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Geology of the Mount Brenner stock near Dawson City, Yukon Territory Lambert, Maurice Bernard 1966-12-31

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GEOLOGY OF THE MOUNT BRENNER STOCK NEAR DAWSON OITY YUKON TERRITORY b y MAURICE BERNARD LAMBERT. B . S c , 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 , 1963 A- THES IS SUBMITTED I N PART IAL FULF ILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SC IENCE i n t h e D e p a r tmen t o f GEOLOGY We a ccep t , t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BR I T I SH COLUMBIA A p r i l , 1966 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 the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Co lumbia , I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree 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 copy ing of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s „ I t i s unders tood that c o p y i n g or p u b l i  c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d wi thout my w r i t t e n p e r m i s s i o n . Lambert) Department of G e o l o g y The U n i v e r s i t y of B r i t i s h C o l u m b i a , Vancouver 8, Canada. Date i-lay 3. 1 9 6 6 •ti 11 ABSTRACT The Mount B r e n n e r s t o c k h a s i n t r u d e d f o l d e d s e d i  men t a r y and m e t a s e d i m e n t a r y r o c k a t h a t l i e AO m i l e s n o r t h  e a s t o f Dawson C i t y , Y u k o n T e r r i t o r y . • The s t o c k c o n s i s t s o f f o u r m a j o r c o n c e n t r i c z o n e s : ( l ) an o u t e r z one o f f i n e - t o m e d i u m - s r a i n e d a u s i t e - b l o t i t e m o n z o n i t e ; (2) a z one o f v e r y c o a r s e - g r a i n e d m o n z o n i t e p o r p h y r y ; (3) a n i n t e r m e d i a t e zone o f p o r p h y r i t l c h o r n b l e n d e m o n z o n i t e ; a n d (4) a c e n t r a l z one o f c o a r s e - g r a i n e d p i n k q u a r t z m o n z o n i t e p o r p h y r y . E x c e p t f o r t h e o u t e r z o n e , a l l r o c k t y p e s a r e p o r p h y r i t l c a n d t h e a l i g n m e n t o f f e l d s p a r p h e n o c r y s t s g i v e s t h e r o c k s a p r i m a r y f l o w s t r u c t u r e w h i c h c o n f o rm s t o s t e e p l y o u t w a r d d i p p i n g g r a d a t i o n a l i n t e r n a l c o n t a c t s . A l l e x t e r n a l c o n t a c t s a r e s h a r p . The r e g i o n a l s t r u c t u r a l t r e n d i s m o d i f i e d i n t h e v i c i n i t y o f t h e s t o c k so t h a t b e d s a r e g e n e r a l l y c o n f o r m a b l e w i t h t h e i n t r u s i v e c o n t a c t . F rom s t r u c t u r a l e v i d e n c e , i t i s c o n c l u d e d t h a t a t t h e p r e s e n t l e v e l o f e r o s i o n , t h e s t o c k was e m p l a c e d b y f o r c e f u l i n j e c t i o n . The d i f f e r e n t r o c k z o n e s o f t h e s t o c k c a n b e a c c o u n t e d f o r b y d i f f e r e n t i a t i o n o f a n a u g i t e - b i o t i t e m o n z o n i t e magma b y a c o m b i n a t i o n o f c r y s t a l f r a c t i o n  a t i o n , v o l a t i l e a n d a l k a l i d i f f u s i o n , and m u l t i p l e i n t r u s i o n . Pag© mmowGHion 1 • LOO AT I OK AND AGO •iSOl B l i . I X ^ . . . . . . . . . . . . . . . . . . . . . . . 1 TOPOGRAPHY, DAAIiMGA AKD ALACIATION.»,.,«,..,,.• . 1 PREVIOUS GEOLOGICAL <*OHi£. 4 ACKNOWLEDGMENTS.... ......................... 5 Q A K A A A L OSOLOGY« « 6" THK MOUNT D^aLAKER OTOC A............................... 8 GAKEfctAL DLSORIfTIOiS*. .»«..**..•..«• ......... 6 PETROGRAPHY.,,«*»**•..,•.,,,*...»,..,•........... 13 Au g l t e - b i o t l t e fen&onit®.................... 13 Monaoolte Porphyry 16 Porp h y r t t l c Hornblende Monzonlte............ 18 Pink Quartz Monzonlte Porphyry.»...*...*...« 21 A p l l t e 24 Inclusions. ...» 24 CA:A4IGAL CO.A?OAlTIOft A A L VARIATION* »«.,»».».»#.», 29 COAT •'•Of ;AArA^OAPiiI A«t, ,,.»,,.•,,.,..,.*...*.,•..,, 36 STA JGTURA, »,,..... ......,.«..»..., «... 37 Intern a l Structure® 37 F o l i a t i o n and L i neat Ion 37 J o i n t i n g , 40 Intern a l Contacts. *.... 44 i n t e r n a l Structures Interpretation of Structures .and Mechanics of Sfiplac6ffl@rit•••.•••••••«•••••••••••••»•• As s iiu i. xoti • ••••••••••••••••••••••• • l) .11 X til ' . d i i t X 1 Gli • • • • • • • • • • • • t • Suttuaary of iSaplacement, C r y s t a l l i z a t i o n and l) i £ f c i' on 11 & t jL on • •••••»••••«••••••«#••••••• iii l i ^ l s JL 0 C? h A.t'jri i t « i i i i i « t M « t i t * t * t * M i i « i i i i M « t i i * « -A V i4»p' Cm@lo%lml map o f %b* Ht« 5r»Dn*r 3too*s, In Xufcon "territory ..... pao ;»t 1 led em ;sap »howtag ta® fjfcwaon area Had locution of the Mount Brenner stock*,*** 2 2 lodes of sp#ot;a&$3® f r o * th® Mount 3re»n®r 3 t O O T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3 V a r i a t i o n i n eooipa^itlon of g r a n i t i c roo'*8 with respect to distance froa the s&rgin of «rtcU rack t y p c » . 12 4 Variation dinpras, for ra.-'r *oo*s of the 'ouot r» noer t»toe1«» TU« s.v@rag« %f«laht per cent of O X U U B of «mch rock tan® e"r« plotted ftualnst total silica,»*••*»*•,,« 32 5 Contoured dia^xaa-, of oxide® m » <3,lff«r- c.-.ti . t IOJ I index on vcica analysts© of roc <a f rasa th® ' .oa^t nr«srjn«r atoo'A have been *uperl3poa.-*<l••*•«»»»••••»«*•«****»« 33 € TriJM)£ular ooaipos-ttloo dltigrfta on which the f o l l o w i n g are p l o t t e d ; rm'x.® of the .'••'.aunt brmmv utooltj Daly*© awrsf-e sa l t , andealt®, <Haoit«, S I K ! rhycHlt#$ aad £ d t of composition v a r i a t i o n of th® a a j o r t t y of ci«la-alic»ll voio«nlo ao£ plu t o n l c etquences,«,.,,.,,»,.»«»...«•«• 33 ? Structure Trend ,«ap of ^ t» Srenner atoeit, 'laXoa Territory*•*«••••••*•••••••*»»•••• fl 172 poles to f i l i a t i o n plottwd on & achaleSt n«t sad contoured*. Contours 2, 5, 15, »«a over l ' v Pfe-r 1,-i urea, .*.«.•«*••«.»•*.*• • 41 v i Figure 9 10 213 poles to j o i n t s p l o t t e d on a Schmidt net and contoured. Contours 2, 7, 14, 21, 28, and over per 1^ area,..,,..,... Diagrammatic sketch showing a hypothe t i c a l development of rock zones o f the Mount Brenner stock*.•»•*••••«-••*»«•*•••••• Page 42 55 Tables I I I Modal Analyses o f G r a n i t i c Rooks of the Mount Brenner stock.•«•«•»•.••«»«••••«••••» X0 C a l c u l a t e d C h e m i c a l Composition of Hooks Mount Brenner stocks .«••*.*««»•«»«»••***••» * 31 Pla t e s f o l l o w i n g I I . I I I . A. Au?jtt@~blotit@ Monaonlt* with rounded plat y aggregates of b i o t i t e (X 1 } . . . . . . . . . . B. Porphyrinic Hornblende Manzonito with d i s t i n c t alijmaeot o f f e l d s p a r c r y s t a l s (-X. 1).•••.•••<»«..« . . . . . . . . . « « » • A» Zoned, twinned p l a g i o e l a s e with broad a l t e r e d core i n b i o t i t e quartz d i o r i t e (Grossed n i c o l s X 1 0 ) . . . . . . . . . . . . . . . . . . . . . . B* Bent p l a ^ i o c l a s e with s t r e s s twinning i n a u g i t e - b l o t i t e monzonlte ( C r o s s e d n i c o l a X 10)iMiMttfl«i«i«t*i.iiiaita«fi*«*4»***t« Texture o f b i o t i t e ( M . ) I n a u g i t e - b l o t i t © aon?onite (Grossed n i c o l s X 10) ........... hedral augite ( / i u j : J with rim of horn blende (Hb) i n a u g i t e - b i o t i t e aonzonit© (X 10)..•...*......•.....«....•«........... Page 13 13 14 14 15 15 A. ".oaxonite p o r p h y r y (X l/2) E. V e i n perthit® i n p h e n o l r y a t o f monzonite p o r p h y r y (Crossed* a i c o l s X 45). A. F i l m p e r t h i t e i n ortho&l--*ne o f monzonite p o r p h y r y ( C r o s s e d n i c o l s X 4 5 ) , 11bite ' l e n s e s ' t r e n d p e r p e n d i c u l a r t o 151G) oleavag,© i n o r t h o e l a s e . ...*. B. N o n - p e r t h l t l c a r e a s around p e r i p h e r i c o f plagloclas© g r a i n s i n o r t h o e l a s e o f sj o o z o n i t e p o r p h y r y (Oroeeed n i e o l s X 45) A# Corroded, o r t h o e l a s e c r y s t a l (Or) i n c o r e o f an o r t h o s i sBe phenocryst ( P h ) . (Crossed, n i c o l s X 1 0 ) . . . . . . . . . . . . . . . . . . . . 0. Pla.g.1 aclas© I n e l u a i o ; s i n o r t h o e l a s e o f t h e glome ro p o r p h y r i t l c ph; ae o f t h e p o r p h y r i t l c h o r n b l e n d e n o n z o n i t e ( C r o s s e d n l c o l a X 1 0 ) . . . . . . . . . . . . . . . . . . . • 4 . P i n k q u a r t z monzonite p o r p h y r y . (.MI) . 13. f e r t a i t i c o r t h o e l a s e u h e n o c r y s t w i t h I n c l u s i o n s o f euaedr;-!, u n s t r . i n e d q u a r t s ( ») wrosHef! n l c o l a X 10) , P . Zoning and allf/n*ae..rt o f p l a ; ; t l o o l j . ; ee I n c l u s i o n s i n o r t h o e l a s e phenooryat• o f p i q a a r t i i :riooxonitv p o r p h y r y (';ro:-;..cc ^, - a r t o f p h e n o c r y s t In p i s t e A u t h i c .J »* ."J 'lo.vtion ( G r o s s e d n i c o l s X 1 0 ) . . . . . . Xrie>;i,Ht Ion o f pli- ^ i o c l u o e i o a l u a i o n y i n o r t h o s i s s © pnfraocry s t o f t a f c p i - ; ' < qufcr i p n s / j i i i t e p o r p h y r y ( G r o s s e d n l c o l a .•>. X} . . X . : : l a . _ l o o l • a e c r ^ s t u l s w i t hi;; nnX p-..rtl i n c l u d e d i n t n e aargi . - j o f ortaoeles© phen a r y o t p ^ r o a t i c P n i o l s X X) P l a t e s v i l i '•"ollowlaj? Pac e X I . A. Combination twinned plagiooleB© i n c l u s i o n on o r t h o c l a s e p a e n o c r y s t (Crossed n i c o l s X 10} B. rtyrmekite rial on pl«g\ocl«se surrounded by potash f e l d s p a r (li) of the pinfc q u a r t z raonzonite p o r p h y r y . . . . . . . . . A . O s c i l l a t o r y z o n i n g i n p l a g l o c l f s s e of pink quarta monzonite porphyry. (Groused n i c o l s X 1 0 ) . . . . . . . 22 22 B. a l l n a l t e i n nietacaict s t a t e {?) i n  c l u d e d I n h o r n b l e n d e (Hfo). Kobe p l e o - c h r o i c h:;lo end r a d i a t i n g f r a c t u r e s In h o r n b l e n d e . (Pl*.«e l i g h t X 10) . . . . . . . . . XII» A. I n c l u s i o n i n pin k q u a r t z rsoozonit© p o r p h y r y . P o t a s h f e l d s p a r p h e n e c r y s t s • stream* eround t h e I n c l u s i o n (X 1/3).* i i . I n c l u s i o n i n pin k q u a r t z raon.-.onite p o r p h y r y . ftote pheaocrysfcs In b o t h q u a r t z ;flonzonlte and i n the i n c l u s i o n 1 1 ) « . . . . . . . . . . . . . . « . . . . . . . . . . . . . . . . . . X I I I . A. P o r p h y r o b l a s t o f p e r t h l t e i n g r s n o - b l a s t i c m a t r i x , hate l i n e o f t i n y i n c l u s i o n s and I r r e g u l a r b o r d e r . ( G r o s s e d n i c o l s X 5)..... t>. O s c i l l a t o r y z o n i n g i n o r t h o c l u s e raegacryst •. , ( c r o s s e d n i c o l s X 3).... XIV, A , Photomicrograph showing c o r r o d e d p l a g i o o l a s s p h e n o c r y s t s In an I n c l u s i o n , Block: background i s p o t a s h f e l d s p a r . (Grossed 1 n i c o l s X 10) B.( P h o t o m i c r o g r a p h showing p o i k i l i t i c h o rnblende ( C r o s s e d n i c o l s ? A: 1 0 ) . *3 23 26 26 26 WJOAflOl M® AOOSaSZBZUTX The map-area lias la west-central Yukon Territory about 40 allee a@rtli.aait o f Dawson City and 5 alias north of tha Tombstone liver (fig» 1 ) . Th© Beateter Highway leaves the Taylor Highway 20 ml%m. east of Dawson city and follows the Korth Klondike River* Both of these gravel highways are kept la excellent condition for summer travel. At mile 4§ of the lesster Highway (in the vicinity of Morth Fork Pass) the north Klondike River swings southweatwari. along a broad valley. fhis valley leads to a low, flat pass into the valley of the $oohaton® River at about 11 miles from the Pewter Highway. the map-area is a two day walk from the highway by way of these valleys. The area Is accessible by helicopter or, with dtff&tt&tar; by horses* V O K X K t A J H X * B8AIM® U t £ a L A O t t X X G V The region lies within th® physiographic unit known as the Ogilvie Mountains (Bostoek, 1948). "The range has a rugged and mountainous aspect and consists of long* branching, knife-edge crests, with sharp and often Figure I. Index map showing the Dawson City area and location of the Mount Brenner stock (lined pattern). p r e c i p i t o u s peaks* separated by deeply out va l leya»• (Coefc - f i e l d , 1919}* fa® map**rea Is e n t i r e l y a b o v e ti«fc-er-lls@ w h i c h l a a t as e l e v a t i o n of approximately 4000 f e o t r •Average r e l i e f I s 1500 f##t and peak® reach & aaxiaua e l e v a t i o n of ?§GQ f e e t * l a s r w s o f grr*»ltio r«ek» the topography hag a u n i q u e aha m o t o r wh l o t i i»as boot* d o e o r i b o d by - c C o n n e l l ( l y 0 3 ) i a th® f o l l o w i n g word®. This rock Is s t r o n g l y j o i n t e d v e r t i c a l l y «nd wea- t h e r e into r n A n o a a , wed^e-en^eC ricVe--, e a r - >o . : t e d &y 11 nen of r h ' - r p > 1 .nides ..•• *d l o f t y tower-shaped p e a k s * The p i l l a r e d c h a r a c t e r of the r a t i o n i s so remarkable t h s t the pros pectors neve .riven i t t h e oaas© o f t h e t o A s t o n e country. The ares i s d raised by tfere© r l v o r syite.nst i n the west, the south f l o w i n g C h a o d l n d u S i v o r s y s t em with i t s i s a l n westward flowing t r i b u t a r i e s , the T a s b s t o a o a n d k i t t l e Twe l v e m i l e Rivers j l a the east, the north JClondike l i v e r ay s t e a l and i n the s»o.riht. t h e Blackstoo® E l v e r ay stoat* The O g l i v i e wranialns display o o r t a i d o r a b l e e v i d  ence of g i a e l a t i o n * Main v n l l e y s have U-shaped c r o s s - profile© and the up - . -e rmost-parts o f t r i b u t a r y v a l l e y s g e o e r e l l y t e r m i n e t o I n g l a c i a l c l r a . u a a, w h i ^ h cosaaonly hold tut-nn. - . r o t e s , uor-'«, «: id a • • r t n - : v.t i l e y c a r e co-xiifion f e'it a r c s , ,>a^ii Ice pa tones e t i l l occupy a few of the s i r ; a c a on t ;.e norto. nX< e s of , - a per ^e .ID: t h of '* S y e n i t e Lakes'*,* Valley g l a c i e r s emerged f r o m tae a o u a t a l n s a n d o c c u p i e d t h e valleys of t h e North K l o n d i k e and ' Chandindu R i v e r s b a t e x t e n d e d o n l y a s h o r t dlataoee beyond t h e m o u n t a i n s (Green a n d R o d d l c k # 1962).. S i n c e g le . e l a t i o n * s t r e a m s have cut narrow t r e n c h e s a n d canyons i n t o o l d e r v a l l e y o o t t o m s . PREVIOUS QmimiQAL mm Early i n v e s t i g a t i o n s In t h e T o m b s t o n e a r e a were mad® by M c C o n n e l i (1903) a n d C o e k f l e l d (1916 a n d 1929). The work c o n s i s t e d of r e c o n a o l t e r l n g th® c o u n t r y a n d examining a l n e r a l d e p o s i t s * G r e e n a n d R o d d i c k (1961) mapred th® area a t a s c a l e of 1 i n c h t o 4 a i l e s a s p a r t of a p r o j e c t known as O p e r a t i o n Ogilvte. Vernon a n d Hughes (1961) s a p p e d the a u r f l e t a l geology* Teapelman-fflult (1964 a n d 1965) c a r r i e d out m a p p i n g i n t h e T o m b s t o n e :uap- a r e a a t a s c a l e of 1 Inch t o 1/2 ; a i l e f o r e v e n t u a l p u b l i c  a t i o n at 1 I n c h to 1 a i l © * The p r e s e n t f i e l d work was c a r r i e d o u t by t h e w r i t e r d u r i n g t h e months o f J u l y a n d A u g u s t , 1964, while employed by the G e o l o g i c a l Survey of C a n a d a , AQ.i * ) <LXD3 -11 .13 the writer was ably assisted i n the f i e l d by the late Mr, Beanie Lastiuka. Thanhs are dm to Mr. .D, J . Temp-el3«ar<- 1 u.lt f o r encouragement and stimulating discussion during the coars© of f i e l d wor*t. and to Mr. E, Montgomery for preps ratios of t h i n sections* 1 wish to expresa apwclal appreciation to Professor S, 0 , MeTgtggart, o f the University of B r i t i s h , , Columbia, under whose supervision t h i s thesis was written* Rocks of Silurian &ge (Teapel.nnn-Al.ait, 1965} ooeupy the northwestern comer of the map-area (see map In pooket)* these rocks oonalst mainly of interbedded black cr.erto and a r g l l l l t e a and are here about 10G0 foet thick. In. the northeastern and southwestern parts of th® mac-area, the black cherts and a r g i i i l t e s are overlain confor-aauly by a series consisting of black shale, a r g i l l l t e , s late,phyllite a^d thin bedded quartsite of Jurassic age. A oontlnous thin bed of limestone, which contains 'iddle Permian f o s s i l s , marks the contact between these two rook units. Da rk blue-grey to grey qua rt;' i t e of Lower Cretaceous age (Tetapelaan-Sluit, personal communication)« occupies the southeastern part ©f th© map area,. *iusrtz- ites > are massive and obaracterlstloally have thin partings of slate and p h y l l i t e (commonly grsphitic) between thicker beds* The. maximus thickness of t h i s unit has been est Lias ted to be 45,000 feet (Green and Roddick, 1962)* Resent work, however, suggests that the roc its are Iso- o l i n a l l y folded with steeply dipping axial plc.ies and that 1 the true Va.iokne.sa i s l a the order of 5000 f e e t , The contact between the quartsite and th® underlying rooka " l a considered to be a gently southeast-dipping thrust surface upon which the quartzit® has aoved to the northwest.* (Teajpeliaun-Kluit, 1965). Two large stocks that intrude th® sedimentary and aetamorphia roc&e In the Tombstone map-area range i n composition froxn d l o r i t e to syenite. Textures of these rocks range froa fine-grained end equlgranulor, to coarse grained and porphyritic. f o l i a t i o n i n th© rock i a shown by alllament of tabular feldspar pbenocrysts. Inclusions are re.ro. Age of the g r a n i t i c rocks I s not known, though they are thought to be co;ate.tiparsneoue with granitic rooks far to the southeast which have been dated as Middle Cretaceous (Green and 'Roddick, 1962) . 1 T e m p e l m a n - K l u i t , p e r s o n a l c ommun i c a t i o n DESCRIPTION Mount Brenner i a the highest peak of the moat northern granitic body in the To.&b stone asp-orea* In t h i s thesis the g r a n i t i c body i s referred, to as th© Mount Brenner stocs* Th© i n t r u s i o n o^eupies s roughly e l l i p t i c a l area with i t s lo/ig axis trending northeastward. It crops out over an area of about 1? square mllee and exhibits a more or less, concentric arrangement of i t s various subdivisions* A segment of auglt#-*blotlte laonaonite l i e s around the western part of the etoeW A orescent* shaped* narrow band of <aonsonlte porphyry l i e s along the inner contact of this segtse-it* Inward from t hi a band, and forcing s broad irregular ring, i s a body of porphyritlc hornblende aonzonite, the central psrt of the stocfc i s composed aslaly of pink quarts aoBzo.-ilt* porphyry. A body of apllte l i e s near the eastern side of the pioK quartz .wnzonite porphyry. The cont eta between each of the rock 'types ere In aost places gradetional, although the nonsonite porphyry l o c a l l y shows a © h a r p i n t r u s i v e contact age inst augite*biotite moosonlte. (4odes of each rock type are shown 1 B fable I* Dykes are not common within the stock and very few of theia were found l a the adjacent country rocks, j series of dykes i s found i n th© east central hart of th© pink quartz monzonite porphyry near where the porphyritlc hornblende mon*oiite protrudes into the core. In t h i s area aplite dykes, that range frota a few inches to 20 fes-t thick, follow steeply dipping north to northeast trending joints* Dykes of pinfc quartz won&onlte porphyry f i l l Joints in pink quarts aonmoatt© porphyry of approximately the same coaponiton and texture. So dykes were traced outward into the surrounding country rocks* Sear the southeastern contact of the stock, however* & few s i l l s of porphyritlc hornblende s ode s i t e , that range from 0*5 to 15 feet wide intrude the shale. In the same ares a f e l d  spar porphyry dyke cuts across the f o l i a t i o n in black p h y l l i t e , Euhadrsl, thin*tabular potash feldspar pbenoorysts are aligned p a r a l l e l to walla of the dyke to give the rock a d i s t i n c t f o l i a t i o n . T A B L E I MODAL ANALYSES OF GRANITIC ROCKS MOUNT BRENNER STOCK Rock Type A u g l t e - B l o t l t e Monzonite 1 Monzonite Porphyry P o r r h y r l t i c Hornblende Monzonite Pink quartz Monzonite Porphyry A p l i t e Kornblende- B i o t i t e F y r o x e n i t e Specimen Number 1 2 3 4 5 6 7 8 , .9 10 11 12 13 14 15 P l a g l o e l a s e 42.5 34.6 41 38.8 42.6 39. S 50 24,1 35.7 29 39.2 34.9 34.3 38.0 2.9 P o t a s h F e l d s p a r 3.8 27.1 20 .2 25.5 23.6 43.0 31.7 56.8 43 .6 50.6 36.7 41.9 48.6 30.1 3.4 4uartz 26.4 7.2 1.2 2,6 — 1.4 2.3 1 .0 5.3 10 13.8 13.7 11.3 27.5 — B i o t i t o 27.2 17 . 5 1 6 0 4 15.6 5.1 1 . 0 1 .2 0 .2 0.5 0.4 t r . 0.1 25.6 Hornblende t r . 0.7 4.2 15.3 7.6 11 . 9 14.5 12 .2 7.9 9.3 6.7 5.5 t r . 7.9 A u g l t e t r . 12.7 13 . 5 11.5 10.7 6 .5 1.0 0.4 0 . 3 0.2 . 0 . 3 t r . 56.1 M u s c o v i t e ( s e r i c i t e ) t r . 1.0 0.5 — 2.7 T o t a l A c c e s s o r i e s 1 . 0 0.9 2 . 0 1.6 2.7 . 1.7 1.1 2.0 . 3.0 1 . 0 0.5 2.1 0.3 1.6 4.1 A p a t i t e t r . 0 .2 1.1 0.8 0.9 t r . 0 .4 0.2 0 .3 0.3 0.2 0.1 0.2 t r . 2.0 E p i d o t e t r . 0.2 0.8 t r . t r . t r , t r . t r . t r . t r . t r . t r . A l l a n i t e 0.1 ___ t r . t r . 0.1 0.4 t r . t r . Sphene t r . t r . 0.14 t r . 0 .5 t r . 0.2 . 0.9 0.2 t r . Z i r c o n t r . 0.1 t r . t r . ——- t r . t r . t r . t r . t r . t r . t r . t r . t r . Garnet t r . —— C a l c i t e t r . t r . t r . t r . 1 . 0 0,8 0.7 0.3 0,3 0.3 0.3 0.2 C h l o r i t e t r . 0.1 t r . 0.14 ' t r . t r . 0.4 t r . t r . t r . t r . 1 Myrmeklte 1.5 1.6 t r . t r . 1.4 ' 2.7 1 .0 t r . t r . t r . Opaque t r . 0.3 t r . 0.3 1 .5 1.7 0.7 1.2 1.5 0.3 0.3 0.5 t r . 0 .3 3.o Average P e r c e n t a g e An In p l a g i o c l a s e 43 44 41 54 50 33 31 45 27 32 28 26 30 . 28 45 •atlo o f j - f e i a s p - r : t b j l u.iasej 1:11 1-1.2 l - s l . 5 l i i . 3 1:0.9 1:1,6 1:0 .4 1:0.8 1:0.5 1:1 1:0.8 1:0.7 1:1 1:2.8 ^odes i r e p l o t t e r . 5; F i L .--e z o f specimens iz, s. . v*n lis * l c . r e QUARTZ L '13 10 J 4 .12 POTASH FELDSPAR PLAGIOCLASE L E G E N D A Aplite • Pink quartz monzonite porphyry + Porphyritic hornblende monzonite a Monzonite porphyry o Augite biotite monzonite Figure 2. Modes of specimens from Mount Brenner Stock. Numbers refer to specimens in Table I and In Figure 4. 12 Ld H X LU t— W CC < o _] 5 °-2 _ O LU ^ . a ? i: •70 • 60 . 50 •40 . 3 0 • 20 - 10 . 0 - 3 0 - 2 0 - 10 N H CC < o 0 t— o z Q:. w z ce ui 0. - 0 -90 - 8 0 -70 -60 -50 - 4 0 - 3 0 h - 2 0 10 • 0 •15 _i < cc ^ ? o o z < <T H cc UI a. 3* 2 » 10 .6 14 Aplite 13 12 Pink quartz monzonite porphyry Porphyritic hornblende monzonite Monzonite porphyry Augite biotite monzonite APPROXIMATE AVERAGE DISTANCE FROM BOUNDARY OF EACH ROCK TYPE Figure 3. Variation in composition of granitic rocks with respect to distance from the margin of each rock type. Location of specimens shown in Figure 7. -4 13 ?*ETiiOGEAFHY The a u g i t e - b i o t l t e a o n z o n i t © u n i t f o r m a an i r r e g  u l a r aegsnent a r o u n d the w e s t e r n a n d s o u t h w e s t e r n b o r d e r s o f t h e i s t o c i u A z o n e o f d a r l r . - g r e y , f i a e - g r a l o e d , g a r n e t - I f e r o u a b i o t i t e - q u a r t z d i o r i t e ( i ) 1 , l e s s t h a n 1 f o o t w i d e , l i e s a l o n g t h e o u t e r c o n t e s t w i t h h o r n f e l s . T h i s z o n e g r a d e s i n t o grey, f i n e - g r a i n e d s u g i t e - b i o t i t e monsBonlte (2 and 3) t h a t h « s a d i s t i n c t f o l i a t i o n shown by t r a c h y t o i d a l i g n m e n t o f e u h e d r a l p l a K l o c l a . s e c r y s t a l s * The b i o t i t e f o r m s h e x a g o n a l p l a t e s 1 t o 2 mau i n d i a m e t e r * b e t w e e n 150 end 200 f e e t f r o m t h e c o n t a c t t h e t e x t u r e o f t a l e rook, g r a d e s f r o m f i n e - t o m e d i u m - g r a i n e d (4) a n d t h e b i o t i t e o c c u r s b o t h a s hexagonal p l a t e s and a a p l a t y a g g r e g a t e s * The p l a t y a g g r e g a t e s , u p t o 2 c * . I n diameter, l i e a l o n g m i n u t e f r a c t u r e s i n t h e r o c k (pi-. I A ) , A z o n e o f d a r k - g r e e n , medium-grained, h o r n o l e n d e - 1 Nuaibere In pare- . i thes&s r e f e r t o a p e c i a e a s i n T a b l e s I and I I and i n r - l g u r e s 2, 3 , an<^ 7 . J r l a t e 1 biotit© pyr-oxenite ( 1 5 ) , 1^0 feet wide and at l e a s t 2000 feet lone, l i e s along the contact between the u u g i t e - b l o t i t e monzonite and the monzonite porphyry* 'The contacts between t h i s rock and the surrounding rocks are g r a d a t i o n a l over a distance o f about 5 feet* In t h i n section, p l a g l o c l a s e from near th® outer oontuot d i s p l a y s o s c i l l a t o r y zoning and broad, euhedral, s a u s a u r l t i z e d oores ( p i , II/*) • whereas plagloclase from th© main pert of t h i s u n i t d i s p l a y s normal zoning and i s r e l a  t i v e l y unaltered. The s u b - t r a c h y t l c a l l y s l i c e d gr&ias commonly ar© bent ( p i , IIB) and show stress twinning, (curved poly synthetic twin l a m e l l a e ) * % r m e k l t e occurs along some contacts between plagloclase sod orthoelase. Weakly pe r t h i t l c orttiools.se (27^* 52 degrees) i s Int e r  s t i t i a l to p l S j / i o c l s s e and auglte, or encloses and p a r t l y replaces plaglocl'.se, broad zone of randomly o r i e n t  ated i n c l u s i o n s o f p l a g l o c l a s e , a p a t i t e , z l r o n , and b i o t l t e occurs i n the cores of some ortboclese grains* Brown b i o t i t e ( p i . IIIA) has the foll o w i n g p l e o c h r o l c ache-Tie i X, pale tan to yellowish-tan; Y, medium brown; Z, dark i. rovin to Cr.rk reddisu-brown, Bent c l e .vyges are common, i l r o n i n c l u s i o n s produce c;-. rk brown pleochrolc h«los. Green hornblende commonly forms rima round s^nhefral to subhe'.: m l grains of fU-^lte ( p i . H I E ) . dornblv ode *md r l a t e 11 Zoned, twinned p l & g i o c l a s e w i t h broad a l t e r e d core I n b i o t i t e q u a r t z d i o r i t e (Grossed a i c o l 3 X 10) Bent p l a g l o c l a B e w i t h s t r e s s t w i n n i n g i n a u g l t e b i o t i t e monzonite (Grossed n i c o l s X 10) 15 b i o t i t e f o r i s.aall patches turou^hout augite giving I t a mottled texture, Auglte has en optic rngle (2V Z) of 60*2 degrees and an extinction an^le (Z Ao) of 46 decrees. 4uartz occupies irregular areas between almost a l l other minerals. Fractured graina and undulatory extinction ©re very c-xamon* In the gernetlferous b i o t i t e qu r t z d l ^ r i t e , quartz commonly contains inclusions of sub rounded plagioclase laths. Pale green, weakly pleochroic dlopsidlc-auglte of the hornblende-blotlte pyroxenlte has aa optic aagle (2V Z) of obout 60 degrees and an e x t i n c t i o n angle (Z Ac) of 45 degrt j.©. .rlaglooluee, potash feldspar &oc; i o t l t c are I n t e r s t i t i a l to the suhedral pyroxene, b i o t i t e commonly has bent clci-. vft&es* Green hornblec.de a .id b i o t i t e form irreg.ilur patches that have replaced pyroxene. A . Texture of b i o t i t e (31) i n augite-biotlte monzonite (Croeaed nloole X. 10) 16 'Monzonite,.Porphyry Monzonite porphyry (Plate IV) forms an arcuate bond, 500 to 1000 feet wide, which lie® between b t o t i t e - euglte monsonlte and aediua-grained hornblende monzonite. Lenac-s of t i l l s rook also occur at the contact between the porphyritlc monzonite and. the pink quartz monzonite prophyry. Pel© grey, eubedral, tabular phanocrysts of orthoelase mtcroperthite,-. that avers g,« 6 cm, by 2 l/2 ca, by 1 1/2 cm,, are set in a medium- to coarse-grained trachytold monzonite matrix. Lustrous, dark-greea hornblende prisms are i n t e r s t i t i a l to pla.^loeisse and orthoelase. Streaks end elongated clots of hornblende crystals locolly give the rook a weak l i n e a t l o n . The lenses of monxonlt© porphyry d i f f e r from the main band i n th:;t they have a coarse-grained matrix and the alignment of cr s t a l s i s i n d i s t i n c t . In thin section, the orthoelase .aicropert.il te ph«nocrysts have a euhedral general form, though th© crystal boundaries ?<re minutely irregular and the outermost portions partly or wholly enclose plagloclase, pyroxene and opaque minerals of th© matrix* Oscillatory zoning, i s d i s  tinguished by variable concentrations of pert.;ite in& by difference In extinction angles, A &rsat v a r i e t y of H . Vein perthlte In phenocryst o f monzonite porphyry (Orooeed nlcole X 45) 17 nicroperthitle textures that rang® from very fine films or strings, to veins or networks of veins (braid perthlte) and Irregular patches, (Emmons, 1953), may be displayed within a single phenocryst. film perthlte (pi, V h) is made up of a .multitude of lenaoid pl&bioclase segrega tions, averaging 0 , 0 5 ma, wide by 0 , 2 mm. long, that are orientated perpendicular to the (010) cleavage in orthelase* In some places, the lenc-es coalesce to form long narrow "strings" (pi* ¥ 3), Pla. l o c i . ae i n vein perthlte (pi* IV B) occurs as long, narrow, l o c a l l y branch ing forms, that are generally elongated in the saae direction aa film and string perthlte, Orthelase between the veins, and <••«round the edges of oquant plagiocl.-se grains (pi, V f,) , i s almost non-pertnitic, The v.:. ry fine, regularly orientated perthitic Intergrowths, the absence of cross-cutting relationships, and the gradatiom.l nature of the various types of perthlte, suggest an absolution origin. Inclusions In the orthelase phenocryats are mainly pi a;.?, loc la se but auglte, hornblende, blotlte, apatite and occasionally orthoelase are also present. Included plagloclase crystals are oriented most commonly with their long di.uen - ions parallel to the (010) plane of orthocln Be but fllao l i e p a r a l l e l to ol er cryst I faces. The 1 -rger crystals, that range in length from 1 to 2 am., are i l a t o V Non-partnltlc a m i around perlpherlaa of clagloclaae gralne In orthoclaaa of naonionita porphyry (Croaaed nleola X 4 5 ) euhedral whereas s m a l l e r crystals are subhe^ral to anhedral and have irregul-.-r boundaries. Alaaoat a l l plagloclase Inclusions c isplay weak, normal z o n i n g and poly synthetic twinning. SubUedral Inclusions of weakly zoned, sparsely per t h l t i c orthoelase occur Just within the borders of the phenocryst and are orientated p a r a l l e l t o a crystal face of the phenocryst* The included orthoelase i s not in optical c o n t i n u i t y with the orthoelase host* Orthoelase of the matrix occurs as randomly o r i e n  t a t e d p e r t h l t i c patches, up to 2,3 tarn* In u l & j i e t e r , that are i n t e r s t i t i a l t o plagloclase. Crystals of subheJr.-ii, wee:<ly zoned, p l a g l o c l a s e , t h a t range In size from 0.3 x 0*5 <B». to 2 x 4 , 5 m*, generally are bent and. show stress twinning, My r .a© kite I s common along cont-.-ets between plagiocluse oad o r t h o e l a s e , .-.ug.ite occurs as subbedral grains riai.ned by green hornblende, or ss s m a l l cores within l a r g e anhedral g r a i n s of hornblende, f o r p h y r l t 1 c Hornblende ;tonaonlte P o r p h y r i t l c hornblende .aonzonite forma an irregular r i n g with an e x t e n s i o n i n t o the central core on the e a s t e r n s i d e . T h i s l i g h t grey roc'* has a d i s t i n c t trashy told t e x t u r e . Pole grey orthoelase for.as euheoral, tabul r pnenocrysts that average 2 to 3 .aa* wide and 10 to 15 fflffl. l o n g , Light g r e y plagloclase and c l a c k , euhedral h o r n b l e n d e o f the aediua-grftined m a t r i x a r e i n t e r s t i t i a l t o the l a r g e r o r t h o e l a s e c r y s t a l s . Hear the i n n e r c o n t a c t o f t h i s u n i t , the r o c k has a g l o m e r o p o r p h y r i t i c t e x t u r e formed by c l u s t e r s , a v e r a g i n g 2 to 5 -MB, i n dia meter, o f anhedral t o subhedral h o r n b l e n d e c r y s t a l s , O r t h o e l a s e p h e n o c r y s t s h e r e have v e r y i r r e g u l a r o u t l i n e s and t h e traehytold t e x t u r e i s i n d i s t i n c t . In t h i n s e c t i o n , weakly p e r t h l t i c , s u b h e d r a l o r t h o e l a s e p h e n o c r y s t s have s a i n u t e l y I r r e g u l a r b o r d e r s that p a r t l y e n c l o s e minerals o f the matrix* O r t no class shows weak o s c i l l a t o r y aonlng, and t h e o p t i c a n g l e s (2VX) o f t h e zones range from 50 t o 70 d e g r e e s in the c e n t e r o f trie crystals to 55 d e g r e e s in the rlas* Some pheno crysts have c o r r o d e d orthoelase crystals In t h e i r c o r e s ( P l a t e VI A), Included plagloclase latns a r e o r i e n t  ated with l o n g d i m e n s i o n s p a r a l l e l t o the crystal bound a r i e s o f t h e host, E u h e d r a l to subbedral normally zoned pla,; 1 j c l a s e o f t h e matrix b e a r s t i n a l b l t l o mantles where in c o n t a c t w i t h o r t h o e l a s e , y r a e k i t © i s n o t rare. Bent p l a g l o c l a s e c r y s t a l s , that show polysyn thetic s t r e s s twinning, are most common i n specimens from n e a r tne o u t e r c o n t a c t o f t h i s u n i t , Zoned h o r n b l e n d e hi-e the f o l l o w i n g p i c o e h r o l e scheme; P l a t e VI Corroded orthoclaee c r y s t a l (Or) I n core of a n orthoclase phenocryst (Pa). (Crossed n i c o l s X 10) P l a g l o c l a s e i n c l u s i o n s i n orthoclase of the gloa e r o p o r p h y r i t i c phase of the p o r p h y r l t l c hornblende monzonite ^Crossed n i c o l s X 10) Gores pale brown gree•:. tsh-brown o l i v e green aims pale green- brownish-green bluish-green i s n brown E x t i n c t i o n a n g l e s (?. Ae) are auout 25 decrees i n th© core and 30 degrees i n th© rims. Pyroxene occurs as rounded cores within hornblende o r as subbedre1 grains w l t a reaction rims o f hornblende, -v.ua.rtz, showing undulstory e x t i n c t i o n , f i l l s a n g u l a r spaces between a l l of the o t h e r m i n e r a l s . In t h i n s e c t i o n s of the g l o m e r o p o r p h y r i t i c pnas© of t o i s u n i t , e l o n g a t e d , anheoral o r t h o c l a s e g r a i n s have a "spongy" t e x t u r e that I s due t o abundant in c l u s i o n s of p l a g i o c l a s e ( p i , VIA), Orientation of the i n c l u s i o n s of see csJ? to be related to the s u b t r a c h y t i c texture of the roc t rather than to any s p e c i f i c cry s t e n o g r a p h i c d i r e c t i o n i n o r t h o c l a s e , Subhedral p l a g i o c l a s e phenoeryats ( A - O ^ ^ Q ) have I r r e g u l a r , t h i n , a l b l t l c borders where i n contact with o r t h o c l a s e . P l a g i o c l a s e of the mntrix ( A n ^ ) has a s i m i l a r texture, but where enclosed i n orthoclase the g r a i n s are rounded and have i n d i s t i n c t boundaries. Hornclenrie has formed between the l o r g e r p l a g i o c l ' j s e cry s t a l s and has p o l ' t l l l t l c a l l y enclosed the ©mailer - p l a g i o  c l a s e g r - i n s , a p a t i t e , magnetite, and c l i n o p y r o x e n e . 21 Pink .Quartz J'ori&onlte Porphyry Pink quartz monzonite porphyry forms the core of the gtook, Preferred o r i e n t a t i o n of pinfc, t h i c k tabular orthoelase phenocrysts, that range from 8 to 12 mm. long and from 3 to 5 mm. wide, gives the rock an i n d i s t i n c t f o l i a t i o n . Fine- to medium-grained pi a ..loolase, born- blende and quirta are i n t e r s t i t i a l to the orthoelase phenocrysts* Lustrous, dark green hornblende forms euhedral prisms up to 3mm. long. In t h i n section, m i e r o p e r t h i t l c ortnocl^se phenocrysts ( p i * VIII) have a euhedral general haoit, though t h e i r boundaries are minutely i r r e g u l a r . A l l phenocrysts display d e l l c o t e but obvious o s c i l l a t o r y Boning. "bin outer margins of the c r y s t a l s are not zoned. Optic angles ( 2 V X ) of adjacent zones may vary as much ns 10 degrees, end the v a r i a t i o n of angles measured withi n a single c r y s t a l i s from 52 degrees to 65 degrees. The lowest value ( ? V x ^ A ') was obtained In the unzoned outer m rgln of a c r y s t a l . Euhedral to subhedral plagloclase i n c l u s i o n s , generally l e s s than 1 ma. long, are o r i ' -titted most commonly with side pinecolds p a r a l l e l to the (010) plane of orthoclese but are a l s o p a r a l l e l to other c r y s t a l faces ( p i . IX A ) . 3ome pla;.ioele»ee Plate V i i B. lertnitlo orthoclase phenocryst with inclusions of euhedral, unstrained quartz ('4) (Crossed nlcole X 10) A« booing and alignment of plagloclase inclusion* in orthoelase phenoeryst of pink quarts acnzonit* porphyry (Crossed nlcola % 5) • I a r t of phsnocryst in plate A at higher signification (Croaked nlcols A 10) 22 c r y s t a l s are only p a r t l y Included ( p i . IX ~) or are l y i n g a t the edge of the orthoclase phenocrysts ag i f they were ettac.-.ed to the crystal face of the phenocrysts ( p i . IX B}« Combination twinning (Ross, 1957)# i n included plagioclase c r y s t a l s i a common ( p i . X A). Inclusions show weak normal zoning with compositions ranging from Aa-^ i n cores to r.ani. In' rims. CO Textures of orthoclase phenocryste sug.-est growth i n a f l u i d magma. The o r i e n t a t i o n of inclusions we£3 probably effected by a process (described by Hlbbard, 1955) of continual attachment of plagioclase c r y s t a l s at the sides of growing .-rthoclase c r y s t a l s . Orthoclase formed early enough to b© aligned by magmatlc flow, and the growth of paenocry ats continued u n t i l the l a s t stages of solidification of the magma. The irregular borders on tae generally euhedral crystals, and the presence of l a t e forating minerals, such as quarts and hornblende. Included In the outer margins of phenocryste, are evidence of the l a t e r stages of growth. Plagioclase of the matrix where in contact with pe r t . i l t o , has a well developed rim of myraeklte ( p i , X E), Complex o s c i l l a t o r y zoning Is common with zones tending to be more albltlc toward the periphery ( p i , XI h) * Plate A. O r i e n t a t i o n o f p l a g l o c l a s e i n c l u s i o n s i n o r t h o e l a s e p h e n o c r y s t o f t h e p i n k q u a r t z monzonite p o r p h y r y ( C r o s s e d nicols X 5 ) B. P l a g l o c l a s e c r y s t a l s w i t h i n and p a r t l y i n c l u d e d i n t h e margin o f o r t h o e l a s e p h e n o c r y s t ( G r o s s e d n i c o l s X 5 ) Plate A 23 Composition ranges from An,,-* to Aa»>,» Quartz occurs i n two formsj (l) i r r e g u l a r , i n t e r s t i t i a l , fractured grains w i t h undulatory extinction; and (2) euhedral, unfractured grains, with even e x t i n c t i o n , that are included i n the unzoned margins of pe r t h l t e phenocrysts ( p i . VII 13), Zoned green hornblende that has a pleochrolo scheme that i s very s i m i l a r to hornblende i n porphyritlc hornblende monzonite (see p.20 ) f p o l k i l l t l c a l l y encloses i n c l u s i o n s of plagloclase, auglte, a p a t i t e , z i r c o n , and magnetite* Trace amounts of auglte occurs either as small grains rimmed by hornblende or a s tiny grains p a l k i l t I c a l l y enclosed i n hornblende* h l l s n i t e , spheae and zircon are very common accessory miner-Is in t h i s rock, AllanIte f-<ro»B euhedral prismatic crystals that are pleochrolo from dark brown to 11..hit brown, some of which are twinned * An isotropic, yellow mineral, having very high r e l i e f , surrounded by H pleochrolo halo and radiating fractures in hornblende, and with a n- rrow rim of epidote, h/.s been tentatively i d e n t i f i e BS a:.l- i t e In the me tablet state ( p i , XI .-)» Sphene has a c a r r a c t c r i o t l c acute rhombic habit. Zircon occurs as minute grains that produce pleochrolo h^los in hornblende* A. O s c i l l a t o r y zoning i n p l a g l o c l a s e of pink quartz monzonite porphyry (Grossed n i c o l s X 10) b. A l l a n l t e i n naetamict s t a t e ( ? ) included In hornblende (lib). Note pleochrolo halo and r a d i a t i n g f r a c t u r e s In hornblende (Plane l i g h t X 10 ) 24 A p l l t e A body o f aplit© occupies a s m a l l a r e a in t h e eouthcenteral part o f t h e s t o c k . T h i s is a p a l e grey, fine-grained rock o f q u a r t z monzonite composition. In some p l a c e s , the rock c o n t a i n s s p a r s e l y d i s t r i b u t e d p o t a s h feldcper p h e n o c r y s t s and a s m a l l amount ( g e n e r a l l y l e s s t h an 2/S) o f h o r n b l e n d e . In t h i n s e c t i o n , an allotrlo- morphlc granular t e x t u r e l a formed by i n t e r l o c k i n g grains o f p l e g i o e l a e e , orthoclase and q u a r t z . Non-perthitic orthoclase i s partly altered t o sericite which forms minute shreds throughout the c r y s t a l s . I n c l u s i o n s I n c l u s i o n s a r e r a r e in t h i s s t o c k . Two d i s  t i n c t t y p e s a r e found; ( l ) p l a i n l y r e c o g n i z a b l e w a l l r o c k xenoliths and (2) dark x e n o l i t h s whose o r i g i n i s not at once e v i d e n t . The second type makes up the m a j o r i t y o f i n c l u s i o n s in t h e stock.. X e n o l i t h s o f c o u n t r y rock avr. s p a r s e l y distrib uted in auglte-biotite monzonite n e a r t h e c o n t a c t o f t h i s u n i t with h o m f e l r l c w a l l roeKs. The i n c l u s i o n s are dar't-grey, hor . f e l s i c roc<s w i t h a n g u l a r t o subangul- r , 25 b l o e k l y ant" y l a c b y f o r m s , t b r . t r a n g e l u s l ^ e f r o m a few I n c h e s t o s e v e r a l f e e t * B e d d i n g I n I n c l u s i o n s i e not coaaonly p a r a l l e l t o b e d d i n g I n w a l l r o c k s , a n d t h e In c l u s i o n s h a v e obviously b e e n r o t a t e d . Occasionally, • elonga'.e i n c l u s i o n s l i e p a r a l l e l t o f o l i a t i o n i n t h e enclosing g r a n i t i c r o c k s . C o n t a c t s b e t w e e n i n c l u s i o n s a n d t h e . m r r o u n d i n g . h o s t r o c k a r e s h a r p * P r o x i m i t y o f b o r n f w i s I n c l u s i o n s ' t o s i m i l a r h o r n f e l s w a l l r o c k s , t h e r e l i c t bedding, a n d f o r m s o f t h e I n c l u s i o n s leave l i t t l e d o u b t t h a t t h e s e I n c l u s i o n s a r e x e n o l l t h s of l o c a l wall rock. A l a r g e i n c l u s i o n o f q u a r t z i t e , a b o u t 3500 f e e t long a n d a maximum o f 375 feet w i d e , l i e s w i t h i n the south eastern m a r g i n o f t h e stock* The o u t l i n e o f t h e s o u t h e r n side o f t h e i n c l u s i o n m a t c h e s t h e o u t l i n e o f t h e a d j a c e n t q u a r t z i t e - - . a i l r o c k , T h i s i n c l u s i o n , t h e r e f o r e , p r o b a b l y was n o t r o t a t e d o r t r a n s p o r t e d i n t h e magma.- ' The d a r k i n c l u s i o n s ( p i . XI1) a r e s p a r s e l y d i s t r i b u t e d In p i n k q u a r t z monzonite p o r p h y r y a n d i n p o r  p h y r i t l c Hornblende m o n z o n i t e b u t a r e n o t f o u n d l a augite- b i o t l t e m j o z j n i t e . They v a r y f r o m subrounded, equant fragm-" ••.•ts t o w e l l roundJ* ovoid and c i g a r shaped f r a g m e n t s t h a t r a n g e In s i z e f r o m 1 o r 2 Inches t o a b o u t 1 f o o t . i . o t e phenocrysts in both in th© inclusion (X 1) and 2 6 Elongated I n c l u s i o n s l i e p a r a l l e l t o primary f o l i a t i o n i n p i n k q u a r t z monzonite porphyry. Boundaries a r e g e n e r a l l y s h a r p but i n c l u s i o n s w i t h d i f f u s e b o u n d a r i e s were o c c a s i o n a l l y f o und. In some p l a c e s t h e i n c l u s i o n i s e n v e l o p e d by a t h i n r i m o f h o r n b l e n d e c r y s t a l s . T e x t u r e v a r i e s from sugary t o p o r p h y r o b l a s t l c . .Mega- c r y s t s o f aubhedral t o euhedral p o t a s h f e l d s p a r have random o r i e n t a t i o n In a dark-green sugary m a t r i x . In t h i n s e c t i o n o f dark i n c l u s i o n s ( p i . X I I I ) , m i c r o p e r t n l t l c o r t h o c l a s e megacrysts, t h a t a v e r a g e 4iaa» by 10 m.0. have euhedral c o r e s and b r o a d , i r r e g u l a r , p o i f c i l o - b l a s t i e margins. Gores e x h i b i t complex o s c i l l a t o r y z o n i n g , and c o n t a i n euhedral p l a g i o c l a s e I n c l u s i o n s some o f which show combination t w i n n i n g , t h a t ' r e o r i e n t a t e d p a r a l l e l to t h e (010) p l a n e o f o r t h o c l a s e h o s t . The tro-->d i r r e g u l a r un zoned margins enclose randomly o r i e n t a t e d ailo- r a l s o f t h e m a t r i x but do not e n c l o s e p l a g i o c l a s e s i m i l a r t o that found In the c o r e , Aohedral o s o i l l a t o r i l y zoned p l a g i o c l a s e ph..nocrysts (•*'ng..1- )^ t h a t average 1 am. by 3 airs,, are corroded and embayed by c o t e s h f e l d s p a r of t h e m a t r i x ( p i . XIV), Subbedral t o enhedrel h o r n b l e n d e ( p i . XIV c ) , t h a t ra > e s up t o 5 mm. i n long e s t d i x e n s i n, c o l k l l i t i c a l l y • n cloae g r a i n s o f a u ^ i t e , plfigiocl*»se and p e r t h l t e . The m a t r i x h-s a <? r.\noble e t i c t e x t u r e made up of i n t e r l o c k i n g P l a t e X 1 1 1 A. P o r p h y r o b l a s t of p e r t h l t e In granoblaatlo m a t r i x , bote l i n e of t i n y Inclusions and I r r e g u l a r b o r d e r (Crossed n i c o l s X 5) P l a t e XIV Photomicrograph, showing polkilltic hornblende (Crossed nicols X 10) g r a i n s t h a t are generally lag® than 0»5 am. i n d i a m e t e r . P a l e g r e e n , weakly pleochroic dlopsidic-augite faras e u h e d r a l t o ^ n h e d r a l c r y s t a l s , some o f which b e a r r e a c t i o n rime o f h o r n b l e n d e * - C o r r o d e d , latbllke cry stala o f plngioeleee (Angy) a r e l e e s t h a n 0.2 mm* I o n s . Anaadra-1, a o n - p e r t h l t i c ortb.oela.se, t h a t e n c l o s e s , c o r r o d e s , end f i l l s the area between, a l m o s t o i l other ainerals makes up 45 p e r c e n t o f t h e matrix* t h e o r i g i n o f th® dark inclusions I s not r e a d i l y apparent because their textures »*vre developed after tuey were enclosed in the magma. Hornfe la le textures indicate r e o r y s t a l l l z a t l u n o f t h e x e n o l i t h s . T e x t u r e s o f c o r e s of megj'crysts (••'•licate o s c i l l a t o r y stoning and preferred oris..tailin o f i n c l u d e d p l a g i o c l a s e ) a r e i d e n t i c a l , t o textures of phenoorysta i n otner rock zones of the ©took* fh«se large c r y s t a l s probably are pnenocrysts that developed pol*ilobla»tic margins as t h e y c o n t i n u e d t o grow d u r i n g r e c r y s t a l l i z a t i o o f t h e inclusion, A aiagma enn re not ^ l t h Inclusions and e f f e c t changes whicn * i v s t n e a a z i i n e r d ae>.". vbla t i e s i m i l a r t o t h a t o f the en :. oalng cry stallXsing .ma» ma, Ho 1 1 i U l d , saturated with a certain ;;»muer of a reaction series, can aelt I n c l u s i o n s consist 1 i g of minerals fcelo ging to an 2c earlier s t ^ e of t.-.e re-.ction series (bowen, 192o, p. 221) • ?aus, augite would be oat of equilibrium In a ai^aw of quarts monzonite composition where bornble.-de Is the stable a-.flc mineral pb^se. The presence of abundant augite in the Inclusions Indicates eltber non»equllibriu3» or, perhaps*, that the xenolith was relatively anhydrous ard impermeable, Pletributtoo of inclusions In the porphyrltio horn, lends ttonsohltc and in the pink quartz monaorjlte por'hyry but not in the au<;..Ite biotite monzonite, the presence af ahundnat <H »p»idio»auglte, and of otic Hintory zoning In cores of meifiorysts, auggeai t h a t the inclusions are cognote a n d w« r<* originally uuglts-biotit© monzonite, which h a been engulfed and reoryst'-ilized by the surround 1:.*^, .tttgao. 29 Chemical composition o f the main rock zones of t h i s stock changes aystesatioally from the periphery of th© stock to the core. This v a r i a t i o n i s i l l u s t r a t e d by nodal analyses (Table I ) , by calculated cnej&lcal analyses (fable II), and by variation diagrams ( f i g s . 4, 5, and 6). y»odes (Table I) were calculated by the standard point-count method averaging 1800 points per t h i n - s e c t i o n . In coar sely p o r p h y r i t l c rocks the r a t i o of phenocrysts to matrix was measured from hand specimens by tracing the respective areas on mil l i m e t e r gridded transparent paper, and th© matrix composition WJS computed from thin sections. Theoretical chemical analyses (Table II) of the rocks ware- calculated from, the modes. Compositions of feldspars, quart*, a p a t i t e , sphan© and magnetite were calculated from standard formilae. The average plagloclase compositions were estimated from the ran.e of zoning and from tae r-iU-t- ive widths of respective zones. Compositions of horn blende, b l o t l t e , Muscovite, ullanite a n d dlopsldic-augite were taken from tables of chemical coalyses, given i n Deer, iowie and Passman (1952), for minerals frsm similar rock types and with s i m i l a r o p t i c a l properties to tuose of the aount hrenner stock. Average values of the chealcal 30 a n a l y s e s from each, r o c k zone a r e used t o p l o t t h e v a r i a t i o n d i a g rams shown In Figures:., 4 t 5 , and 6 . D i f f e r e n t i a t i o n In' ices*, that a r e - p l o t t e d a g a i n s t various, oxides In F i g u r e s Ja and oh, a r e superimposed on f r e q u e n c y d i a g r a m s which r e p r e s e n t 5000 a n a l y s e s In W a s h i n g t o n ^ t a b l e s . These a n a l y s e s I n c l u d e t h e c o m p o s t i t i o n a o f a l l i g n e o u s r o c k s . G o ^ p o s i t i o n o f the main r o c k zones v a r i e s system a t i c a l l y from tne p e r i p h e r y o f the stock t o th© c o r e In t h e f o l l o w i n g manner. 1. T o t a l m a f i c m i n e r a l s , and conse • ue-tly o x i d e s I r o n and magnesium, d e c r e a s e ( f i g . 3 and 4 ) , 2. Anorthite c o o t e n t of p l e g l o c l a s e g e n e r a l l y d e c r e a s e s ( f i g , 3 ) . 3. «mount o f q u a r t z and a l k a l i e s i n c r e a s e s ( f i g * 3, 4 , 5) 4 . Differentiation i n d i c e s i n c r e a s e (fig. 5 ) . f i g u r e s 6 and 9 c l e a r l y I l l u s t r a t e the degree of d i f f e r e n c e between r o c k s of the Houat rrenner stock and most r o c k s , _ ^ D i f f e r e n t i a t i o n Index i s d e f i n e d by Thornton and 'Puttie (19*0) as the sum o f t h e weight p e r c e n t a g e s o f n o r m a t i v e q u a r t z + o r t h o e l a s e + a l b i t e + n e p h c l i n e + l e o e l t f c + k a l e l l i t e . TABLE I I CALCULATED CHEMICAL COMPOSITION OF ROCKS Mt. B r e n n e r S t o c k 1 2 3 4 . 5 Average 2 to 5 6 7 8 9 A v e r a g e 7 to 9 3 1 0 2 62.BT 57.30 53.76 53.43 53.96 54.61 59.42 60.77 59.39 61.53 61,25 T10'2 .92 .73 .75 .64 .47 .51 .15 .15 .38 .12 .14 A 1 2 ° 3 17.11 17.61 18.00 - 19.02 18.83 18.36 18.57 19.92 16.15 17.53 18, .72 F e 2 0 3 1.29 1,62 1.74 1.56 1.64 1.54 .75 1.33 1.75 .72 1.02 FeO 4,45 4.64 5.32 5.35 4.92 5.05 2,47 2,45 2.71 1.77 2.11 HnO .04 .05 1.06 .28 1.10 .03 .03 .01 MgO 2.50 2.77 3.27 2.76 3.05 2.96 1,37 . 1 . 5 8 1.63 1.28 1.43 CaO 4.18 5.63 7.92 7.46 8.21 7.35 4.75 5.62 4.15 3.88 4.75 • Na 20 2.75 2.35 3.49 2.55 3.33 2.95 4.24 4.86 3.10 4.23 4.54 K 20 3.02 6.16 ' 3.22 4.71 3.65 4.48 5.80 4.60 7.91 6.04 5.32 P 2O 5 .06 .06 .43 .31 .35 .29 — - .16 .08 .38 .25 * C h e m i c a l c o m p o s i t i o n s a r e C a l c u l a t e d f r o m modes, and numbers r e f e r t o s p e c i m e n s i n T a b l e I and i n F i g u r e s 3 and 4. 31 10 11 12 13 Average 10 t o 13 65.38 .10 17,94 .84 1.42 .02 .89 3.01 3.69 7.18 .12 64.91 .16 16.83 .73 1.31 .02 .95 3.59 4.25 4,90 .08 62.15 .42 19.73 ,43 1.06 .01 .75 6.38 2.16 5.91 .04 66.22 .14 17.99 .32 .55 .57 2.97 4.03 6.61 .19 64.79 .20 18.12 . 5o 1.08 .01 .79 3.98 3.53 6.15 .11 14 15 72.38 16.03 .27 .36 .13 2. 32 3.96 4.27 .08 43.05 1.51 7.69 6.81 13,69 .15 8.14 13.20 .68 3.03 .78 Figure 4 . Variation diagram for.rook zones of the Mount Brenner stock. The average weight per cent of oxides of each rock zone are plotted agalnat to t a l s i l i c a : A= augite-biotite monzonite: B = monzonite porphyry; C.= porphyrltic hornblende monzonite; D=pink quartz monzonite porphyry; ro E = apllte; and F = hornblende-biotite pyroxenlte. 33 100 90 80 70 60 50 40 30 20 10 0 DIFFERENTIATION INDEX Figure 5 a Figure 5 . Contoured diagrams of oxides vs. d i f f e r e n t i a  t i o n index on which analyses of rocks from the Mount Bren ner stock have been superimposed. Contour diagrams, which represent 5 0 0 0 analyses i n Washington's Tables, are modified a f t e r Thornton and T u t t l e , I 9 6 0 , p. 6 7 ^ - 6 7 9 . A= a u g i t e - b l o t i t e monzonite, B= monzonite porphyry, C=* p o r p h y r i t l c hornblende monzonite, D - pink quartz monzonite porphyry, E = a p l i t e , and F= hornblende-biotite pyroxenlte. 100 90 80 70 60 50 40 30 20 10 0 DIFFERENTIATION INDEX Figure 5b 35 Fe " +• F e ' " F i g u r e 6 . T r i a n g u l a r c o m p o s i t i o n d iagram on w h i c h t h e f o l l o w i n g d a t a a re p l o t t e d } 1. Rocks o f the Mount Brenner s tock? A = a u g i t e - h l o t l t e m o n z o n i t e , B = monzonite p o r p h y r y , G = p o r p h y r i t l c hornblende monzon i t e , D = p i n k q u a r t z monzonite p o r p h y r y , E = a p l l t e , F = h o r n - b l e n d e - b i o t i t e p y r o x e n l t e . 2. D a l y ' a average b a s a l t ( 1 ) , a n d e s l t e (2), d a o i t e (3) and r h y o l i t e (A). 3. B e l t o f c o m p o s i t i o n v a r i a t i o n o f t h e m a j o r i t y o f c a l c - a l k a l i v o l c a n i c and p l u t o n l c sequences ( a f t e r T l l l e y , 1950, p . 4 8 ) ; the shaded a r e a . 36 th® smooth trend towards "Petrageny's residua system"-, and the degree of s i l i c a o v e r s a t u r a t l o n or undersaturatlon of each rock zone, j J r . J T /gr,» Contact e f f e c t s i n sla t e s and shales on weatern and northern boundaries of the stock extend up to 200 feet from the igneous contact* Immediately adjacent to the contact h o r o f e l s i e texture i a well developed and b e d d i n g in the rock has been almost completely o b l i t e r a t e d . 'Farther from the c :<ntaot the h o r n f ^ l e i e texture gradually ; ;lves way to the o r i g i n a l texture of shales and slf-te. In t h i n section, texture of the hornfels i s porphyroblas 11 c, with spongy porphyroblasts of o o r d l e r i t e i n a granoblaatio -matrix. P l ^ o c h r o l c , red-brown o l o t l t e occur© along bedding planes or as t i n y v e i n l e t a f i l l i n g f r a c t u r e s i n h o m f e l a . The t y p i c a l mineral assemblage i s quartz, plaglooiese, c o r d i e r i t e , s e r l c i t e , b i o t i t e , and Experimental studies by- Bo wen (19 ;7), and by Thornton and T u t t i e (1950), demonstrate that the system S I O 2 - Unf, l o i O j - ::AISIO4 Is the ?-:oal toward which a l l :uag-antlc l i q u i d a move on 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 . Bowen (1937) has named t h i s system "Petrogeny's residua system". 37 m i n o r a m o u n t s o f p y r l t e and z l r o n . • T h e amount o f p l a g  l o c l a s e a n d a e r t c i t e i n t h e h o m f e l s i n c r e a s e s t o w a r d t h e I g n e o u s c o n t a c t . C o n t a c t e f f e c t s i n . q u a r t z I t e r , a r e r e c o g n i z a b l e f o r n o t more t h a n 150 f e e t f r o m t h e i g n e o u s c o n t a c t , M e t a a o r p h l s m h a s h a d a " b l e a c h i n g " e f f e c t ; q u a r t " i t ® i m m e d i a t e l y a d j a c e n t t h e c o n t a c t l a p a l e g r e y t o w h i t e , w h e r e a s q u a r t z l t e f u r t h e r f r o a t h e c o n t a c t I s medium t o d a r k b l u i s h - g r e y . W i t h i n t h e b l e a c h e d .--one, b l o t i t e i s c o n c e n t r a t e d a lony- b e d d i n g p l a n e s and f i n e l y d i s p e r s e d t h r o u g h o u t t h e r o c k * F i n e - g r a i n e d p y r l t e I s d i s  s e m i n a t e d t h r o u g h o u t t h e a u r e o l e a n d was n o t e d b e y o n d t h e z o n e o f b l e a c h i n g , STRUCTURE I n t e r n a l Structures. F o l i a t i o n a n d L i n e a t i , p n » - F o l i a t i o n , h e r e c o n s i d e r e d t o be p l a n a r f l o w s t r u c t u r e , i s marked by t h e p r e f e r r e d o r i e n t a  t i o n o f (010) f a c e s o f t a b u l a r f e l d s p a r s . I t s a t t i t u d e l a a l m o s t e v e r y w h e r e v e r t i c a l b u t l o c a l v a r i a t i o n s o f d i p t o 75 o r BO d e g r e e s a r e common ( f i g . 6 ) . The © t r u c t u r e i a present i n a l l r o c k z o n e s o f t h e s t o c k and I t i a 39 g e n e r a l l y m o s t d i s t i n c t I n t h e o u t e r a n d i n t e r m e d i a t e z o n e s . The o v e r a l l c o n t i n u i t y a n d c o n c e n t r i c p a t t e r n o f t h e s t r u c  t u r e a r e I l l u s t r a t e d I n F i g u r e 7 , F o l i a t i o n I n a u g i t e - b l o t l t e m o n z o n i t e and I n p o r  p h y r i t l c h o r n b l e n d e m r n z o n i t e i s e v e r y w h e r e p a r a l l e l t o t h e i n t r u s i v e c o n t a c t . I n f i n e - g r a i n e d , a u g i t e - b l o t l t e m o n  z o n i t e t h e g e n e r a l l y i n d i s t i n c t f o l i a t i o n l a a c c e n t u a t e d by s u b p a r a i l e l b i o t l t e p i s t e s , I n some a r e a s o f t h e mon z o n i t e p o r p h y r y , t h e m a t r i x h a s s e g r e g a t i o n s o f d a r k a n d l i g h t m i n e r a l s w i t h i n t a e p l a n e o f f o l i a t i o n , g i v i n g th© r o c k a g n e l s s i c s t r u c t u r e , F o l i a t i o n i s p a r a l l e l t o t h e c o n t a c t o f t h i s o r e s e n t s h a p e d b a n d e x c e p t i n t h e n o r t h e r n a n d s o u t h e r n t i p s w h e r e i t c u t s a c r o s s t h e g r a d a t i o n a l c o n t a c t a n d f o l l o w s th© t r e n d i n t h e a d j a c e n t p o r p h y r i t l c h o r n b l e n d e m o n z o n i t e . F o l i a t i o n i n t h e p i n k q u a r t z m o n z o n i t e p o r p h y r y i s w e l l d e v e l o p e d n e a r t h e p e r i p h e r y o f t h e u n i t b u t i a i n d l a t i n o t o r a b s e a t i n t h e c o r e . I t g e n e r a l l y c o n f o r m s t o t h e o u t e r c o n t a c t o f t h i s z o n e . L i n e a r s t r u c t u r e s a r e r a r e . I n m o n z o n i t e p o r p h y r y s t r e a k s a n d e l o n g a t e d c l o t s o f h o r n b l e n d e i n t h e m a t r i x g i v e a l i n e a r e l e m e n t t o t h e r o c k . I n d i v i d u a l h o r n b l e n d e p r i s m a w i t h i n t h e s t r e a k s . nd c l o t s commonly show a random o r i e n t a t i o n . Where e l o n g a t e d I n c l u s i o n s 40 ar® present, they l i e w i t h i n the plane of f o l i a t i o n with their longest dimensions p i t c h i n g at very steep angles. •Jointlo»f.- Two prominent sets of steeply dipping j o i n t s arc- w e l l devsloped throughout the stock; one set i s parallel or aubparallel to planar structure; the other set Is normal to the planar structure or outs across I t at large angles. Along the western aergla- of the stock, j o i n t * that ar® normal to f o l i a t i o n out across the igneous contact and continue into the country rocks. J o i n t s that are parallel to f o l i a t i o n occur i n a l l ro«H zones* Put they are most well developed i n th* monzonite porphyry* Poles to Joints are plotted on a lower hemisphere Schmidt net p r o j e c t i o n in /igure 9 . They form two amin con centration* ; the concentration In the south*"stem quadrant corresponds to Joints that are parallel to planar structure; concentrations i n northeastern and. southwestern quadrants correspond to j o i n t s that cut planar structures at large Angles, The j o i n t s are a l l very closely spaced, and @ R c h a t t i t u d e on the wp represents 8 to 10 j o i n t s of the same a t t i t u d e . Generally, the j o i n t s are saooth, remarkably even and p e r s i s t e n t , Son® shows »llc<c sides. A few j o i n t s i n pink quartz monzonite porphyry are f i l l e d with s p l i t s and pink quartz monzor.it© F i g u r e 8. 172 p o l e s t o f o l i a t i o n p l o t t e d on a S c hm i d t n e t and c o n t o u r e d , , C o n t o u r s 2 , 6, 1 6 , a n d o v s r 16% p e r 1% a r e a 0 N 1 W F i g u r e 9 . 231 p o l e s t o J o i n t s p l o t t e d on a S c hm i d t n e t and c o n t o u r e d , C o n t o u r s 2 t T 14 2 1 , 2 8 , a nd o v e r 28# p e r 1% a r e a . ' 43 p o r p h y r y dykes. h i n o r f r a c t u r e s u r f a c e s i n many a r e a s have been " h e a l e d " by dark green h o r n b l e n d e . T h i s f e a t u r e i s seen i n a l l rock phases, even t h o s e t h a t a r e h o r n b l e n d e p o o r . S h a l l o w dipping, j o i n t s were o b s e r v e d In o n l y t h r e e l o o a l i t i e s . In one a r e a , i n t h e l o w e r p a r t s o f t h e w a l l s o f a U-shaped g l e c i a l v a l l e y , j o i n t s d i p p i n g about 35 d e g r e e s a r e s u b p a r a l l e l o r p a r a l l e l t o the r o c k s u r f a c e s , g i v i n g a s h e e t e d e f f e c t . In a n o t h e r a r e a , c l o s e l y spaced j o i n t s a r e n e a r l y h o r i z o n t a l . hocks i n t h e v i c i n i t y o f t h e s e j o i n t s a r e d e e p l y weathered, and viewed from a d i s t a n c e t h e s t r u c t u r e has t h e appearance o f s e d i m e n t a r y b e d d i n g , .'Shallow d i p p i n g j o i n t s a r e not a p p a r e n t In a r e a s o f t h e s t o c k where t h e s t e e p l y d i p p i n g j o i n t s a r e w e l l d e v e l o p e d . Very t i g h t c u r v e d f r a c t u r e s t h a t b r a n c h and j o i n t o form a network o f l e n t i c u l a r p r i s m s t h a t ran f ce i n t o i c k - ness from 1/2 t o 3 i n c h e s o c c u r a t t h e western end s o u t h e r n b o r d e r s o f the stoc't. These f r a c t u r e s o c c u r w i t h i n 5 f e e t o f the i n t r u s i v e c o n t a c t and a l s o a r e w e l l d e v e l o p e d f o r a few f e e t In the a d j a c e n t a o r n f e l s c o u n t r y r o c k . The f r a c t u r e s e i t h e r p a r a l l e l p r i m a r y f o l i a t i o n o r cut a c r o s s i t a t low a n g l e s . I n t e r s e c t i o n o f t h e c u r v e d 44 fracture surfaces forms a llneation that•plunges steeply in the direction of dip of the Intrusive contact. "racture surfaces are coated with reddish-brown llmonlte, This type of fracturing has been given the term "slip-cleavage" by Gompton (1955). I n t e r n a l Contacts.- Almos-t a l l contacts between igneous rock zones ere gradatlonsl and thus are somewhat approx imate (See map. i n pocket), Their steeply dipping attitudes are shown by t h e i r lack of d e f l e c t i o n i n crossing ridges and valleys. The boundary between eugite-biotite monzonite and the monzonite porphyry, which c-aj be defined within distances ranging from 5 to 20 feet, i s th© least gradatlonal of a l l the Internal contacts, .a aharp contact between these two rock types occurs at one l o c a l i t y near the northern end of the monzonite porphyry band. The boundary between a u g i t e - b i o t l t e monzonite and porphyritlc hornblende monzonite l a accurate to within 150 feet. Contact between monzonite porphyry and p o r p h y r i t l c horn blende monzonite i s gradatlonol over a dlstance of about 100 feet. Glomerophyritie hornblende monzonite for us a transition zone between porphyritlc h o r n a l c d e monzo.-.lte and the pink quartz monzonite porpnyry, This boundary Is very d i f f i c u l t to locate more accurately t h a n within 200 feet. 4 5 Contact between a p l l t e and the surrounding rock zones was not observed. External Structures In plan the s«!ount Brenner stock i s roughly e l l i p t i c .1 with i t s long axis trending northeastward. The northeast regional trend of toe country rock structures Is generally concordant with the o u t l i n e of the stock ( f i g * 4), Along the southwestern and northeastern margins of the stock, the bedding makes on abrupt swing to conform with the flanks of the i n t r u s i o n . Along the southern boundsry of the stock, shale beds that dip north©-'-.stward to eastward, about 1000 feet from the igneous contact, d i p steeply southward Immediately adjacent to the contact. The q u a r t s i t e shows t h i n p l a t y cleavage i n a zone 500 to 800 feet wide along the southeastern boundary of the stock. beyond t h i 3 distance the qua r t z i t e i s massive. Discordant r e l a t i o n s h i p s occur i n the north western corner of the map-area, where the Intrusion cuts across the limestone and chert units and i n the eastern part- of the map ares, where the stock cuts across the contact between q u a r t z i t e , and shale and p h y l l l t e . Contact with the country rocks i s Invariably sharp. o 46 Intense breceiatlon or mylonitizatlon l a found i n contact zonea. HI 3?OhY OF THi PLUTO& I n t e r p r e t a t i o n of Structures and i-iecha nica of Emplacement Foliation can be produced by three d i f f e r e n t mechanisms; (1) dimensional o r i e n t a t i o n of phenocrysts by laminar flow i n an uprising, magma * ( primary flow structure) j (2) tectonic orientation of phenocrysts during regional metamorphismj and (3) mimetic orientation of phenocrysts by growth around minerals that already have a preferred o r i e n t a t i o n (Gellatly, 19-4). The non-layered nature of the rock, and the lnck of ublqultus cataclasm i n pheno crysts and in trie matrix, suggest that the f o l i a t i o n l a not the r e s u l t of tectonic oreintatlon, I'll met 1c o r i e n t a t i o n snould be characterized by phenocrysts having,cores of. e a r l i e r formed plagloclase c r y s t a l s whose o r i e n t a t i o n c r y s t a l s i n \ '1 ^ * i S l i 3 8 °f d i m e n s i o n a l o r i e n t a t i o n o f 7 f v ^ Xluld are discussed by ~ 8 l v ( i g x 7 \ (1901), Hutchinson (1956), and K i l l s (1963). 4 7 r e f l e c t s the alignment of plugloclace In the matrix. These features ere not common i n the Blount Brenner rocks. The o v e r a l l conformity of f o l i a t i o n with rock zone boundaries and the presence of elongated Inclusions orientated p a r a l l e l to f o l i a t i o n suggests that the f o l i a t i o n Is a primary flow structure. The steep outward dlpolng attitudes of flow structures throughout the stock iodic-te that v e r t i c a l movement has been prominent end that the stock i s not domed at the present l e v e l of erosion, .'lost of the Joints were measured In the c e n t r a l and northwestern parts of th© stock. The perpendicular r e l a t i o n s h i p between the two sets of steeply dipping Joints shown in Figure 9 , therefore, i s s t a t i s t i c a l l y v a l i d only for t h i s region and not for the e n t i r e stock. The presents of a p l l t e and pink quartz aonzonlte porphyry dykes f i l l i n g a case of the steeply dipping joints and the occurrence of hornblende and quartz along the fractures, strongly suggests that the joints are primary. Fractures normal to planar structure are interpreted as tension Joints related, to a alight arching of the r i g i d upper parts of the stock due to upward pressure fro i n the magma below. Xuznetsov (1951) suggests that as cooling, proceeds from above, & succession of the tension-joints can be forced 48 progressively at depth. The Joints are analogous to the cross-joints'described by Balk (193?) and to the B-G j o i n t s described by : a r t i n (1951) 1. J o i n t s p a r a l l e l to f o l i a t i o n are poaaibly due to contraction during cooling; the fractures tend to develop along planes of r e l a t i v e mechanical weakness, s t r u c t u r a l r e l a t i o n s suggest that the stock was emplaced a f t e r the country rocks were folded and f a u l t e d . The j o i n t s , therefore, probaoly are not related to regional compressive stress i n the enclosing rocks. The shallow dipping j o i n t s probably are not of primary o r i g i n . Their broadly undulatory nature and t h e i r sabparallellam to the topography Indicate e x f o l i a t i o n phenomena. Jahne (1943) a t t r i b u t e s such large-scale e x f o l i a t i o n structures to r e l i e f through removal of superincumbent load, b l i p cleavages and the l l n e a t i o n formed by t h e i r Intersection "Indicate c i r c u m f e r e n t i a l stretchier-, of the Balk (193?) defines cross-Joints as tnose j o i n t s that are normal to flow l i n e s . .--artIn (1951) describes B-C j o i n t s that are normal to the planar structure of a g r a n i t i c d l a p l r that bus no l i n e a r structures. •a 49 b a t h o l i t h i o walls, combined wit a coiapression and flattening normal to the walls,*' ( h i l l s , 1963, P» 357), That the stock was eaplaced i n a fluid or partly f l u i d state i s suggested by the primary flow structures, the presence of rotated wall rock inclusions without d i s r u p t i o n of t h e i r i n t e r n a l structure, the lack of raylooltlzatlon or br o c c i a t i o n along the outer contact, and the presence of a hornfela contact aureole around the stock, S t r u c t u r a l data Indicate that at the l e v e l now exposed by erosion the stock was e&placed by f o r c e f u l I n j e c t i o n , The main lines of evidence are; ( l ) near v e r t i c a l planar and l i n e a r flow .structures; (2) o v e r a l l continuity and concentric pattern of primary flow structures; (3) s l i p cleavages and platy cleavages in the outer contact zone; (4 ) warping of country rock structures ...round the stock; and (5) bedding i n shales upturned to confona with the contact of th© stock. The foregoing structural evidence seeas to Indicate that the stock was emplaced i n the f o l l o w i n g ai&nner, ^ r i s l n e fluid magma aaade rooaa for i t s t l f i&alnly b y should*.ring aside the regionally folded sedimentary and me ta sedimentary rocks. In response to the upward and. outward pressure exerted by tne upsurging magma, bedding in the country rocks deflected upwards and outward3 to -*4 50 conform with the Intrusive contact, and the flanking, rocks fractured to form s l i p cleavages and plat/ cleavages. The magus engulfed a large segment of quartzite j u s t within the souther-stern margin of the stock, and i t also engulfed and rotated a few much smaller blocks of country rock along the outer margin. isfter p a r t i a l consolidation of the upper end outer portions of the magma, to form the fine grained auglte-biotlte monzonite, the magma continued to surge upward, and i t Intruded this outer " s h e l l " . That the upward movement of the fluid core continued until the lust stages of consolidation is suggested by the vertical flow structures in almost a l l parts of the pink quartz monzonite porphyry. fracturing took place before the lower part of the stock was completely consolidated, and j o i n t s formed to accommodate stresses due to magmatic pressure from below and to-cooling and contraction of the rock. Assimilation Uoota ainatlon of the magma has occurred along the eastern m. rgln of the stock, where a u g l t e - b i o t l t e monzjolte i s i n contact with p e l i t i c hornfeis. The r e s u l t of c i.'ita&liv-ition i s to change the & u ^ l t e - b l o t l t e 51 monzonite Into a garnetlferous quartz d i o r i t e , In a zona which Is l e s a than one foot wide, Ro evidence f o r con- tarain -tion occurs where g r a n i t i c rocks are i n contact with q u a r t z i t e . I f a s s i m i l a t i o n had taken piece i n s i g n i f y ioant amounts the f o l l o w i n g evidence would be expected; ( l ) numerous i n c l u s i o n s of country rock In a l l stages of resorption; ( 2 ) the number of Inclusions shoul-" increase toward the periphery; ( 3 ) heterogeneity of outer . ones showing various degrees of conversion to the present rock types; and (4) the outer zones should become increasingly more s i l i c e o u s toward the contact since highly s i l i c e o u s country rocks would, be es s i ml l a ted, Such evidence i s v i r t u a l l y aoaent i n t h i s stock, At the present l e v e l o f erosion, toarefore, contamination of th> magma by a s s i m i  l a t i o n of country rock has not been a fac t o r In causing compositional v a r i a t i o n of the stock. D i f f e r e n t i a t i o n The systematic compositional v a r i a t i o n within the stock (See p.30 : n (' the following figures) l a compatible with the concept of d i f f e r e n t i a t i o n - of a ma:: ma as i t c r y s t a l l i z e d inward from the margin. The a u g i t e - b i o t i t e monzonite i s conride red to represent th© ^imposition of the 52 parent f l u i d because I t was the f i r s t rock zone to be eopl cad and because i t has & composition from which a l l other rock types can be formed by r e l a t i v e l y simple processes of d i f f e r e n t i a t i o n . That the main rock types of the stock pass from under-saturated, through saturated to oversaturated types (fl&. 5ai seems to suggest that the thermal b t r ^ l e r of the system b l 0 2 - nahlblC^ - S A I 0 I O 4 (Bowen 1937) has been crossed. T l l l e y (1957) suggests, however, that the thermal b a r r i e r which prevents the transition from syenite to granite in toe experimental melts '"say be "Inoperative i n a natural melt where i t s composition Is modified by the presence of nafic components, and fu r t h e r , notable d i s p a r l t In v o l a t i l e content". The trend from undersaturated to ovsrseturatec" magaa can ce accompli oh ed by various processe of e l i t e ; t i o n of undersaturated map-mas, louring, c r y s t a l l i z a t i o n of trie magma, the residual l i q u i d can be enriched i n s i l i c a by reaction or inc.* of reaction of th© l i q u i d with minerals that have c h a r a c t e r i s t i c s of lneon- gruent melting,, T l l l e y (1957) suggests that " p r e c i p i t a  t i o n of mwgnetlte In the place of aenerlna w;-uld tnrow excess s i l i c a i n t o the l i q u i d i f t h i s oxide pnase f a i l e d to resorb". The formation of hornblende by reaction of l i q u i d with pyroxene w i l l also r e s u l t i n s e t t i n g free of 53 quartz, arid thus the possible quantity of a .auartzose d i f f e r e n t i a t e w o u l d be a u g m e n t e d (Bowes, 1923, p, 9 0 ) , The change o f t h e SlOg c u r v e ( f i g . 5a) from tae u n d e r - s a t u r o t e d Into the s a t u r a t e d areas of the diagram corresponds with the a p p e a r a n c e of hornblende as the m a j o r mafic mineral. The 5 l 0 o c o n t e n t Increases toward t h e ovc-rsaturated area w i t h ino easing amojot of hornblende (compare p o i n t s 3 end C with the corresponding, modes i n T a b l e I ) . Thus, the formation o f hornblende may hove played a signifies.*at role I n s i l l c a t l o n of t h e r e s i d u a l l i q u i d . The foregoing processes w i l l a f f e o t t h e compostlon of the f i n a l r e s i d u a l l i q u i d s and t h e corresponding rocks, b u t can only cause d i ffer t - n tia11 on i f r e l a t i v e movement b e t w e e n c r y s t a l s and residual l i q u i d i s brought about by p r o c e s s e s such a a c r u v l t y separation or " f i l t e r p r c s s l r g " . C e r t a i n o x i d e s o f the h o r n b l e n d e - c l o t I t e p y r o x - e n l t e show s i g n i f i c a n t d e p a r t u r e s from t h e emooth v a r i a t i o n curves ( f i g s , 4 and 6 ) . T h i s s o r t of departure i s a t t r i b u t e d by bowen il92a) to c r y s t a l a c c u m u l a t i o n . I f t h e p o r p h y r l t i c hornblende monzonite i s to be f o r m e d from t h e a u g l t e - b l o t i t e m o n z o n i t e by t h e s e p a r a t i o n of components o f b l o t i t e - h o r n b l e n d e p y r o x e u l t e alone, the r a t i o of volumes of the p y r o x e n l t e to components of t h e m o n z o n i t e 54 should be approximately 1 to 3 (calculated fro a f i g . 4 ) . Migration of water and a l k a l i s can a l s o c o n t r i  bute to d i f f e r e n t i a t i o n of a. -magma. Water w i l l diffuse and distribute i t s e l f in a magiaa so that the chemical potential of the water Is the sane throughout the magma chamber. Al k a l i s and certain metals w i l l co-ordinate with the water and w i l l be concentrated In the regions of lowest pressure and temperature (Kennedy, 1355)# A hypothetical sequence of events that i s prop osed to explain the development of rock zones, i s Illustrated d l a g r a a a t l c a l l y In Figure 10, The processes of v o l a t i l e and a l k a l i d i f f u s i o n and of f r a c t i o n a l c r y s t a l  l i z a t i o n , which effected differentiation of the parent magma, were Interrupted by Intrusion. During the f i r s t ©tag© of Intrusion ( f i g , 10a) the upper and outer parts of the magsaa which formed a cupola of a larger zaagiaa chamber, cooled very rapidly to form the fine-grained auglte-blotite monzonite. .Effects of the hot magma on the relatively cool country rocks were to produce a zone of cordlerlte h o r n f e l s In c e l l t i c roc'<s, garnetiferous quartz d l o r i t e at the contact with p e l i t i o rocks, end a "bleached" zone In quartzite. V>ith the Feldspar Pyroxene F i g u r e 10a Figure 10c Figure 10b LEGEND A p l i t s Pink quartz monzonite porphyry P o r p h y r i t l c hornblende monzonite Monzonite porphyry Hornblende-blotite pyroxenlte A u g i t e - b i o t l t e monzonite Country rocks Present l e v e l of erosion Figure 10. Diagrammatic sketch showing a h y p o t h e t i c a l development of rock zones of the Mount Brenner 3tock„ I n i t i a l emplacement of the aagaia, temperature and pressure gradients were e s t a b l i s h e d i n the magma chamber* Water and alkali® tended to d i f f u s e In the magma and they grad u a l l y c o l l e c t e d and became concentrated In the upper and outer regions of the cupola, the regions of lowest pressure and temperature. Large potassium feldspars c r y s t a l l i s e d from the higaly f l u i d sikali-rleh magma thus produced. Early formed pyroxene c r y s t a l s sank In the fluid l i q u i d and tended to accumulate oa the more viscous magma Immediately"below this region* The magma below t h i s region was a l s o beginning to c r y s t a l l i z e , and processes e f f e c t i n g d i f f e r e n t i a t i o n of the magma were constantly taking place, that l e , d i f f u s i o n of volatlles and of alkalis, and s i l i c a t i o n of r e s i d u a l fluids by the mechanisms previously mentioned (See page 52 ), and gravity se-pa ration, Following c o n s o l i d a t i o n of the outer find up er parts of the cupola, the saagiaa continued to surge upward, and i t intruded the augite-blotlte monzonite (fig* 10b), The accumulated pryoxene and the large orthoclase crystals, that l i e immediately below tue outar zone, were dragged up and spread along the wall of the chamber by the upward, and outward force of the i n t r u d i n g magiaa. This cryatal 57 aiush l a t e r cooled to form toe hornblende-biotite pyroxen- It® and the monzonite porphyry* The newly Intruded magma continued to c r y s t a l l i z e inward i n a zone which la now the porphyritlc hornblende aoazonlts (th© intermediate zone), 'Che medium- to coarse-grained texture of this zone suggests that the magma cooled ©ore slowly than d i d the auglte-blotite monzonite, p o s s i b l y because the country rooks were preheated by the e a r l i e r stag© of i n t r u s i o n , The mobile core continued to surge upward, C r y s t a l s suspended In the f l u i d were aligned by magma-tic flow. The magma reacted with the p a r t i a l l y consolidated Inner margin of th© Intermediate zone to form the t r a n s i t i o n zone of glomeroporphyrltio hornblende monzonite, Th© lenses of monzonite porphyry, which occur In some places at the contact between the core and the porp~.y r i t i c horn blende monzonite, may have formed by processes s i m i l a r to those which formed the main band of monzonite porph..<ry» The core cooled slowly to produce the coarse-graiced pink quarts monzonite porphyry ( f i g . lOo), Fracturing occurred before the core was complete ly consolidated. I t ef f e c t e d a sudden release of pressure, and a sudden escape of v o l a t l l e s from the remain ing l i q u i d . These changes would b r i n g about a 58 s i g n i f i c a n t r i s e of the temperature of c r y s t a l l i z a t i o n of the remaining l i q u i d , and possibly would ease a . "sweep ing-out" a c t i o n of i n t e r s t i t i a l f l u i d s * Consequently, tne p a r t i a l l y fluid core crystallized r a p i d l y to form the zone of fine-grained leuco-quartz monaonlte, and the f l u i d s which f i l l e d f r actures cooled r a p i d l y to form aplite dykes (fig* 1 0 c ) . Some of the c r y s t a l mush of the core was swept i n t o f r a c t u r e s , where I t consolidated to form pink quartz asonzonite porphyry dykes* ouafftar?/ of emplacement. Crystallization n and D i f f e r e n t i a t i o n The Mount Brenner stock has intruded folded rocks of S i l u r i a n to bower Cretaceous age. The regional structural trend i a modified In the v i c i n i t y of the atock so that bed a are generally conformable with the lntrunlve contact. That the stock was eatplaced by f o r c e f u l i n j e c t i o n of a f l u i d magma ia indicated by ( 1 ) near vertical planar and linear primary flow structures that have an o v e r a l l continuity and concentric pattern} ( 2 ) structures in the country rock that warp around the stock; (3) bedding i n shales that turns upward to conform with the contact of the a t o c k j and ( 4 ) slip cleavages and piety cleavages that 59 occur along the outer contact z 5ne. Piecemeal atoping was of only minor Importance during, emplacement of the stock. Chemical sad atlneraloglcal v a r i a t i o n s of the rock zones have a systematic trend toward *'petrov.e?jy *• residua system*1, from th® periphery of the stock to the core, This v a r i a t i o n i s consistent with the concept of d i f f e r e n t i a t i o n of an auglte-blotlte monzonite parent magma as It crystallized from the wa l l s of the magma chamber inward. The following, hypothetical sequence of events i s proposed to explain the development of the rock zones, A r i s i n g f l u i d magma, possibly guided by the regional structure, made room f o r I t s e l f mainly by shouldering aside the country rocks. The upper and outer portions of the magma c h i l l e d to form a " s h e l l " of f i n e  grained auglte-biotlte monzonite. D i f f e r e n t i a t i o n of the magma was co n t r o l l e d by gravity separation of mafic minerals and by d i f f u s i o n oi' volatile®, ahd a l k a l i e s . The magma continued to surge upward, and intruded the partially consolidated outer " s h e l l " . Inclusions of the " s h e l l " were engulfed and carried, along with the rising soag.aa. Pyroxene c r y s t a l s and large orthoelase c r y s t a l s that l i e in the magma just below the augite-blotite 50 monzonite, were dragged up and spread against the side of the chamber by the upward and outward force of the Intruding magma* The c r y s t a l muah l a t e r cooled, to form the horoblende-biotite pyroxenlte and the monzonite porphyry. The magma proceded to crystallise inward In the intermediate zone. The mobile core continued to surge upward. The saagma reacted with the p a r t i a l l y consolidated Intermediate zone and formed the gloioero- porpayrltic hornblende monzonite. The core cooled slowly to produce pink quartz monzonite porphyry. Fracturing took place before the lower part of the stock wan completely consolidated. J o i n t s formed to accommodate stresses due to magmatio pressure form below and to cooling-and contraction of the rock. The fracturing effected a sudden release of pressure and of volatiles from th© remaining l i q u i d . As. a result of these changes, the partially fluid core crystallized r a p i d l y to form the zone of fine-groined lauco quartz monzonite, and the fluids that f i l l e d fractures cooled rapidly to form a p l l t e dykes. The e f f e c t s of wall rock contamination are insignificant compared to the overall ©volution of rock zones by the processes of magmatie d i f f e r e n t ! a. tlon. 51 TBLlOGRaPHLY Balk, R. 1937s Structures In Igneous :ioc -r; G&ol. Soc, Aiaer., •.'lem. 5. B a l k , 3, and Gr o u t , ?.F. 1934; S t r u c t u r a l Study of The Snowbank "took; Geoi, Soc, Amer, B u l l , , V. 45, p, 621*635, Bostock, H.S, 1957; "'ukon T e r r i t o r y ; Geol* Surv,- Canada, '%m» 284, 1948J Physiography of The Canadian C o r d i l l e r a , with Special Reference to Th® Area Korth of the f i f t y - F i f t h P a r a l l e l ; . Geol. Surv. Canada, tte-n. 247, Bowen, h.b. 1922s Sahavlour of Inclusions i n Igneous har.aa; Jour, Gaol, v. 30, p, 513-570. 1928: The .Evolution of the Igneous Hocks; Princeton U n i v e r s i t y Press. ~1937; Recent high-temperature research on s i l i c a t e s and I t s s i g n i f i c a n c e i n Igneous c e o l o g g j Amer, -Jour. S c i . , v. 3 3 , p. 1-21, Buddlngton, A . F . 1959$ Granite ampl. cement with S p e c i a l Reference t o >.-orth -merica| Geol, Soc. Amer,, B u l l . , v* 70, p. 671-747. C o c k f l e l d , W.ia, l i l h : S i l v e r - l e a d Deposits of" the L i t t l e Twelvemile Area; Geol, Surv, Canada, hum. nept., lj>lu, pt. a, p , 1 and p t , B, p , 1-17. 1913: Explorations In the O g i l v i e iiangej Geol. Surv,, Canada, Sum, Rept., 1919, ft. A, :.. 1, and pt. a, P. 1 - 7 . Co aptan, a » a « C a l i f o r n i a ; Geol. .3sc. ' s s r , C u l l . , v, 5; p. 9-44, Deer, w»A,, owl©, »t,A, , s r d -usf. uar, J, 1932; - t . >l , ^ 1.. «\ J t » 1 ' v., b o m : >n; i O j . ,w-P, r ? a n a n d o, ; * r l . Emmons, H.C, 1953$ S e l e c t e d f e t r o g e n l c " e l s s t l o a s h l p s 3f fl«glociaee| S e o l . Coo* America, 4© A, 52, Fra^l, Ganther 1354$ ." nxc1.:..on e c n ..elz " l u j a t n c n rn' h JC„! .p^rierten ^ iu; a n r . n a ' J i J i ' i r ; " ' 11 IC ap-r" . n I .>,/r "' o- p y r j . : 1 I . •, ; c l ,« m** i u _ a - 0 n t I> c &' t r r n i - i . ' t r • a , Cc and a* I t , ; a a . , a*. J ? , r. 71-13.1* C i t e d i n - l l t u r c ^ C ^ p , . O e l l a t l y , C.O, 19£'!" ; a p - l i n e a tC i l c ^ p r r Trlr t s t l -i* * I n <,•:,,«.! in*-, ' /<. ^  ' ee f r,T i r ; a i " l c , du , 1 1 a r a . i c ; ' , i s r , ro r . : 3 l . , v, 2 2, C ^ I - ^ c . Craen, L.9.. and '.oddick, J»«, 1 9 6 ? $ D a w s o n , Larson C r e e k , a i d \ &h „ r < i up- rt">fj, u'can T e r r i t o r y ; O o o l . a. 1.., ' a a, „ nfcr '"-7, G r o a t , C.f. 1937J Gaol. 3oc, &mvm B u l l . , v* 4a p. 1531. 1345; S c a l e Models o f S t r u c t u r e s delated t o 8» t ; v o l i the j Aser. -Tour, C o l . , v . 2 4 3 A , p # 260-2C4. H a r l o f f , 0 . 1927$ Za--al S t r u c t $re i n P.lagiocla ; :-aida.a:.# Gaol. - . e d e a e - H i . , v , 2, p. 9J-114. ali bard , a. J, 19-55$ i i In of f. >«e ia- u -el U7.<r - ^  • >cryets and tr«olr coring in fctr> t - sit ; ..r, Tour. v. 2"^, y. -2 63 H i l l s , E.O. 1963d Elements of S t r u c t u r a l Geology| Wiley and bona, Inc,, Kew York. Hutchinson, R.'-I, 1956; Structure and Petrology of Enchanted Rock Befool1th, Llano and Gellesple counties, Texas., Geol, 3oe, Amer* B u l l . , v» 67, p* 763-dQS. Jahns, R»H# 1943*. Sheet Structure i n f r a n i t e s s I t s Origin and 'ses as a .ieauure of G l a c i a l Erosion i n Hew England,, Jour. Ceol., v. 51, p. 71-98. Kennedy, G.C. 1955: Some Aspects of th© Role of Water i n Rock a e l t s j Seol. aoc. Amerloa, Spec, paper 62, p» 4d9~504» V.I, The Place of P e g m a t i t e s In the Process of Form ing, a Granite : i a a a i f j L'Vovskor G e o l . Obsch., .-Ilneralogy C o l l . , No, 5* P* 99-112» Cited In . H i l l s , 1953, p» 3-67. Martin, h,a, 1951s, Structure of the Granite Massif of :7*la aanvllle j-banchs, North-West France,, Geol. Soc, London, . , four,, v» 108, p i 311-331, Kuznetsov, 1951J '1941i Deformation in The Inte r v a l Mt. L y e l l - l t . Whit- nay, C a l i f o r n i a Ceol. 3oc. nmerieu, '-hull., v. 52, p.. 1001-10o4, , aieConnell, R»G. 1903s Prospecting i n O g i l v l e Range; Ceol, Surv,, Canada, Sum. Rept, f o r 1903 (1904) and Ana, n e p t . , v. XV, c t . A, p, 34-42, ^oble, J.A. 1952$ Evaluation of C r i t e r i a f o r the For c i b l e I n t r u s i o n of aagmaj Jour. Geol. v. c'i, p. 34-57, P i t c a i r , Vi,C, and :?ead, U.K. 1953s Contact aotamorphe.-la i n Relation to -fanner of Emplacement of the. Granites of "'onepal, Ireland} Jour, Ge.il., V. 71, no, 3, p . 261-296, 54 Keesor, -J.K. 1958s Be war Creek Map-Area With Special Ampha-Is on The White Greek 3atholith» British Columbiaj Geol. Surv* Canada, S5»«a, 292. Roes, J* V. 1957$ Combination Twinning; i n Plagloclase Feld soars; Amer, Jour, S o l , , v. 255, p.~ 650-655, Schermerhorn, L,J .Q, 1956: The Granites of franscoso (Portugal)j a study of a i e r o c l i n l z a t l o n ; Amor, four, 3ci», v, 264, P. 329,' Terapelman-Sluit, P.J, 1965s Tombstone rdver (116 B/7) -''lap Area; Report of A c t i v i t i e s s F i e l d , 1964, Geol, Curv, Canada, Spec. Paper 65-1 . 1966: Tombstone River (116 B/7) tep Area; Report of A c t i v i t i e s : Field, 1 9 5 5 , Geol* Survey. Canada, Spec, Paper 65-1, Thornton, C.P, and T u t t i e , 0,F, I960: Che aistry of Igneous Rocks, I, S i f f e rent i a t i o n Index; Amer, -Tour, S c i , , v* 664-504, T l l l e y , C.£. 1957: Problems of A l k a l i Rock Genesis; Quart, Jour, of the Geol. Soc. London, v, 113, p. 323-357. Turner, F.J. and Verho>gen, J. 1950s Igneous and Matamorphic Petrology, 2nd ed., ^ c y r a w - K i l l , ti&w fork. T u t t i e , 0 . ? , 1952s Optical Studies on A l k a l i Feldspars; Amer, -Jour, S c i , , owen v o l * , p, 553-567. 

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