAR10* Peak,Bkd # pk-1 pk-2 bkd- 1 C o u n t i n g P o s i t i o n s T i Ba bkd Two Theta A n g l e s 36.07 87.01 Ba+.4. 0 Count Times 10 10 10 T a r g e t (Kv-Ma) Chromium Tube (50-40) C r y s t a l LIF (2 00) Co u n t e r (Voltage) FPC(8.7) Gain 128 C o l l i m a t o r F i n e F i l t e r No F i l t e r Lower Level-Window 360-320 Counts on AGV 258115 17478 424 R e g r e s s i o n E q u a t i o n 1 2 3 6.2x-25.-8 S t a n d a r d D e v i a t i o n 3. 4-13.6 C o m p o s i t i o n Range 440^-1860 137 TABLE 9: OPERATING CONDITIONS FOR NICKEL Peak,Bkd f bkd-1 pk-1 bkd-2 Counting Positions bkd Ni bkd Two Theta Angles Ni-.63 48,63 Ni+1.37 Count Times 20 40 20 Target (Kv-Ma) Molybdenum Tube (60-40) Crystal LIF(200) Counter (Voltage) FPC (8. 6)+Sc (10. 8) Gain 128 Collimator Coarse F i l t e r Aluminum F i l t e r Lower Level-Window 300-300 Counts on AGV 17220 39042 13083 Regression Equation 16.72x-.47 Standard Deviation 1.02 (3. 27) Composition Range 6-17 (6-200) T A n i . E 1 0 : OPERATING CONDITIONS F O R NIOBT U M-Z'T. R CON III tl-Y I T T R I IIH.-S T R O H TI UM —P.U DI D IIJ M P e a k , D M it hkd- 1 Count ing P o s i t i o n s bkd Two Thetn Angles N h - - 3 ' Count Times 2 0 Target (Kv-Ma) C r y s t a l Counter (Vol tage) Gain • C o l l i m a t o r F i l t e r pk- 1 pk- 2 b k d - 3 P k - 3 bkd-'i pk-'t bkd - 5 p k - 5 bkd - 6 Nb Zr bkd Y bkd S r bkd Rb bkd 2 1. 23 2 2 . '10 Y - . 2 5 2 3 . 6 3 S r - . '1 2 5 . 0 1 R b - . 4 2 6 . 4 9 R h v 1 .H '4 0 140 2 0 4 0 2 0 4 0 2 0 ) t 9 4 0 , 2 0 Tungsten Tube ( 5 0 - 4 0 ) L . I F ( 2 0 0 ) S c i n t i l l a t i o n ( 0 . 4 5 ) 1 2 8 Fine No F i l t e r Lower Level-Window 3 0 0 - 4 5 0 Counts on AGV 2 2 2 0 1 4 6 4 3 2 1 2 6 2 1 1 1 5 8 0 7 Regress ion Equat ion 1 1 . 0 x 0 . 0 2 2 7 . . 5 x - 1 5 . 7 Standard D e v i a t i o n . 8 4 2 . 7 Compos i t ion Range 9 . 5 - 2 9 1 0 5 - 5 0 0 3 9 0 6 4 1 3 3 3 2 2 0 8 3 0 9 1 0 7 2 3 1 0 . 5 x + 3 - 6 6 5 8 . 6 * * 7 . 4 3 . 4 9 . 0 1 2 - 3 7 1 9 0 - 6 6 0 3 7 1 1 9 8 1 3 5 6 9 - 1 x - - 3 2 . 4 2 1 - 2 5 0 03 TABLE H i OPERATING CONDITIONS FOR CERIUM-NEODYNIUH Peak,Bkd # bkd-1 pk-1 pk-2 bkd-2 Counting Positions bkd Ce Nd bkd Two Theta Angles Ce-.85 71.56 72.05 Ce+ 1. 30 Count Times 40 100 100 40 Target (Kv-Ma) Molybdenum Tube (60-•40) Crystal LIF (200) Counter(Voltage) FPC (8. 4) +Sc(9.5) Gain 128 Collimator Fine F i l t e r No F i l t e r Lower Level-Window 200-500 Counts on AGV 5750 19540 16750 5108 Regression Equation 138.3x-46.9 37. 6 x-1. 5 Standard Deviation 6. 2 3.4 Composition Range 21-410 16-148 TABLE 12: CONCENTRATIONS (1TM) AND MASS ADSORPTION COEFFICIENTS FOR STANDARD ROCKS Concentrations (parts per mill i o n) Mass Absorption Coef f I c l e n t s Cr V Ua Ni Nb Zr Y " Sr Rb Ce Nd per •(3V (3 Da pSr pNd ACV 12 125 1090 17 1 5 . 0 220 26 660 67 74 35 1 3 4 . 4 1 6 4 . 2 2 3 0 . 1 1 1 . 6 1 4 6 . 2 W-l 120 240 160 70 9 . 5 105 25 190 21 21 16 14 4 . 3 1 7 6 . 2 246 . 1 1 4 . 3 1 5 6 . 8 fi-2 9 34 1060 6 1 4 . 0 300 12 ' 4 80 170 160 54 1 3 0 . 4 1 6 1 . 6 2 2 6 . 9 9 . 4 ' 1 4 1 . 9 CSP 13 49 1300 9 2 9 . 0 5 0 0 "' 32 230 250. 410 •140 1 3 3 . 8 1 6 5 . 1 2 3 1 . 6 1 0 . 4 14 5 . 6 OCR 16 410 6 0 0 13 1 4 . 0 105 37 330 . 4 7 53 20 1 3 8 . 4 1 6 4 . 5 ' ' 2 3 0 . 1 1 4 . 2 1 5 0 . 5 CA 12 ' 38 850 7 107 150 21 310 175 70 257 1 3 0 . 0 1 6 1 . 5 2 2 6 . 7 9 . 5 141.4 Cll ' 6 5 22 3 057 150 70 10 390 507 217 1 2 7 . 2 1 5 9 . 4 ' 1 2 2 4 . 0 0 . 6 1 3 8 . 5 SY - 2 107 . 50 460 10 270 130 270 220 213 73 1 4 5 . 1 1 8 0 . 9 269 . 3 1 2 . 2 157.81 SY - 3 87 51 440 11 1457 340 740 300 210 20007 5 0 0 7 1 4 5 . 5 1 0 1 . 5 2 5 3 . 7 1 2 . 3 1 5 8 . 2 NiM-r 240 560 30 47 347 57 1 1 5 . 8 1 4 4 . 4 2 0 3 . 1 1 3 . 2 1 2 6 . 1 NIM-S 13 10 26007 6 3 . 5 7 457 37 64 550 1 5 6 . 1 1 9 5 . 2 2 7 3 . 1 1 0 . 6 1 6 9 . 8 NIM-N 34 210 957 120 2 . 0 7 227 7 . 260 57 1 4 2 . 6 1 7 7 . 5 2 4 8 . 0 1 3 . 1 1 5 5 . 0 NIM-C 14 2 1107 0 5 2 . 0 290 125 10 330 1 2 8 . 4 16018 . 2 2 5 . 9 8 . 9 1 3 9 . 8 NIH-D 2 9 0 0 41 107 2100 107 37 1 0 4 . 2 1 3 0 . 7 1 8 4 . 3 1 4 . i 1 1 3 . 6 NIM-L 147 78 4607 67 920 2 3 4600 195 1 3 2 . 6 1 6 4 . 1 2 2 9 . 8 1 3 . 3 144 . 2 JC 5 3 24 460 07 1107 317 185 185 1 2 9 . 3 1 6 1 . 1 2 2 6 . 3 9.-1 1 4 0 . 7 Jl) 400 210 490 135 155 267 440 41 1 4 1 . 1 1 7 1 . 2 2 3 9 . 4 1 3 . 1 1 5 3 . 4 KRC 4 2 0 520 200 • 2 0 . 0 7 100 207 260 8 1 5 7 . 8 1 0 2 . 0 2 5 3 . 6 • 1 8 . 3 171.4 DTS 4 4 0 0 13 2 4 0 0 1 0 3 . 8 1 3 0 . 3 1 0 4 . 1 1 0 . 3 1 1 3 . 1 PCC 3000 31 2 5 0 0 1 0 2 . 2 1 2 8 . 3 1 0 1 . 2 1 0 . 0 111.4 QLO 5 2 . 5 1401 77 1707 3507 1 3 1 . 5 . 1 6 2 . 4 2 2 7 . 9 1 0 . 3 1 4 3 . 1 RCM 1 4 . 7 082 2107 1107 1707 1 2 7 . 7 1 5 9 . 2 2 2 3 . 6 8 . 8 1 3 9 . 0 n n v o 3207 306 1 3 2 . 5 1407 197 1607 277 4007 107 1 4 9 . 7 ; 1 7 6 . 3 2 4 6 . 2 1 5 . 1 1 6 2 . 6 Source for concentrations i s Abbey ( 1977) — 1 7' indicat e s less c e r t a i n value Mass absorption c o e f f i c i e n t s - c a l c u l a t e d from major element chemis ty (Abbey , 1977) Mass attenuation values taken from the Handbook of Spectroscopy( 1 9 7 4 ) 141 Appendix IVb:_ Trace Element Reduction Program EASIC language computer programs have been written for the reduction of trace element data. As conditions f o r each set of trace elements d i f f e r with respect to shape of backgrounds, interferences, and counting times, f i v e separate programs have been written f o r the reduction of the f i v e sets of trace elements discussed above. The general reduction procedures for a l l the trace elements are presented below; s p e c i f i c differences and data input formats for each set of elements are discussed under separate headings. General reduction technique A complete run for a given set.of trace elements includes counting the i n t e n s i t i e s of peaks and backgrounds for each element of i n t e r e s t , and for any elements which give r i s e to interferences. Data reduction involves the following steps: - Reduction of raw counts on a l l peaks and backgrounds to counts per second Subtraction of background counts per second from peak counts per second to give net peak counts per second - Calculation of the i n t e n s i t y of any interferences and subtraction of the appropriate amounts from the net peak counts per second - M u l t i p l i c a t i o n of net peak counts per second times the mass absorption c o e f f i c i e n t for the appropriate wavelength - Calculation of the r a t i o of the above product for each rock with that of AGV-1 - Calibration of the standard rocks by regression of the above 14 2 ra t i o s against nominal concentrations Comparison of nominal concentrations of standards with concentrations calculated from the regression l i n e , and rejection of any standards which d i f f e r by more than two standard deviations of the regression - R e c a l c u l a t i o n of the regression l i n e i f any standards have been rejected - Calculation of unkown concentrations from the regression l i n e derived from standard rocks - Calculation of 95% confidence l i m i t s f o r each of the computed concentrations Program Options Several options for data reduction are made available to the user with the us of input statements which demand 'yes' or •he1 answers (the number •1• s i g n i f i e s 'yes 1; the number '0' s i g n i f i e s •no 1). Option One: 'Compiled Regression S t a t i s t i c s ' This option enables the user to compile the res u l t s of a s p e c i f i c run with previous runs. I t also allows unknown samples to be processed without running any standard recks (AGV-1 mijst always be run as i t i s the reference standard); i t i s recommended that t h i s be done for qu a l i t a t i v e work only. A 'yes' response brings tack a demand to input the previous regression s t a t i s t i c s f o r each element being analyzed, These s t a t i s t i c s can be read o f f any previous computer outputs. The data should be typed on one l i n e , with a l l e n t r i e s separated by commas. 143 Option Two: 'Print Suppressor' A 'yes' response generates a f u l l printout of preliminary calculations p r i o r to pri n t i n g of the regression eguation and s t a t i s t i c s . This printout includes a tabulation of the net counts per second times mass absorption c o e f f i c i e n t for each standard, a l i s t of nominal concentrations versus concentrations calculated from the regression l i n e for each standard, and s t a t i s t i c s of the f i t of the background curves for the niobium-rubidium program. A 'no' response considerably shortens the computer printout and the time take i n data reduction. The regression eguation and associated s t a t i s t i c s are printed and the calculated concentrations f o r unknown rocks are tabulated. Option Three: 'Weighted Least Squares F i t ' A 'yes' response causes the c a l i b r a t i o n l i n e to be calculated using a s t a t i s t i c a l weighting of the standard reck compositions. The weighting factor, defined at l i n e # 140, i s equal to the reciprocal of the squared concentration; t h i s weiqhtinq f a c t o r can be altered by chanqing l i n e # 140,. It i s suggested that a weighted f i t be used only i f a wide range of standard i compositions are used i n the regression l i n e . The best f i t i s obtained by using an unweighted f i t to standards which closely bracket the expected concentrations of unknown rocks. During operation of the reduction program, the user i s required to respond to one addit i o n a l input guestion: •Number of Standards?' The user must input the number of standard rocks which are to be used i n the c a l i b r a t i o n l i n e . This number must agree with the 144 number of data l i n e s which have been written for the standard rocks (data statements are discussed below). The number of correction p e l l e t s run f o r any set of trace elements i s not included i n the number of standards input at t h i s time. Data Input and Reduction Program Procedures In order to operate the reduction program, i t i s c r i t i c a l that data be input i n the correct format and i n the prcper order. A l l data i s input i n the form of data statements which have the form: 'l i n e number-DATA-any data entries separated by commas* where •-' refers to a blank space i n the l i n e . I f a comma i s the l a s t entry of a data l i n e , the computer w i l l interpet t h i s to mean that another data entry has been made with the default value of *0*. Any number of data entries can be made i n a single l i n e (space i s the only limitation) ; the computer reads sequentially through these data l i n e s i n order to f i n d as many data entries as i t needs to s a t i s f y any 'data read' statements that i t encounters. In order to avoid ambiguity, s p e c i f i c formats for each set of trace elements are presented below. The numbers associated with peaks and backgrounds refer to the same numbers l i s t e d i n the tables of operating conditions. The number 10' must be entered in the data statements after a l l data for any correction p e l l e t , standard, or unknown has been typed; t h i s t e l l s the computer that the data which follows the • 0* i s data for the next rock. Data for more than one run on a given rock follows seguentially without separation with a •0'; for a l l peak and 145 background positions, type the counts for the f i r s t run, and then type the counts for any ad d i t i o n a l runs, using commas to separate a l l data e n t r i e s . Recommended values for the concentrations of the various trace elements for the standard rocks, and mass absorption c o e f f i c i e n t s for the reguired wavelengths are l i s t e d i n Table 12. In the data format sections below, numbers at the beginning of l i n e s refer to the l i n e numbers at which the data statements should be typed; 'ppm' refers to the concentration i n parts per mill i o n ; 'mac* refers to the mass absorption c o e f f i c i e n t at the appropriate wavelength. Data Format f o r Chromium-Vanadium Series 5990: date of run (in guotation marks) 5999: two theta positions for bkd-1,pk^1,bkd-2 6000-6009: counts for TiO -correction pellet—bkd-3,pk-2,pk-3— repeat for a l l runs 6010-6019: counts f o r Vanadium correction pellet—bkd-1,tk-1rbkd-2,bkd-3,pk-2,pk-3 for a l l runs 6020: AGV (in quotes),Cr ppm,Cr mac,V ppm,V mac 6021-6029: counts on AGV—bkd- 1,pk-1,bkd-2,bkd-3,pk-2,tk-3-repeat for a l l runs 6030-6999: data for other standard rocks in same form as that for AGV 7000- : data for unknowns—name of sample(in guotes),Cr-nac,V mac,counts for a l l two theta positions i n same order as above The correction factor for T i interference on V i s equal to 146 the background-corrected counts/second on V/Ti, taken from the TiO^ -correction p e l l e t . As the V peak overlaps the T i peak, a correction factor egual to the background-corrected c/s on Ti/V i s calculated from the V correction p e l l e t . Because cf these two mutual interferences, peak counts on standards and unknowns are computed by i t e r a t i o n with both correction factors u n t i l a constant value i s reached. The,V correction p e l l e t also gives a correction factor for V interference on Cr, which i s egual to the background-corrected c/s on V/Cr. The background i n t e n s i t y at the Cr peak i s determined by putting a s t r a i g h t l i n e through the background positions on either side of the peak. Data input and Reduction Procedures for Barium 59S9: date of run (in guotes) 6000-6009: counts on T i 0 2 - c o r r e c t i o n pellet—pk-1,pk-2,bkd-1— repeat for a l l runs 6010: AGV(in quotes), Ba ppm, Ba mac 6011-6019: counts on AGV—same order as above—repeat for a l l runs 6020-6099: data for other standards—same form as for AGV 7C00- : data for unknowns—name(in quotes), Ea mac, counts i n same order as above As backrounds are f l a t across both peak positions, the counts at the background position are subtracted frcm both peaks- The TiO^-correction p e l l e t gives a correction factor egual to the background-corrected c/s on Ba/Ti. 147 Data Input and Reduction Procedures f o r N i c k e l 5990: two t h e t a p o s i t i o n s f o r bkd-1,pk-1,bkd^2 5999: date of run (i n quotes) 6000: AGV(in quotes) , Ni ppm,Sr mac 6001-6009: counts f o r AGV i n same order as a b o v e — r e p e a t f o r a l l runs 6010-6999: data f o r other standards i n same form as f o r AGV 7000- : data f o r unkowns—name (in quotes),Sr mac,counts i n same order as above No c o r r e c t i o n s a re necessary f o r r e d u c t i o n of Ni data. Background i n t e n s i t y at the N i peak i s determined by p u t t i n g a s t r a i g h t l i n e through the backgrounds on e i t h e r s i d e of the peak. Data Input and Reduction Procedures f o r Niobium to Rubidium S e r i e s 5999: date of run ( i n guotes) 5990: two t h e t a p o s i t i o n s f o r a l l peaks and backqrounds —bkd-1,pk-1,pk-2,bkd-3,pk-3,bkd-4,pk-4,bkd-5,pk-5,bkd-6 6000-6010: counts f o r c o r r e c t i o n p e l l e t — f o r a l l p o s i t i o n s i n same order as a b o v e — r e p e a t f o r a l l r u n s ) l 6020: AGV ( i n quotes),Sr mac,Nb ppm,Zr ppm,Y ppm,Sr ppm,Rb ppm 6C21-6C29: counts on AGV f o r a l l peaks and backgrounds i n same order as above 6030-6999: data f o r other standards i n same form as t h a t f o r AGV 70C0- : data f o r unknowns—name ( i n quotes),Sr mac, counts f o r a l l peaks and backgrounds i n same order as above Note: Due t o the len g t h of t h i s program a l l data f o r 148 unknowns may not be able to be reduced at one time. After loading master program, enter data u n t i l computer prints the error message *PTB». Erase the data l i n e s for the unkown rock preceding t h i s message. Eeduce data, and then delete data l i n e s for those unknown rocks; type data for next batch of unknowns and reduce as above. Backgrounds are determined at a l l peak positions by f i t t i n g an exponential curve to a l l background positions. The 'Rb+Sr1 correction p e l l e t i s used to determine the correction factors f o r Sr interference on Zr, and Rb interference on Y. These factors are egual to the background corrected counts/second on Zr/Sr, and Y/Rb, respectively. Data Input and Reduction Procedures for Cerium-Heodymium 5990: date of run (in guotes) 5999: two theta positions—bkd-1,pk-1,pk-2,bkd-2 6CCC-6C09: counts for Ce correction pellet—same order as above—repeat for allruns 6020: AGV (in guotes),Nd mac,Ce ppm,Nd ppm 6021-6029: counts f o r AGV—same order as above—repeat for a l l runs 6030-6999: data for other standards—same form as for AGV 7000- : data for unknowns—name(in guotes),Nd mac,counts in same order as above Background i n t e n s i t i e s are determined at peak positions by assuming a straight l i n e f i t between background postions. The Ce p e l l e t gives a correction factor egual to the background-corrected c/s on Nd/Ce. 149 Operation of Reduction Program — Calculate mass absorption c o e f f i c i e n t s f o r the appropriate wavelegths for a l l unknown rocks; use BASIC program discussed i n Appencix Va. As mass absorption c o e f f i c i e n t s for elements 28-47 are l i n e a r l y related, use the mass absorption c o e f f i c i e n t f o r Sr for reduction of data for n i c k e l , and for the niobium to rubidium series. As Nd and Ce mass absorption c o e f f i c i e n t s are extremely close i n t h e i r values, the Nd mass absorption c o e f f i c i e n t i s used for both elements. — Turn teletype switch to 'line* — Type 'SCR'; t h i s clears the memory of the computer so that the reduction program can be loaded -— Load the reduction program from the paper tape feeder — Enter data either by typing i t i n or by feeding i t i n from paper tape. A l l data should be stored on paper tape for future reference — Type * RUN' — Answer the 3 option guestions by typing *0' or '1', and then 'return' — Answer the '# of standards' question by typing 'x' and then 'return', where 'x' eguals the number of standards not including correction p e l l e t s — After successful reduction of data and storage of data on paper tape(s), type 'SCR' which erases the memory of the computer and leaves the terminal ready for the next user. 150 APPENDIX IVC :. DETERMINATION OF TOTAL WATER AND CAREON DIOXIDE Description of Apparatus: The apparatus and procedure involved has been modified from that of Hutchinson (1S74). Figure 36 presents a l a b e l l e d sketch of the apparatus- I t consists of an open-bore furnace with a three foot long, 18 mm inter n a l diameter s i l i c a tube running throughit and - in which samples are placed. I t i s attached at both ends to drying tubes by mean of tygon tubing and rubber stoppers wrapped i n t e f l o n tape. Nitrogen delivered from a storage tank, i s cleaned by passsing through the f i r s t two drying tubes, sweeps through the s i l i c a tube, and then passes through the f i n a l drying tubes i n which the amount of water and carbon dioxide gained frcm the sample i s measured. Water i s absorbed i n the f i r s t drying tube (H20) which i s f i l l e d with magnesium perchlprate. Carbon dioxide i s absorbed i n the second tube (C02) which contains ascarite. The one-way flow of nitrogen ends i n a beaker containing mineral o i l , i n which the flow rate can be v i s u a l l y estimated. Supply: Magnesium perchlorate and ascarite can be ordered frcm Fisher S c i e n t i f i c ; one-pound bottles of each are now kept i n the X-ray lab. The drying tubes need not be r e f i l l e d for scores of samples. Ascarite changes from a brown to white color when i t i s exhausted, and magnesium perchlorate should be changed only i f blank values appear to be e r r a t i c or i f the H20 tube loses weight on blank runs. Combustion boats and crucibles are kept i n the X-ray lab. The c o l l e c t i o n consists of 5 five-centimeter v i t r e o s i l boats, 5 ten-centimeter v i t r e o s i l boats, 2 ten-centimeter Coors porcelain v a l v e s F I G U R E 3 6 : S c h e m a t i c d r a w i n g o f a p p a r a t u s f o r d e t e r m i n a t i o n o f t o t a l HO a n d C O 2 . 152 boats, and 3 five-centimeter Coors porcelain boats. Eorcelain boats should be used at temperatures above 1100 degrees C e l s i c s . Procedure: Switch variac on, turn up to 115 v o l t s , and allow to warm up for 2 hours. Temperature should be i n the range 1050-1100 degrees Celsius, but w i l l climb slowly with time. After 4-5 hours turn the variac down to 110 v o l t s . A c a l i b r a t i o n chart of temperature versus variac voltage i s attached to the variac. Open a l l valves i n the four drying tubes, cpen the pressure valve on the nitrogen tank, and open the needle valve cn the regulator. Slowly turn the main adjusting valve on the regulator u n t i l bubbles of nitrogen can be seen i n the mineral o i l bath. Flow should be continuous and just slow enough that bubbles can be counted i n d i v i d u a l l y . Determination of Blank: As the flow of nitrogen gas alcne causes the water and carbon dioxide c o l l e c t i o n tubes to gain weight, a blank value should be determined before each batch of samples i s run. These correction factors should not be more than 0.3 mg and 2 mg per hour for C02 and H20, respectively. Using a l i n t free cloth to handle drying tubes, close valves on H20 and C02 tubes, remove tygon tubing, accurately weigh each tube, and reconnect. As pressure w i l l b uild up once the valves are closed, disconnect tygon tube 1 from the H20 tube as soon as the f i r s t valve i s closed. Disconnect tube 2 from the H20 tube, unscrew clamp and weigh tube. Eeclamp i n position and reconnect tube 2; disconnect tube 2 and tube 3 frcm the C02 tube, unscrew clamp, weigh, reclamp, and reconnect tubes 2 and 3. Open valves i n both drying tubes and reconnect tube 1. Adjust flow rate as above. 153 Note time. Run blank for 1 hour. Following the weighing procedure above, obtain the weight gained by each drying tube, and divide by the time of the run to ar r i v e at a correction value for both H20 and C02. Determination of H2Q- i n samples: Accurately weigh approximately one gram of each sample into Coors porcelain c r u c i b l e s . Dry at 110 degrees centigrade for one hour. Cool and reweigh. Weight loss equals H20-. Store samples in dessicator for determination of H20+ and C02. Determination of 1120* and C02 i n sample: Accurately weigh approximately one gram of sample in t o small v i t r e o s i l combustion boat. I f sample i s to be reused l a t e r f o r further chemical analyses, use larger v i t r e o s i l or Coors porcelain combustion boats l i n e d with nic k e l f o i l i n order to avoid contamination between samples. Note time. I f more than 15 minutes has passed since the l a s t weighing of the drying tubes, i t i s best to reweigh to obtain i n i t i a l values. Reconnect tube 1 to the H20 tube and immediately p u l l stopper A from the s i l i c a tube. The flow of nitrogen through the tube prevents a i r from entering the system. Place combustion boat with sample into the end of the s i l i c a tube and, using the iron push rod, push the boat into the furnace u n t i l the red mark on the push rod i s aligned with the end of the s i l i c a tube. Quickly, but smoothly, remove the push rod and replace the stopper at the end of the s i l i c a tube. Check the mineral o i l 154 bath for the flow of nitrogen. Adjust the rate of flow by leans of the regulator or needle valve so that bubbles are continuous but just slow enough to be i n d i v i d u a l l y counted. This gives a flow of approximately 3 l i t e r s per hour. Care should be taken that the rate of flow i s the same as that during the blank determination. Vapour w i l l condense on the inside of the s i l i c a tube, slowly progress down the tube, into the pyrex tube inserted i n rubber stopper A, and eventually onto the arm cf the H20 tube. The run can be terminated when condensation droplets are no longer v i s i b l e on the arm of the H20 tube. Note time. Close valves on the H20 and C02 tubes, and remove rubber stopper A. Push sample as fa r as possible with the flattened end of the push rod. Remove stopper B, and with the other end of the push rod, hook the combustion boat and draw i t out of the s i l i c a tube u n t i l i t overhangs the edge enough to be grasped with a pair of tweezers. Set the boat on the asbestos pad to cool. Replace stopper B, then stopper A, and disconnect tube 1 frcm the H20 tube. Weigh the two drying tubes according to the procedure outlined above. Load next sample into the combustion apparatus to begin second determination. Weigh the combustion beat plus sample which, by then, should be cool enough to touch. Calculations.: Obtain the weight gained by each drying tube by subtracting the i n i t i a l weights of the tubes from the weights a f t e r the run. Subtract the appropriate correction values (adjusted to the length of the run). Divide each cf these values by the i n i t i a l weight of the sample to obtain the weight 155 per cent of H20+ and C02 i n the sample. Subtract the f i n a l weight of the combustion boat plus sample from the i n i t i a l value and divide by the i n i t i a l weight of the sample, to obtain the t o t a l weight per cent of sample l o s t . This value should agree with the sum of the H20+ and C02 values to within 5%. I f net, a duplicate run should be made. Shut Down: Turn down voltage on variac and switch o f f . Release pressure of nitrogen by backing off on regulator. Wait for bubbles to stop i n mineral bath; then close needle valve on nitrogen regulator and main pressure valve on tank, and shut a l l valves on drying tubes. This insures that no a i r w i l l enter the system and that nitrogen pressure w i l l not b u i l d up within the system. 156 APPENDIX IVD: DETEEMINATION OF FERROUS IEON reagents: Boric Acid (10 G/sample) Barium Diphenylamine Sulfonate (.01 G/10 Potassium Dichromate(.6825 G) Phosphoric Acid (50ml/10 Samples) Hydroflouric Acid In Dispensing Bottle (2ml/sample) Sulf u r i c Acid In Dispensing Bottle (2 Ml/sample) D i s t i l l e d Water (400 Ml/sample) equipment;: 5-10 Teflon Test Tubes + Caps 1 Sand Bath And Hotplate 1 P l a s t i c Coated Wire Back 1 Microburet Plus Stand 1 Magnetic S t i r r e r 2-5 Magnetic S t i r r i n g Bods 2-3 100 Ml Volumetric Flasks 1 1 L i t r e Volumetric Flask 1 10 Ml Graduated Cylinder 5-10 600 Ml Pyrex Beakers 2 100 Ml Pyrex Beakers 1 Glass S t i r r i n g Eod 1 Timer (10 Minutes) 1 Metal Tongs S u t ^ i J l A l l reagents and equipment are kept i n Dr. K. Fletcher's lab (room 213), with the following exceptions: A timer can be borrrowed from the department darkroom, and metal tongs from the X-ray lab. D i s t i l l e d water, and hydroflouric and sulphuric acid i n dispensing bottles are available from the strontium chemistry lab. Boric acid (crystals) are available from geology supplies. Method: Prepare the following solutions (solutions 1 and 2 can be made one week early but solution 3 should be made just before the rest of the procedure i s done): 157 1) Indicator solution: dissolve 0.01 g barium diphenylamine sulfonate i n 50 ml water,. Add 50 ml phosphoric acid and d i l u t e to 100 ml. It i s not c r i t i c a l that a l l the barium diphenylamine i s dissolved completely; i t only e f f e c t s the i n t e n s i t y cf the colour of the f i n a l solution. 2) T i t r a t i o n s o l u t i o n : dissove ,,6825 g potassium dichrcmate (dried at110°C for 2 hours) i n water and d i l u t e to 1 l i t e r . Must be accurate. 3) Boric acid solution: dissolve 10 g boric acid in 400 ml water (in 600 ml beaker) and bring to vigorous b o i l . Allow solution to cool. Repeat for each sample to be analyzed. This solution forms a complex with the ferrous ion to prevent oxidation to f e r r i c ion. weigh accurately samples of approximately 400 mg each i n t o a series of t e f l o n test tubes. Rinse sample down sides of test tube with as l i t t l e water as possible. Add 2 ml s u l f u r i c acid to test tube and then 2 ml hydroflouric acid cap immediately and bring to rapid b o i l i n sand bath f o r 10 minutes-Note : Sample oxidizes readily once HF i s added so be guick with procedure once i t i s added. I f very l i t t l e water was used to wash down sample i n test tube, the acids can be mixed with a small amount of water i n a t e f l o n test and then added to sample. Since the mixture of these reagents involves a strongly exothermic reaction, addition of t h i s hot acid mixture w i l l allow sample to reach a b o i l more quickly. Use timer to make sure bo i l i n g time i s not more than 10 minutes. Risk of oxidation of ferrous iron increases greatly with prolonged b o i l i n g . While sample.is b o i l i n g f i l l graduated cylinder with 10 ml 158 indicator solution. Four about 100 ml of boric acid from 600 ml beaker into 100 ml teaker. Using metal tongs, remove test tube from sand bath and immediate plunge i t (cap side down) into 600 ml beaker containing 300 ml boric acid. Use glass s t i r r i n g rod tc push cap off. test tube. Keep test tube immersed (sample out of contact with air) while r i n s i n g glass rod and test tube cap with boric acid from small beaker into large one. L i f t test tube from beaker and guickly f i l l several times with boric acid.from small beaker emptying contents each time into large beaker. Add 10 ml indicator solution to 600 ml beaker containing boric acid plus sample and begin to s t i r on magnetic s t i r r e r . T i t r a t e with potassium dichromate solution u n t i l permanent purple tinge i s obtained. Colour w i l l often appear and then dissappear as mixing of solution proceeds. Note: i n the entire procedure, only three neasurements are c r i t i c a l to the accurate determination of ferrous i r o n : the proportions of the t i t r a t i o n s o l u t i o n , the weight of sample, and the volume of t i t r a t i o n solution used. Calculations: the oxidation-reduction eguation i s : Cr207-2 + 14 H+ + 6 Fe+ 2 === 6 Fe+* + 2 Cr+ 3 • 7 H20 moles Cr207 = (. 6825/294. 2) * (volume t i t . s o l n . i n l i t r e s ) moles FeO = (wgt of sample (mg)) (% FeO)/71.85 % FeO = 6 * .6825 * 71.85 * v o l . Tit.sl(ml) * 100 294.2 * wgt sample (mg) %FeO = 100 * vol t i t . s l ( m l ) / wgt sample (mg) 159 APPENDIX V: COMPUTER PROGRAMS Various programs have been written that f a c i l i t a t e reduction of whole-rock compositional data and representation of this data i n a variety of ways useful to p e t r c l c g i s t s . These programs are designed to complement the X-ray fluorescence spectrometry a n a l y t i c a l techniques recently established i n the UBC Department of Geology, and should be used in the following manner: 1) raw XRF whole-rock data i s reduced to a hydrous basis and mass absorption c o e f f i c i e n t s are calculated by the 'mass absorption c o e f f i c i e n t ' program described i n Appendix Va. 2) whole-rock data from step 1 i s run through a cation term program and an output f i l e i s generated which contains the whole-rock chemistry and normative compositions of a l l rocks. Steps 1 and 2 can be combined by u t i l i z i n g the *XRF c a l i b r a t i o n ' program written by G.T. Nixon. This program puts analyses on an hydrous basis and generates a data f i l e which i s read by the norm program. Mass absorption c o e f f i c i e n t s are calculated i n t h i s version of the norm program. 3) whcle-rock data i s tabulated for presentation using the program described in Appendix Vb. 4) whole-rock data i s graphically plotted using the program described i n Appendix Vc, i n conjunction with a program written by E.H- Perkins. In addition, steps 3 and 4 have been adapted so that microprobe analyses of minerals can be tabulated and plotted using the programs described i n Appendix Vd and Vie, respectively. 160 APPENDIX VA: MASS ABSOBPTION COEFFICIENT COMPUTATION: This program computes mass ' absorption c o e f f i c i e n t s for various wavelengths from major element analyses. C o e f f i c i e n t s are computed f o r barium and neodymium (L alpha), and chiondum, vanadium, strontium, and rubidium (K alpha) wavelengths, using mass attenuation values from The Handbook of Spectroscopy, 1974. Several options are available for re c a l c u l a t i n g najor element analyses prior to the computation of the mass absorption c o e f i c i e n t s ; these options are intended to complement two primary situations encountered i n obtaining major element analyses by the fused d i s c . X-ray fluorescence technigue used at UBC. The f i r s t option i s used for treating major element analyses of rocks used as standards i n c a l i b r a t i o n curves, This option converts analyses from Abbey (1977), which are cn a dry basis (H20- removed), to analyses i n a completely v o l a t i l e - f r e e and oxidized state; these analyses correspond to the state of these rocks i n fused disc form and should be used as primary values i n c a l i b r a t i o n curves. The analyses are then reconverted to a vol a t i l e - i n c l u d e d basis, recalcualted to 100%, and mass absorption c o e f f i c i e n t s are computed. The second option i s used to treat analyses of unknown rocks which have been determined on fused discs by X-ray fluorescence. This option converts these analyses to a v o l a t i l e -included basis, recalculates them to 100%, and computes mass absorption c o e f f i c i e n t s . If neither of the above options are chosen, the program w i l l calculate mass absorption c o e f f i c i e n t s without adjustnent 161 of the major element chemistry. Major element chemistry i s supplied by the user i n the form of data statements. These statements must occur between l i n e s 1000 and 1999, or after l i n e 2500. The data statements must be in the following form: sample name (in guotes),Si02,Ti02,A1203,Fe203,FeO,MnO, MgO,CaO, Na20,K20,P20 5,H20+, S,C0 2, E20-A l l oxide data i s i n weight per cent. I t i s not important how much data appears on a single l i n e , as lcng as the name of the sample and oxide data are i n the proper order. Data for each sample should follow sequentially i n the same prder as l i s t e d above. I f any of the above elements or oxides have not been determined, a zero must be entered i n th e i r place. The only difference between data statements for standards and unknowns i s that data for standards includes a nominal sum (including trace elements) which follows the l a s t oxide entry. A second input-cption i n the program allows the user to specify which data format has been used. In order to run the program, a l l analyses should be typed in data statements and kept on paper tape so that they can be reused at a l a t e r time i f necessary. Load the master program from the paper tape and enter the analyses from paper tape i f they have not already been typed i n . Type *EOHNH'. The program then asks the user which option i s to be used. Type either • 2 1, M 1 , or »0». I f »0' i s typed, the program asks whether the data format i s for unknown rocks or standard rocks. Type ' 1» or '2*. 162 APPENDIX VB: WHOLE-BOCK TABULATION PBOGRAM This program reads the output f i l e of the norm program(refer to G.T. Nixon, 1979) which consists of major and trace element chemistry and normative compositions, and tabulates them i n a f i l e which can be run on the FMT system. The tables i n Appendix I are examples of the f i n a l output of t h i s program. The program should be run from a terminal with the following command: $RUN OB.WRTABLE 3='DATAFILE' 7='0UTPUT' where 'E ATAFILE' contains the output from the norm program, and •OUTPUT' w i l l be the f i l e read by the FMT system. One option i s presented to the user, and demands an input of how many columns/page are to appear i n the f i n a l table. The program f i r s t asks 'same # of columns/page?'; the user must type '0' f o r 'yes', or '1' for 'no 1. I f the answer i s 'yes' the program asks the user to input the number of columns to appear on each page. I f the answer i s 'no', the program asks how many pages of output are to be produced and the # of columns to appear on each page starting with page one(up to 20 pages). A l l information must be ri g h t j u s t i f i e d . i n 12 format. Before running the output f i l e on the FMT system, t h i s f i l e should be edited by replacing l i n e s 1-3 with the following l i n e s : NO LIST NO PAGE GO Then issue the command: 163 $RUN *FMT SCARDS= 'OUTPUT' SPRINT= 'FINAL TABLE' Release the f i n a l table to the,special * TN' printer with the following commands: $CONTROL *PRINT* HOLD PRINT=TN FORM= TYPE $COPY 'FINAL TABLE' *PRINT* SRELEASE *PRINT* where 'TYPE' refers to the type of paper (8 x 11, or blank) 164 APPENDIX VC: WHOLE-BOCK PLOT PROGRAM This program i s designed so that various compositional parameters and combinations of these parameters can be plotted using plot programs written by E. H. Perkins.. The program reads the output f i l e of the norm program, so that major and trace elements, i n addition to normative compositions, can be plotted. Each of these compositional parameters i s given a reference number within the program, so that choices of plot parameters i s performed by user input of the appropriate numbers. Examples of plots generated by use of t h i s program are shewn i n a l l figures of t h i s thesis that contain compositional data. The program i s run from conversational terminal by the command: $RON OB.WRPLOT 3=«DATAFILE f 7= f-FILE» where 'DATAFILE' contains the output of the norm program, and '-FILE* i s a temporary f i l e which i s read by the plot program. The program i s written so that the X- and Y-axes can contain r a t i o s with numerators and denominators consisting of the sum of up to six compositional parameters. The choice of parameters i s performed by four separate input statements for X-axis numerator, X-axis denominator, Y-axis numerator, and Y-axis denominator. The format of the input i s 612, where each two-place integer i s the reference number of a desired compositional parameter. I f less than s i x parameters are desired, the remainder of an input l i n e i s l e f t blank. A denominator (or numerator) can be set egual to * 1", by input of the reference number '50* at the appropriate input, guestion. 165 Triangular plots are created within the program by rearranging the data such that the X-axis numerator i s translated to the lower right apex of an e q u i l a t e r a l t r i a n g l e , and the Y-axis numerator i s translated to the top apex of the trian g l e . Both denominators must contain the sum of a l l parameters desired at the three apices of the tria n g l e . A l l parameters within numerators and denominators can be multiplied by chosen factors by responding 'yes' ('1') to the appropriate question. In t h i s case the user i s asked to input these multi p l i c a t i v e factors f o r each numerator and dencminator. The input i s i n 6F6.3 format, and i s easiest i f a l l parameters are separated by commas. I f less than six m u l t i p l i c a t i v e factors are desired, the remaining part of the input l i n e can be l e f t blank. Other input questions require *yes' or 'no' responses, which are s i g n i f i e d by typing (11 format) '1* or 'O1, respectively. These options are f o r : — a large square plot as opposed to a smaller rectanqular plot with long axis horizontal — a l l major elements plotted on a molecular basis (divided by molecular weights) — a l l major elements recalculated on a v o l a t i l e - f r e e basis — the natural log of a l l plot parameters — a l l iron converted to the ferrous state (for AFM diagrams) — a l l major elements converted to parts per m i l l i o n by multiplying by • 10,000'. . If a rectangular plot i s chosen, the program then pri n t s 166 the minimum and maximum values for the X- and Y-axes- The user must then type the minimum and maximum values desired for loth axes i n 4F10.3 format. These values w i l l normally be chosen so as to encompass the printed minimum and maximum values. In the l a s t input, the user enters labels for both axes which may contain up to twenty characters. Triangular plots reguire neither of the f i n a l two inputs. After termination of the program, the user can plot the data by using the command: $EUN THB2:PLOIG.O 3= ,-FILE' (for rectangular p l o t s ) , or $RON EHP:TRIIG.O 3=?-FILE , ! (for triangular p l o t s ) . In either case, the user i s then asked by t h i s program •what device are you on? 1, and responds by h i t t i n g the ' r e t t r n ' key. The plot w i l l be drawn, and can be copied to a larger s i z e by putting the cross-hairs on the 'copy' command, and typing •1*. To make a hard copy of the plot, press the 'copy* button on the right side of the Tektronix terminal. To return to command mode, press the 'return' key. To terminate the plot program, put the cross-hairs on the 'stop' command, and type '1'. Many other plot e d i t commands are available but use of them should not be attempted without further personal i n s t r u c t i o n s . NOTE: This plot program can.only be run on the Tektronix terminal now located i n Dr. T.H. Brown*s computer room. His permission to use that terminal i s a necessary condition for using t h i s plot program. 167 APPENDIX VP: MINERAL TABULATION PBOGBAM This program calculates formula bases and various end member compositions for pyroxenes, amphiboles, feldspars, b i o t i t e s , magnetites, and ilmenite analyses, and tabulates them in an output f i l e which can be run on the FMT system. Examples of tables produced by t h i s system are presented i n Appendix II. The program reads analyses including up tc 13 elements (format: A4,10F7.2,/,4x,3F7.2) for a l l minerals except feldspars, which contain up to 10 elements(format: AU,10F7.2). The order of the data input i s : sample name, Si0 2 , T i 0 2 , A l 2 0 3 , FeO, KnO, MgO, CaO, BaO, Na20, K 20, C r 2 0 3 , V 20 3 , NiO,. The program should be run from a conversational terminal with the following command: $EDN OB.MINTABLE 3='DATAFIIE* 7=»OUTPUT' 8='PLOTCATA' where 'DATAFILE* contains the mineral analyses 'OUTPUT* i s the f i l e which w i l l be run on the FMT system and 'PLOTDATA' i s a f i l e which w i l l contain the analyses and calculated formula bases of the tabulated minerals, and can be used to plot mineral compositions using the program described i n Appendix Ve. After issuing the above command, the program w i l l ask the user to input the formula basis (# of oxygens) appropriate for the mineral compositions that i t w i l l read. In order tc key the program into c a l c u l a t i n g appropriate end-member compositions, the following formula bases should be used: 6=pyroxenes 8=feldspars 22=bictites 23=amphiboles 24=magnetites 32=ilmenites 168 The desired formula basis i s input at the same time as the desired number of columns per page and the number of elements i n the mineral analyses (312 format) . In addition to c a l c u l a t i n g formala bases, the program t i l l c alculate — F e 3 * , A l V I , A l I V , and end-member compositions for pyroxenes using the procedures of Cawthorne and Collerson (1974) — feldspar end-member compositions — F e 3 + in amphibole analyses by solution of the charge balance eguation of Papike et a l . (1974): Na (A)+K ( A)+2Ba(A)+Al V I+Fe 3 +2Ti = Al I V+Na(M4) wJiere l e t t e r s i n parantheses refer to amphiblcle s i t e s Na i s distributed between the A and M4 s i t e s by set t i n g Na (M4) egual to the difference between the i d e a l sum of t i e X and Y s i t e s (7) and the sum of the cations (Mg, Fe, Ni, A1 V I, V, C T , Ca, Mn) f i l l i n g these s i t e s . — Fe 3 + and ulvospinel contents of magnetites by the procedure of Anderson (1968) or Carmichael (1967) — F e 3 + and hematite contents of ilmenites by the procedure of Andersen (1968) or Carmichael (1S67) If Fe-Ti oxides are being tabulated, the program w i l l ask the user which reduction procedure to use. Respond by inputting •0* for the procedure of Anderson (1968), or '1' f o r that of Carmichael (1967). It i s often useful to run the program twice because the two reduction technigues can y i e l d guite d i f f e r e n t r e s u l t s . These differences can lead to s i g n i f i c a n t variations i n calculated temperatures and oxygen fugacities i f applied to the experimental data of Buddington and Lindsley (1964),. 169 Before running the output f i l e on the FMT system, e d i t the same changes i n t h i s f i l e as discussed i n Appendix Vb. 170 APPENDIX VE: MINERAL PLOT PROGEAM This program enables users to plot mineral compositions using the programs written by E-H. Perkins. Examples of plots generated by t h i s program are Figures 23 and 25 of t h i s t h e s i s . The program i s run from conversational terminal with the command: $RDN OB.MINTABLE 3='DATAFILE' 7='-FIIE" where 'DATAFILE' i s the f i l e generated by the 'nineral tabulation' program described i n Appendix Vd and '-FILE' i s the f i l e which w i l l be read by the plot program The program i s set up i n a sim i l a r fasiiicn to that of the 'whcle-rock plot' program (Appendix Vb) , and the compositional parameters to be plotted are designated in four input statements for the X- and Y-axis numerators and denominators (612 format). Triangular, q u a d r i l a t e r a l , or rectangular plots can be generated by responding '1',«2', or '0', respectively to the appropriate input question. After termination of the program, the data may be plotted using the command: $B0N THB2:PLOIG.O 3='-FILE' (for rectangular p l o t s ) , or $EUN EHP:TRIIG.O 3='-FILE« (for triangular or qua d r i l a t e r a l p l o t s ) . Operation of these plot programs i s described at the end of Appendix Vc. 

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