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UBC Theses and Dissertations

A study of plagioclase zoning Greenwood, Hugh John 1956

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A STUDY OF PLAGIOCLASE ZONING by HUGH JOHN GREENWOOD A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF ' MASTER OF APPLIED SCIENCE i n the department ' of GEOLOGY We accept t h i s t h e s i s as conforming t o the standard r e q u i r e d from candidates f o r the degree of MASTER OF APPLIED SCIENCE. Members o f the Department of Geology THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1956 A STUDY OF PLAGIOCLASE ZONING ABSTRACT The zoning of p l a g i o c l a s e f e l d s p a r s was st u d i e d w i t h the f o u r - a x i s u n i v e r s a l stage. The..composition,, i n terms o f the e x t i n c t i o n angle X fA010,JLa, was measured f o r each zone i n s e v e r a l c r y s t a l s i n each of n e a r l y f i f t y r o c k s . The v a l -ues o f the e x t i n c t i o n angles f o r each zone were p l o t t e d a g a i n s t the distance of the zone from the r i m of the c r y s t a l , and the r e s u l t i n g zone-curves f o r each rock compared. . Three degrees o f c o r r e l a t i o n between zone-curves are re c o g n i z a b l e , and the rocks s t u d i e d may be a r b i t r a r i l y grouped on t h i s b a s i s as f o l l o w s : 1. Rocks i n which the c o r r e l a t i o n i s poor o r absent. These i n c l u d e l a v a s and some i n t r u s i v e g r a n i t e s . 2 . Rocks i n which the c o r r e l a t i o n i s good or p e r f e c t . These i n c l u d e h o r n f e l s e s and, the f o l i a t e d and t g n e i s s i c metamorphic r o c k s . 3. Rocks i n which the c o r r e l a t i o n i s i n d e f i n i t e . This group, which contains o n l y twelve ^ percent of a l l the rocks s t u d i e d , i n c l u d e s some i n t r u s i v e g r a n i t e s and some f o l i a t e d metamorphic r o c k s . The degree o f m o b i l i t y of magmas may be estimated. The m o b i l i t y appears t o be s e v e r e l y r e s t r i c t e d by the con-t i n u e d growth o f i t s f e l d s p a r phenocrysts, and by the c o n f i n i n g w a l l s of i n t r u d e d country rock. The author concludes t h a t extreme complexity and non-c o r r e l a t i o n o f zoning are due to r e l a t i v e motion between growing c r y s t a l s , and t h a t these f e a t u r e s are most common i n magmatic rocks which have been thoroughly mixed during the f l u i d stage. • He concludes f u r t h e r t h a t s i m p l i c i t y and c l o s e c o r r e -l a t i o n o f zoning are due t o the growth of c r y s t a l s i n a q u i e t , r e l a t i v e l y undisturbed environment i n which the c r y -s t a l s do not move r e l a t i v e l y t o one another. F i n a l l y , i t i s concluded t h a t c y c l i c s u p e r s a t u r a t i o n , as proposed by H i l l s , (1936), i s a l e s s important cause o f p l a g i o c l a s e zoning than changing pressure-temperature en-vironments due t o mixing or turbul e n c e . TABLE OF CONTENTS CHAPTER PAGE I . INTRODUCTION 1 P r e l i m i n a r y Statement 1 Acknowledgement • 1 I I . METHOD OF INVESTIGATION 3 S e l e c t i o n o f Rock Specimens . . . . . . . . 3 Examination of Rock Specimens • 3 Representation of Data . . . . . . . . . . . 4 Figure 1, The D e r i v a t i o n of the Cumulative Departure Curve • • 7 E r r o r s i n C o n s t r u c t i n g the Curves £ I I I . THE SPECIMENS AND THEIR ZONE-CURVES 9 Remarks on the Curves 9 F i g u r e 2, D i s t r i b u t i o n of the Degrees of C o r r e l a t i o n i n D i f f e r e n t Rock-Types • • 11 IV. INTERPRETATION OF RESULTS . . . . . 26 General Considerations • • • • • 26 Temperature • 26 Pressure 2g V o l a t i l e C o n s t i t u e n t s . . . . 2d Close C o r r e l a t i o n 29 Non-Correlation 30 CHAPTER PAGE I n d e f i n i t e C o r r e l a t i o n 31 The S i g n i f i c a n c e of Zone-Curves of S i m i l a r Shape . . . . . . . . . . . 32 The E f f e c t of Plagioclase,Crowding on C o r r e l a t i o n 33 V. CONCLUSIONS * . . * . i . . . 35 BIBLIOGRAPHY . . . . . . . 37 LIST OF PLATES PLATE PAGE I. C r y s t a l Drawings 11a I I . Lava, Specimen P1022 . . . . . . . *.,\ . . . 12a I I I . Lava, Specimen 535 13a IV. Lava, Specimen '327 . . 14a • V. Shap Granite, Specimen P97I . . * 15a VI. Granitic Dyke, Specimen 2a ". 16a VII. Feldspar Porphyry Dyke, Specimen 6 17a VIII. Ben Nevis Porphyritic Granite, Specimen P1253 18a IX. Pilchuck Granite Stock, Specimen 318 . . . . 19a X. Comrie Granodiorite, Specimen P1050 . . . . 20a XI. Hornfels, Specimen P731 21a XII. Hornfels. Specimen 16 22a XIII. Hornfels, Specimen 3 22b XIV. F o l i a t e d Metamorphics, Specimen 2b . . . . . 23a XV. F o l i a t e d Metamorphics, Specimen 2c 23b XVI. Banded Meta-Sediment, Specimen H-37 • • • • 24a XVII. Granitic Dyke and Schist Wall-Rock, Specimen H-24 25a XVIII. Log-tan slope of Cumulative Departure Curves Vs Percent of Zoned Plagioclase i n Rock . 34a .1. INTRODUCTION P r e l i m i n a r y Statement The w r i t e r became i n t e r e s t e d i n the problem of the o r i g i n of g r a n i t e two years ago w h i l e working i n the c e n t r a l Yukon. I n an attempt t o solve the problem, he s t u d i e d i n d e t a i l many of the t e x t u r a l f e a t u r e s of g r a n i t i c r o c k s , at f i r s t w i t h l i t t l e success. C a r e f u l study o f the zoning o f p l a g i o c l a s e s i n g r a n i t e s , however, provided some i n t e r e s t i n g and s u r p r i s i n g data, which l e d f u r t h e r t o the study o f p l a g i o c l a s e zoning i n v o l c a n i c and conventional metamorphic r o c k s . The r e s u l t s o f t h i s study have not l e d t o a d i r e c t s o l u t i o n o f the " g r a n i t e problem", but they do seem t o t e l l something of the o r i g i n and h i s t o r y of the rocks i n v o l v e d . Acknowledgement I t i s not p o s s i b l e to give e x p l i c i t c r e d i t to a l l who, d i r e c t l y or i n d i r e c t l y , gave f r e e l y of t h e i r ideas and time towards t h i s study, but the author wishes to express h i s g r a t i t u d e to a l l those w i t h whom he discussed the ma-t e r i a l o f t h i s r e p o r t . The author i s p a r t i c u l a r l y indebted t o h i s research 2 a d v i s o r , Dr. K. C. McTaggart, f o r h i s i n v a l u a b l e suggestions, c r i t i c i s m s , and d i s c u s s i o n s , and t o the other members of the s t a f f o f the Geology Department who c o n t r i b u t e d ideas and r e a d i n g m a t e r i a l , p a r t i c u l a r l y Drs. W. H. Mathews and J . M. C a r r . The work could never have been done without the help o f these people and those not d i r e c t l y acknowledged. I I METHOD OF INVESTIGATION S e l e c t i o n of Rock Specimens The m a t e r i a l f o r t h i s study was s e l e c t e d from c o l -l e c t i o n s from w i d e l y separated l o c a l i t i e s , thus ensuring t h a t any conclusions reached would have more than l o c a l s i g n i f i c a n c e . The l o c a l i t i e s i n c l u d e the igneous t e r r a i n s o f the B r i t i s h I s l e s , the i n t r u s i v e stock o f the P i l c h u c k G r a n i t e of Washington S t a t e , U. S. A., the Glen Lyon Range of c e n t r a l Yukon, the Coast Range of B r i t i s h Columbia near Terrace, and the s o u t h - c e n t r a l p a r t of B r i t i s h Columbia. Examination of Rock Specimens Thin s e c t i o n s of the specimens were f i r s t examined w i t h the o r d i n a r y petrographic microscope i n order t o s e l e c t and mark zoned c r y s t a l s s u i t a b l e f o r measurement on the u n i -v e r s a l stage. S u i t a b l e s e c t i o n s were examined on the 4-axis u n i v e r s a l stage. Each c r y s t a l was o r i e n t e d w i t h i t s c r y s t a l l o g r a p h i c a-axis p a r a l l e l to the a x i s of the microscope and the angles X'A(OIO ) measured. D e t a i l e d s c a l e drawings were made of every c r y s t a l examined and the p o s i t i o n s of measured com-p o s i t i o n s marked. The d i s t a n c e of each zone from the edge 4 of the c r y s t a l was measured w i t h a graduated o c u l a r a t t a c h -ment, and a curve r e c o r d i n g the e x t i n c t i o n angles versus d i s t a n c e from the edge of the c r y s t a l p l o t t e d . I n u n i v e r s a l stage work, the measured angles are c o r r e c t e d because of the t i l t of the stage and the d i f f e r -ence i n index between the hemispheres and the m i n e r a l . These c o r r e c t i o n s were not a p p l i e d because only c r y s t a l s r e q u i r i n g a low t i l t were measured. The c r y s t a l s were o r i e n t e d by making v e r t i c a l the a l b i t e - t w i n composition plane and the (001) cleavage, probably w i t h n e g l i g i b l e e r r o r . There i s an e r r o r i n the e s t i m a t i o n of complete ex-t i n c t i o n i n the zones, averaging perhaps two degrees f o r wide zones. Where the zones are narrow, or where the s e c t i o n i s cut so t h a t the s h e l l s of d i f f e r e n t composition are not p a r a l l e l t o the a - a x i s , the e r r o r may be f o u r degrees or more, because of s u p e r p o s i t i o n o f e f f e c t s from adjacent zones. Representation o f Data The o r i g i n a l data has been p l o t t e d w i t h d i s t a n c e from the edge as a b c i s s a , and e x t i n c t i o n angle as o r d i n a t e . Cor-r o s i o n unconformities are marked on the curves as w e l l as on the drawings, t o help i n t e r p r e t a t i o n . The curves f o r the c r y s t a l s of a given rock are r e -p l o t t e d on a new graph, u s i n g the same o r d i n a t e values as b e f o r e . Adjustments corresponding t o widths o f zones are . 5 made i n the a b c i s s a s c a l e f o r each curve s e p a r a t e l y i n an attempt t o make the curves resemble one another. C e r t a i n conventions have been adopted i n the r e - p l o t t i n g t o s t a n -da r d i z e the r e s u l t s . I t i s e s s e n t i a l t h a t these conventions be understood, f o r much of the i n t e r p r e t a t i o n depends on the r e - p l o t t e d curves. The f i r s t c o n s i d e r a t i o n i s matching peaks and hollows of comparable shape and o r d i n a t e v a l u e , w i t h due regard t o unco n f o r m i t i e s . I f two curves, f o r example, have r e c o g n i z -able f e a t u r e s at both r i m and core, the r i m o f one may be matched w i t h the r i m o f the other, and the core o f t h e f i r s t w i t h the core of the second. One curve may have a set of complex o s c i l l a t o r y zones between i t s core and r i m , and the oth e r an unconformity. The curve w i t h the unconformity i s s t r e t c h e d 1 i n the a b c i s s a d i r e c t i o n so t h a t the two prom-inences o f each curve are opposite one another. The blank space l e f t i n the second curve by s t r e t c h i n g the unconformity gap i s opposite the complex set o f zones i n the f i r s t . F o l l o w i n g the adjustment of un c o n f o r m i t i e s , zones of compar-ab l e ordinate-value but of d i f f e r e n t widths are brought opposite one another by v a r y i n g the widths of the zones. As the observed width o f a zone depends, besides on i t s t r u e w i d t h , on the p o s i t i o n i n the c r y s t a l o f the s e c t i o n plane, on the t i l t of the stage, and on the time-duration t h a t the c r y s t a l spent i n a p a r t i c u l a r environment, i t has been 6 considered l e g i t i m a t e t o vary the widths of zones t o improve c o r r e l a t i o n . Zones may be widened to improve comparison, but not narrowed, because by compressing s e c t i o n s of poor c o r r e -l a t i o n , the o v e r a l l apparent c o r r e l a t i o n may be improved by c o n c e a l i n g c o m p l e x i t i e s . Zones are not p l o t t e d as though they are a l l of the same width, because o f t e n a p a r t i c u l a r zone i s o b v i o u s l y o f major importance i n the s t r u c t u r e o f the c r y s t a l . The r e - p l o t t e d curves are compared w i t h one another, and s e m i - q u a n t i t a t i v e values assigned t o the degree of c o r -r e l a t i o n . This i s done by p l o t t i n g cumulative curves o f the departure o f one zone-curve from another. For example, to compare two curves, the a b c i s s a d i r e c t i o n i s d i v i d e d i n t o a number o f equal u n i t s o f a r b i t r a r y l e n g t h , here c a l l e d the standard a b c i s s a step. The u n i t used i n comparisons through-out t h i s paper i s equal t o two and one h a l f degrees on the o r d i n a t e s c a l e . The departure, o r s h o r t e s t o b l i q u e d i s t a n c e between the curves at the end of each a b c i s s a step, i s measured. The f i r s t a b c i s s a step and the f i r s t departure are l a i d o f f on a graph i n t h e i r r e s p e c t i v e a b c i s s a and o r d i n a t e d i r e c t i o n s . The second a b c i s s a step i s then added to the f i r s t , and the second departure e r e c t e d i n the o r d i n -a t e . This process i s i l l u s t r a t e d i n F i g u r e 1 . The cumulative departure curve has a v a r i a b l e p o s i t i v e s l o p e , p r o p o r t i o n a l t o the departure of one curve from another. 7 The slope o f t h i s curve i s c o n t r o l l e d by t h r e e f a c t o r s ; the a r b i t r a r y a b c i s s a step taken, the s e p a r a t i o n of the curves being compared, and the estimate o f the s h o r t e s t d i s t a n c e between the curves. I t i s thus p o s s i b l e , w i t h i n known l i m i t s , t o make a q u a n t i t a t i v e estimate of the degree of c o r r e l a t i o n between p a i r s o f curves, and t o estimate the degree of s i m i -l a r i t y i n the growth h i s t o r i e s o f any two c r y s t a l s . Figure 1 The d e r i v a t i o n of the cumulative departure curve E r r o r s i n C o n s t r u c t i n g the Curves When the o r i g i n a l readings were taken, any tendency to be i n f l u e n c e d by the shape o f p r e v i o u s l y prepared curves was reduced by p l o t t i n g each new curve, as i t was measured, on a new sheet of graph paper. The combined e f f e c t of a l l e r r o r s g i v e s the cumulative departure curves a low though a p p r e c i a b l e slope even f o r com-pa r i s o n s between two curves which o b v i o u s l y c o r r e l a t e very w e l l . The standard slope f o r good c o r r e l a t i o n amounts, i n t h i s paper, t o about twenty-three degrees o f a r c . Cumulative departure curves steeper than t h i s represent imperfect c o r r e l a t i o n . I l l THE SPECIMENS AND THEIR ZONE CURVES Remarks on the Curves During t h i s study more than s i x t y specimens were s t u d i e d , f o r t y - s e v e n o f which were u s e f u l i n the study of p l a g i o c l a s e zones. Of t h i s f o r t y - s e v e n , twenty-nine c o n t a i n zoned p l a g i o c l a s e which was measured on the u n i v e r s a l stage, and eighteen contain unzoned p l a g i o c l a s e . The twenty-nine specimens w i t h zoning comprise seventeen igneous and i n t r u -s i v e r o c k s , ten metamorphic rocks, and two rocks of u n c e r t a i n o r i g i n . The eighteen rocks which have completely unzoned p l a g i o c l a s e comprise f o u r t e e n metamorphic rocks and f o u r o f u n c e r t a i n o r i g i n . Figure 2 i l l u s t r a t e s the d i s t r i b u t i o n of good, bad, and i n d i f f e r e n t c o r r e l a t i o n i n the d i f f e r e n t rock-t y p e s . A s e l e c t i o n of curves has been made from these data, showing the extreme types and some intermediate types of zoning and c o r r e l a t i o n . The r e s t o f t h i s chapter c o n s i s t s of the graphs, c r y s t a l drawings, and d e t a i l e d d e s c r i p t i o n s which pr o v i d e the b a s i s f o r subsequent i n t e r p r e t a t i o n and c o n c l u -s i o n s . I n c o n s i d e r i n g the f o l l o w i n g p l a t e s , the reader should compare the> slopes of the cumulative departure curves o f the d i f f e r e n t r o c k s . I t should be noted, f o r i n s t a n c e , t h a t the 10 curves f o r i n t e r - c r y s t a l c o r r e l a t i o n s i n the v o l c a n i c rocks are steep, while the i n t r a - c r y s t a l curves are r e l a t i v e l y f l a t . I n the h o r n f e l s e s the i n t e r - c r y s t a l c o r r e l a t i o n i s as good as the i n t r a - c r y s t a l c o r r e l a t i o n . This i s a l s o apparent . i n the curves f o r the f o l i a t e d metamorphic r o c k s . I 11 D i s t r i b u t i o n of the degrees of c o r r e l a t i o n i n d i f f e r e n t rock-types PLATE I l l a C ry oXu I D rowings PLATE I I Lava Specimen P10221 Specimen P1022 i s a red o l i v i n e b a s a l t from the Markle Quarry near Edinburgh, S c o t l a n d . The rock has phenocrysts of l a b r a d o r i t e and o l i v i n e set i n a groundmass o f a u g i t e , b i o -t i t e, qu a r t z , and f e l d s p a r . I t i s one of a sequence of b a s i c l a v a s o f the Carboniferous of S c o t l a n d . Specimens w i t h numbers preceded by "P" are from the rock c o l l e c t i o n o f the U n i v e r s i t y of B r i t i s h Columbia. _i4 < PLATE II SPECIMEN 1 4 2 5 , P \OZt z 12a ADJUSTEO ZONE-CURVES INCREASING DIST. FROM RIM la-Wo DISTANCE C U M U L A T I V E D E P A R T U R E " CURVES PLATE I I I Lava Specimen 535 Specimen 535 i s a P l e i s t o c e n e andesite l a v a from G a r i b a l d i Park, B r i t i s h Columbia, c o l -l e c t e d by W. H. Mathews. The rock c o n s i s t s o f s t r o n g l y zoned p l a g i o c l a s e phenocrysts set i n a very f i n e grained m a t r i x of p l a g i o -c l a s e m i c r o l i t e s and g l a s s , w i t h some b i o t i t e and very minor s e r i c i t e . PLATE Ml 13a <1 SPECIMEN 535 O < " X AOJUSTEO ZONE-CURVES INCREASING DIST. FROM RIM PLATE IV Lava Specimen 327 Specimen 327 i s a v o l c a n i c rock, s i m i l a r t o specimen 535, a l s o from G a r i b a l d i Park, PLATE IV SPECIMEN 327 14a o O x ADJUSTED ZONE-CURVES INCREASING DIST. FROM RIM 1 - 3 a-3 CUMULATIVE DEPARTURE CURVES DISTANCE PLATE V Shap Granite Specimen P971 Specimen P971 i s from the Shap Granite of the English Lake D i s t r i c t . The rock mass i s i n -t r u s i v e , with dragged and hornfelsed country rocks of p y r o c l a s t i c s and limestone. I t i s described by Grantham, (Proc. Geol. Assoc., V o l . XXXIX, p. 299.). In t h i n section i t i s a porphyritic (orthoclase, plagioclase) granite, with euhedral orthoclase and plagio-clase, and rounded pebble-like quartz grains set i n a fine-grained quartz-orthoclase groundmass. PLATE V 15a -. u o.icenwjocl. 956 PLATE VI G r a n i t i c Dyke Specimen 2a Specimen 2a was c o l l e c t e d by the author from a s i x - i n c h g r a n i t i c dyke near Shames, about t h i r t y m i l e s west o f Terrace, B r i t i s h Colum-b i a . The dyke i n t r u d e s the s c h i s t s , amphi-b o l i t e s , and gneisses of a migmatite complex, at a p o i n t one m i l e from i t s contact w i t h the main Coast B a t h o l i t h . I n t h i n s e c t i o n the- rock i s seen t o be an equigranular mosaic of zoned p l a g i o c l a s e , o r t h o c l a s e , q u a r t z , and b i o t i t e . The borders of the dyke show no signs of c h i l l i n g , and i n Walton 1s t e r m i n o l -ogy the rock would be c a l l e d an harmonious g r a n i t e . PLATE V I I Feldspar Porphyry Dyke Specimen 6 Specimen 6 was c o l l e c t e d by Peter M o r r i s ^ from a l a r g e p o r p h y r i t i c dyke near H e l l f s Gate i n the Fraser Canyon of B r i t i s h Columbia. The phenocrysts o f zoned p l a g i o c l a s e range i n l e n g t h from one e i g h t h o f an i n c h t o h a l f an i n c h , and are set i n a groundmass of quartz and o r t h o c l a s e . The dyke i s probably an offshoo t o f the Coast Range b a t h o l i t h of southern B r i t i s h Columbia. c Peter G. M o r r i s , "A P e t r o l o g i c a l Study o f I n t r u s i v e Rocks Along the F r a s e r Canyon Near H e l l * s Gate, B r i t i s h Columbia" (unpublished Master*s t h e s i s , The U n i v e r s i t y of B r i t i s h Columbia, Vancouver, 1955) p. 39. PLATE VII SPECIMEN 6 17a ADJUSTED ZONE-CURVES INCREASING DIST. FROM RIM io ui AC r -QS < Q. U i O DISTANCE CUMULATIVE DEPARTURE CURVES PLATE V I I I Ben Nevis P o r p h y r i t i c G r a nite Specimen P1253 Specimen P1253 i s a weakly p o r p h y r i t i c ( p l a g i o -c l a s e ) g r a n i t e from the south face of Ben Nev i s , Scotland. Ben Nevis i s composed of a Caledonian g r a n i t i c complex of the cauldron subsidence type, w i t h an outer g r a n i t e , an i n n e r g r a n i t e , and a c e n t r a l block o f v o l c a n i c s and sediments. The outer contacts are a l l s t r o n g l y h o r n f e l s e d by the g r a n i t e . The specimen was taken from the middle of the "Inner G r a n i t e " . Zoned p l a g i o c l a s e phenocrysts make up about twenty-f i v e percent of the rock, and i n t e r s t i t i a l e q uigranular quartz, potash f e l d s p a r , and a l -b i t e make up the remaining s e v e n t y - f i v e percent. INCREASING DIST. FROM RIM ,1-4-/ -i.u1. vJrcenwoocl, o56 PLATE IX P i l c h u c k Granite Stock Specimen 318 Specimen 313 was c o l l e c t e d by W. R. Danner from an i n t r u s i v e g r a n i t e near Mt. P i l c h u c k , Washington, U. S. A. The g r a n i t e has the form of a stock which i n t r u d e s and h o r n f e l s e s lower Cretaceous sandstones and s h a l e s . I n the g r a n i t e near i t s contacts are numerous t o u r m a l i n i z e d vugs, but towards i t s c e n t r e , where specimen 318" was taken, the rock i s a massive, weakly p o r p h y r i t i c g r a n i t e . The zoned p l a g i o c l a s e phenocrysts are sh a r p l y euhedral w i t h l a t e coatings o f p l a g i o c l a s e g i v i n g them broadly sinuous o u t l i n e s . The groundmass i s an equigranular mosaic of p l a g i o c l a s e , o r t h o c l a s e , b i o t i t e , and q u a r t z . PLATE X Comrie G r a n o d i o r i t e Specimen P1050 Specimen P1050 i s from the Comrie g r a n o d i o r i t e of Scotland. This rock mass was e v i d e n t l y an unusually hot i n t r u s i o n , as i t r a i s e d the surrounding s l a t e s to the pyroxene-hornfels f a c i e s . I n t h i n s e c t i o n the g r a n o d i o r i t e may be seen t o c o n s i s t of zoned euhedral p l a g i o -c l a s e phenocrysts forming s e v e n t y - f i v e percent of the rock, and i n t e r s t i t i a l quartz and ortho-c l a s e . Minor b i o t i t e , hornblende, and a p a t i t e make up the r e s t o f the rock. The abundant l a r g e p l a g i o c l a s e phenocrysts c o n t r o l the t e x t u r e of the rock and e x h i b i t a weak proto-c l a s t i c t e x t u r e . CUMULATIVE DEPARTURE CURVES DISTANCE  -..1/ o ' c e n w o c c L . a s s PLATE XI Hornfels Specimen P731 Specimen P731 i s a garnet-quartz-homblende-plagioclase hornfels from a metamorphic seri e s on Kwoiek Creek near Lytton, B r i t i s h Columbia. The specimen was c o l l e c t e d about h a l f a mile from the east contact of one of the coast range batholiths of B. C. In t h i n section i t s texture may be seen to be h o r n f e l s i c , with a granoblastic mosaic of zoned plagioclase, garnet, quartz, and hornblende. PLATE XI 2 1 * < j SPECIMEN P 731 > + 4 0 or o O KM H I --4-20-o o X j ADJUSTED ZONE — CURVES INCREASING DIST. FROM RIM UI CC 3 I-QS < OL Ui a DISTANCE CUMULATIVE DEPARTURE CURVES PLATES XII, XIII Hornfels Specimens 16 & 3 Specimens 16 and 3 were c o l l e c t e d by E. W. Grove^ from the c o r d i e r i t e - a n t h o p h y l l i t e -hornfels zone i n the p e l i t i c sediments sur-rounding the Harrison l e u c o - d i o r i t e . The hornfelses are made up of b i o t i t e , antho-p h y l l i t e , c o r d i e r i t e , quartz, and zoned plagioclase porphyroblasts. 3 Edward W. Grove, "A Study of Contact Metamorphism at Harrison Ridge, Harrison Hot Springs, B. C." (unpublished Master*s thesis, The University of B r i t i s h Columbia, Vancouver, 1955) PP. 34, 81. < r— CO > cr o PLATE XII SPECIMEN |6 22a 2 H 30 O O X ADJUSTEO 2ONE — CURVES INCREASING 0IST. FROM RIM </>' UJ t-os < a. UJ a 2-3 CUMULATIVE DEPARTURE CURVES DISTANCE .u vi'eenwoo'i. 956 -J-I < CO > cr o +40* PLATE XIII S P E C I M E N 3 22b 4-30° o o X "-+-2D" 3 2. A D J U S T E O Z O N E — C U R V E S INCREASING DIST. FROM RIM in Ui cc 3 as < a. UJ a 2.-3 1-3 D I S T A N C E C U M U L A T I V E D E P A R T U R E CURVES PLATES XIV, XV F o l i a t e d Metamorphics Specimens 2b, 2c Specimens 2b and 2c were c o l l e c t e d by the author from a metamorphic complex near Shames, about t h i r t y m i l e s west of Terrace, B r i t i s h Columbia. The complex i s a s e r i e s o f s t r o n g l y metamorphosed v o l c a n i c s which on one hand i s i n contact w i t h the Coast Range B a t h o l i t h and on the other hand may be t r a c e d i n t o r e c o g n i z -able v o l c a n i c r o c k s . Both specimens were taken about two m i l e s from the contact w i t h the gran-i t e , specimen 2b from a f o l i a t e d g r a n i t i c l a y e r of q u a r t z - f e l d s p a r - b i o t i t e g n e i s s , and specimen 2c from a f i n e g r a i n e d a m p h i b o l i t i c l a y e r c o n t a i n i n g hornblende, p l a g i o c l a s e , and minor quartz and b i o t i t e . PLATE XIV SPECIMEN 2b 23a ADJUSTEO ZONE-CURVES INCREASING DIST. FROM RIM ui cc os < Q. UI O S-7 CUMULATIVE DEPARTURE CURVES DISTANCE < > cc o - f 4-5"' o PLATE XV SPECIMEN 2c 23b 2 - 3 H o o < X INCREASING DIST. FROM RIM A D J U S T E D 2 O N E — C U R V E S 05 Ui CC z> J-QS < a. ui a 3-4-C U M U L A T I V E D E P A R T U R E C U R V E S DISTANCE PLATE XVI Banded Meta-sediment Specimen H-37 Specimen H-37 was c o l l e c t e d by the author from the Glen Lyon Range of the Yukon. The rock appears to be a meta-sediment w i t h a s t r i p e d aspect due to d i f f e r e n t concentrations of b i o t i t e i n bands about two inches t h i c k . I t was taken from a t h i c k f o l d e d s e r i e s of gneisses and s c h i s t s which appear to be caught up i n the main g r a n i t i c mass. In t h i n s e c t i o n i t i s composed of zoned p l a g i o -c l a s e , quartz, b i o t i t e , and minor i n t e r s t i t i a l o r t h o c l a s e . PLATE XVi 2 4 a ADJUSTED ZONE-CURVES INCREASING DIST. FROM Rl DISTANCE CUMULATIVE DEPARTURE CURVES PLATE XVII G r a n i t i c Dyke and S c h i s t Wall-Rock Specimen H-2A Specimen H-24 was c o l l e c t e d by the author from an intrusive-metamorphic complex i n the Glen Lyon Range of the Yukon. The rocks range through s c h i s t s and gneisses t o migmatites. Some f i f t y - t o f i v e hundred-foot beds of c a l c -s i l i c a t e gneiss appear i n the metamorphic rocks, and l a r g e septa of the same rock occurs i n the g r a n i t e . This specimen was taken from the contact of an i n t r u s i v e dyke one foot wide and i t s country-rock of quartz-mica-feldspar s c h i s t . The dyke contains many r o t a t e d s c h i s t fragments and has matching w a l l s . The t h i n s e c t i o n contains the contact and some of each rock-typeo PLATE XVII 25a < CO > cc o Li- 1 O 4^ ' H o o ~<1 Dyke SPECIMEN H-24 Wall-Dock 5" ' z. •3 ADJUSTED ZONE-CURVES INCREASING DIST. FROM RIM IU or 3 h-06 < a. ui o ^ 1-5 CUMULATIVE DEPARTURE CURVES DISTANCE IV INTERPRETATION OF RESULTS General Considerations The c r i t e r i o n of c o r r e l a t i o n r e l i e d upon here i s the slope of the cumulative departure curve, and thus to some extent s i m i l a r i t i e s of gross shape or form are ignored. The s i g n i f i c a n c e of s i m i l a r i t y of form or shape i s discussed near the end o f t h i s chapter. I n order t o i n t e r p r e t the r e s u l t s , i t i s d e s i r a b l e f i r s t t o look i n t o the o r i g i n of zoning i n p l a g i o c l a s e . The l i t e r a t u r e on t h i s subject i s too extensive t o r e v i e w here, but the previous work does show t h a t the three most important f a c t o r s i n f l u e n c i n g the zoning and composition of p l a g i o c l a s e are temperature, pressure, and the presence of v o l a t i l e c o n s t i t u e n t s . Temperature Bowen suggested, on the b a s i s of h i s 1913 l i q u i d u s -s o l i d u s curves, t h a t temperature v a r i a t i o n s are the cause of zoning. These curves are known now t o apply r i g i d l y o n l y t o h i g h temperature p l a g i o c l a s e . The f a c t t h a t l a v a s have zoned phenocrysts of h i g h temperature p l a g i o c l a s e suggests t h a t i n l a v a s , at l e a s t , these curves are a p p l i c a b l e . I t i s probable t h a t temperatures as h i g h as the dry-f u s i o n temperatures of p l a g i o c l a s e are not reached i n l a v a s and i n t r u s i v e s . P o l d e r v a a r t and G i l k e y (1954) remark t h a t the t h r e s h o l d temperature f o r i n t r a - l a t t i c e i o n i c m i g r a t i o n i n p e r f e c t c r y s t a l s i s about nine-tenths of the f u s i o n temper-ature o f the c r y s t a l . From t h i s i t appears t h a t the formation temperature of zoned p l a g i o c l a s e s does not reach a value as high as nine-tenths of the d r y - f u s i o n temperature f o r t h a t composition. This suggests e i t h e r t h a t the presence o f v o l a t i l e s and high pressures reduce the f u s i o n temperature c o n s i d e r a b l y , o r t h a t the h i g h temperature d r y - f u s i o n phase r e l a t i o n s should not be used when c o n s i d e r i n g low temperature f e l d s p a r , which probably formed under hydrous c o n d i t i o n s . The low thermal c o n d u c t i v i t y of s o l i d and l i q u i d rock renders heat t r a n s f e r a very slow process unless convection can occur. Convection might e a s i l y take place i n magmas, but i t i s c l e a r l y impossible i n non-deforming metamorphics. Reasoning thus, heat t r a n s f e r should be f a s t e r and more i r r e g u l a r i n l a v a s and i n t r u s i v e s than i n metamorphic r o c k s , and any zoning r e s u l t i n g from temperature changes should be more complex and i r r e g u l a r i n l a v a s and i n t r u s i v e s than i n metamorphics. The occurrence of these f e a t u r e s i n n a t u r a l r o c k s suggests t h a t the complexity of zoning and l a c k o f c o r r e l a t i o n i n la v a s and i n t r u s i v e s i s a r e s u l t of mixing, which may be due t o convection. 28 Pressure C a r r , (1954)* suggests changes i n pressure as a cause of zoning i n p l a g i o c l a s e . Inferences drawn from c o n s i d e r a t i o n of the Clausius-Clapeyron equation suggest t h a t i n c r e a s e d pressure causes more sodic p l a g i o c l a s e t o p r e c i p i t a t e . Thus, i n a given convection c e l l , i f the change of temperature from top to bottom i s not grea t , the c r y s t a l s which happen t o be at the bottom w i l l be r e c e i v i n g a more sodic c o a t i n g than those which happen to be at the top. I n d i v i d u a l c r y s t a l s may be un i q u e l y a f f e c t e d by pressure changes i f they are c a r r i e d i n separate convection c e l l s , as they appear t o have been i n the Skaergaard Complex. Homma, (1932), suggested t h a t the i r r e g u l a r zoning of v o l c a n i c p l a g i o c l a s e i s due t o a f l o t a t i o n a c t i o n , i n which c r y s t a l s are s a i d t o be trapped by r i s i n g gas bubbles, r a i s e d , and allowed to s i n k . The r e s u l t i n g changes i n pressure and temper-ature could c e r t a i n l y cause zoning, i f the presence of gas bubbles i n magmas at depth could be demonstrated. V o l a t i l e C o n s t i t u e n t s The l o s s o f the v o l a t i l e f r a c t i o n of a magma was suggested by Phemister (1933) as the cause of reverse zoning i n igneous rocks, but H i l l s (1936), showed t h a t the e f f e c t of l o s i n g v o l a t i l e s i s t o produce normal zoning. I t i s worth n o t i n g at t h i s p o i n t t h a t the e f f e c t on the system of a de-crease of pressure (Carr, 1954) i s opposite t o the e f f e c t of a l o s s of v o l a t i l e s , and tha t n e i t h e r the absolute nor r e l -a t i v e magnitudes of these e f f e c t s are known. Close C o r r e l a t i o n Zoned c r y s t a l s must grow i n a changing environment. Two c r y s t a l s growing i n the same changing environment must have i d e n t i c a l zoning. T h e i r zone curves must show c l o s e c o r r e l a t i o n , and t h e i r cumulative departure curve must have a f l a t s l o p e . The best examples of c l o s e c o r r e l a t i o n are t o be found i n the i n t r a - c r y s t a l curves, i n which the zone-curve f o r one end of a c r y s t a l i s compared w i t h the zone-curve f o r the other end of the same c r y s t a l . Without exception, the r e l a t e d cumulative departure curves have f l a t s l o p e s , u s u a l l y l e s s than t w e n t y - f i v e degrees (see P l a t e I I , g r a i n 1, and P l a t e VI, g r a i n 1). This supports the statement t h a t i d e n t i c a l l y changing c o n d i t i o n s should produce i d e n t i c a l zoning curves, f o r i t i s c e r t a i n t h a t both ends of the same c r y s t a l grew i n the same environment. Examples of close c o r r e l a t i o n are found a l s o i n the metamorphic rocks, p a r t i c u l a r l y the h o r n f e l s e s . I t i s c e r t a i n t h a t adjacent porphyroblasts of h o r n f e l s e d p e l i t e s grew i n i d e n t i c a l pressure-temperature environments,•and t h i s i s borne 30 out by the e x c e l l e n t c o r r e l a t i o n shown between the zones of t h e i r f e l d s p a r s . The f o l i a t e d metamorphic rocks a l s o show e x c e l l e n t c o r r e l a t i o n between t h e i r f e l d s p a r s (see P l a t e s X I , X I I , X I I I , XIV, XV, X V I ) . Close c o r r e l a t i o n i s a l s o found i n some i n t r u s i v e g r a n i t i c r o c k s . (See P l a t e s V I I , IX, X.) This f a c t seems to be at variance w i t h the t r e n d shown by most magmatic rocks, which g e n e r a l l y show poor c o r r e l a t i o n . The explanation of t h i s apparent anomaly,is t w o - f o l d . F i r s t , i n small d y k e - l i k e i n t r u s i o n s and apophyses, the f l u i d may be so r e s t r i c t e d by the container that no mixing can occur, y i e l d i n g c r y s t a l s w i t h c l o s e c o r r e l a t i o n . Second, i f the magma has a h i g h p r o p o r t i o n of c r y s t a l s , i t s m o b i l i t y may be s e r i o u s l y r e s t r i c t e d by crowding, w i t h the same r e s u l t . Non-Correlation C r y s t a l s which grow s e p a r a t e l y i n d i f f e r e n t l y changing environments have d i s s i m i l a r zone curves and steep cumulative departure curves. Examples of n o n - c o r r e l a t i o n between adjacent c r y s t a l s are t o be found i n the l a v a s and some of the more f l u i d i n -t r u s i v e g r a n i t i c r o c k s . (See P l a t e s I I , I I I , IV, and V.) I t seems l i k e l y t h a t i n these i n t r u s i v e s and l a v a s many pheno-c r y s t s had independent h i s t o r i e s , u n t i l the volume r a t i o of 31 c r y s t a l s t o t o t a l a v a i l a b l e space became l a r g e . At t h i s stage the mixture o f c r y s t a l s and melt became l o c k e d or wedged t o -gether so th a t f u r t h e r r e l a t i v e movement between c r y s t a l s was r e s t r i c t e d , r e s u l t i n g i n d e p o s i t i o n of the same f e l d s p a r on adjacent c r y s t a l s . The cumulative departure curve f o r two c r y s t a l s w i t h t h i s k i n d o f h i s t o r y i s steep i n the p o r t i o n r e p r e s e n t i n g the i n n e r zones, and f l a t i n the p o r t i o n repre-s e n t i n g the outer few zones. These r e l a t i o n s are a c t u a l l y found t o e x i s t i n rocks showing evidence of past m o b i l i t y . (See P l a t e IX.) I n d e f i n i t e C o r r e l a t i o n I t might be expected t h a t some g r a n i t i c rocks would f a l l between the extremes of clo s e c o r r e l a t i o n and non-cor-r e l a t i o n . Figure 2, (p. 11) shows t h a t although the v o l c a n i c s and h o r n f e l s e s are r e a d i l y c l a s s i f i e d , twenty percent of the migmatites and twenty percent of the i n t r u s i v e s show i n d e f i n i t e c o r r e l a t i o n . Rocks which might be expected t o show i n d e f i n i t e c o r r e l a t i o n are those of mixed o r i g i n , such as normal magmatic rocks which have been metamorphosed subsequent t o emplacement, metamorphic rocks which have been s l i g h t l y m o b i l i z e d , and i n t r u s i v e rocks confined by r e s t r i c t e d space. (See P l a t e s V, V I , V I I , and XVII.) 32 The S i g n i f i c a n c e of Zone-Curves of S i m i l a r Shape The cumulative departure curves show the degree of c o r r e l a t i o n between curves on the b a s i s of t h e i r s e p a r a t i o n , and thus are i n f l u e n c e d more by the o r d i n a t e values of the curves than by t h e i r o v e r a l l shapes. I n some rocks the zone-curves are s t r i k i n g l y s i m i l a r i n shape, although t h e i r o r d i n -ate values are not s i m i l a r . (See P l a t e s VI and IX.) I f c r y s t a l s grow i n one pressure-temperature system, but i n d i f f e r e n t chemical surroundings, such as beds of d i f f e r e n t composition, changes i n pressure and temperature w i l l produce p a r a l l e l but not i d e n t i c a l changes i n t h e i r zone-curves. For i n s t a n c e , i f p l a g i o c l a s e porphyroblasts grow i n a s e r i e s of a l t e r n a t i n g calcareous and p e l i t i c beds under changing pressure-temperature c o n d i t i o n s , the f e l d s p a r s i n adjacent beds would have g e o m e t r i c a l l y s i m i l a r zone-curves, although the values would be d i f f e r e n t . I t might be argued t h a t e i t h e r c o r r e l a t i o n of shape or c o r r e l a t i o n of v a l u e i s more important, but i t i s c l e a r t h a t a s o l u t i o n t o the arguement i s impossible because two d i f f e r e n t s e t s of c o n d i t i o n s are represented. Good c o r r e l a t i o n of shape along w i t h poor c o r r e l a t i o n of values shows t h a t pressure and temperature changes were imposed on c r y s t a l s i n d i f f e r e n t chemical environments. In metamorphic rocks c l o s e c o r r e l a t i o n of both shape and value are found. The E f f e c t of P l a g i o c l a s e Crowding 33 on Correlation Plate XVIII, at the end of this chapter, il l u s t r a t e s graphically the effect of an increasing proportion of crystals on the zone-correlation in magmatic rocks. The ordinate i s the log-tangent of the slope angle of the cumulative departure curve. Tangents of the average slope angles are used because, by the method of constructing the cumulative departure curves, tangents are directly proportional to the separations of the curves. The logarithms of the tangents are used to make the scale of manageable size. The abcissa i s the percentage of zoned plagioclase crystals in the rock. It i s assumed that the zoned plagioclase crystals are among the earliest-formed minerals, and that the percentage of plagioclase, by volume, i s roughly equal to the volume percentage of the mass which was crystalline while the plagioclase feldspars were forming. Three types of mobile rocks are designated on the graph: lavas, harmonious granites, and disharmonious granites.^ Of these, the lavas appear in the upper l e f t part of the graph because of their poor correlation and low proportion of feld-spars to matrix, and the granitic rocks are distributed towards 4 Matt Walton, (1955), defines harmonious granites as those intruded into high grade metamorphic terrains, and caus-ing no strong contact metamorphic effects. He defines dishar-monious granites as those intruded into low grade terrain, causing strong contact metamorphic effects. 34 the lower right-hand p o r t i o n . The graph i l l u s t r a t e s a tendency towards c l o s e c o r r e -l a t i o n w i t h i n c r e a s i n g p r o p o r t i o n , or crowding, of p l a g i o c l a s e i n the magma. I t i s i n f e r r e d from t h i s graph t h a t the con-t i n u e d growth of phenocrysts i n a melt p r o g r e s s i v e l y r e s t r i c t s i t s m o b i l i t y , thus improving c o r r e l a t i o n . Assuming t h a t decreased m o b i l i t y accompanies a decreased p r o p o r t i o n of c r y s t a l s , some gneisses and h o r n f e l s e s have been p l o t t e d near the one hundred percent mark on the a b c i s s a . The h o r n f e l s e s f a l l c l e a r of the p r o j e c t e d band of magmatic rocks, but the gneisses l i e on and c l o s e t o the band. This shows t h a t under some c o n d i t i o n s , probably those of r e s t r i c t e d space and h i g h c r y s t a l l i n i t y , magmatic rocks can show as good cor-r e l a t i o n as metamorphic rocks. -70 -60 -50 -•40 —30 -20 - 00 a o o <D U> O <u QL • ' 0 I c a •20 Z> o _l -30 -40 PLATE XVIII Log-tan slope of Cumulative Departure Curves Vs Percent of Zoned Plagioclase in Rock L - L a v a H-Harmonious granite D - Disharmonious granite G - Gneiss F - Hornfels D \ —-* Percent zoned plagioclase 1 . Decreasing mobility 90 • G • G • G • G F • F • V CONCLUSIONS The degree of n o n - c o r r e l a t i o n i s considered t o be a measure of the m o b i l i t y of the environment i n which the c r y s t a l s grew. Extreme complexity and n o n - c o r r e l a t i o n of zoning are concluded t o be due, r e s p e c t i v e l y , t o r a p i d l y changing en-vironmental c o n d i t i o n s and r e l a t i v e motion between c r y s t a l s during growth. These f e a t u r e s are found i n l a v a s and many i n t r u s i v e g r a n i t e s . S i m p l i c i t y and clo s e c o r r e l a t i o n of zoning are found i n metamorphic.rocks such as h o r n f e l s e s and gneisses, and are apparently the r e s u l t of f e l d s p a r growth i n a q u i e t , undisturbed environment. C y c l i c s u p e r s a t u r a t i o n , as proposed by H i l l s , (1936), i s considered t o p l a y a l e s s important r o l e i n the zoning of p l a g i o c l a s e than v a r y i n g pressure-temperature c o n d i t i o n s due, perhaps, t o mixing o r turbulence. The rocks f a l l i n t o three groups showing d i f f e r e n t degrees of c o r r e l a t i o n ; those w i t h e x c e l l e n t c o r r e l a t i o n , those w i t h n o n - c o r r e l a t i o n , and those w i t h i n d i f f e r e n t cor-r e l a t i o n . The group showing cl o s e c o r r e l a t i o n i n c l u d e s two types o f rock; metamorphic rocks, and some magmatic rocks. The f e l d s p a r s i n the rocks of t h i s group are considered by the w r i t e r t o have grown i n t r a n q u i l environments w i t h no r e l a t i v e motion between the c r y s t a l s . This c o n d i t i o n i s ob v i o u s l y f u l f i l l e d by the metamorphic ro c k s , as t h e i r f e l d s p a r s grew s i d e by side as por p h y r o b l a s t s . T h e i r f e l d s p a r s show the c l o s e s t c o r r e l a t i o n of a l l those s t u d i e d . The magmatic rocks i n t h i s group, the disharmonious g r a n i t e s , are a l s o concluded to have c r y s t a l l i z e d under calm c o n d i t i o n s , w i t h l i t t l e o r no mixing. P l a t e X V I I I suggests t h a t the low degree of m o b i l i t y o f these magmas may have been due t o crowding of the numerous p l a g i o c l a s e phenocrysts. The group showing n o n - c o r r e l a t i o n i n c l u d e s three types of rock; l a v a s , harmonious g r a n i t e s , and one disharmonious g r a n i t e . The p l a g i o c l a s e s of these rocks have the f e a t u r e i n common of having grown, the author concludes, i n t u r b u l e n t , mixing magmas, w i t h extreme r e l a t i v e motion between the c r y s t a l s . I n these rocks the percentages of p l a g i o c l a s e are low, the m o b i l i t i e s high, and the n o n - c o r r e l a t i o n extreme. The r e l a t i v e l y small group showing i n d i f f e r e n t cor-r e l a t i o n contains some i n t r u s i v e g r a n i t e s and some f o l i a t e d metamorphics. I t i s assumed t h a t there may have been some r e l a t i v e motion between the c r y s t a l s of t h i s group and t h a t some of the rocks may be of mixed o r i g i n . BIBLIOGRAPHY B a r t h , T. F. W., T h e o r e t i c a l P e t r o l o g y . New York, Wiley & Sons, 1952, p. 96, p. 149. Bowen, N. L., "The M e l t i n g Phenomena of the P l a g i o c l a s e F e l d s p a r s " , Am. Jour. Sci.« v o l . 35, (IV s e r i e s , 1913), pp. 577-599. , The E v o l u t i o n of the Igneous Rocks. New York, P r i n c e t o n U n i v e r s i t y Press, 1928. Buerger, M. J . , "The Genesis of Twin C r y s t a l s " , American  M i n e r a l o g i s t , v o l . XXX, 1945, pp. 469-482. Ca r r , J . M., "Zoned P l a g i o c l a s e s i n the Layered Gabbros of the Skaergaard Complex", Min. Mag.. v o l . XXX, No. 225, (June, 1954), PP. 367-375. Compton, R. R., "A Trondhjemite B a t h o l i t h near B i d w e l l Bar, C a l i f o r n i a " , B u l l . Geol. Soc. Am.. v o l . 66, (January, 1955), pp. 9-44. Emmons, R. C , and Mann, "Twin-Zone R e l a t i o n s i n P l a g i o c l a s e " , Geol. Soc. Am., Memoir 52, Ch. 4, 1953. Ghika-Budesti, ( S t . ) , "Les P l a g i o c l a s e s des B a n a t i t e s etudies par l a methode Fed o r o f f " , Schweiz. Min. P e t r . M i t t . . J v o l . 12, 1931, pp. 12-26. Grove, Edward W., "A Study of Contact Metamorphism at H a r r i s o n Ridge, H a r r i s o n Hot Sp r i n g s , B. C", Unpublished M a s t e r 1 s t h e s i s , The U n i v e r s i t y of B r i t i s h Columbia, Vancouver, 1955. Harker, A l f r e d , The N a t u r a l H i s t o r y of the Igneous Rocks. MacMillan, lSt5£, pp. 2^2-234. , Metamorphism. London, Methuen, 1952 r e p r i n t , p. 83. H i l l s , E. S., "Reverse and O s c i l l a t o r y Zoning i n P l a g i o c l a s e F e l d s p a r s " , Geol. Mag.. v o l . L X X I I I , No. I I , (February, 1936), pp. 45^5o". Hitchen, C. S., "The Skiddaw Granite and i t s R e s i d u a l Products", Jour. Geol. Soc.. v o l . XC, 1933, pp. 158-196. 38 Homma, F., "Uber das Ergebnis von Messungen an Zonaren P l a g i o c l a s e n aus Andesiten mit H i l f e des U n i v e r s a l -Drehtisches", Schweiz. Min. P e t r . M i t t . . v o l . 12, 1932, pp. 345-352. Larsen, E. S., " B a t h o l i t h and. Associated Rocks o f Corona, E l s i n o r e , and San L u i s Rey Quadrangles, Southern C a l i f o r n i a " , Geol. Soc. Am., Memoir 29, 194#, pp. 152-154. Larsson, Walter, "Petrology of the I n t e r g l a c i a l V o l c a n i c s from the Andes of Northern Patagonia", B u l l e t i n of the  G e o l o g i c a l I n s t i t u t e o f Upsala. v o l . X X V I I l , 19407 M o r r i s , Peter G., "A P e t r o l o g i c a l Study of I n t r u s i v e Rocks Along the F r a s e r Canyon Near H e l l ' s Gate, B r i t i s h Columbia." Unpublished Master's t h e s i s , The Univer-s i t y of B r i t i s h Columbia, Vancouver, 1955* Noble, James A., " E v a l u a t i o n o f C r i t e r i a f o r F o r c i b l e I n t r u s i o n o f Magma, at Homestake Mine", J o u r . Geog.. v o l . 60, 1952, pp. 34-57. P a l i u c , G., " P l a g i o k l a s e aus Ergussgesteine Siebenbttrgens", Schweiz. Min. P e t r . M i t t . , v o l . 12, 1932, pp. 423-444. Phemister, James, "Zoning i n P l a g i o c l a s e F e l d s p a r s " , Min. Mag., v o l . 23, 1932-34, pp. 136-137, pp. 541-555. P o l d e r v a a r t and G i l k e y , "Clojuded P l a g i o c l a s e " , American  M i n e r a l o g i s t , v o l . 39, book I, 1954, pp. 75-91. Turner, F. J . , " E v o l u t i o n of the Metamorphic Rocks", Geol. Soc. Am., Memoir 30, 1948", pp. 114-124. T u t t l e and Bowen, "High Temperature A l b i t e and Contiguous F e l d s p a r s " , Jour. Geol.. v o l . 58", 1950, pp. 572-5o3. Vogt, J . H. L., "The P h y s i c a l Chemistry of the C r y s t a l l i -z a t i o n and Magmatic D i f f e r e n t i a t i o n of Igneous Rocks", Jour. Geol.. v o l . 31, 1923, pp. 233-252. Walton, Matt, "The Emplacement of G r a n i t e " , Am. Jour. S c i . . v o l . 253, January 1955, pp. 1 - lS. 

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