Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Geology of the Mount Breakenridge area, Harrison Lake, B.C. Reamsbottom, Stanley Baily 1971

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1971_A6_7 R34.pdf [ 10.43MB ]
Metadata
JSON: 831-1.0053175.json
JSON-LD: 831-1.0053175-ld.json
RDF/XML (Pretty): 831-1.0053175-rdf.xml
RDF/JSON: 831-1.0053175-rdf.json
Turtle: 831-1.0053175-turtle.txt
N-Triples: 831-1.0053175-rdf-ntriples.txt
Original Record: 831-1.0053175-source.json
Full Text
831-1.0053175-fulltext.txt
Citation
831-1.0053175.ris

Full Text

THE GEOLOGY OP THE MOUNT BREAKENRIDGE AREA, HARRISON LAKE, B.C. by STANLEY B. REAMSBOTTOM. B.Sc. A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE, IN THE DEPARTMENT OF GEOLOGY. We accept t h i s thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA. SEPTEMBER 1971. In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date °\. \\. 11 i i ABSTRACT. The met amorphic rocks of the Breakenridge and Cairn Needle Formations are correlated with the Upper Paleozoic and Mesozoic (Jurassic) s t r a t a r e s p e c t i v e l y . Those of the Chilliwack Group - Peninsula Formation range in age from Upper Paleozoic to Lower Cretaceous. A gneissic granodiorite on Mount Breakenridge i s cored by a younger (Early Tertiary) porphyritic auartz d i o r i t e . The Scuzzy granodiorite (Upper Cretaceous) i s the main plutonic rock of the area. Between the Jurassic and Mid-Cretaceous the formations were folded into northwest trending antiforms and synforms. Three phases of f o l d i n g are recognised. Major f a u l t s were produced in Mid-Cretaceous time. Contemporaneous with the fold i n g the rocks were migmatized and r e g i o n a l l y metamorphosed to form a kyanite-a i l l i m a n i t e f a c i e s series in which the metamorphic grade increases r a p i d l y from South to North. The mineral assemblages i n p e l i t i c gneisses are considered to have approached equilibrium. The bulk composition of these gneisses may not only have controlled the presence of s t a u r o l i t e but also, through the opaque minerals present, the f s 2 » of the .coexisting f l u i d phase. Extreme gradients in f l u i d phase composition (X C O 2 ) are demonstrated to have existed during the metamorphism of closely associated calc -i i i s i l i c a t e and dolomitic limestone. An episode of contact metatnorphism, which produced andalusite and s i l l i m a n i t e bearing schists was associated with the emplacement of the Scuzzy f l u t o n . ^U. Cretaceous;. i v ACKNOWLEDGEMENTS; The writer wishes to acknowledge the f i e l d assistance and valuable advice rendered by C.T. Duffy and R.L. Wheeler U970). RiL.: Wheeler also supplied computer programmes to process s t r u c t u r a l data. The assistance of the Geological Survey of Canada and W.W.Hutchison i n p a r t i c u l a r have been invaluable throughout this study. The constructive c r i t i c i s m , advice and d i r e c t i o n of r r o f . H.J. Greenwood (U.B.C.) i s greatly appreciated by the writer. The author was supported during the study by a National Research Council, post - graduate scholarship. V CONTENTS. Page INTRODUCTION 1 Previous work 1 MAJOR LITHOLOGIC UNITS 12 BREAKENRIDGE FORMATION 10 Description and Petrography .11 Grey Gneiss* 11 Amphibolites. .•.•••••••••...••••••••••••.••••12 P o l i t i c Gneiss 13 Migmatites. •• ...15> Skarn. • 17 CAIRN NEEDLE FORMATION "..18 Description and Petrography. 19 Conglomerate. 19 Cale s i l i c a t e s 20 Limestone. 21 (iarnet horneblende schist and amphibolite. . . ...22 P o l i t i c schists 22 Meta basic igneous granulite 21* PEGMATITES 2$ Mineralogy • 26 ' CHILLIWACK GROUP OR PENINSULA FORMATION 28 Description and Petrography 28 Meta rudites. ..28 P o l i t i c schists 29 Calc s i l i c a t e s . • • 30 v i IGNEOUS ROCKS 32 MOUNT BREAK ENRIDGE PLUTONIC COMPLEX #2 Gneissic granodiorite quartz d i o r i t e 33 Mineralogy .33 Epizonal core 35 Mineralogy, • 35 SCUZZY PLUTON 3& The marginal phase of the pluton underlying Cairn Needle, 36 Mineralogy. » 37 OTHER IGNEOUS ROCKS 38 CORRELATION AND AGES OF ROCK UNITS 1*0 SEQUENCE OF EVENTS kk STRUCTURE. k*> Minor f o l d a x i a l surface data 57 Minor f o l d a x i a l / data. 57 Lineations and mineral grain alignments. 66 Lineations, minor f o l d axes and axialsurfaces i n Chilliwack Group or Peninsula Formation s t r a t a . .73 Note on strained pebbles i n the meta conglomerate of the Cairn Needle Formation • 7^ Major structure 76 RELATIONSHIP BETWEEN METAMORPHISM AND DEFORMATION. ...77 MET AMORPHISM &h Regional met amor phi sm. &k Possible reactions. 91 v i i Opaque minerals* 92 Met amorphism of calc s i l i c a t e s and limestones. .....99 Contact metamorphism. 106 Petrogenetic grid. 107 SUMMARY. 110 CONCLUSIONS. 113 FURTHER WORK. 113 REFERENCES. ^^k APPENDIX . 115 v i i i L I S T O P F I G U R E S Figure Page 1 Geological sketch map of Mt. Breakenridge area . •• 5 Gross sections A - A , B - B, E - F - G 7-9 2 Important s t r u c t u r a l elements of Mt. Breakenridge area. k& 3 Equal area p l o t of 107 poles to f o l i a t i o n and compositional l a y e r i n g . •••• ..50 k Histogram of Height width r a t i o s of Fg minor f o l d s . 5^ 5 Histogram of Height Width r a t i o s of F c minor f o l d s . «»56 6 Equal area p l o t of 17 poles to ax i a l planes of F B minor f o l d s . 59 7 Equal area plot of 20 poles to a x i a l surfaces of F c minor f o l d s . 61 8 Equal area plot of 19 F 1 3 minor f o l d axes. .63 99 Equal area plot of 25 axes of F q minor f o l d s . ..65 10 Representative l i n e a t i o n s of Mt. Breakenridge area. .....68 11" Equal area plot of 137 mineral grain alignments from the Mt. Breakenridge area. 70 Figure Page 12 S l i p l i n e s of F c f o l d s , Mt, Breakenridge area ..72 13 Relationship between metamorphic r e c r y s t a l l i z a t i o n and f o l d i n g episodes i n the Mt. Breakenridge area. •••79 1l| The d i s t r i b u t i o n of p o l i t i c metamorphic index minerals which define the zones of metamorphism of the Mt. Breakenridge area. 83 15 A. F. M. diagrams of p o l i t i c assemblages. C h l o r i t e to s i l l i m a n i t e grade. 86 1b Schematic chemical p o t e n t i a l diagram of the system F e - S - O - T i C ^ showing phases i n equilibrium with ilmenite. 0*9k 17 Phase r e l a t i o n s i n the system FeO-Alp^-SiC^-HgO -02 as functions of f and T.( 10kb.total P Q The s t a b i l i t y f i e l d of s t a u r o l i t e and magnetite i s shown cross hatched. •......•• »»97 18 Isobaric ( Ikb. ) T-X c o diagram f o r reactions in metamorphosed s i l i c e o u s dolomites. The s t a b i l i t y f i e l d of the assemblage for3feerit^"trem0lifee""calcite;is: shown ruled 102 19 Calculated T-X diagram f o r the CaO-AlgO^-SiOg -f^O-CO,, system at 5kb. t o t a l pressure. The s t a b i l i t y f i e l d of the assemblage c a l c i t e quartz z o i s i t e grossular i s shown r u l e d , lOlj. 20 Potrogenetic g r i d showing P.T. conditions of regional and contact metamorphism ••••109 X LIST OF TABLES. Table. Page 1 Major l i t h o l o g i c units. 3 2 Grey gneiss of Breakenridge Formation. • 115 3 Amphibolites of Breakenridge Formation 117 14 P e l i t i c gneiss of Breakenridge Formation • ....120 5 Migmatites of Breakenridge Formation. . . . . . . . . .125 6 Calc s i l i c a t e s of Cairn Needle Formation .127 7 Limestone of Cairn Needle Formation. ... , 128 8 Garnet hornblende schist and amphibolite of Cairn Needle Formation. 129 9 P o l i t i c schists of Cairn Needle Formation 1 30 10 Pegmatites of Breakenridge and Cairn Needle r Formations. •• .13^ 11 Meta rudites and pelites of Chilliwack Group or Peninsula Formation. 135 12 Calc s i l i c a t e s of Chilliwack Group or Peninsula Formation. 137 13 Mount Breakenridge Plutonic Complex. Gneissic granodiorite quartz diorite 138 J\l± Mount Breakenridge Plutonic Complex. Gneissic quartz di o r i t e . liiiO 15 Epizonal core of Mount Breakenridge Plutonic Complex. . .1^1 16 Scuzzy Pluton. The marginal phase of the Pluton underlying Cairn Needle. 1U3 17 Style elements of folds. 51 x i LIST OP PLATES. Plate Page 1 Orey gneiss of Breakenridge Formation with well developed Fg mega s t r a i n s l i p f o l i a t i o n , ....Ifyb 2 btriped amphibolite of Breakenridge Formation with well developed Fq minor f o l d s , ••••• Il|b 3 V Kyanite gneiss of Breakenridge Formation which has been i s o c l i n a l l y folded ( Fg ) .,.1fy8 i | jMigmatite of Breakenridge Formation with boudinaged pegmatite. ................. • .1lij.8 5 Sheared conglomerate at base of Cairn Needle Formation. ...........................1^0 6 Calc s i l i c a t e pod and symmetrically zoned layers within Cairn Needle Formation. • . . . . . . . . •150 7 White c r y s t a l l i n e limestone and red calc s i l i c a t e of Cairn Needle Formation. . ..152 8 " Folded and boudinaged e a r l i e r pegmatite within rusty schist of Cairn Needle Formation. . . . . . . . . 1 5 2 9 Three phases of f o l d i n g i n striped amphibolite of Breakenridge Formation. • 1 10 Kyanite s t a u r o l i t e garnet gneiss of Breakenridge Formation. • .15U 11'" Kyanite s t a u r o l i t e schist from Cairn Needle Formation, ••••I 5° 1 2 Kyanite garnet gneiss of Breakenridge Formation, 15© x i i Plate Tage. 13 S i l l i m a n i t e garnet schist of Cairn Needle Formation. ..... ..158 11+ S i l l i m a n i t e garnet schist from Cairn Needle Formation. • •••••••••••13>8 15 Folded and symmetrically zoned calc s i l i c a t e of Cairn Needle Formation. ••.••••••••••••••160 16 S i l l i m a n i t e p a r t i a l l y pseudomorphed by muscovite. Contact aureole of Scuzzy Pluton, •••160 17 Andalusite p a r t i a l l y pseudomorphed by muscovite. Contact aureole of Scuzzy Pluton. •.,162 1b Platey aggragates of muscovite a f t e r alumino s i l i c a t e s of contact aureole of Scuzzy Pluton. 162 1 INTRODUCTION. The geology of the Mount Breakenridge region, Harrison Lake, B.C., was completed on a reconnaissance scale i n the summer of 1968. (Roddick and Hutchison, 1969). It i s a mountainous region situated between l a t i t u d e s i|9°35' and i|9°50' and longitudes 121°U5' and 122°00'. (N.T.S. 92H/12W and 92H/13WJ. Logging roads on the east side of Harrison Lake and the Riv-Tow Marine f e r r y , make the area r e a d i l y accessible. The present study, which involved f i e l d mapping at the scale of 1:2^00 i n the summer of 1970, was designed to expand on the work of Roddick and Hutchison and r e l a t e the metamorphism, structure and plutonism of the area to the geological h i s t o r y of the Southern Coast Mountains. PREVIOUS WORK. Roddick and Hutchison (1969), described the broad s t r u c t u r a l , metamorphic and plutonic character of the area. Santer (1969) studied the petrology of the p e l i t i c gneisses north of Mount Breakenridge. The metamorphic rocks of the Stokke Creek pendant, immediately to .vthe west of the area, were described by Roddick (1965). 2 MAJOR LITHOLOGIC UNITS. The major rock types are l i s t e d i n Table 1, and t h e i r d i s t r i b u t i o n i s shown in the sketch map of Figure 1 . No f o s s i l s have been found i n the rocks and sedimentary "way-up" structures are lacking. I t has therefore been t e n t a t i v e l y assumed that s t r u c t u r a l l y deeper horizons are older. Thus the u n i t s l i s t e d i n Table 1 are l i t h o l o g i c , tectonic u n i t s , not s t r a t i g r a p h i c u n i t s . Attempts to correlate these rocks with others in surrounding areas are consistant with t h i s general view of the structure, but the present data are inadequate for proof. TABLE 1« MAJOR LITHOLOGIC UNITS AGE AND EQUIVALENT METAMORPHIC ROCKS IGNEOUS ROCKS TECTONISM. METAMORPHISM L. T e r t i a r y U. Cretaceous M. Cretaceous L. Cretaceous U. Paleozoic Ju r a s s i c U. Paleozoic (Custer and Skagit gneiss) Peninsula Fm. Chilllwack Gp. Cairn Needle Fm. conglomerate Breakenridge Fm. Andesite dykes. Porphyritic qtz d l o r l t e continued u p l i f t of Mt. Breakenridge Scuzzy Pluton Contact metamorphism Dunite, P e r i d o t i t e Faulting and retrograde met amor phi sm. Gneissic granodlorite on Mt. Breakenridge Folding and Deep seated regional metamorphism U p l i f t Figure 1 Geological sketch map of Mt. Breakenridge area, LEGEND IGNEOUS ROCKS Quartz andesine porphyry and quartz d i o r i t e . Scuzzy granodiorite-quartz d i o r i t e Mt. Breakenridge gneissic granodiorite quartz d i o r i t e Dunite METAMORPHIC ROCKS Chilliwack Group - Peninsula Formation calc - s i l i c a t e p o l i t i c s c h i s t , g r i t and conglomerate. + 4- + Cairn Needle Formation conglomerate p e l i t i c s c h i s t , calc - s i l i c a t e , gt. hb. sch. limestone meta - igneous gr a n u l i t e . Breakenridge Formation grey gneiss amphibolite striped amphibolite p e l i t i c gneiss • Fault N.B. See f o l d out i n back cover f o r l o c a l i t i e s c i t e d i n the text. CROSS SECTIONS . A - A* B - B» P - G For Legend see Figure -A* 9 BREAKENRIDGE FORMATION The Breakenridge Formation consists of the following rock types, l i s t e d in order of greatest abundance. 1) Homogeneous grey gneiss, i i ) ' Amphibolite. i i i ; j y e l i t i c gneiss. Iv) Migmatite. v) Minor skarn. The areal d i s t r i b u t i o n of these unite i s shown i n Figure 1. The formation i s considered to be a mixture of metavolcanic and metasedimentary s t r a t a . Amphibolites are presumably metavolcanic, while grey gneiss, which In i t s homogeneous or i n c l u s i o n r i c h form Is decidedly igneous.in aspect, may be the metamorphic equivalent of graywacke. The l l t h o l o g i c a l persistence of bands of grey gneiss, which can be traced for several miles, coupled with the aasociatic of migmatites, (which are possibly p a r t i a l l y derived from mixtures of volcanics and graywacke), with the obvious metasedimentary units are strong arguments in favour of a metasedimentary o r i g i n for the migmatites. Kalsbeek U970) on the basis of detailed chemical and petrograpbic data, considers a similar migmatitic terrane i n South - West Greenland to be the r e s u l t of metamorphism of mixtures of graywacke and basic volcanic rocks. 11 DESCRIPTION AND PETROGRAPHY. 1) Grey Gneiss:-Most of the orealrenridge formation i s homogeneous grey g r a n o d i o r i t i c gneiss. Migmatites are commonly developed i n zones between grey gneiss and amphibolite u n i t s . Within the gneiss-migmatite t r a n s i t i o n zone the gneiss contains many mafic inclusions which impart an igneous "xenolothic" aspect to the u n i t . Plate 1 i s t y p i c a l of much of the gneiss. MINERALOGY. The mineralogy and approximate modes of the gneisses studied are shown in Table 2. The modes were estimated by eye. The anorthite content of the plagioclase i s shown in brackets. They are medium grained allotriomorphic granular b i o t i t e - auartz - plagioclase gneisses, with or without muscovite, garnet and microcline. The composition of the plagioclase (determined on f l a t stage by the _L'r a method; varies from specimen to specimen. It ranges from An 10-3U* Zoning i s absent. Myrmekite commonly develops at the boundary between intergranular microcline and a l b i t i c p l a g i o c l a s e . A pronounced f o l i a t i o n or l i n e a t i o n defined by b i o t i t e or lensoid augen of quartz and feldspar i s c h a r a c t e r i s t i c of the gneiss. Deformation lamellae and s t r a i n extinction in ouartz, kink bands i n b i o t i t e , and granular b l a s t i c polygonization of quartz and feldspar are features common to a l l . extinction angle measured i n sections cut perpendicular to 'a' . 12 11) Amphlbolites:-Two v a r i e t i e s of ampbibolite are present in the Breakenridge Formation. The main type i s homogeneous with well defined f o l i a t i o n , while within these are more schistose v a r i e t i e s with a c h a r a c t e r i s t i c striped appearance. Plate 2 i s t y p i c a l of the l a t t e r v a r i e t y . MINERALOGY. The mineralogy and approximate modes of amphlbolites studied are shown in Table 3. The modes were estimated by eye. Common mineral assemblages include;-a) Hornblende- Plagioclase- Qtz (Amphibolite) -b; Hornblende- Plagioclase- B i o t i t e - Qtz (Bi o t i t e - Ampbibolite; c) Hornblende- Plagioclase- B i o t i t e - Garnet- Qtz (Bi o t i t e -- Garnet - Amphibolite) di Hornblende - Plagioclase- Diopside- C a l c i t e - Qtz (Banded Amphibolite) Epidote i s common to a l l assemblages and occurs either as a primary mineral or as l a t e veins, or the r e s u l t of s a u s s u r i t i z a t i o n of plagioclase. The plagioclase composition as measured in grains i _ ' r a, varies from specimen to specimen, ranging from An 30-i|U« Zoning i s absent. In Table 3 the anorthite content of the plagioclase i s shown in brackets. The f o l i a t i o n or s c h i s t o s i t y i s defined by b i o t i t e , hornblende or l e n t i c u l a r ouartz and feldspar. Garnet occurs in knots associated with hornblende and surrounded by quartzo -feldspathic 'depletion' haloes. I t also occurs as i d i o b l a s t i c or 13 xenoblastic c r y s t a l s which p o i k i l o b l a s t i c a l l y include quartz, magnetite and c h l o r i t e . Banded c a l c i t e diopside v a r i e t i e s are rare and consist of pale oands [jg cm. wide; of c a l c i t e , diopside and plagioclase, which alternate with dark bands of hornblende, diopside and p l a g i o c l a s e . 111; P e l i t i c gneiss. From Figure 1, i t i s apparent that the p e l i t i c gneisses are a minor constituent of the breakenridge formation. However they play a c r i t i c a l r o l e i n the elucidation of the s t r u c t u r a l and metamorphic h i s t o r y of the area. These medium to coarse grained gneisses are distinguished by bladed blue-grey kyanite, coarse garnet, and s t a u r o l i t e s with well formed interpenetration twins. The most continuous horizon pinches and swells from a few feet to t h i r t y feet as i t i s traced around the antiformal and synformal structures. Traced to i t s extremities on the limbs of folds the unit appears to pinch out completely, f l a t e 3 shows i s o c l i n a l l y folded gneiss within the main horizon. Closely assosciated with these gneisses are muscovite r i c h hornblende bearing s t a u r o l i t e kyanite gneisses. Hornblende c r y s t a l l i z e s within the f o l i a t i o n i n spectacular rosette form. MINERALOGY. The mineralogy and approximate modes of 29 p e l i t i c gneisses studied i s shown in Table l\. The modes were estimated by eye. The anorthite content of the plagioclase i s l i s t e d in brackets. Specimens i n which c h l o r i t e appears to be t e x t u r a l l y stable are indicated by (S), opposite c h l o r i t e . The mineral assemblages noted a l l include muscovite and quartz and most include c h l o r i t e . a; Kyanite. b; B i o t i t e - Garnet. c; B i o t i t e - Garnet - S t a u r o l i t e . dj B i o t i t e - Garnet - Kyanite. e; B i o t i t e - S t a u r o l i t e - Kyanite. f ; Garnet - S t a u r o l i t e - Kyanite. g; B i o t i t e - Garnet - S t a u r o l i t e - Kyanite. h) B i o t i t e - Garnet - S t a u r o l i t e - Kyanite - Hornblende. The main assemblage i s g; as 20 of the 29 rocks studied contain those minerals. A polished specimen from the H- series which contained assemblage g) was found to contain hematite, ilmenite and magnetite In that order of abundance, while the polished specimen of the graphite bearing assemblage d; (specimen 2hr\\/l0) contained ilmenite i n addition to the abundant graphite. Textural features of these rocks are discussed f u l l y i n the section r e l a t i n g deformation to metamorphism. 15 i v ; Migmatlte:-In Figure 1, migmatites are not d i f f e r e n t i a t e d from grey gneiss, but they occur i n zones between the grey gneiss and s amphlbolites. The p e l i t i c gneisses and skarn i n v a r i a b l y occur within these migmatitic horizons. Plate h i s of boudinaged pegmatite within the migmatites of the Breakenridge formation. Though the following types are recognised, the dominant one i s - r e g u l a r l y to i r r e g u l a r l y banded gneiss. a) Grey gneiss with abundant mafic i n c l u s i o n s . b; Amphibolite with leucogneiss screens and i n c l u s i o n s . c) Grey gneiss with ptygmatic veins and disconnected " i n t e s t i n a l " qusrtzo - feldspathic lenses, d; Banded to i r r e g u l a r l y banded gneiss composed of l e u c o c r a t i c b i o t i t e gneiss, amphibolite and conformable or cross cutting pegmatites. e; Speckled hornblende gneiss. Pale ouartz plagioclase - b i o t i t e gneiss with i r r e g u l a r porphyroblastic c l o t s of hornblende which give the rock a speckled appearance. f) Medium grained grey gneiss with d i s t i n c t i v e magnetite porphyroblasts. 16 •MINERALOGY., The mineralogy and approximate modes of nine specimens studied are shown in Table Modes were estimated by eye. Four specimens are from the gneiss dome to the East, while the rest are from the cirque I4. miles S.E. of Cairn Needle. The mineralogy of the le u c o c r a t i c and melanocratic portions of specimen 206/70 are l i s t e d separately. Gneisses of the dome are banded and have a medium grained hypidiomorphic granular texture. B i o t i t e or Hornblende define the f o l i a t i o n and the l i n e a t i o n . Mafic bands of hornblende and b i o t i t e alternate with quartz and feldspar. Other essential minerals include garnet and muscovite. Some banded gneisses within the ciraue S.E. of Cairn Needle are similar to those of the dome but contain intergranular microcline myrmekite. The plagioclase (as determined on grains 'r a) i s homogeneous, but varies from specimen to specimen. This variation ranges from An 28-IJ.IJ., though most are around An 30. The microfabric of the boundary between mafic and l e u c o c r a t i c portions of the migmatites exhibit features commonly noted at 'leucosome - melanosome' boundaries. (Mehnert 1968 p. 60). The leucogneiss i s in places convex towards the concave shaped part of the melanosome. Within t h i s l e u c o c r a t i c portion are trains of b i o t i t e and hornblende which appear to have been l e f t behind as the leucosome 'advanced' to incorporate the 17 melanosome. These textural features may be the r e s u l t of a migmatitic f r o n t . A more l i k e l y explanation, however, i s cited in' Ramsay (1967 P 382). When a single plane surface separating two rocks of d i f f e r e n t v i s c o s i t y i s deformed in such a way that the p r i n c i p a l compressive s t r a i n i s p a r a l l e l to the boundary surface, the surface i s folded. As deformation progresses the folded surface develops a series of broad rounded antiforms (competent rock) separated by synforms (incompetent rock) which <have a tighter cross section and a c h a r a c t e r i s t i c "pinched" appearance. The small scale structures noted in the above migmatites may be explained by t h i s model. vi ) Sksrn;-Spectacularly coloured calc - s i l i c a t e pods and boudins are associated with the migmatites and p e l i t i c gneisses of the Breakenridge formation. These skarns have a high CaO, FeO content r e f l e c t e d i n their mineralogy which consists of orange andradite, bright green hedenbergitic pyroxene, green epidote and auartz. (Specimen 19^/70.- Table 5"). In addition they are cut by pegmatites with large c r y s t a l s of hornblende and epidote. 18 CAIRN NEEDLE FORMATION. The areal extent of the Cairn Needle Formation i s shown in Figure 1. The formation can be traced out of the map area to the southeast and i s also encountered i n the v a l l e y of Stokke Creek immediately West of the map. The group consists of;-10 Conglomerate. II) Calc - S i l i c a t e s c h i s t s . III) Limestone. iv) Garnet Hornblende Schist 8nd Amphibolite. v) P e l i t i c s c h i s t s . vi) Meta - basic igneous g r a n u l i t e . The rusty weathering p e l i t i c and garnet hornblende schists; form the bulk of the metasedimentary part of the group, as the calc s i l i c a t e s , limestone and conglomerates are comparatively rare. The meta igneous portion forms a broad band half - to - one mile wide which extends from Hunger Creek in the north, southwards along the v a l l e y of Big S i l v e r Creek for 12 miles. The depositional environment of these rocks varied between t e r r e s t i a l ( as indicated by the conglomerate) and shallow water marine ( as indicated by the limestone). 19 DESCRIPTION AND PETROGRAPHY. 1) Conglomerate;-The boundary between Breakenridge and Cairn Needle formations, in the v i c i n i t y of Cairn Needle i s marked by six thin conglomeratic horizons which range in thickness from 3 to 1$ f e e t . Intercalated with the conglomerates are c a l c - s i l i c a t e schists and kyanite gneiss. The lowermost conglomerate can be traced for three miles from the headwaters of Butter Creek into the Northeast t r i b u t a r y ' o f Stokke Creek. The conglomerates have g r a n i t i c (granite - granodiorite) quartz - d i o r i t i c , amphibolitic and q u a r t z i t i c c l a s t s , set in a dark medium grade matrix of b i o t i t e garnet amphibolite. The pebbles have been strained into pancake e l l i p s o i d s having t h e i r long axes sub-parallel to the antiformal axes of the region. These meta-conglomerates are l i t h o l o g i c a l l y similar to those described by Roddick (196£j i n the Snowcap Lake and Stokke Creek pendants. A t y p i c a l sheared meta-conglomerate i s shown in Plate 5. 20 11) Calc - S i l i c a t e s : -Banded calc - s i l i c a t e s are confined to the lowermost portion of the formation. They are rusty weathering with thin bands a l t e r n a t e l y r i c h in garnet, diopside, hornblende, epidote and plagioclase. rods of banded calc - s i l i c a t e gneiss appear to have been t e c t o n i c a l l y rotated producing a spectacular 1 mega -snowball' e f f e c t . ^Plate 6). MINERALOGY;-The mineralogy and approximate modes of f i v e calc -s i l i c a t e s sectioned i s shown i n Table 6. Modes were estimated by eye. The mineral assemblages are as follows;-a) Plagioclase - Epidote - Hornblende - Garnet,- Qtz. b; r l a g i o c l a s e - Epidote - Hornblende - Garnet - Diopside - Qtz. c) r l a g i o c l a s e - C l i n o z o i s i t e - Diopside - Tremolite - Qtz. They a l l contain quartz, sphene, mica and retrograde c h l o r i t e . The garnet of specimens I1I4I/7O, and 1^6/70 i s Pyrope ^ Grossular.^ Almandine . The detailed mineralogy, and possible o r i g i n of banding in these calc s i l i c a t e s i s f u l l y discussed in the section on metamorphism. 21 The granular polygonal or decussate texture of these rocks i s i n d i c a t i v e of s t a t i c r e c r y s t a l l i z a t i o n either during an interkinematic phase of the regional metamorphism or during the contact metamorphism which accompanied emplacement of the Scuzzy Pluton. i i i ; Limestone:-One t h i r t y foot wide horizon of banded black and white c r y s t a l l i n e limestone with i n t e r c a l a t e d garnetiferous calc -s i l i c a t e was found immediately to the West of Hunger Creek. The medium grained white limestone has a s c h i s t o s i t y defined by white mica while t i n y yellow brown fl e c k s of weathered o l i v i n e give the rock a spotted appearance. The coarse red green garnet diopside calc - s i l i c a t e s have been folded and boudinaged. Plate 7 shows the white limestone with associated red c a l c - s i l i c a t e . MINERALOGY. The mineralogy and eye-estimated modes of the meta -limestones studied i s shown in Table 7. The laminated grey limestone i s e s s e n t i a l l y c a l c i t e with minor magnetite. The white c r y s t a l l i n e limestone was o r i g i n a l l y dolomitic as indicated by the mineral assemblage, f o r s t e r i t e , tremolite and c a l c i t e . r e l i t i c impurities include muscovite and retrograde c h l o r i t e . The garnet of the associated calc - s i l i c a t e s i s Grossularyg AlmandineqY Andradite^ . 22 i v ; Garnet Hornblende Schist and Amphibolite. Garnet hornblende schists form a major portion of the Cairn Needle formation. They are unlike the striped amphibolites of the Breakenridge formation as they are rusty weathering and are in t e r c a l a t e d with the calc - s i l i c a t e s , limestones and p e l i t i c s c h i s t s . MINERALOGY. The mineralogy and approximate modes of the rocks sectioned are shown i n Table 8. They are characterised by assemblages of b i o t i t e garnet and hornblende or b i o t i t e and hornblende. The plagioclase i s homogeneous, and varies from specimen to specimen within the range An32 - Anjjlj.. The r e l a t i o n s h i p of the garnet to the well defined s c h i s t o s i t y v a r i e s . On the one hand i t may i d i o b l a s t i c a l l y overprint the s c h i s t o s i t y , while on the other, sieve textured p o i k i l o b l a s t s surrounded by quartzo - feldspathic "depletion" haloes are wrapped around the s c h i s t o s i t y . v; P e l i t i c Schists:-The p e l i t i c schists of the Cairn Needle group are fine to medium grained rusty weathering rocks. Their red colour i s due to the weathering of abundant p y r i t e . 23 The areal d i s t r i b u t i o n of these sc h i s t s i s widespread, rusty weathering p e l i t e s outcropping as far South as Hornet Creek and beyond, and Westwards within the valley of Stokke Creek. The schists envelope the domal structure on Clear Creek. MINERALOGY. The mineralogy and approximate modes of twenty two p e l i t i c schists sectioned i s shown in Table 9. In addition to the assemblages l i s t e d below, the majority of the specimens contain muscovite and quartz. In Table 9, specimens with stable c h l o r i t e are indicated by (S) opposite c h l o r i t e . aj C h l o r i t e - b i o t i t e - garnet. b/ Garnet - b i o t i t e - gedrite. c; S t a u r o l i t e - garnet - b i o t i t e - c h l o r i t e . d) Kyanite - s t a u r o l i t e - garnet - b i o t i t e . e; S i l l i m a n i t e - s t a u r o l i t e - garnet - b i o t i t e . f ; S i l l i m a n i t e -. garnet - b i o t i t e . g; S i l l i m a n i t e - andalusite - garnet - b i o t i t e . T e x t u r a l l y the rocks have a well developed s c h i s t o s i t y or folded s c h i s t o s i t y , defined by either muscovite, b i o t i t e , f i b r o l i t e , s i l l i m a n i t e or opaques. Porphyroblasts Include garnet, s t a u r o l i t e , kyanite, s i l l i m a n i t e and c h i a s t o l i t e . S i l l i m a n i t e may have c r y s t a l l i z e d during the regional and contact metamorphic events, while andalusite i s r e l a t e d to the contact event. The s i l l i m a n i t e in schistose rocks commonly occurs as f i b r o l i t i c needles c l o s e l y associated with b i o t i t e . Within the contact aureole of the Scuzzy Pluton, i t occurs as robust c r y s t a l s with diamond shaped cross section and good (010) cleavage. Andalusite, with well developed c h i a s t o l i t e cross occurs singly or i n association with s i l l i m a n i t e . There ts good tex t u r a l evidence which shows a l l stages of replacement of the alumino - s i l i c a t e s within the aureole by platey aggregates of muscovite and t i n y needles which are pos s i b l y f i b r o l i t e . The r e l a t i o n s h i p between metamorphic r e c r y s t a l l i z a t i o n and deformation i s discussed in the appropriate section. vi) Meta Basic Igneous Granulitet-The elongate unit of metamorphosed basic igneous granulite consists of garnet hornblende, and b i o t i t e cummingtonite granulites and minor hornblendite. This unit i s extensively veined by gneissic garnetiferous pegmatite while at i t s Southern extremity i t i s associated with bronzite p e r i d o t i t e which may be of a younger age. PEGMATITES: Pegmatites are major constituents of both the Breakenridge and Cairn Needle formations. The pegmatites of the migmatites of the Breakenridge formation have been previously mentioned, while Plate 8 amply demonstrates th e i r abundance within the rusty weathering Cairn Needle formation. The pegmatites can be c l a s s i f i e d into three types on the basis of features noted in the f i e l d . i ) Thin qusrtzo - feldspathic layers which are either conformable with the f o l i a t i o n or transgressive and hence ptygmatically folded. i i ) Thick coarse grained pegmatites which have been folded or boudinaged. (see Plate 8) i i i ) Transgressive coarse grained pegmatites some of whi are compositionally or t e x t u r a l l y banded. The f i r s t two types have been involved in the deformational events of the area while the transgressive pegmatites apparently post-date the youngest n o n - b r i t t l e deformation. MINERALOGY:-The mineralogy and approximate modes of the pegmatites sectioned Is shown i n Table 10. Modes were estimated by eye. Plagioclase composition was determined by sections -L'r to a and i s shown in brackets. E a r l i e r Pegmatite:-The mineral assemblage common to e a r l i e r pegmatites a) Quartz - plagioclase - muscovite - b i o t i t e - epidote + garnet + c h l o r i t e . The plagioclase i s unzoned and varies from specimen to specimen within the range Anj^ - An-|2 • Accessories include garnet }apatite and zir c o n . Microscopic textures of the e a r l y pegmatites indicate that they have been subjected to complex deformation. A l l the features noted i n the gneisses with which they are associated, i . e . - stra i n extinction and deformation lamellae of auartz, bent plagioclase twins, kink bands i n mica and granular mortar texture of ousrtz are common. 27 Later Pegmatite The mineral assemblage of the " l a t e r " pegmatites i s ; -bj Quartz - plagioclase - microcline - muscovite - b i o t i t e -garnet. Thus the l a t e r pegmatites contain potassium feldspar and generally have a true pegmatitic aspect. Micrographic intergro-wths of cuartz and a l k a l i feldspar are common. The plagioclase i s Ang . 28 CHILLIWACK GROUP OR PENINSULA FORMATION:-The rocks on the northeast shore of Harrison Lake between Big S i l v e r and Stokke Creeks include;-I) Meta r u d i t e s . G r i t s and conglomerates, i i ; P e l i t i c s c h i s t s , i i i ) Calc - s i l i c a t e s . To the northeast these rocks are i n f a u l t contact with grey gneiss of the Breakenridge formation. DESCRIPTION A N D PETROGRAPHY;-1' Meta r u d i t e s . G r i t s and sheared conglomerates are found on the lake shore immediately northwest of Big S i l v e r Creek. These conglomerates, though containing f i n e grained ' g r a n i t i c pebbles are unlike those of the Cairn Needle formation. G r a n i t i c , white and dark ouartzite or chert pebbles are set. in a fine micaceous matrix. Though many of the pebbles have been flattened and elongated within the plane of s c h i s t o s i t y some r e t a i n t h e i r roundness. The meta g r i t s have c l a s t s of feldspar and opalescent blue quartz i n a matrix of pale green c h l o r i t e and quartz. i i j P e l i t i c s c h i s t s : -Pale green ouartz mica s c h i s t , garnet schist and rusty weathering sulphidic schists form the major portion of rocks on Harrison Lake shore. MINERALOGY. The mineralogy and approximate modes of 8 meta -rudites and p e l i t e s sectioned ere shown i n Table 11. The anorthite content of plagioclase i s shown i n brackets and stable c h l o r i t e i s indicated with (S). The following mineral assemblages which i n addition include muscovite and quartz are noted, a; C h l o r i t e , b) B i o t i t e - c h l o r i t e , c; Garnet - b i o t i t e - c h l o r i t e . The g r i t s have porphyroclasts of quartz and saussuritized plagioclase set i n a schistose matrix of c h l o r i t e 8nd granular ouartz. Well defined pressure shadows of ouartz have developed at the margins of the c l a s t s . The p e l i t e s have a pronounced s c h i s t o s i t y defined by c h l o r i t e , micas, quartz and feldspar. In some specimens a strain s l i p cleavage has developed sub - perpendicular to t h i s s c h i s t o s i t y . I d i o b l a s t i c garnets with marginal pressure 30 shadows include st r a i g h t t r a i n s of ouartz inclusions which are interpreted as an even e a r l i e r s c h i s t o s i t y . These garnets have been extensively pseudomorphed by retrogressive c h l o r i t e . i i i ) Calc - s i l i c a t e s . Two thick horizons ( 500') of calc - s i l i c a t e have been mapped. Common mineral assemblages, and approximate modes are shown i n Table 12, and include garnet - a c t i n o l i t e -plagioclase + epidote * b i o t i t e + muscovite. Randomly oriented sheaves of a c t i n o l i t e and bright red garnet vPyrope ^ Grossular ^6 Almandine <\Q .) set i n a white matrix of granular quartz and feldspar ensure that t h i s unit i s r e a d i l y mappable. In places i t displays a crude banding; garnet - hornblende layers alternating with quartz -plagioclase l a y e r s . In some outcrops thin garnetiferous layers which have been i n t r i c a t e l y folded can be traced for several f e e t . Microscopic examination shows blue green a c t i n o l i t e laths and i d i o b l a s t i c garnets set in a granular polygonal matrix of quartz and plagi o c l a s e . The plagioclase i s unzoned and varies from specimen to specimen within the range An 20 ~ • A n • W h e r © developed, the s c h i s t o s i t y i s defined by micas and c h l o r i t e , while b i o t i t e porphyroblasts 8re 31 sometimes kinked. Thus though te x t u r a l features are i n d i c a t i v e of s t a t i c r e c r y s t a l l i z a t i o n the rocks have had a complex deformational h i s t o r y . IGNEOUS. ROCKS. The d i s t r i b u t i o n of plutonic igneous rocks i n the area i s shown in Figure 1. Two major " g r a n i t i c " bodies are recognised. i ; The plutonic complex underlying Mount Breakenridge and r e l a t e d rocks, i i ; The Scuzzy Pluton. In addition minor ultramafic rocks and andesitic dykes have been found i n the area. MOUNT BREAKENRlDGJi PLUTONIC COMPLEX. The plutonic complex which makes up most of Mount Breakenridge consists of grey medium grained gneissic hornblende b i o t i t e d i o r i t e (Hb<Bi) and granodiurite, with 10/» rounded to elongate mafic inclusions which are r i c h in b i o t i t e and hornblende. The core of the complex i s occupied by younger "high l e v e l " porphyries and quartz d i o r i t e s . In plan view the core i s elongate ( 1.5 x 7 miles) and i s composed of pink quartz b i o t i t e andesine porphyry marginally zoned by mesocratic p o r p h y r i t i c quartz d i o r i t e . These epizonal intrusions have small rounded xenoliths of f i n e to medium grained g r a n i t i c and d i o r i t i c rocks. 33 Gneissic Granodiorite - Quartz D i o r i t e . The most s t r i k i n g feature of the gneissic granodiorite i s i t s well developed f o l i a t i o n and l i n e a t i o n which are most pronounced towards the contact with the gneisses of the breakenridge formation. In places t h i s f o l i a t i o n i s sub-concordant tothat of the gneisses, making i t d i f f i c u l t to mark a d e f i n i t e contact between gneissic plutonic rock and Breakenridge gneiss. Further, b i o t i t e r i c h mafic inclusions within the pluton have been strained into cigar - shaped e l l i p s o i d s with long axes approximately p a r a l l e l to the l i n e a t i o n of the region. To the east on Big S i l v e r Creek, the granodiorite i s in sharp contact with a g n e i s s i c , mesocratic, garnet bearing hornblende - b i o t i t e quartz d i o r i t e ( Hb>Bi;. This marginal zone of quartz d i o r i t e i s in abrupt concordant contact with v e r t i c a l l y dipping gneisses on Big S i l v e r Creek. The long axes of stretched inclusions are p a r a l l e l to l i n e a t i o n s in the gn e i s s. MINERALuGY. the mineralogy and approximate modes of seven rucks sectioned i s shown i n Table 13. They range from granodiorite to quartz d i o r i t e ^ Bi>Hb). Texturally they are allotriomorphic granular with a f o l i a t i o n defined by b i o t i t e , 3k hornblende and quartz feldspar lenses. These lenses often have long axes p a r a l l e l to b i o t i t e grain alignments. The plagioclase i s homogeneous and varies from specimen to specimen within the range An 1 Q - An . In specimen 369/70 the plagioclase of the hornblende b i o t i t e i n c l u s i o n was An -^ g, while that of the host rock was An yj . The boundary between inclusions and host exhibit features similar to those found i n the i n c l u s i o n r i c h Breakenridge gneisses. In f i n e d e t a i l quartzo - feldspathic host i s convex towards the hornblende - b i o t i t e i n c l u s i o n and would appear to be invading and p a r t i a l l y a s s imilating the xenolith. Specimen 313/70 has glomero - p o r p h y r i t i c aggragates of b i o t i t e , epidote and quartz which may represent remnants of o r i g i n a l inclusions i n the igneous rocks. Specimen 311/70 has textural features i n d i c a t i v e of l a t e stage deformation and r e c r y s t a l l i z a t i o n ; i ) Plagioclase twins have been bent, i i B i o t i t e has been kinked, i i i ) Hornblende has r e c r y s t a l l i z e d in a xenoblastic manner and includes granular quartz c r y s t a l s . The mesocratic f o l i a t e quartz d i o r i t e K Hb>Bi; on Big S i l v e r Creek shows the same effects of shearing and r e c r y s t a l l i z a t i o n . The mineralogy and approximate modes of two sections studied are shown in Table i l l . Note that the 35 plagioclase I An ^ J though extensively saussuritized i s mure basic than the adjacent igneous rocks. This basic margin was emplaced contemporaneously with the b i o t i t e quartz d i o r i t e s although absolute r e l a t i o n s h i p s cannot be determined as any c h i l l e d margins which may have existed at t h e i r contacts have since been destroyed by shearing. Epizonal Core:-The elongate core of the Mount Breakenridge plutonic complex has the following features of epizonal i n t r u s i o n s . i ) P orpbyritic to sub - porphyritic texture. i i ) M i a r o l i t i c c a v i t i e s f i l l e d with quartz, c a l c i t e and black b i o t i t e . These c a v i t i e s are common i n rocks of porph y r i t i c aspect but also occur in medium grained quartz d i o r i t e s . MINERALOGY. The mineralogy and approximate modes of seven specimens sectioned i s shown in Table 15. In the porphyries quartz, b i o t i t e and hornblende, i n addition to complexly zoned plagioclase, are common phenocrysts. The groundmass i s composed of f i n e grained granular quartz, muscovite, plagioclase and a l k a l i feldspar. The plagioclase has a 3b maximum va r i a t i o n from An ^ - An within specimen 367/70. Medium grained d i o r i t e s have plagioclase of a similar composition but no a l k a l i f eldspar. Generally the b i o t i t e content i s greater than hornblende. Detailed contact r e l a t i o n s h i p s of the epizonal core to the f o l i a t e exterior of the complex are mostly obscured by snow. However one specimen of b i o t i t e gneiss from the contact contained nodules of green globular spinel (pleonaste) and polygonal ouartz. These nodules are possibly the product of contact metamorphism by the epizonal core. I t i s concluded : that the epizonal core post dates the gneissic exterior of the complex. SCUZZY PLUTON. The Marginal Phase of the Pluton underlying Cairn Needle. The hornblende b i o t i t e ouartz d i o r i t e { Hb>Bi ) on Cairn Needle i s part of the large Scuzzy Intrusion. The body also crops out on Stokke Creek and becomes part of intrusions mapped by Roddick U9fc>5>) . Plutons in Stokke Creek include coarse melanocratic d i o r i t e and f o l i a t e ouartz d i o r i t e very si m i l a r to that on Cairn Needle. Around Cairn Needle the contact between rusty schists and the quartz d i o r i t e dips steeply to the northwest. The pluton i s transgressive to structures within the s c h i s t s , but has a. pronounced marginal f o l i a t i o n which was produced during emplacement. In the course of emplacement.this f o l i a t i o n has also been drag folded. The contact zone of the Scuzzy Pluton at the head of Big S i l v e r Creek has a similar f o l i a t i o n which gives way to a t y p i c a l h o l o c r y s t a l l i n e texture deeper within the i n t r u s i v e . MINERALOGY. The mineralogy and estimated modes of rocks sectioned are shown in Table 1b. The plutonic rock on Cairn Needle has a f o l i a t e d hypidiomorphic granular texture. Bent plagioclase twins and st r a i n extinction i n ouartz point to the shear which probably accompanied emplacement. The d i o r i t e on Stokke Creek however has no f o l i a t i o n and has c r y s t a l l i s e d with good hypidiomorphic granular texture. The Scuzzy Pluton to the east of Cairn Needle i s predominantly granodiorite (Roddick and Hutchison 1969i. The rocks of the marginal f o l i a t e d phase of this pluton are r i c h e r in dark minerals and s l i g h t l y more basic than those of the i n t e r i o r . 38 OTHER IGNEOUS ROOKS. On the Eastern limb of the antiform which crops out on Big S i l v e r Creek, two types of basic igneous rock are found in t e r c a l a t e d with the gneisses, amphlbolites and s c h i s t s . A dyke-like body of hypersthene - augite diabase occurs within the grey gneiss and amphibolite of the Breakenridge formation. The areal extent of the i n t r u s i o n i s unknown but i t s contacts are sub - p a r a l l e l to the gneissic f o l i a t i o n . A fresh medium grained dyke of bronzite - augite -p e r i d o t i t e was found on P i r Creek, within the metamorphosed mafic igneous rocks of the Cairn Needle formation. Rounded o l i v i n e c r y s t a l s are p p i k i l i t i c a l l y included i n large c r y s t a l s of pinkish bronzite. The bronzite has a pronounced s c h i l l e r texture produced by f i n e p a r a l l e l inclusions of opaques, and augite i s marginally altered to hornblende. Thus the rock has the texture of an orthocumulate with cumulous augite and o l i v i n e set in large intercumulus c r y s t a l s of bronzite. On Hunger Creek a p a r t i a l l y metamorphosed dunite pod outcrops on s t r i k e with a well defined lineament. Olivine has been metamorphosed to pink weathering t a l c which has c r y s t a l l i z e d along i r r e g u l a r fractures in the brown weathering dunite. 39 Andesine porphyry dykes cut the Breakenridge Plutonic complex. These East - West trending dykes have a trach y t i c texture with phenocrysts of o s c i l l a t o r y zoned intermediate plagioclase set in a f e l t e d mass of feldspar l a t h s , i n t e r s t i t i a l chlorophaeite, and disseminated magnetite and p y r i t e . CORRELATION AND AGES OP ROCK UNITS: Breakenridge Formation The formation i s l i t h o l o g i c a l l y s i m i l a r to the Custer gneiss (McTaggart and Thompson 1967), and the Skagit gneiss (Misch 1966). The former i s the migmatitic equivalent of the rermian Hozameen group and the l a t t e r the tentative equivalent of the Upper Paleozoic Chilliwack Group. Cairn Needle Format!on Although i t contains minor limestone and p e l i t e the Cairn Needle formation lacks the abundant chert and greenstone to be a direct l i t h o l o g i c equivalent of the Hozameen group. Rocks within the Hope Map Sheet (Monger 1970) which contain conglomerates with g r a n i t i c clasts , include;-a) Ladner Group. L-M J u r a s s i c . b) Kent Formation. U. Jura s s i c . c) Dewdney Creek Group. U. Ju r a s s i c . d) Peninsula Formation. L. Cretaceous, ej Jackass Mountain Group. L. Cretaceous. In the Ashcroft area (Duffel and McTaggart 195*2; there are g r a n i t i c conglomerates at the base of the Jurassic, and also within the Lower Cretaceous Brew group. The description of conglomerates within the Snowcap Lake and Stokke Creek pendants, described by Roddick (1965) in the P i t t Lake map sheet, which have been assigned to the pre - Jurassic Twin Islands formation, i s similar to the conglomerates i n the Cairn Needle formation. Thus, generally the age of the formation i s problematic but i t may contain rocks of Jurassic Age. Chllllwack Group -- Peninsula Formation rocks. The c l a s t i c rocks on the northeast shore of Harrison Lake are l i t h o l o g i c a l l y s i m i l a r to the Peninsula Formation (L. Cretaceous). The p e l i t i c and calc - s i l i c a t e units may be eouivalent to older Chilliwack group s t r a t a . I Monger 1970). Igneous Rocks; Scuzzy Pluton;-Recent K -as follows. Ar age dates on the Scuzzy Pluton are B i o t i t e K - Ar age = 70 + I4. m.y. Hornblende K - Ar age = 72 + 1+ m.y. Ages on the Spuzzum Pluton are;-Hornblende K - Ar 73 ^ ^ m.y. B i o t i t e K - Ar 7k ± k m.y. (Hutchison 1971 pers. comm These data indicate that the Scuzzy Intrusion i s presumably a le u c o c r a t i c core within the Spuzzum quartz d i o r i t e , and that, providing they r e f l e c t time of emplacement the Scuzzy phase i s no younger than the Spuzzum phase. flreakenrldge - Plutonic complex: The te x t u r a l features of the gneissic plutonic complex on Mount Breakenridge suggest that i t was In place during the waning stages of regional metamorphism and deformation, and i s thus older than the Scuzzy which post -dates these events. The fresh epizonal core i s probably equivalent to younger T e r t i a r y high l e v e l intrusions such as Hells Gate Pluton. This has been dated at 35 m.y. (Baadsgaard, Polinsbee and Lipson, 1961), and more recently with both b i o t i t e and hornblende giv i n g ages of I4.I4. + 3 m.y. and 1+0 + 1+ m.y. r e s p e c t i v e l y . (Hutchison 1971 pers. comm.J Uther Igneous Rocks: The p a r t i a l l y metamorphosed dunite may have been emplaced during mid - Cretaceous f a u l t i n g . The bronzite p e r i d o t i t e i s similar to rocks 7 mil Northwest of Hope.lAho 195cJ. These rocks are possibly Cretaceous in age. hh SEQUENCE OF EVENTS. a) There i s no st r u c t u r a l evidence to indicate that the Breakenridge Formation was subjected to major deformation and metamorphism prior to the deposition of the Cairn Needle formation. The presence of conglomerates in the l a t t e r formation however may point to a minor di s c o n t i n u i t y between the two formations. b) The main formations underwent deep seated deformation and metamorphism between the e a r l i e s t Jurassic and Mid -Cretaceous time. During the late stages of t h i s episode of metamorphism and f o l d i n g the gneissic portion of the Mount Breakenridge Plutonic complex was emplaced. c) U p l i f t , with the development of a major thrust f a u l t between Breakenridge formation gneisses, and Chilliwack group and Peninsula formation rocks probably occurred in the Mid - Cretaceous as t h i s f a u l t may be t h e northern e x t e n s i o n of the Mid - Cretaceous Shuksan Thrust. (Misch 1971). Minor retrogressive metamorphism accompanied the thrusting. The outcrop pattern of the u l t r a b a s i c rocks, in conjunction with the well defined f a u l t i n the northern map region, may define amid - cretaceous zone of c r u s t a l weakness, along which the u l t r a b a s i c s were emplaced or intruded. dj The i n t r u s i o n of the Scuzzy Pluton and accompanying contact metamorphism occured in the Upper Cretaceous. e; Early T e r t i a r y intrusion of the Epizonal Core of the Mount Breakenridge Plutonic complex. I f t h i s i n t r u s i o n was emplaced to within 1+ km. from the surface, and the Scuzzy Intrusion was emplaced at pressures low enough to s t a b i l i z e andalusite which i s found in i t s contact aureole ( approx. 5 k b = 1 7 km), the rate of u p l i f t from Upper Cretaceous ( 7 0 m.yrs.) to Lower T e r t i a r y (1+0 m.yrs.), was about 2 - 3 km/million years, or 1 cm. every 3 or k ye f ) Intrusion of Andesite dykes. STRUCTURE. The l i t h o l o g i c a l units which were h e l p f u l i n defining the gross regional structure have been shown i n Figure 1. Of these the p e l i t i c u n i t s , grey gneiss bands and amphlbolites within the Breakenridge group, and the conglomeratic horizons within the Cairn Needle group proved to be the most useful marker horizons. The important s t r u c t u r a l elements recognised in the area, are shown i n Figure 2. The major antiforms and synforms have a predominantly northwest - trend and plunge. A least squares f i t to 265 poles to f o l i a t i o n and compositional l a y e r i n g of gneisses has a pole of 329 / 56 . (Computations were c a r r i e d out on the I.B.M. 360/67 U.B.C. Programme used was "Main Program Testing P i f i t and Stddev" by R.L. WHEELER. Princeton U n i v e r s i t y ) . The g i r d l e formed by poles to f o l i a t i o n s measured around the area i s shown i n Figure 3- This g i r d l e has a pole of 315/ 1+0-60 . In addition to the gross regional structure which i s defined by l i t h o l o g y , i n d i v i d u a l minor f o l d patterns within the l i t h o l o g i c units indicate three phases of minor f o l d i n g . Evidence for the e a r l i e s t phase i s scanty but i s deduced from refolded f o l d r e l a t i o n s h i p s such as shown in Plate 9. The style elements of the three f o l d i n g episodes V4 FIGURE 2 : Important s t r u c t u r a l elements of Mount Breakenridge 8rea. KEY: 50 s t r i k e and dip of f o l i a t i o n antiform synform •^T* fa u l t ^ .94 Figure 3 Equal area plot of 157 poles to f o l i a t i o n and compositional l a y e r i n g . Contours 1ft 3% 5% So 51 TABLE 17 STYLE ELEMENTS OP FOLDS 'B ro o t l e s s , i s o c l i n a l . s u b - i s o c l i n a l limbs sometimes sheared o f f . open to chevron similar s i m i l a r s i m i l a r , but.- where layer anisotropic more concentric t i g h t curved hinge broadly curved hinge sharp hinge straight to broadly broadly curved curved limb limb straight limb moderately harmonic harmonic HINGE LINE may be short and straight or long and curved folded compositional folded comp, laye r i n g with axial layering s c h i s t o s i t y with axial s c h i s t o s i t y mainly folded comp. lay e r i n g ( s c h i s t o s i t y ) with l i t t l e a x i a l s c h i s t o s i t y . 52 are l i s t e d i n Table 17. In addition to these elements of fo l d s t y l e , a measure of the r e l a t i v e asymmetry of the folds can be obtained by measuring the r a t i o of the perpendicular height between adjacent antiformal and synformal hinge areas, to the perpendicular width between adjacent a x i a l traces, as viewed down the f o l d axis. Height / width data c o l l e c t d f or F B and F Q folds are shown i n the histograms of Figures k and 5. Fg data have a mean of 2.56 with a standard deviation of 1.05. The 68# confidence i n t e r v a l i s 1.51 to 3.62. F c data have a mean of 1.1+3 with a standard deviation of 1 .36. The 68% confidence i n t e r v a l i s 0.08 to 2.79. (Computation carried out on I . B . M . 360/67 U.B.C. with prograrr?me"xMEAN, S, single HISTOGRAMS" by R.L.Wheeler, Princeton U n i v e r s i t y ) . I t i s evident that the modes are not s i g n i f i c a n t l y d i f f e r e n t within the 68/0 confidence i n t e r v a l . The wide spread of H/W r a t i o s within each f o l d generation i s doubtless the r e s u l t of the wide angular variations between surfaces being folded (compositional lay e r i n g , s c h i s t o s i t y ) and the a x i a l surface of the "re f o l d i n g " f o l d . (Ramsay, 1967 p.539). Thus fh e wide range of H/W r a t i o s which are t h e o r e t i c a l l y possible within any one fo l d i n g episode make these r a t i o s unreliable c r i t e r i a to use in the c l a s s i f i c a t i o n of successive generations of f o l d s . FIGURE U, Histogram of Height/Width r a t i o s of Fg minor f o l d s mode = 2.56 I Histogram of Height/width r a t i o s of P Q minor f o l d s . mode = 1.U3. 5b 3o 15 15 10 FIG 5 H W MINOR FOLD AXIAL SURFACE DATA. F^ :- The axial surfaces of F A folds generally l i e within the l o c a l f o l i a t i o n . Fg :- The angular variation between f o l i a t i o n and Fg axial surface varies between 2 and 19 . The p a r t i a l girdle formed by the poles to the axial surfaces of F 0 f o l d s (Figure 6; indicates that these folds have been refolded about an axis of 311 /kO , which is sub - p a r a l l e l to the regional F Q axes. F^ The poles to a x i a l surfaces of F c f o l d s are shown in Figure 7. Their northwest subvertical trend compares favourably with the r e g i o n a l l y defined a x i a l surfaces. MINOR FOLD AXIAL DATA:-F :- Very l i t t l e a x i a l data exists for F. f o l d s . F A pl o t of 19 F 3 minor f o l d axes i s shown in Figure 8. There i s a maximum trend and plunge at 315 / l|2 . Figure 6 Equal area p l o t of 17 poles to a x i a l planes of Fy. minor folds . Contours $% 10?fe 15/* . 5 9 06 Figure 7 Equal area plot of 20 poles to a x i a l surfaces of P Q minor f o l d s . Contours 5> 10£ 20% . 01 FIGURE 8; Eoual area plot of nineteen F minor f o l d D axes. Contours. $% 10ft 20% 30ft 63 Figure 9 Equal area p l o t of 25 axes of F minor f o l d s C Contours 10% , 15% , 30% , 65 P c :- A plot of 25 F A minor f o l d axes i s shown i n Figure 9. There i s a maximum trend and plunge at 316 / 37 . The high d i r e c t i o n a l s t a b i l i t y between the Fg and F Q f o l d axes would appear to indicate that the successive f o l d i n g episodes were v i r t u a l l y homoaxial. LINEATIONS AND MINERAL GRAIN ALIGNMENTS. The map vFigure 10 J shows representative l i n e a t i o n s measured in the area. A plot of 137 mineral grain alignments (Figure 11; has a greater spread than f o l d axial data, but th maximum trend end plunge at 328 / 1x1 i s comparable with the minor f o l d axial maxima and the general structural trend of the region. The absence of a pronounced g i r d l e of l i n e a t i o n s would appear to indicate that these grain alignments are mostly sub - p a r a l l e l to the l a t e r F Q f o l d axes. Further, the pronounced homoaxiality between Fg and F^ precludes the d i f f e r e n t i a t i o n on a regional scale, between Fg and F Q l i n e a t i o n s . However, a few l i n e a t i o n s which have been refolded by F minor f o l d s have been found in the f i @ l d . The manner of r e d i s t r i b u t i o n of the e a r l i e r l i n e a t i o n s i s a FIGURE 10: Representative l i n e a t i o n s of Fiount Breakenridge Area. KEY: Trend and olunge of l i n e a t i o n Fault. FIGURE 11. Equal area plot of 137 mineral grain alignments from the Mount Breakenridge area. Contours 1ft 5ft 10ft 15ft FIGURE 12 : S l i p l i n e s of F f o l d s , Mount Breakenridge ,Area. KEY: B = F c f o l d axes. A.P. = a x i a l plane of F Q minor f o l d . R.P. = r o t a t i o n path of folded l i n e a t i o n s . S.L. =,slip l i n e . 72 valuable index of the type of f o l d mechanism involved i n the r e f o l d i n g . (Ramsay, 1967/. Figure 12 shows the rotation paths of the refolded l i n e a t i o n s and the s l i p l i n e s of the f o l d mechanism involved. A si m i l a r ( s l i p ) mechanism i s deduced for F G f o l d i n g . The s l i p l i n e s are sub - perpendicular to FQ f o l d axes. The s c a r c i t y of l i n e a t i o n s refolded by F Q minor folds may be due to extreme r e c r y s t a l l i z a t i o n which followed the F^ f o l d i n g , thus e s s e n t i a l l y o b l i t e r a t i n g the e a r l i e r l i n e a t i o n s . Lineations. minor f o l d axes and axial surfaces in  Chilliwack Group Peninsula Formation Strata:-Lineations and minor f o l d axes st r i k e 315* and plunge northwards or southwards between 5 and 20 . Minor f o l d a x i a l surfaces strike between 305 - 318 , and dip steeply at 65 - 83 to the northeast. These minor f o l d trends may be associated with a major f o l d which has s i m i l a r l y oriented a x i a l surface and axis. This f o l d may be the reason for the two horizons of calc -s i l i c a t e noted, but the present data are inadequate for proof. 7k Note on strained pebbles i n the meta - conglomerate of the  Cairn Needle Formation. The pebbles within the sheared meta - conglomerates in the Cairn Needle formation have widely varying shapes. The pebbles have been flattened within the f o l i a t i o n into pancake e l l i p s o i d s whose longest axis X ( X>Y>Z ') i s p a r a l l e l to the steeply plunging f o l d axis in the area. The wide v a r i a t i o n in pebble shape i s demonstrated at Station 225» where the pebbles have the following range in Y ' / z ' r a t i o . GRANITIC: k2 pebbles Y'/Z' = 1.96 - 57.66 with 52.3% in the 0 -10 range. GRANODIORITIC: 17 pebbles Y'/Z' = 1 .k - 31.25 with 6k.7ft in the 0 - 1 0 range. DIORITIC: 7 pebbles Y'/Z' = 3.63 - 18.5 with 71-kft in the 0 - 1 0 range. AMPHIBOLITIC: 11pebbles Y'/Z' = 7-k - 17 with 90.9% i n the 1 0 - 2 0 range. QUARTZO - FELDSPATHICt 7 pebbles Y'/Z' = 6 -k2.k with k2.8ft in the 0 - 1 0 range and 28.kf^ in the kO - 50 range. The wide range of shape within g r a n i t i c and quartzofeldspathic rocks may be a r e f l e c t i o n of the fact that during high grade metamorphism these rocks were close to their minimal melting temperatures. The variable shape may also be the r e s u l t of i n i t i a l shape variation coupled with some competence difference during deformation. Thus, as stated by Ramsay (19t>7 P. 222;, even i f the r e s t r i c t i o n s r e s u l t i n g from the o r i g i n a l differences could be overcome, the wide range in pebble shape makes i t extremely d i f f i c u l t to calculate the bulk rock s t r a i n . . What can be said of the pebbles i s that they form e l l i p s o i d s of f l a t t e n i n g type (Flinn 195>&J with long axes sub - p a r a l l e l to the major f o l d axes. I f their shape was only controlled by similar f o l d i n g , one would not expect to f i n d e l l i p s o i d s of t h i s form around the f o l d nose. The XY plane of s t r a i n e l l i p s o i d s in. s i m i l a r folds i s always i n c l i n e d at some angle to the layers, a high angle around f o l d noses a low angle on f o l d limbs. (Ramsay 19&7 P- h29). In t h i s case the XY plane of the e l l i p s o i d s l i e s within the f o l i a t i o n and the conglomerate occurs around the antiformal f o l d nose. Thus the shape of the pebbles was predominantly controlled by stress regimes operative during the e a r l i e r F A or F^ f o l d episodes. A l t e r n a t i v e l y , they may have been fla t t e n e d byemplacement of the Scuzzy Pluton. The e a r l i e r hypothesis i s a p o s s i b i l i t y as striped amphibolites immediately below the conglomerate have amphibolitic layers which have been boudined (stretched within the f o l i a t i o n J by an e a r l i e r event, and then refolded by the F event. (see Plate 9;. C MAJOR STRUGURE; The three cross sections A - A', B - B', E - F - G, show successively deeper st r u c t u r a l l e v e l s which are exposed as one goes from North to South. The main f a u l t in the area separates the Chilliwack group - Peninsula Formation rocks on Harrison Lake from the Breakenridge gneisses. The northwest trending lineament in the north i s interpreted as a shear zone which extends to great depth as a •"•partially metamorphosed dunitic pod has been emplaced along RELATIONSHIP BETWEEN MET AMOR PHTSM AND DEFORMATION. The time r e l a t i o n s h i p s between metamorphic r e c r y s t a l l i z a t i o n ' and deformation are c r i t i c a l to the elucidation of the geological h i s t o r y of any metamorphic t e r r a i n . . The textural r e l a t i o n s h i p s between porphyroblasts and s c h i s t o s i t y enable one to c l a r i f y the sequence of events which led to the f i n a l high grade r e c r y s t a l l i z a t i o n of the metamorphic rock. These features have been well documented by Zwart (1962), and Spry U969), and enable one to assign the c r y s t a l l i z a t i o n of a porphyroblast to a pre - syn or post - tectonic stage. In t h i s study the pelitic rocks of the Breakenridge and Cairn Needle formations, and the Chilliwack group -Peninsula Formation have been treated separately and an attempt has been made to r e l a t e similar generations of fo l d s within each formation. With these f o l d s and t h e i r r e l a t e d s c h i s t o s i t i e s as reference points the metamorphic index minerals can be assigned to the appropriate stage of r e c r y s t a l l i z a t i o n . Examples from the rocks studied are shown i n Plates 10 through 1k. FIGURE 11. Relationship between metamorphic r e c r y s t a l l i z a t i o n and f o l d i n g episodes i n the Mt. 3reakenridge Area. Green = Chilliwack Group- Peninsula Formation, blue = Breakenridge Formation. Red = Cairn Keedle Formation. F- F. Fc C h l o r i t e PRC. | SyM. | PoST. I SYM.I PosT 1 SYN. 1 Po$T B i o t i t e O C _ J > -— o -G a r n e t « ^ < ^ Staurolit e o K y a n i t e Si l l imanite Muscovite -• Q u a r t z o Plagioclase _ . Q F IG 13 80 The h i s t o r y of r e c r y s t a l l i z a t i o n and deformation i s summarised in Figure 13'. The following conclusions can be drawn; -i ; Matrix formers ( c h l o r i t e - b i o t i t e - muscovite) have a long h i s t o r y of c r y s t a l l i z a t i o n and r e c r y s t a l l i z a t i o n having responded chemically and mechanically to every event both thermal and deformational. i i ; A l l the rock groups studied were at l e a s t at garnet grade before P D. D i i i j Within the Breakenridge group, s t s u r - l i t e i s found included i n pre - F G garnets, but the main period of s t a u r o l i t e r e c r y s t a l l i z a t i o n i s post - F . S i m i l a r l y , C Kyanite c r y s t a l l i z e d post - F ^ . . Iv; S t a u r o l i t e i n the Cairn Needle formation c r y s t a l l i z e d pre - kinemstically to syn - kinematically with F^, while s i l l i m a n i t e may be pre - F^ {plate 13)» hut mainly post - F Q . (Plate 1/jj. v) The major metamorphic r e c r y s t a l l i z a t i o n post - dated F C . The simultaneous post - F C c r y s t a l l i z a t i o n of Kyanite i n the Breakenridge formation and s i l l i m a n i t e in the Cairn Needle sc h i s t s implies that a temperature gradient existed between the two formations ?t t h i s time. v i j Retrograde effects include c h l o r i t i z a t i o n of garnet and s e r i c i t i z a t i o n of kyanite. Within the rocks on Harrison Lake pre - P g garnets are wholly retrogressed to c h l o r i t e . This retrogression may well be associated with the phase of thr u s t i n g . Figure 111 The d i s t r i b u t i o n of p e l i t i c metamorphic index minerals which define the zones of metamorphism of the Mt. Breakenridge area. Ch= Chlorite Bi= o i o t i t e Gt= Garnet St= S t a u r o l i t e Ky= Kyanite S = S i l l i m a n i t e A = Andalusite R = Reaction isograd St + muse. + qtz = S i l l . + bio.+ H 20 Ky-st-gt-bi. gneiss shown i n red METAMORPHISM. Two main phases of metamorphism are recognised i n th area; -a; A deep seated regional event which i s broadly contemporaneous with the f o l d i n g . b) A higher l e v e l contact event which post dates a l l f o l d i n g and i s rela t e d to the emplacement of the Scuzzy Pluton. a) Regional Metamorphism; From the map Figure 11+, i t i s apparent that the grade of metamorphism increases from the South to North, going through zones of c h l o r i t e , b i o t i t e - garnet, s t a u r o l i t e ( i l l - defined), s t a u r o l i t e - kyanite, and s i l l i m a n i t e bearing rocks.. This f a c i e s series corresponds to the Kyanite - s i l l i m a n i t e (Harrovian) type of Miyashiro (19M ). The co-existing p e l i t i c minerals within the successive zones plotted on AFM diagrams (Thompson 1957) of Figure 15, form one, two, three, four and f i v e ( i f in some cases c h l o r i t e i s consifered to be stable ) phase assemblages. For divariant equilibrium at constant P, T, in the simple six component model system, the presence of FI GURE 1 5 • AFK' diagrams of p e l i t i c assemblages. Chlori t e to s i l l i m a n i t e grade. FIG 15 Staurol i te Grade FIG 15 b 88 S i l l Sillimanite Grade greater than three co-existing minerals plus muscovite and quartz, v i o l a t e s the phase r u l e . I f the rocks are considered to approach equilibrium extra components (e.g. CaO, MnO i n garnet, ZnO in s t a u r o l i t e ) could i s t a b i l i z e the excess mineral within the A.P.M. diagram, thus s a t i s f y i n g the assumption of equilibrium. Santer (1969) demonstrated that the assemblage b i o t i t e - garnet - s t a u r o l i t e and kyanite in the Breakenridge formation approached equilibrium and that the CaO content of the garnet was s u f f i c i e n t to s t a b i l i z e t h i s mineral within the system. However, H o l l i s t e r (1966) has demonstrated that excluding a retrograde zone of MnO the outer zone of garnet in p e l i t i c schists i s often of pyrope almandine composition. Thus i f the rock only has eauilibrium r e l a t i o n s with t h i s portion of the garnet, th CaO, MnO contents are i n s u f f i c i e n t to s t a b i l i z e the mineral within the system. In t h i s cast?, the zinc content of s t a u r o l i t e may be important. Detailed microprobe analyses are required to resolve t h i s problem. The four phase assemblage s t a u r o l i t e - s i l l i m a n i t b i o t i t e , garnet within the Cairn Needle schists has also been noted i n the lower s i l l i m a n i t e zone of the Oquossoc area, Maine (Guidotti 1970). Here the excess phase has been explained by the fugacity of H20 being •buffered and i n t e r n a l l y controlled by such r e l a t i o n s as : 9 0 Low Zn. St. + Na muse. + Qtz. = S i l l . + b i o . + Zn. r i c h St. + K r i c h muse. + H20 + Ab. + Gt. In this way water would have to be treated as7 an immobile component within the A.F.M. system and thus account for the extra phase. A favourable model to view reaction processes within a polymetamorphic terrane i s that used by H o l l i s t e r , U9b°J and Naggar and Atherton (1970 J. In this model early formed porphyroblast indicator minerals c r y s t a l l i z e by~ groundmass reactions which a t t a i n equlibrium, and once formed are no longer involved i n successive reactions. By the r e f r a c t o r y nature of the early porphyroblasts the reacting system could be continuously changing composition. Thus m spite of the fac t that the t o t a l assemblage did not c r y s t a l l i z e together the progressive reaction assemblage could have attained equilibrium. In t h i s way the assemblage b i o t i t e - garnet - s t a u r o l i t e -kyanite, which apparently v i o l a t e s the phase ru l e , i s the r e s u l t of an early reaction which produced garnet and a l a t e r equlibrium reaction which produced b i o t i t e -s t a u r o l i t e and kyanite. POSSIBLE REACTIONS. S t a u r o l i t e. As no chloritoldhas been found in the p e l i t e s , s t a u r o l i t e may be the r e s u l t of the following react i o n . — C h l o r i t e + muscovite = Sta u r o l i t e + b i o t i t e + Qtz. + E^O. (Hoschek 1969) Spec. 35/70 has the above assemblage plus garnet and may be close to t h i s reaction. S t a u r o l i t e - Kyanite. Within the s t a u r o l i t e - kyanite zone these minerals have c r y s t a l l i z e d simultaneously . As garnet may have acted as a r e f r a c t o r y constituent i t was not involved i n the formation of s t a u r o l i t e and kyanite. — Mg/Pe c h l o r i t e + muscovite = b i o t i t e + s t a u r o l i t e + kyanite + H2O. (Naggar and Atherton 1970) S i l l i m a n i t e . There Is no textural evidence for the formation of s i l l i m a n i t e from kyanite. It i s closely associated with micas or occurs as independent needles which mimic minor f o l d s . Muscovite i s stable with quartz and no 92 potassium feldspar has been found. I f magnesium r i c h c h l o r i t e i s s t i l l stable to within the s i l l i m a n i t e zone the e a r l i e s t s i l l i m a n i t e forming reaction may be;--- Mg c h l o r i t e + muscovite = Mg b i o t i t e + s i l l i m a n i t e + H^O. (Naggar and Atherton 1970) In schists close to the boundary of Breakenridge and Cairn Needle Formations, s i l l i m a n i t e i s associated with a minor amount of s t a u r o l i t e . Farther north, s t a u r o l i t e i s absent. This could be the result of variable rock composition or of the r e a c t i o n ; -- - S t a u r o l i t e + muscovite + quartz = S i l l i m a n i t e + b i o t i t e + H 20. (Hoschek 19&9J OPAQUE MINERALS. The opaque minerals present i n p e l i t i c rocks o f f e r an important means of gaining information on the composition of the f l u i d phase present during metamorphism, and hence f u g a c i t i e s of oxygen and sulphur (P 02 e t c « ) Opaque minerals within the s t a u r o l i t e - kyanite zone and t h e i r associated s i l i c a t e s include FIGURE 1b Schematic chemical potential diagram of the system Fe - S - 0 - T I O 2 showing- phases in equilibrium with ilmenite. (after Hounsl'ow and Moore 1967; 9k 95 a) pyrrhotite - p y r i t e - ilmenite b i o t i t e - garnet -chalcopyrite - graphite. s t a u r o l i t e - kyanite. b) hematite - ilmenite -magnetite c) ilmenite - graphite b i o t i t e - garnet kyanite. The opaque assemblages buffer the f_ , f " 0£ 7 s£ within a range similar to that of the s t a u r o l i t e grade rocks studied by Hounslow and Moore (1967). See Figure 16. The d i s t r i b u t i o n of s t a u r o l i t e i s considered to be r e s t r i c t e d by the host rock composition. (Williamson 195.3) Ganguly (1968) has shown that in addition to t h i s , the s t a b i l i t y " f i e l d of s t a u r o l i t e i s r e s t r i c t e d to a l i m i t e d range of defined mostly i n the upper part of the magnetite f i e l d , and has. a narrow range of thermal s t a b i l i t y " . (Figure 17). Further, the fQ^ dependant rea c t i o n -- 6St. + 3Qu. + 2 0 2 = 27Ky. + lj.Mt. + 3H~20 i s cited to explain the r e s t r i c t i o n of s t a u r o l i t e to less FIGURE 17 Phase r e l a t i o n s in the system F e ^ - A l ^ - S i 0 2 - H2<$)- 0 2. as functions of f o 2 and T. I lOkb t o t a l pressure) aft er Ganguly 1968. The s t a b i l i t y f i e l d of s t a u r o l i t e and magnetite i s shown cross-hatched. 97 oxidized environments and kyanite to more oxidized ones. However in t h i s study St a u r o l i t e i s found i n association with kyanite i n both oxidized and reduced environments. The s t a u r o l i t e and non s t a u r o l i t e assemblages, are c l o s e l y associated within the main p e l i t i c gneiss horizon i n the Breakenridge formation. S t a u r o l i t e , according to Ganguly, i s incompatible with magnetite in f C 2 conditions equivalent to the lower magnetite f i e l d . (Figure 17). Such conditions may be r e a l i z e d by the presence of graphite in the rock. Thus the gra p h i t i c non s t a u r o l i t e bearing assemblage lc) could have passed d i r e c t l y to kyanite grade, by-passing s t a u r o l i t e by the reaction; — 12St + kbMt. + 1lkQu. = 5kAlm. + 6H 20 + 230 2. However i f t h i s was i n v a r i a b l y the case one would not expect to f i n d s t a u r o l i t e associated with assemblage (a). Thus, although t h e o r e t i c a l l y s t a u r o l i t e s t a b i l i t y may be r e s t r i c t e d by f C 2 dependant reactions, the c o n f l i c t i n g evidence discussed above suggests that rock bulk composition not only controls the presence of s t a u r o l i t e but also the f 0 2 , f3p of the rock. 99 MET AM OR PHI SM OF CALC SILICATES AND LIMESTONES« Banded calc - s i l i c a t e s In Cairn Needle Formation; The calc - s i l i c a t e s of the Cairn Needle formation are banded in a crudely symmetrical fashion. (Plate 1 £ ) . Specimens k 2 9 / 7 0 and i+79/70 have the following zones, i n which zones B to E are repeated on either side of the central zone A. k29__;~ 2QNE •ASSEMBLAGE THICKNESS A" Gt-hb-ep-sphene-qtz-plag (Ankk) 6 mm. B Hb-ep-gt-apatite-qtz-plag k mm. C Plag-otz-ep-sphene-apatite 2 mm. D Hb-plag (AnkO;-sphene-qtz 10 mm. ZONE ASSEMBLAGE THICKNESS A Di-gt-cz-plag(An66j-sphene-qtz 15 mm. b Plag-qtz- (hb-gt-sphene) 2 mm. C Hb^gt-sphene-qtz-^plag (An£6) 3 ram* D hb-sphene-plag-qtz 5> K Bi-qtz-plag-gt-sphene 10 mm. The outer zones i n specimen i;79/?0 are p e l i t i c . These band may be the r e s u l t of chemical reactions which take place between carbonate r i c h rocks and interlayered carbonate free p e l i t i c rocks, under open system conditions. O r v i l l e (1969 p.78) f u l l y discusses how reaction between incompatible phases of the p e l i t i c and calc - s i l i c a t e rocks can produce zones r i c h in compatible phases such as garnet - clinopyroxene, plagioclase - clinopyroxene, hornblende - plagioclase and plagioclase - b i o t i t e . Vidale U969J has carried out experimental reactions between limestone and p e l i t e bands i n the presence of chloride bearing hydrous f l u i d , which produce zones not unlike those of specimen U79/70. The high m o b i l i t y of Ca, and K cations during these reactions may be r e f l e c t e d in the variation i n plagioclase composition from central to outer zones, the composition of the garnet I Py^6 G r 3 i ^23 ^* a n d t n e ^ a c ^ °? muscovite in the outer p e l i t i c l a y e r s . LIMESTONE. Tbe c r y s t a l l i n e limestones and associated calc -s i l i c a t e s of the Cairn Needle formation are in the s i l l i m a n i t e zone. The mineral assemblages present are;-LMST:- C a l c i t e - tremolite - f o r s t e r i t e - muscovite. Calc - S l l : - Grossular - diopside - c l i n o z o i s i t e -c a l c i t e - qtz. FIGURE 18 Isobaric dkb; T - Xcc>2 diagram for reactions in metamorphosed s i l i c e o u s dolomites. I after Metz and Trommsdorff 1968) The s t a b i l i t y f i e l d of the assemblage F o r s t e r i t e + Tremolite + C a l c i t e i s shown ruled. FIGURE 19. Calculated T-X diagram for the CaO- AI2O3- S i 0 2 -E2O- C0 2 system at 5 0 0 0 bars t o t a l pressure, (after Gordon 1969;. The s t a b i l i t y f i e l d of the assemblage Cal c i t e - quartz-z o i s i t e - grossular i s shown ruled. 105 The lxmestone assemblage has a s t a b i l i t y f i e l d , i n the system 0 80 - KgO - S i 0 2 - H 20 - C0 2, which i s shown in Figure 18. (Metz and Tromsdorff. 1968J I t i s probably the r e s u l t of the reaction;-1 Tremolite + 11 Dolomite = 8 F o r s t e r i t e + 13 C a l c i t e * 9C0 2 +1H20. Squlibrium temperatures of reactions i n Figure 18 were determined at 1 Kb. As the f o r s t e r i t e forming reaction occured at pressures above the alumino - s i l i c a t e t r i p l e point I 5.5 &h ), the extrapolated temperature would be around 670°C. The assemblage f o r s t e r i t e - o.?lcite -tremolite i s stable with a f l u i d phase which has a high mole f r a c t i o n of C0 2 ( X Q02 )• The calc - s i l i c a t e assemblage can be represented in the system CaO - A1 20^ - S i 0 2 - B"20 - C0 2. The s t a b i l i t y f i e l d of z o i s i t e , grossular, c a l c i t e and quartz i s fixed within a very narrow temperature and X Q Q 2 range. Figure 19, after Gordon (1968), shows that at 5 Kb t h i s assemblage would co-exist with a f l u i d phase with X Q 0 2 = 0.1, ata temperature of 600° +. I t i s l i k e l y that no temperature gradient existed between these assemblages, as they are so c l o s e l y associated. However, the composition ( X Q Q ^ ) of the f l u i d phase was buffered and i n t e r n a l l y controlled by the mineral assemblage with which i t co-existed. Thus extreme gradients i n f l u i d composition existed during metamorphism. b; Contact Metamorphism. Assemblages of p e l i t i c minerals around the Scuzzy Pluton on Cairn Needle include i ; Andalusite - garnet - b i o t i t e . i i j Andalusite - s i l l i m a n i t e - garnet - b i o t i t e . i i i ) S i l l i m a n i t e - garnet - b i o t i t e . In addition they contain muscovite and ouartz, and no c o r d i e r i t e has been found. Andalusite has only been found immediately to the South of Cairn Needle, forming elongate ( hem.) c r y s t a l s with s t r i k i n g c h i a s t o l i t e crosses. The s i l l i m a n i t e forms similar robust elongate c r y s t a l s with good IQIOU cleavage. The alumino - s i l i c a t e s appear to have c r y s t a l l i z e d independently of one another, the association of both apparently being due to the metastable persistence of an e a r l i e r porphyroblast. A s t r i k i n g feature of the alumino - s i l i c a t e s i s their ubiouitous replacement by large plates of muscovite. Varying stages of replacement are shown in Plates 16, 17, 16 Within these platey aggregates are t i n y needles of s i l l i m a n i t e . Thus the waning stages of metamorphism may have been marked by a stage of metasomatism not unlike that noted in the aureole of the Thorr granodiorite in Donegal. (Pitcher and Read, 196.3)• 107 PETROGENETIC GRID :-The P.T. conditions of metamorphism are estimated by comparing the natural minerpl assemblages with experimental data. Figure 20 shows the physical conditions which existed during the regional and contact met amorphism of t h i s study, as defined by the data f o r the alumino -s i l i c a t e s I Richardson, G i l b e r t , B e l l . 1969), s t a u r o l i t e (Hoschek 1969) and the breakdown of muscovite. ( Evans 1965;. The P.T. conditions of regional metamorphism ranged from 300 to 670°C, above 5.5 Kb, while those of the contact metamorphism were around 550 to 650°C at 3 to 5.5 Kb. Figure 20 Petrogenetic g r i d showing P.T. conditions of regional (R) and contact (C) metamorphism as defined by a ) Aluminum s i l i c a t e curves and t r i p l e point with uncertainty area .(Richardson, G i l b e r t , and B e l l . 19t>9 ) bj Ch. + muse. = St + b i o . + qtz. + ( lioscbek , 1 9 6 9 ) c) ST +musc. + qtz. = A l - S i l . + bio. + H 20 ( Hoschek , 1 969 ) d) Muse. + qtz. = K-feldspar + A l 2 S i O ^ + H 2 0 ( Evans,1965. ) 110 SUMMARY a) The major map units studied include; i ; BREAKENRIDGE FORMATION: A eugeosynclinal seouence of volcanics, graywacke and minor p e l i t e which has been metamorphosed to amphibolite, grey g r a n o d i o r i t i c gneiss, kyanite gneiss and migmatite. IIJ CAIRN NEEDLE FORMATION.: A sequence of p e l i t i c s c h i s t , garnet hornblende sch i s t , calc - s i l i c a t e , c r y s t a l l i n e limestone, sheared conglomerate with g r a n i t i c c l a s t s , and metamorphosed basic igneous granulite. The meta sedimentary units were deposited in a shallow water marine environment. i l l ) CHILLIWACK GROUP - Peninsula Formation. A sequence of c l a s t i c g r i t s , conglomerate I with g r a n i t i c c l a s t s j , p e l i t e and calc - s i l i c a t e which i s in f a u l t contact with the Breakenridge and Cairn Needle Formations. i v ; IGNEOUS ROCKS: The main plutonic rocks are the gneissic granodiorite/ quartz d i o r i t e of Mount breakenridge which i s cored by quartz andesine porphry and ouartz d i o r i t e , and the Scuzzy granodiorite/ auartz d i o r i t e . Minor intrusions of dunite, p e r i d o t i t e and andesite dykes are also present. b; CORRELATION AND AGES. The ages of the metamorphosed rocks based on co r r e l a t i o n with similar l i t h o l o g i e s of known ages are: Breakenridge Formation:- Upper Paleozoic. Cairn Needle Formation:- Mesozoic probably Jurassic. Chilliwack Group - Peninsula Formation:- Upper Paleozoic L. Cretaceous. The Scuzzy Pluton i s Upper Cretaceous i n age ( (70 m.yrs.;. The epizonal core of the Mt. Breakenridge plutonic complex i s probably of Early T e r t i a r y age (kO m.yrs while the gneissic granodiorite i s post-Jurassic, pre-Mid Cretaceous i n age. c) STRUCTURE AND DEFORMATION. Between the Jurassic and Mid-Cretaceous the rocks were folded into antiforms and synforms with a northwest trend and plunge (329/^b), Minor f o l d r e l a t i o n s h i p s indicate at least three phases of fo l d i n g with the l a t t e r two (Fg, F Q ) being e s s e n t i a l l y homoaxial. 112 A si m i l a r mechanism i s deduced for the l a t e s t phase of f o l d i n g ( P G ) . A Mid-Cretaceous reverse f a u l t juxtaposed breakenridge and Cairn Needle formations against Chilliwack Group - Peninsula Formation rocks. d) The r e l a t i o n s h i p between r e c r y s t a l l i z a t i o n and deformation. Pr i o r to the second episode of f o l d i n g (Fg) the metamorphic rocks were at least at garnet grade. Maximum r e c r y s t a l l i z a t i o n occured a f t e r the l a t e s t phase of f o l d i n g (F^) as both kyanite and s i l l i m a n i t e post date t u i s event. e; METAMORPHISM. The metamorphic rocks form a kyanite - s i l l i m a n i t e facies series, with grade increasing r a p i d l y from South to North. The P.T. conditions of regional metamorphism range from 3^0-670° above 5.5 Kb. Multiphase mineral assemblages in p e l i t i c gneiss are considered to have approached equilibrium. The mineral assemblages of p e l i t i c and calcareous rocks are considered to have played an important role i n c o n t r o l l i n g the composition of the f l u i d phase. Retrogressive metamorphism accompanied the phase of Mid - Cretaceous f a u l t i n g . Contact metamorphism associated with the emplacement of the Scuzzy Pluton (U. Cretaceous) produced andalusite and s i l l i m a n i t e bearing s c h i s t s . 113 CONCLUSIONS. Upper Paleozoic and Mesozoic strata of the Mount Breakenridge region were folded, metamorphosed and migmatized between the Jurassic and Mid-Cretaceous. A period of u p l i f t , f a u l t i n g and minor retrogressive metamorphism in the Mid-Cretaceous was followed in Upper Cretaceous by the int r u s i o n of the Scuzzy Pluton. Andalusite and s i l l i m a n i t e bearing schists were produced in the contact aureole of the l a t t e r i n t r u s i o n . ' U p l i f t continued at the rate of 2-3 km/million years. In the early T e r t i a r y a por p h y r i t i c ouartz d i o r i t e intruded the core of the gneissic granodiorite on Mount Breakenridge. FURTHER WORK Mapping w i l l be continued to the East and Southeast of the present area, between l a t i t u d e s U9°35' and it9°U5 ' , and longitudes 121°U0' and J\2J\°k5i , to r e l a t e the structure, metamorphism and plutonism of that area to the present work. Detailed microprobe analyses w i l l be carried out on minerals of p e l i t i c gneisses to determine how cl o s e l y , and by which reactions, the rocks approached chemical eouilibrium, and to document chemical v a r i a t i o n in minerals with increasing grade of metamorphism. LIST OP REFERENCES. AHO A.E. 1956. Geology and genesis of ni c k e l copper -pyrrhotite deposits at the P a c i f i c Nickel Property. Southwestern B r i t i s h Columbia. Econ. Geol., Vol 511 pp kkk-k8l. BAADSGAARD H., FOLINSBEE R.E., and LIPSON J . , 1961. Potassium - argon dates of b i o t i t e s from C o r d i l l e r a n granites. B u l l . Geol. Soc. Am., Vol 72, pp 689 - 702. DUFFEL S. and McTAGGART K.C. 1952. Ashcroft map area, B r i t i s h Columbia. Geol. Survey Can., mem. 262. EVANS B.W. 1965. Application of a reaction rate method to the breakdown of muscovite and muscovite + quartz. Am. J . S c i . , Vol. 263, pp 6k7 - 667. GANGULY, J . 1968. Analysis of the s t a b i l i t i e s of c h l o r i t o i d and s t a u r o l i t e and some e q u i l i b r i a in the system FeO - Al20^ S i 0 2 - H20 - 02. Am. J. S c i . , Vol. 266 pp 277-298. FLINN D. 1956. On the deformation of the Funzie conglomerate, F e t l a r , Shetland. J . Geol., Vol. 6k, p k80. GORDON T.M.f 1968. Some s i l i c a t e - carbonate phase r e l a t i o n s in H20 - C0 2 mixtures. PhD. Thesis, Princeton University. GUIDOTTI C.V. 1970. The petrology of the t r a n s i t i o n from lower to upper s i l l i m a n i t e zone. Oquossoc area, Maine. J.Pet., Vol. 11 p 277. HOLLISTER L.S. 1969. Contact metamorphism in the Kwoiek area of B.C. An end member of the Metamorphic process. B.G.S.A. Vol. 80 p 2I|6£. -- and ALBEE A.L. 1965- Electron microprobe analyses of some n a t u r a l l y zoned garnets from B r i t i s h Columbia and their i n t e r p r e t a t i o n based on the Rayleigh f r a c t i o n a t i o n model. Spec. Paper. G.S.A. Vol. 87, p 79. HOSCHEK G. 1969. The s t a b i l i t y of St a u r o l i t e and C h l o r i t o i d and t h e i r s i g n i f i c a n c e i n Metamorohiism of P e l i t i c Rocks. Contr. Min. Pet., Vol. 22, pp 208-232. HOUNSLQW A.W. and MOORE J.M. 1967. Chemical Petrology of Gr e n v i l l e Schists near Pernleigh, Ontario. J.Pet., Vol. 8, PP 1-28. KALSBEEK P. 1970. Petrography and orogin of gneisses, amphibolites and migmatites i n the Qasgialik area, S.W. Greenland. Med.om Gr^n. B.D. 1o9, NR 1. McTAGGART K.C. and THOMPSON R.M. 1967. Geology of part of the Northern Cascades in Southern B r i t i s h Columbia. Can. J . Earth. S c i . , Vol. k, PP 1199-1228. MEHNERT K.R. 1968. "MIGMATITES". E l s e v i e r Publishing Company, Amsterdam. METZ P. and TROMMSDORFP V., 1968. "On Phase E q u i l i b r i a in metamorphosed s i l i c e o u s dolomites". Contr. Min. Pet., Vol. PP 305-309. MISCH P. 1966. Tectonic evolution of the Northern Cascades of Washington State. Can. I n s t r . Mining Met., Spec. Vol. 8, pp 101-18L. 1971. Metamorphic Facies types i n the Northern Cascades in "Metamorphism in the Canadian C o r d i l l e r a " . Cord. Sect. G.A.C Program and Abstracts p22. MIYASHIRO A. 1961. Evolution of Metamorphic Be l t s . J . Pet., Vol. 2 pp 277-311• MONGER J.W.H. 1970. Hope Map-area. West Half. B r i t i s h Columbia G.S.C. Paper 69-U7. NAGGAR M.H. and ATHERTON M.P. 1970. The Composition and metamorphic h i s t o r y of some aluminium S i l i c a t e bearing rocks from the aureoles of the Donegal granite. J . Pet., Vol. 11 p 5U9. ORVILLE P.M. 1969. A model for metamorphic d i f f e r e n t i a t i o n o r i g i n of thin - layered amphibolites. Am. J . S c i . , Vol 267 pp 6)4-86. 11U c PITCHER W.5. and READ H.H. 1963. Contact metamorphism in r e l a t i o n to the manner of emplacement of the granites of Donegal, Ireland. J . Geol., Vol. 71 P 261. RAMSAY J.G. 1967. "Folding and Fracturing of Rocks". McGraw-Hill, New York. RICHARDSON S.W., GILBERT M.C., and BELL P.M. 1969. Experimental determination of kyanite - andalusite and andalusite - s i l l i m a n i t e e a u i l i b r i a ; the aluminium s i l i c a t e t r i p l e point. Am. J. S c i . , Vol.267 PP 259-272. RODDICK J.A. 1965. Vancouver North, Coquitlsm and P i t t Lake Map Areas, B.C. G.S.C. Memoir 335. RODDICK J.A. and HUTCHISuN W.W. 1969. Northwestern part of Hope Map Area, B.C. (92H/w|) G.S.C. Paper 69-1 part A., p 29-38. SANTER G. 1969. Petrologic Study of a gneiss north of Harrison Lake, B.C. B.Sc. Thesis, U.B.C. SPRY A. 1969 "Metamorphic Textures". Pergamon Press Ltd. THOMPSON J.B. 1957. The graphical analysis of mineral assemblages in p e l i t i c s c h i s t s . Am. Miner. Vol. I i 2 pp8i4.2-56 11k d VIDALE R. 1969. Metasomatism in a chemical gradient and the formation of c a l c - s i l i c a t e bands. Am. J. S c i . Vol. 267 pp 857-87k. ZWART H.J. 1962. On the determination of polymetamorphic mineral associations and i t s application to the Bosost Area, Central Pyrenees. Geol. Rdsch. Vol. 52 p 38. APPENDIX. 115 TABLE 2 Grey gneiss of Breakenridge Formation; SPEC. NO. 18/70 Lk/70 202/70 206 /70 298/70 381/70 511/70 Qtz. 30 35 30 30 35 35 35 Plag. 30112) 30(10) k0(12) 2512U) 25(32) 35(30) k0(10) Bio. 20 25 15 20 30 20 10 Muse. 5 1 1 - - 5 5 Garnet 2 5 1 2 3 1 -C h l o r i t e 2 1 5 - 1 1 -Epidote 2 1 5 3 5 1 2 Sphene 1 - 1 - - - -Apatite 1 1 1 1 - 1 3 r y r i t e - - - - - - -Magnetite 1 1 - - - 1 -S e r i c i t e - - 1 - 1 - -C a l c i t e - - 1 - - - -Microcline - - - 20 - - 5 Zircon. — _ - -Modes estimated by eye. AnG*rthite content of plagioclase i s shown in brackets. 116 TABLE 2 (ooiitcU; SPEC. NO. 2V69 HS68/29 HS68/72 41/69 Qtz. 35 45 ko 15 * l a g . 20116; 10(10; 20(20; 6 o o 4 ; Bio. 15 5 25 15 Muse. - 3 10 5 Garnet 15 - - 1 C h l o r i t e 3 1 1 Epidote 1 - - -Sphene - - - -Apatite 1 1 1 1 f y r i t e - - - -Magnetite 2 1 1 1 S e r i c i t e - - 3 -C a l c i t e - - - -Microcline - 35 - -Zircon 1 117 TABLE 3 Amphlbolites of Breakenridge Formation. SPEC. NO. HS68/U3 12/69 Qtz. Plag. Bio. Garnet Hornblende Epidote Apatite Magnetite Ch l o r i t e S e r i c i t e Sph en e Zircon Pyrite 35 25(43; 5 5 30 1 1 1 20 30(38; 2 25 15 2 1 1 U2/69 12b/69 1x7/69 15 35(42; 5 10 30 1 3 25 30(34; 25 15 4 20 30(42) 10 30 5 2 1 60 1 1 Modes estimated by eye. Anorthite content of plagioclase i s shown in brackets. SPEC. NO. Quartz f l a g . B i O . Garnet Hornblende Epidote Apatite Magnetite Ch l o r i t e S e r i c i t e Sphene Zircon Pyrite Diopside C a l c i t e Muscovite TABLE 3 (contd.) 3 31/70 388/70 U85/70 HS68/70 20 15 25 20 30 . 25140; 25I 36; 30(40) 5 1 5 10 30 50 40 30 5 1 1 5 1 1 - 1 1 2 - 3 10 5 3 3 1 TABLE 3 ycontd.). SPEC. NO. HS68/57 1U9/70 191/70 218/70 26 3/70 Qtz. 20 20 30 25 f l a g . 10(k3) 30(k0; 20(38) 20130; 25(30; Bio. - 1 5 -• 10 Garnet - 10 - - 10 Hornblende 30 30 50 55 10 Epidote 5 5 - 1 5 Apatite 1 1 1 1 1 Magnetite - 3 - 5 1 C h l o r i t e - 5 1 - -S e r i c i t e - - 1 - -Sphene 1 . - 1 - -Zircon - - - - -P y r i t e - - - - -Diopside 30 - - - -C a l c i t e 10 - - - -Muscovite 1 1 120 TABLE k P e l i t i c gneiss of Breakenridge Formation SPEC. NO. HA Hk. Mi S i HZ M Qtz. kO 20 20 20 20 20 f l a g . 20 10 50(k0) 15 20 20lk2 C h l o r i t e 1 US) US; 1 US) 1 Bio. 20 10 15 l5 15 10 Muscovite 10 3 2 10 2 2 Garnet 3 50 6 25 30 kO Staurolite 2 2 3 3 5 Kyanite 5 5 2 - 10 3 Apatite 1 - 1 1 1 Zircon 1 1 1 -Magnetite 1 1 1 1 1 1 Sphene - 1 1 1 1 Modes estimated by eye. Plagioclase content i s shown in brackets, ft Anorthite. Texturally stable c h l o r i t e indicated by (S). 121 TABLE k (contd.) SPEC. NO. HS68 47-1 HS68 47-3 .159/70 217/70 2^5/70 Qtz. 25 15 20 20 20 Flag. 35(49) 25 15(34) 10(32) 30 C h l o r i t e 1 2(S) 5(S) 5 i s l 1 Bio. 25 10 1 5 5 Muscovite 5 5 20 5 5 Garnet 5 30 15 30 15 S t a u r o l i t e - 2 5 30 20 Kyanite - 6 - 10 10 S i l l i m a n i t e - 3 - - -Apatite 1 - - - -Zircon - 1 - - -Magnetite 5 1 5 5 -Sph ene - 1 - 1 -JSpidot e 1 - - - -Hornblende - — 25 _ 10 10(32) 5 3 45 15 15 TABLE k (contd.J SPEC. NO. 2a.it/70 251/70 26U/70 280/70 30 3/70 Qtz. 20 Plag. 25 C h l o r i t e 1 Bio. 5 Muscovite 5 Garn et 25 S t a u r o l i t e Kyanite 15 Opaque 5 Sphene Graphite 5 20 10(28; 5 25 5 20 5 30 15 1 5 10 20 5 10 5 25 15 ( 3'J ) 1 5 5 30 5 15 1 1 20 10ll4.ll) 1 5 20 20 10 5 5 123 SPEC. NO. Qtz. < Plag. C h l o r i t e Bio. Muscovite Garnet S t a u r o l i t e Kyanite Apatite Zircon Opaque sph ene Epidote Hornblende Tourmaline TABLE U (contd.;  325/70 361/70 376 /70 20 20 40 20(34J 40(45/ 1 - 1 5 20 10 1 15 20 20 5 -5 5 40 1 10 1 2 1 1 3 7 7 / 7 0 3 7 8 / 7 0 383/70 15 10 20 35 30148; 10(50) 2 1 5 15 5 1 1 5 5 20 30 2 20 10 30 5 10 1 1 1 3 5 1 5 25 15 12k TABLE h (contd.J SPEC. NO. 367/70 UU7/70 U53/70 U67/70 U68/70 Qtz. Plag. C h l o r i t e Bio. Muscovite S t a u r o l i t e Kyanite S i l l i m a n i t e Apatite Opaque Sphene Tourmal ine 10 20(50) 2 1 20 5 15 30 10 1 20 10 1 15 1 1 1 kO 5 1 5 25 5 15 20 15(37; 20 3 1 30 1 25 10 5 5 10 10 125 TABLE 5 Migmatites of Breakenridge Formation. SPEC NO. HS6859 HS6860 HS6871 206/70/L 206/70 Qtz. 30 30 30 45 25 Flag. 30(33; 30(28; 30 U4) 45(28; 25(35) Bio. 15 20 20 10 20 Hornblende 15 10 15 - 20 Garnet - 1 1 - -C h l o r i t e 1 . 2 - - -Epidote 2 2 4 5 6 Muscovite - 2 - 1 -Apatite 1 1 1 - 1 Magnefcite 1 1 1 - -Seric i t e 1i 1 - - -Zircon - - 1 - -Sphene — — — 4 126 TABLE 5 (contd.) SPEC NO. HS6869 319/70 310/70 373/70 19U/70 Qtz. 30 30 35 30 20 > Plag. 30131; Uo K 30; 35O0; 35130) Bio. 20 20 5 25 -Hornblende 10 - 20 - -Garnet 5 - 1 2 50 Ohlori te 1 - 1 1 -Epidote 2 2 1 1 20 Muscovite 1 2 - 5 -Apatite I" 1 1 1 -Magn e t i t e 1 1 - k -S e r i c i t e 1 - - 1 -Sphene - - - - -Microcline - 5 - - -Hedenbergite - - - - 10 Anorthite content of Plagioclse shown in brackets. Modes estimated by eye. TABLE 6 Gale - S i l i c a t e s of Cairn Needle Formation. SPEC. NO. U29/70 Ukl/70 UU6/70 U79/70 50U/70 Qtz. 25 Plag. 35 Epidote 10 C h l o r i t e 1 Garnet 10 Hornblende 20 Diopside Apatite 1 Sphene 1 Magnetite S e r i c i t e Bio. C l i n o z o i s i t e Tremolite P y r i t e 30 20 5 20 15 5 2 1 1 15 30 5 5 10 20 30 30 5 10 10 5 2 5 3 5 5 20 5 5 5 10 1 Modes estimated by eye. TABLE 7 Limestone of Cairn Needle Formation. SPEC. NO. U9U/70 U95/70.. 500/70 Qtz. - 10 Calcite 95 5 55 Tremolite - - 15 , x Diopside 25 Olivine 20 Garnet - k0 -C l i n o z o i s i t e 15 C h l o r i t e - - :5 Muscovite - - -5 Magnetite 5 TABLE 8 Garnet - Hornblende Schist and Amphibolite of Cairn Meedle  Formation. HS68 HS68 SPEC. NO. 2U/69 73-2 2k 1+U5/70 505/70 Qtz. 25 35 25 25 30 Flag. 25(37) 25138) 25(32) 25(41+) 25 Musco\iite - 1 - - -C h l o r i t e - 2 - - -Bio. 15 20 12 2 1 Garnet 5 5 - 5 10 Hornblende 25 7 35 40 30 Pyrite - - - - 3 Sphene - - . 1 -Magnetite 3 2 1 . 2 2 Apatite 2 1 1 1 S e r i c i t e - 1 - - -Modes estimated by eye. Anorthite content of Plagioclase shown in brackets 130 TABLE 9 r e l l t i c Schists of Cairn Needle Formation, SPEC. NO. HS68/53 25/69 ?9/6? HS68A-1 HS68/78 Qtz. 25 35 20 kO 25 f l a g . 10 10 20 (26) 30(Uoj 10 Ch l o r i t e - 2 3 1 7(S) Bio. 30 20 25 25 10 Garnet 10 8 5 h 5 S t a u r o l i t e - 6 - - -Kyanite - 3 - - -S i l l i m a n i t e 15 - 3 - -Muscovite - 5 5 - -Gedrite - - - - ko Tourmaline - 1 - - -Apatite 1 - 1 1 1 Zircon 1 - 1 1 -Magnetite 3 - ' 5 1 1 Pyr i t e - 5 - - -R u t i l e - - 1 - -Soh ene 1 Modes estimated by eye. Anorthite content of Plagioclase shown in brackets. Texturally stable c h l o r i t e shown by IS). SPEC. NO. Qtz. Flag. C h l o r i t e Bio. Garnet S t a u r o l i t e S i l l i m a n i t e Muscovite Tourmaline Apatite Zircon Magnetite Pyrite TABLE 9 (contd.J HS68 HS68 HS68 U5 h-2 5U 20 30 25 30U5; 30(10; 25(36; 5 2 5 35 20 25 5 15 10 5 5 1 1 1 1 1 1 131 HS68 HS68 HS68 1 1 1 1 I§ 50 ko 55 10(26; 20 5 2 1 1 30 20 25 10 10 10 -5 3 1 1 1 2 1 1 5 2 2 • TABLE 9 (contd.) SPEC. NO. HS68/79 35/70 U27/70 U59/70 U60/70 Qtz. 30 U5 15 25 35 Plag. 25C33 J ..5 10(28) 10 10(31) Chlorite - i5is) - - -Bio. 5 15 10 15 30 Garnet 5 10 30 15 5 S t a u r o l i t e 15 5 5 - -S i l l i m a n i t e - - 20 - 10 Andalusite - - - 10 -Muscovite 18 1 5 20 10 Tourmaline 1 1 - - -Apatite 1 - - - -Magnetite 1 1 1 - 3 Sphene - - 1 1 --TABLE 9 (contd.; SPEC. NO. U62/70 1x65/70 503/70 510/70 Qtz. 20 30 30 15 Plag. 15(34; 5(32) 5 20(hk) Bio. 25 15 15 5 Garnet 8 15 10 5o S t a u r o l i t e - 5 - 1 S i l l i m a n i t e - 20 20 10 Muscovite 30 10 15 1 Magn et i t e 3 - 5 2 Sphene - — - 1 TABLE 10 Pegmatites of Breakenridge and Cairn Needle Formations. SPEC. NO. 142/79 269/7© 285/70 338/70 396/7 Qtz. 30 30 30 50 30 Flag. 25(8) 40(12) 50(4; 45(101 50(8) Microcline 15 \ - - -Orthoclase 10 - -- - -Muscovite 5 1 3 3 -Bio. 5 15 15 1 15 Garnet 1 - - -C h l o r i t e 1 - 1 - 1 Epidote 1 5 1 1 Apatite 1 - - -Zircon _ - - 1 Modes estimated by eye. Anorthite content of Plagioclase shown i n brackets. TABLE 11 Metarudites and P e l i t e s of Chilliwack Group or Peninsula. Formation. HS68 HS68 HS68 HS68 SPEC. NO. 80-2 k0~1 kO-2 80-1 Qtz. ^0 30 25 30 Plag. 10 25(42) 20(5) 10 C h l o r i t e 30 (S) 1 1 IS) 30 is) Bio. - 8 10 -Garnet - 5 5 -Muscovite 10 1 10 10 Epidote 20 10 30 20 Hornblende - 20 Apatite - 1 -Sphene 1 - 1 1 Magnetite - 1 - -S e r i c i t e - - 1 -Pyrite 1 - - -HS68 8 0 ^ 30 5 5is) ko 10 10 Modes estimated by eye. Anorthite content of Plagioclase shown i n brackets. Texturally stable C h l o r i t e shown by (S). SPEC. MO. 95/70 93/70 118/70 H S 6 8 A 5 Qtz. ho 25 20 20 Plag. 30112; 30 15 30(2) C h l o r i t e i5 is) 15(S) i 5 ( s ) 5 Bio. - 20 - 20 Garnet - - - 10 Muscovite 1 5 15 10 Epidote 15 10 10 -Magnetite - - 20 5 Graphite — 5 -TABLE 12 Calc - S i l i c a t e s of Chilliwack Group or Peninsula Formation. SrEC. NO. 15/69 42/69 131 /70 1 32/70 Qtz. 30 35 30 30 Flag. 20(20; 10(38; 10(40; 5 A c t i n o l i t e 30 25 30 20 Garnet 15 20 10 10 Epidote 1 10 5 1 Z o i s i t e 1 - - 1 I C h l o r i t e 2 1 5 5 Magnetite 2 1 5 1 Muscovite - - 5 20 Bio. - - - 15 Zircon. - - - 1. Apatite - — — 1 Modes estimated by. eye. Anorthite content of Plagioclase shown i n brackets. TABLE 13 Gneissic Granodiorite - Quartz D i o r i t e . SPaC. NO. L 312/70 M 312/70 313/70 358/70 L 366/70 Qtz. 50 30 35 20 35 ?lag. 35(25; 20(30; 30 no; 35(30; 45(29; Bio. 5 35 20 30 5 Epidote 1 1 10 - 1 C h l o r i t e - 1 - 1 1 Magnetite - 1 - 10 1 K-spar 10 - - - 5 Hornblende 1 5 - - 2 Apatite 1 1 3 - 1 Sphene - - 2 - 1 Spinel - - - 5 -S e r i c i t e - 1 -Modes estimated byeye. Anortbite content of Plagioclase shown i n brackets TABLE 13 uontd.J SPEC. NO. L M 369/70 369/70 370/70 311 /70 Qtz. Plag. Bio. Epidote Ch l o r i t e Magnetite K-spar Hornblende Apatite Sph en e 35 3507J 15 10 1 1 30 20(38; 25 15 1 1 35 UO(32; 25 5 1 30 30(35; 5 2 2 1 25 1 1 TABLE Ik Mount Breakenridge Plutonic complex.  Gneisslc Quartz D i o r i t e . SPEC. NO. 5/69 U8/69 Qtz. 20 10 Plag. 301U3) 351U3) Bio. 5. Hornblende 35 30 Garnet 2 5 Ch l o r i t e 2 2 Epidote 1 5 Magnetite 5 5 Apatite - 1 S e r i c i t e - 2 TABLE 15 Epizonal Gore of Mount Breakenridge Plutonic complex, SPEC. N O . 3 4 5 / 7 0 31x9/70 354/70 355/70 356/70 11x1 Qtz. 30 f l a g . 40 K-spar 20 Muscovite 5 Bio. 5 Hornblende Ch l o r i t e 1 Epidote Magnetite 1 Apatite 1 Sphene 30 45 15 5 1 20 50 5 15 10 1 10 60 15 15 2 1 15 60 15 10 1 JfcAnorthite 5-30 5~30 5-37 10-39 12-45 Modes estimated by eye. 11+2 TABLE 15 tcontd.) SPEC. NO. 361/70 367/70 Qtz. 25 10 f l a g . U5 60 K-spar 5 5 Bio. 15 15 Hornblende 10 15 C h l o r i t e 1 1 Sphene - 1 % Anorthite 5-U7 5-k8 TABLE 16 Scuzzy f l u t o n . The Marginal Phase of the Pluton underlying Cairn Needle. SPEC. NO. hO5/70 h10/70 170/70 Qtz. 20 25 10 Plag. hS1 30; ko*32; 30 Bio. 15 15 -Hornblende 15 20 60 Sphene 3 1 -Apatite 2 1 -C h l o r i t e - 1 1 Magnetite - 1 -S e r i c i t e Modes estimated by eye. Anorthite content of Plagioclase shown in brackets. 144 PLATES. PLATE ..1: Grey gneiss of Breakenridge Formation, with well developed F R mega st r a i n s l i p f o l i a t i o n . PLATE 2±_ Striped amphibolite of Breakenridge Formation with well developed F minor f o l d s . PLATE 3 Kyanite gneiss of Breakenridge Formation which has been i s o c l l n a l l y folded. ( F ). PLATE 4 Migmatlte of Breakenridge Formation, with boudinaged pegmatite. PLATE 5 Sheared conglomerate at base of Cairn Needle Formation. Note g r a n i t i c c l a s t s . PLATE 6 Calc s i l i c a t e pod and symmetrically zoned layers within Cairn Needle Formation. (50 I PLATE 7 White c r y s t a l l i n e limestone and red calc s i l i c a t e of Cairn Needle Formation. PLATE 8 Folded and boudinaged e a r l i e r pegmatite within rusty s c h i s t of Cairn Needle Formation. 151 PLATE 9 Three phases of fo l d i n g i n st r i p e d amphibolite of Breakenridge Formation. Rootless F A i s o c l i n e , refolded by F B f o l d . F c minor folds r e f o l d boudinaged amphibolitic layers at top of plate. PLATE 10 Kyanite s t a u r o l i t e garnet gneiss of Breakenridge Formation. I d i o b l a s t i c post F A garnet ( i n t e r n a l s c h i s t o s i t y F A ) included i n post F s t a u r o l i t e which i s mimetic on a s t r a i n slipped Fg s c h i s t o s i t y . x32 PLATE 11 Kyanite s t a u r o l i t e s c h i s t from Cairn Needle Formation. S t a u r o l i t e porphyroblast with sigmoidal i n t e r n a l i n c l u s i o n t r a i n s of graphite which can be traced out into external s c h i s t o s i t y . Thus the s t a u r o l i t e may have c r y s t a l l i z e d syntectonically or post t e c t o n i c a l l y with F . c >< 32 PLATE 12 Kyanite garnet gneiss of Breakenridge Formation F c minor f o l d defined by graphite and ilmenite t r a i n s on which kyanite has post t e c t o n i c a l l y c r y s t a l l i z e d . x32 PLATE 13 S i l l i m a n i t e garnet s c h i s t of Cairn Needle Formation S i l l i m a n i t e flattened around a pre F c garnet. Thesillimanite could have c r y s t a l l i z e d p r i o r to F c f o l d i n g . * 32 PLATE ]> S i l l i m a n i t e garnet sch i s t from Cairn Needle Formation. A polygonal arc of s i l l i m a n i t e needles mimetic on F c minor f o l d . Thus the s i l l i m a n i t e i s post F( X 32 PLATE 15 Folded and symmetrically zoned calc s i l i c a t e of Cairn Needle Formation. The calc s i l i c a t e s are associated with p e l i t i c s c h i s t s . PLATE 16 S i l l i m a n i t e p a r t i a l l y pseudomorphed by muscovite. Contact aureole of Scuzzy Pluton. X 32 crossed n i c o l s . lloO PLATE 17 Andalusite , p a r t i a l l y pseudomorphed by muscovite Contact aureole of Scuzzy Pluton. crossed n i c o l s / 32 . PLATE 18 Platey aggragates of muscovite a f t e r alumino s i l i c a t e s of the contact aureole of Scuzzy Pluton. crossed n i c o l s x 32 . 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0053175/manifest

Comment

Related Items