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Geology of Vedder Mountain, near Chilliwack, B.C. McMillan, William John 1966

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GEOLOGY OF VEDDER MOUNTAIN, NEAR CHILLIWAOK, B.C. WILLIAM JOHN McMILLAN B.A.Sc., The University of Br i t i s h Columbia, 1962. A Thesis Submitted in P a r t i a l Fulfillment of the Requirements for the Degree of MASTER OF APPLIED SCIENCE in the Department of GEOLOGY We accept this thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA January, 1966 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f . > thel'requirements f o r an advanced degree at the U n i v e r s i t y of B ^ t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y available! f'or r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r -• !l ' ; • • • • mi's s i on .for; e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y . \ tr }• ; purposes may be.granted by the Head of my Department or by h i s representatives'., I t i s understood t h a t copying, or p u b l i -/b'ation of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d ' i\ \ w i t h o u t m y ' w r i t t e n p e r m i s s i o n . I • \ • Department of GEOLOGY  The U n i v e r s i t y o f ' B r i t i s h Columbia,, Vancouver 8, Canada. Date APRIL 269 1966.  ABSTRACT Vedder Mountain can be divided i n t o three units? the eastern sediments, the c r y s t a l l i n e rocks and the -(western sediments. Both eastern and western sediments are e s s e n t i a l l y unaetamorphosed whereas the c r y s t a l -l i n e rooks include both medium grade metamorphic rocks and saussuritized d i o r i t i e i n t r u s i v e rocks. The c r y s t a l l i n e rocks are bounded by steep southeast dipping f a u l t s . White mica-amphibole and garnetiferous white mica-amphiboie schists and gneisses, amphibolite, epidote amphibolite and garaet-sphene-white mica schists comprise the metamorphic rocks. The mineral assemblages are t y p i c a l of the almandite-amphibolite f a c i e s of Turner and Verhoogen(1960). Fol i a t e d d i o r i t e s intrude (?) the metamorphic rocks. Basic contact zones, l i g h t e r colored d i o r i t e dikes, amphibole-feldspar pegmatites and small quarts d i o r i t e bodies are thought to represent various phases of '.}-••. d i f f e r e n t i a t i o n of a parent magma. Pervasive s a u s s u r i t l z a t i o n character-ize s these rocks. In s t r u c t u r a l succession, the eastern sediments are comprised of chert, g r a n i t i c and volcanic pebble and cobble conglomerates with plagio-clase volcanic arenite interbedsj plagioclase volcanic arenite with con-glomerate interbeds hear the base of the unit and a r g i l l i t e intercede near the top? and micro-volcanic arenite with interbeds of plagioclase volcanic arenite, a r g i l l i t e , chert and s i l i c e o u s a r g i l l i t e with scattered, impure limestone pods. In structural succession, the western sediments consist of argillitej micro-volcanic arenite? chert lenticule arenite and volcanic chert arenite breccia which contain a band of impure, cherty limestone? argillite;and ehert. Vulcanism produced dacite porphyries which struc-turally underlie the sediments. The crystalline rocks comprise a tabular body believed to have :been emplacedsby faulting. Small, ellipsoidal serpentinite bodies lie along the southeast bounding fault of the crystalline slice. During emplacement of the crystalline slice, i t appears that the sediments were pushed aside in what has been referred to as phase I de-x formation. Folding in the argillaceous units was "similar" in nature but in the more competent units i t was "concentric." The eastern sediments comprise a synform with near horizontal northeast trending fold axis and steep southeast dipping axial plane. The western sediments comprise a steep, southeast dipping homocllne. TABLE OF CONTENTS Page Section I - INTRODUCTION 1 A - L o c a t i o n and Access 1 B - Physiography, Topography and Climate 2 C - Acknowledgements 3 D - Previou s G e o l o g i c a l Work 3 Section I I - STRATIGRAPHY 4 A - Eastern Sediments 7 a - Conglomerates 8 b - P l a g i o c l a s e V o l c a n i c A r e n i t e 9 c - A r g i l l i t e and P h y l l i t e 11 d - Chert 12 e - S i l i c i o u s A r g i l l i t e w i t h Limestone Pods IS f - M i c r o - v o l c a n i c A r e n i t e 14 B - Western Sediments 15 a - Quartz P l a g i o c l a s e Porphyry 15 b - A r g i l l i t e , 16 c - M i c r o - v o l c a n i c A r e n i t e 16 a - R a d i o l a r i a n Chert L e n t i c u l e A r e n i t e 17 e - V o l c a n i c R a d i o l a r i a n Chert A r e n i t e B r e c c i a 18 f - Limestone 19 g - Ribbon Chert 20 C - V o l c a n i c Rocks 20 i i i Page a - A l t e r e d Diabase 21 b - V o l c a n i c P o r p h y r i e s 21 D - C r y s t a l l i n e Rocks 23 a - Metamorphic Rocks 23 i - Hornblendite 23 i i - Amphibolite 24 i i i - Epidote Amphibolite 24 i v - F o l i a t e d Garnet White Mica Hornblende Quartz F e l d s p a r Rock 25 v - Garnet Sphene S c h i s t 26 b - G r a n i t i c Rocks 27 i - F o l i a t e d Quartz D i o r i t e 28 i i - D i o r i t e s 29 i i i - Mixed Rocks and Pegmatites 30 c - D i o r i t e C u t t i n g the Eastern Sediments 31 d - Epidote Amphibolite C u t t i n g the Western Sediments „ 32 e - Serpentine 33 Section I I I - STRUCTURE 34 A - F a u l t s Bounding the C r y s t a l l i n e S l i c e 35 B - Phase I F o l d i n g 36 a - Minor F o l d s 38 C - Phase I I F o l d i n g 38 a - F o l i a t i o n from the G r a n i t i c Rocks 39 b - F o l i a t i o n from the Metamorphic Rocks 40 iv Page c - Deformation ofthe Crystalline Rocks 40 D - Joints from the Sedimentary Rocks 41 a - Phase I Joints 41 b - Phase II Joints 42 c - Concentrations of Poles to Joints with Uncertain Significance 42 d - Cleavage 42 e - Slickensides on Joint Paces 43 Section IV - DISCUSSION OP THE AGE RELATIONSHIPS OP VEDDER MOUNTAIN ROCK UNITS 44 A - Eastern and Western Sediments - Other Workers 44 B - Crystalline Rocks - Other Workers 45 C - Eastern and Western Sediments - Present Work 45 D - Crystalline Rocks - Present Work 46 a - Emplacement of the Crystalline Slice 4? Section V - SUMMARY OP THE GEOLOGIC HISTORY 48 BIBLIOGRAPHY 54 v. LIST OF ILLUSTRATIONS Figure Page 1 G e o l o g i c a l Map of Ve&der Mountain i n pocket 2 C o r r e l a t i o n Chart for Vedder Mountain Rocks 4 3 Vedder Mountain Cross Sections i n pocket 4 Poles to Bedding from the Eastern and Western Sediments 36 5 Minor Folds from the Sedimentary Rocks 37 6 Minor Folds from the Metamorphic Rocks 38 7 Po l e s to Cleavage Planes 39 8 Pol e s to Folidation i n Granitic Rocks 40 9 Poles t o Foliation i n Metamorphic Rocks 41 10 S t r i a e on Joint Faces 42 11 P o l e s to J o i n t s i n Sedimentary Rocks 43 12 P c l e a to Bedding from the Eastern Sediments Near the I n t e r n a t i o n a l Boundary 44 v i . Plate Page 1 Photomicrograph Bhowing well-rounded granitic and volcanic pebbles in plagioclase volcanic arenite matrix in which the fragments are angular. 55 2 Photomicrograph of plagioclase volcanic arenite containing an elongated a r g i l l i t e fragment, 55 3 Hand specimen of color banded argillaceous chert showing intense brecciation and disruption of the banding. 55 4 Hand specimen of brecciated argillaceous white chert. 55 5 Photomicrograph of micro-volcanic arenite. 55 6 Hand specimen i l l u s t r a t i n g step joints as seen on the surface of an a r g i l l i t e outcrop. 55" 7 Photomicrograph of rounded radiolaria from an argillaceous chert fragment in radiolarian chert lenticule arenite. 56 8 Photomicrograph of cigar-shaped radiolaria with rounded cross section from a chert fragment i n radiolarian chert lenticule arenite. 56 9 Photomicrograph of lawsonite from the matrix of radio-larian chert lenticule arenite. 56 Hand specimen of radiolarian chert arenite breccia showing the jumbled distribution of the fragments. Photomicrograph of quartz feldspar volcanic porphyry with strained and broken phenocrysts. Photomicrograph of foliated epidote amphibolite. ' Photomicrograph of foliated garnet white mica hornblende quartz feldspar rock showing bending of the fo l i a t i o n around the garnet porphyroblasts. Photomicrograph of garnet sphene schist. Dike of light-colored d i o r i t i c rock cutting darker d i o r i t i c rock. Photomicrograph of foliated quartz diorite i n which the quartz stringers exhibit pronounced undulatory extinction Photomicrograph of foliated diorite i n which the feldspar has been completely saussuritized. Photomicrograph of thin prisms of prehnite from a veinlet crossing foliated diorite. Photomicrograph of basic mixed rock with very high horn-blende content and saussuritized feldspar. Photomicrograph of a sub-rectangular mesh of bladed anti-gorite crystals from serpentinite. Photomicrograph of tiny, needle-like crystals which project into massive antigorite from the bladed antigorite "walls in serpentinite. Hand specimen of a minor fold in epidote amphibolite. Photomicrograph of a minor fold outlined hy "bent actinolite crystals and formed under synkinematic conditions. Photomicrograph of a mylonite zone in granitic rocks from near the contact with the western sediments. Photomicrograph of a cataclasite derived from volcanic porphyry from the western sediments "block at the contact with the granitic rocks. Photomicrograph of a cataclasite derived from granitic rocks at the contact with the western sediments. 1. GEOLOGY OF VEDDER MOUNTAIN Section I - INTRODUCTION The o b j e c t i v e s of t h i s i n v e s t i g a t i o n were to determine the r e l a t i o n s h i p s between the sediments which comprise the eastern p a r t of . Vedder Mountain, the metamorphic and g r a n i t i c rocks which comprise the western f l a n k of the mountain and the small area of sediments west of the c r y s t a l l i n e rocks. Furthermore, an attempt to determine the s t r u c t u r a l geology of the sediments was to be made i n order to a s c e r t a i n t h e i r s t r a t -igraphy. A. L o c a t i o n and Access Vedder Mountain i s a northeast t r e n d i n g r i d g e , which l i e s on the western f l a n k of the Skagit Range of the Cascade Mountains. I t occurs at l a t i t u d e 49° 00' and l o n g i t u d e 122° 08' and i s e s s e n t i a l l y i s o l a t e d , being bounded by Cultus V a l l e y to the southeast and Sumas P r a i r i e to the no r t h -west. The peak of the mountain i s roughly eight m i l e s S30°W of C h i l l i w a c k , B r i t i s h Columbia. Access around the base of Vedder Mountain i s e x c e l l e n t by means of paved roads. On the mountain i t s e l f , a r e c e n t l y r e p a i r e d d i r t - b a s e road near a l t i t u d e 2,000 f e e t almost circumscribes the mountain. Branches from t h i s road g i v e extensive access, a l b e i t many are overgrown and not d r i v a b l e . Away from these roads, numerous burned, f a l l e n snags combined w i t h heavy second growth make t r a v e l l i n g d i f f i c u l t and dangerous. Prom Vancouver, v i a the P o r t Mann Freeway, Vedder Crossing or 2; Yarrow can be reached i n less than two hours. Consequently, i t was possible to make trips to the map-area, traverse and return to Vancouver again during the day. B. Physiography, Topography and Climate. Vedder Mountain i s elongated i n a northeast-southwest direction. It varies from about a mile to nearly three miles i n width and i s roughly twelve miles long. Pour miles of i t s length extend into the United States. Near Vedder Peak, which has altitude 3,029 feet, the mountain.is almost symmetrical i n cross section. Normally, however, the outline i s somewhat skewed, with steeper northwest slopes. The mountain i s bounded to the northwest by Sumas Prairie which has average altitude near 50 feet above sea level. To the southeast, i t i s bounded by Cultus Lake and i t s valley. Cultus Valley has average altitude near 500 feet and lake level i s 135 feet above sea level. The climate of the Vedder Mountain area i s characteristically mild and moist. Mean average r a i n f a l l i s 62 inches, most of which f a l l s from October to February. Temperature variations from 5 degrees F. to 100 degrees F. have been recorded but the extremes are rare. No major creek valleys are seen along the northwest flank of the mountain. Along the southeast flank Hatchery, Ascaphus and an unnamed creek 4,500 feet southwest of Lindell Beach occupy the only deeply incised valleys. Traverses i n the creek valleys i n the map-area are unrewarding because bedrock exposure i s poor. 3. C. Acknowledgements. Field work for t h i B thesis was carried out during May, 1964, for two weeks in September 1964, and on weekend trips u n t i l November, 1964. Costs of the work were defrayed by grants from the President's Research Fund and the Department of Geology, University of Br i t i s h Columbia. Thanks are extended to Dr. J.V. Ross, who suggested the problem, helped arrange financing of the f i e l d work, visited the author in the f i e l d , supervised and c r i t i c a l l y reviewed the work. Useful discussions with J. Monger, who worked east of Cultus Valley, Dr. K. C. McTaggart, Dr. W.R. Danner, Dr. R.M. Thompson and Dr. W.H. Mathews are also gratefully acknowledged. Dr. J.E. Armstrong of the Geological Survey of Canada kindly loaned the author f i e l d maps, f i e l d notes and thin sections from f i e l d work carried out in 1953 on Vedder Mountain. D. Previous Geological Work. R.A. Daly mapped Vedder Mountain i n 1912 as part of his 49th parallel project. He suggested that the sedimentary rocks were members of the Carboniferous or later Chilliwack Series. He grouped the crystalline rocks and called them the Vedder Greenstone. In his opinion, the Greenstone was an altered igneous s i l l intruding the sediments. Textural differences within the Greenstone were attributed to shearing. C.H. Crickmay (1930) assigned the sediments to the Slollicum Series of Late Triassic age. He thought the crystalline rocks were altered volcanic rocks conformably underlying the sediments. His map omits the sediments west of the crystalline rocks. Sect ion A-A' CD CD (J) CD CD c CD -n — o o o Q CD o o w Ui CD CD C CD m o o CD o o o t i l I t . t v i i I i — r i i S e c t i o n B - B A I / / V A r i l- I S e c t i o n C - C 3 c 3 o co cn cr » c <' o CL O co 3" A Q. 3 CD tn O CV) cn fl> co CL o 3' CO 5' (D 3 ^» 3 to o / I / / / ' 1 t', / 11 / i 7^ iO c CD ro S e c t i o n D-D' • 1^  i > I I I I I I 1 1 11 I i l l i , I ' I M ' I / ^ I i \ i f. I i i i 'i V' 1 i It 11 11 S e c t i o n E - E t n i« I < I I 11 I i 3 ' i » , k ' ' » ' S e c t i o n F-F O o CD a o o a < CD a. a. CD 3 Q 00 CD Q. §' CD —* O 3) O o PC (A I *1 I \ i i I ,'.1/ \ t K <• - • I I I II I V i I 1 1 S e c t i o n C - G • / i • i, i > /v i i i  11 I' 4. J.E. Armstrong (1956) on the "basis of f i e l d work carried out i n 1953, suggested that the crystalline rocks were bounded by steep-dipping faults. D.N. Hillhouse (1956) mapped the eastern side of Vedder Mountain on a reconnaisance scale. W.S. Moen (1959), working i n the Van Zandt Quadrangle, mapped the southern part of Vedder Mountain i n Washington State. He correlated the extension of the eastern sediments with the Chilliwack Group. On the basis of pre-Devonian granitic rocks found by Danner (1957) in the San Juan Islands, Moen suggested that the crystalline rocks are upthrust slices of pre-Devonian basement rocks. Section II - STBATIGBAPHY The thickness of sediments exposed along the southeast side of Vedder Mountain, hereafter referred to as the eastern sediments, ranges from 2,400 to 6,350 feet. Neither the top nor the bottom of the section was exposed. Conglomerate with interbedded plagioclase volcanic arenite i s the lowest unit exposed. Going upward i n the section, plagioclase volcanic arenite becomes increasingly abundant. Finally, conglomerate disappears and plagioclase volcanic arenite with a r g i l l i t e interbeds predominates. The conglomerate-bearing unit has a maximum exposed thickness of 3,500 feet west of Cultus Lake and lenses out about three miles southwest of the lake. The unit which i s predominantly plagioclase volcanic arenite i s 5. only 275 f e e t t h i c k a t the north' • . end of Cultus Lake hut r a p i d l y thickens to the southwest and i s at l e a s t 3,350 f e e t near the southwest end of the l a k e . A r g i l l i t e i s more abundant i n the upper p o r t i o n s of t h i s u n i t and forms bhe upper boundary of i t i n se c t i o n s D-D' and 0-0'. Occasional t h i n lenses of m i c r o - v o l c a n i c a r e n i t e occur i n se c t i o n s A-A' and B-B*. Throughout much of the area, m i c r o - v o l c a n i c a r e n i t e o v e r l i e s the a r e n i t e u n i t . At the north; . t i p of Cultus Lake, however, chert i s the o v e r l y i n g rock. F i f t e e n hundred f e e t of chert crop out but only one t h i n i n t e r b e d of m i c r o - v o l c a n i c a r e n i t e occurs, that being one hundred f e e t below the top of the chert. Elsewhere i n the map-area, chert occurs as i n t e r -beds ranging from a few to three hundred f e e t i n thic k n e s s i n the micro-v o l c a n i c a r e n i t e . Near Vedder Peak, three hundred f e e t of s i l i c i o u s a r g i l l i t e w i t h limestone pods crop out w i t h i n t h i s u n i t . S i m i l a r limestone-b e a r i n g a r g i l l i t e crops out a t the c r e s t of the mountain near the I n t e r -n a t i o n a l Boundary. I n t h i s l o c a l i t y , the a r g i l l i t e i s l e s s than f i f t y f e e t t h i c k . • West of Vedder Peak, p l a g i o c l a s e v o l c a n i c a r e n i t e inte-rbeds are a l s o prominent. The top of the predominantly m i c r o - v o l c a n i c araaibe u n i t i s not exposed but i t has a maximum thickness of at l e a s t 1,450 f e e t . The sediments west of the c r y s t a l l i n e rocks, h e r e a f t e r r e f e r r e d to as the western sediments, have a maximum exposed t h i c k n e s s of f i f t e e n hundred f e e t (Pigure 2 ) . N e i t h e r the top nor the bottom of s e c t i o n i s exposed. Quartz p l a g i o c l a s e porphyry i s the oldest exposed u n i t of the western sediments. I t crops out i n a r a i l w a y cut a t the southwest edge of the outcrop area of the sediments where i t i s 100 f e e t t h i c k . O v e r l y i n g r 6 . the porphyry i s a r g i l l i t e which ranges from 0 to 250 feet i n thickness. Micro-volcanic arenite with scattered, thin layers of chert succeeds the a r g i l l i t e . I t reaches a thickness of 150 feet i n the central portion of the sediments hut pinches out to the northeast and southwest. A s t r i k i n g unit unlike any of the eastern sediments overlies the micro-volcanic arenite. I t consists of rad i o l a r i a n chert l e n t i c u l e arenite and volcanic radiolarian chert arenite breccia which contain a t h i n , discontinuous impure cherty limestone horizon. This unit i s continuous over the outcrop area of the western sediments and attains a maximum thickness of 400 feet. The calcareous unit varies up to 50 feet i n thick-ness. Despite the d i s t i n c t i v e features of t h i s unit, i t i s suggested that the limestone from i t i s equivalent to the limestone pods within the s i l i c i o u s a r g i l l i t e of the eastern sediments (Figure 2). A thick, continuous a r g i l l i t e band overlies the limestone-bearing unit. I t i s massive to t h i n l y bedded and has a maximum thickness of 700 feet. The uppermost exposed unit of the western sediments i s argillaceous ribbon chert. I t crops out alongside the highway near the west central edge of the sediments where i t i s 100+ feet thick. Near the way station of S i n c l a i r and i n a small area further north-east, diabasic to porphyritic volcanic rocks crop out. The diabasic rocks are not i n contact with the porphyries so th e i r relationship with them remains uncertain. Sim i l a r l y , the d a c i t i c porphyritic volcanic rocks are separated from the western sediments so no direct correlation can be made. However, since some of the S i n c l a i r porphyries are i d e n t i c a l to the porphyry which underlies the western sediments i t seems probably that they correlate i n part with i t . Furthermore, since the S i n c l a i r porphyries are 7. much thicker, some are probably older than the western sediments porphyry. Amphibolites, epidote-amphibole schists and gneisses, amphibole and epidote-amphibole mica schists and granitic rocks underlie much of the western flank of Vedder Mountain. For easy reference, these have been designated crystalline rocks. The epidote-amphibole schists and gneisses have mineral assemblages which are typical for basic and p e l i t i c rocks from the Aimandine-Amphibole Facies of Turner and Verhoogen (i960). These medium grade metamorphic rocks predominate northeast of Sinclair. Southwest of Sinclair, the metamorphic rocks have been extensively invaded by granitic rocks. Foliated diorite i n which feldspar has been completely saussuritized i s the predominant granitic rock. Where shearing has been of l i t t l e importance, original crystal shapes are pseudomorphed. Where shearing has been important, original crystal shapes have been destroyed. Cataclastically foliated quartz diorites i l l u s t r a t e the latter case. Near intrusive-metamorphic contacts dark-colored d i o r i t i c rocks and pegmatitic plagioclase-amphibole rocks crop out. Along the eastern contact of the crystalline rocks, several ellipsoidal bodies of serpentinized peridotite crop out. A. Eastern Sediments. The following discussion i s intended to give a f a i r l y detailed picture of the various rock types which comprise the eastern sediments. They are covered as near as possible to the order i n which they were deposited. 8. a. Conglomerates. Conglomerates interbedded with volcanic arenites comprise the east flank of Vedder Mountain from the shore of Cultus Lake adjoining the water-manship Training Area to two miles southwest of Lindell Beach. West of Hook Point on Cultus Lake conglomerate outcrops are found up to an altitude of 1,700 feet above sea level; northeast and southwest they crop out at lower altitude as the conglomerate bearing unit thins laterally. Detailed mapping within the conglomerate-arenite unit has not been carried out. From available data, however, i t can be stated that conglom-erate beds range from a few to several hundred feet i n thickness. The conglomerates were massive and a l l attitudes recorded are conglomerate-arenite contact zones. Where contacts are exposed, undulations suggest that the arenite was eroded prior to or during deposition of the conglomer-ate. Whether these readings represent foreset beds or regional beds i s not certain. However, thin arenite beds continuous over 50 feet with no thickening or thinning weigh against the likelihood of the unit being cross bedded. The matrix of the conglomerates i s very similar to the arenites. with which they are interbedded. Ignoring the pebbles, the matrix would be classified as an immature plagioclase volcanic arenite using Folk's (1961) classification. Grains within the conglomerate matrix are angular but not quite so angular as those from the arenites (Plate l ) . Pebbles and cobbles from the conglomerate are characteristically well-rounded. Cobbles often display high sphericity as well. In general, as the diameter of the pebbles to cobbles from the conglomerate increased 9. so also did the roundness and sphericity. Chert, granitic and volcanic pebbles and cobbles are present. Most of the chert is pale green but occasional jasper pebbles occur. Granitic rocks range from hornblende granodiorite i n which feldspar has been extensively saussuritized to micromyrmekitic granite which contains clear, often embayed high temperature quartz and unaltered a l b i t i c oligo-clase, An24> phenocrysts. The volcanic rocks are quite variable. For instance, one well-rounded cobble consisted of equant fragments of volcanic quartz and angular devitrified volcanic glass fragments i n a pale green glass matrix; another was derived from ophitic lava. Porphyries often with quartz and/or albite phenocrysts are the commonest volcanic rocks. Relative abundance of the various rocks which comprise the pebbles and cobbles varies from place to place but the present study was not de-tailed enough to outline zones of distribution. Granitic pebbles seem to be most abundant toward the base of the exposed section yet even this i s not certain on the basis of present information. In the conglomerates as a whole, rocks of volcanic origin are commonest, those derived from chert next and those derived from granitic rocks least common. These conglomerates display an antipathetic relationship i n which mature and immature components coexist. The simplest explanation of this relationship i s that the conglomerates were deposited from turbidity currents. Visible evidence to support this hypothesis i s lacking yet a reasonable alternative explanation i s d i f f i c u l t to envision. b. Plagioclase Volcanic Arenite. Plagioclase volcanic arenites are prominent along the east side of 10. Vedder Mountain. These are interbedded with and overlie the conglomerates. They are commonly dark "brown on a weathered face "but yellow-brown with a greasy luster on a fresh face. Composition varies widely but plagioclase, quartz, volcanic fragments and lesser a r g i l l i t e fragments predominate. The matrix contains clay material. Occasionally, rounded augite grains were seen but they were never prominent. Except where elongated black a r g i l l i t e fragments gave the rock a fabric (Plate 2), bedding was seldom visible i n the arenites. Quartz from these rocks appears to be predominantly of volcanic origin. Erosive or corrosive agents have roughened grain boundaries yet clearly many grains were formerly idiomorphic. Most grains are very clear, inclusions are rare and straight extinction i s the rule. These features f i t volcanic quartz from Krynine's "Genetic Classification of Quartz Types" (Polks (1961) p. 69). Much of the feldspar present has been saussuritized, although some grains are fresh. Sharp edges have been eroded from the grains but they are s t i l l angular. Albite ranges from AnQ to An 5 and comprises the only feldspar grainB identified i n the arenites. Rock fragments of volcanic origin are more prominent than those of sedimentary origin. Epidotized diabase, quartz and albite porphyries and devitrified, sometimes vesicular, volcanic glass are typical of the volcanic rock fragments. Soft black a r g i l l i t e fragments and occasional, chert fragments are the only sedimentary fragments which have been identified. Angular fragments, presence of easily destroyed minerals and abundance of clayey material i n the matrix show that these arenites are 11. immature. Using Polk's (1961) classification, the rocks would "be called immature plagioclase volcanic arenites. Veinlets of quartz or carbonate and prehnite are common cutting the arenites. Prehnite from these veinlets i s often clouded with inclus-ions i n thin sections. It occurs as stubby, often radially arranged crystals which are usually roughly perpendicular to the walls of the veinlets. c. A r g i l l i t e and Phyllite. A r g i l l i t e occurs as interbeds i n the arenites and forms an extens-ive band of outcrops from altitude 1,500 feet on Ascaphus Creek to the northwest tip of Cultus Lake. Within the arenite, a r g i l l i t e bands usually appeared massive. Occasionally, however, differential weathering or color banding could be seen. These bands varied from several to roughly two hundred feet i n thickness. Bedding was more commonly seen in the thicker units. At the north. - end of Cultus Lake, phyllite i s prominent. It i s soft, usually black on a fresh face and often slightly rusty on a weathered face. Although d i f f i c u l t to see i n the f i e l d , thin banding i s readily observed on most specimens when they are cut with a diamond saw; Commonly, this banding consists of very fine grained brown and much finer black bands with 1/16 to 1/4 inch spacing. Within the a r g i i l i t e s and phyllites are interbeds of immature, micaceous arkose. Although they reach thicknesses of 20 feet occasionally, most of these arkose bands are only a few incheB thick. The thin bands commonly pinch out very quickly but i n part this pinching i s of tectonic 12. origin. Most of the grains i n the arkose hands f a l l i n the fine sand size-range (Polks (1961), p. 24). The hands weather brown and are dark gray-brown fresh. Except for aligned white mica flakes, they are massive. At the base of the h i l l half a mile northwest of the watermanship Training Area, sheared, talcose, phyllitic-looking sediments are exposed. Pinching and swelling of bands and differential movement between bands obscure detailed textural data but banding has not yet been destroyed. The rock consists of alternating a r g i l l i t e and volcanic arenite layers. The arenite i s the same composition as that from the arenite unit to the south-west. Alternating finer and coarser beds, evidence of small amounts of erosion at interfaces and what appear to be slump convolutions suggest that this a r g i l l i t e unit may be a turbidite. d. Chert. Chert i s a prominent constituent of the eastern sediments and crops out along the crest of the Mountain from northeast of Vedder Peak almost to the International Boundary. Massive, ribbon and nodular chert, as well as some jasper, are present. Massive chert i s most prominent along the crest of the Mountain near the International Boundary. It weathers white to red-brown and i s pale to dark gray on a fresh face. Intense brecciation with introduction of quartz along the fractures characterizes this massive chert. In thin section, i t i s seen to be microcrystalline, consisting of tiny, sutured quartz grains. Argillaceous material i s prominent and clouds the quartz so that the section looks dark brown under low power i n plane light. A 13. reticulate network of veinlets ~. of clean, sutured quartz crystals cuts the chert. These veinlets range from 0.05 inches to less than 0.01 inches i n thickness. Some of the fractures i n which the quartz veinlets occur are incompletely f i l l e d . These have poorly developed quartz crystals lining their walls. Ribbon chert i s common west of Vedder Peak near the contact with the crystalline rocks. Much of this chert i s gray or gray-green and weathers white to red-brown. Occasionally, the ribbons are jasper rather than chert. Where they are well-formed, the ribbons average two inches in thickness and are continuous over tens of feet. Although the chert i s somewhat argillaceous, no interlayered a r g i l l i t e zones are present. Along the mountain crest southwest of Vedder Peak, dark gray to black gray-green to brown-green color banded chert crops out. Intense brecciation and disruption of the banding i s present; thus the nature and continuity of the banding i s not known (Plate 3). Tension gashes, often lined with quartz crystals, are prominent features of these rocks. Adjoining the road northwest of the Watermanship Training Area near the northwest tip of Cultus Lake, nodules of dark to nearly white chert occur i n a foliated matrix of black argillaceous material (Plate 4). In some areas, the rock consists of ribbons of chert separated by thin layers of a r g i l l i t e . Since the nodular chert i s physically similar and crops out nearby, i t was concluded that the two rock types are the same but that the nodular rock has been disrupted by deformation. e. Silicious A r g i l l i t e with Limestone Pods. Limestone pods enclosed by siliceous a r g i l l i t e crop out at 14. altitude 2,500 feet due south of Vedder Peak. Pods occur over a strike length of 2,500 feet and are sporadically distributed. This a r g i l l i t e i s very similar to that which separated chert ribbons near the \fetermanship Training Area. It i s a dark gray cherty a r g i l l i t e with thin undulose black a r g i l l i t e stringers, which comprise about ten percent of the rock. These stringers have served as l o c i i of slipping, consequently, they are foliated with many well-developed slickensided faces. They display widely variable orientation and have not been useful as bedding indicators. Pods of limestone from two to five feet long and one to three feet wide predominate but one pod with dimensions of 50 feet by 30 feet was found. Uneven nodules of black chert comprise about 25$ of the limestone pods. The limy portion of the pods consists of medium to coarse grained carbonate. It i s pale gray on a weathered face but darker when freshly broken. When a fragment of the limy portion of a pod was immersed i n dilute hydrochloric acid, a vigorous reaction ensued. However, insoluble residue quickly clouded the acid. The pods are cherty, impure crystalline limestone. Limestone pods enclosed by siliceous a r g i l l i t e also crop out near the crest of Vedder Mountain 2,000 feet north of the International Border. These rocks are indistinguishable from the ones near Vedder Peak and are thought to be equivalents. f. Micro-volcanic Arenite. Micro-volcanic arenite, which i s c l i f f forming, i s prominent near the crest of Vedder Mountain, especially near the peak. The rock i s typically massive, dark brown weathering and dark gray-green to brown when fresh. Bedding was not seen i n the f i e l d but i n thin Bection, mineral 15. fragments are often seen to be aligned. Brecciation of this arenite i s common and fractures are p a r t i a l l y or wholly f i l l e d with quartz, prehnite and occasionally carbonate. Angular quartz, feldspar and rock fragments l i e i n a dense, dark brown, often foliated groundmass (Plate 5). Deformation i s indicated by broken, offset twins i n feldspar fragments. Fresh to strongly sericitized plagioclase grainB ranging up to oligoclase, An__, comprise the feldspar seen i n these rocks. Quartz occurs both as volcanic-type and as sutured grain aggregates which are presumably of metamorphic origin. Hock fragments are predominantly of volcanic origin. The groundmass i s dense, dark brown and isotropic. Alteration combined with small grain size render i t s original nature uncertain. The rock i s an immature volcanic arenite. Whether i t had i t s origin i n a turbidity current, was formed by pyroclastic action or by some other mechanism i s not certain. B. Western Sediments. The western sediments occupy an arcuate area which begins one mile northeast and ends about two miles northeast of Kidd while extending up to altitude 500 feet on the flank of Vedder Mountain. They comprise an overturned monocline and w i l l be discussed in the order i n which they were deposited. a. Quartz Plagioclase Porphyry. Quartz plagioclase porphyry i s believed to be the oldest rock in the western sedimentary block. Quartz occurs as rounded crystals which are milky i n hand specimen and comprise roughly 15$ of the rock. .16 Plagioclase crystals are saussuritized and comprise roughly 10$ of the rock. The groundmass i s pale green and consists of microcrystalline quartz and feldspar. This porphyry crops out 4,000 feet northeast of Kidd in a railway cut. In this cut, the porphyry i s i n contact with foliated quartz diorite of the crystalline rocks. Quartz phenocrysts show pronounced undulatory extinction and many feldspar phenocrysts are broken or bent. However, a thin section from a porphyry specimen six feet from the vertical diorite-porphyry contact was easily recognizable despite cataclasis. At the con-tact, both rocks are cataclasites. b. A r g i l l i t e . A r g i l l i t e i s a prominent constituent of the western sediments. Except i n railway and occasional stream cuts, however, i t i s very poorly exposed. Even i n good exposures, i t appears massive at f i r s t glance but careful scrutiny often reveals subtle color banding on the weathered face. P h y l l i t i c f o l i a t i o n has been developed i n places but overall, these rocks are less sheared than the a r g i i l i t e s which crop out near the northwest tip of Cultus Lake. In several l o c a l i t i e s , differential movement along joint faces has resulted i n a stepped appearance on the outcrops (Plate 6). At times, f r i c t i o n during slippage has resulted in bending of lamellae to form small scale folds. Neither step-joints nor folds of this nature were observed i n the eastern sediments. c. Micro-volcanic Arenite. Rocks which are almost identical i n macro- and microscopic detail to the micro-volcanic arenitea which crop out near Vedder Peak are Been in a highway cut at altitude 250 feet, 8,000 feet northeast of Kidd. Ae with the eastern exposures, these rocks are commonly massive. In one small area, however, beds crop out which range from two inches to two feet i n thickness with gross width about 10 feet. As with the eastern arenites, the origin of these rocks i s uncertain. d. Radiolarian Chert Lenticule Arenite. Radiolarian chert lenticule arenite crops out in a railway cut northeast of the quartz plagioclase porphyry which was previously described-and in a railway cut 9,700 feet northeast of Kidd. In both l o c a l i t i e s , i t i s i n contact with volcanic arenite breccia but the nature of the contact i s uncertain. Large to small elongated angular to saucer-shaped black fragments and generally smaller elongated angular white to pale green fragments l i e i n a dark brown generally sand-sized matrix. The fragments are well aligned. In dimensions, the black fragments range up to 2.75 by 0.6 inches but average 0.6 by 0.2 inches; the others range up to 0.8 by 0.25 inches but average 0.4 by 0.15 inches. Fragments comprise 35$ of the rock, of which 20$ are black. The black fragments were found to be argillaceous chert which contain up to 40$ rounded (Plate 7) and occasional cigar-shaped radiolaria (Plate 8). White f a i r l y clean chert fragments also contain a few radio-l a r i a . Volcanic fragments are pale green and consist of devitrified vol-canic glass i n which there are sometimes numerous microlites of feldspar. Well developed systems of cracks cut these fragments but they are planar .18 and not p e r l i t i c . The matrix of this arenite consists of well-aligned sericitized feldspar, lawsonite and volcanic quartz fragments i n an argillaceous ground-mass. The quartz fragments are from former idiomorphic crystals. Lawsonite occurs as groups of radially arranged, fibrous crystals, which are pseudo--morphous after subhedral feldspar crystals (Plate 9). Usually replacement i s complete but occasional feldspar remnants are seen. In plane light, lawsonite i s seen as dense, dark brown masses. Under crossed nicols, interference colors range up to f i r s t order red. Crystal fibers are length fast. Identification was based on x-ray powder data. Whether the lawsonite formed i n place or whether replacement occurred prior to erosion of the source rocks i s not certain. e. Volcanic Radiolarian Chert Arenite Breccia. Volcanic arenite breccia crops out north of the radiolarian chert lenticule arenite outcrops i n the railway cuts and i n a creek valley at altitude 400 feet, 1,000 feet due south of the micro-volcanic arenite outcrop along the highway. This distinctive rock often has an overall greenish tint due to abundant green fragments and a greenish groundmass. Angular fragments pre-dominate although rounded corners are not uncommon. Most fragments are relatively equant and range from 0.5 inches across down to microscopic size. Most, however, are between 0.2 and 0.3 inches across. Fragments comprise roughly 80$ of the rock. Occasional fragments occur which have length to width ratios up to 7:1, yet no alignment has occurred (Plate 10). In thin section, a subtle fo l i a t i o n within the matrix can be seen but 19. r elongated fragments do not conform to i t . Most of the fragments comprising the "breccia are of volcanic origin although white or "black chert and "black a r g i l l i t e fragments occur. Within the chert fragments i n the breccia, as in those of the lenticule arenite, scarce to abundant radiolaria are seen. Fragments of volcanic quartz, some of which are idiomorphic, are scattered throughout the matrix. A wide variety of rock types comprise the volcanic fragments. For instance, pale green slightly devitrified glass, gray volcanic glass with dark green amygdules, feldspar porphyry with a dark green microcrystalline groundmass, gray-brown microcrystalline volcanic rock and quartz porphyry with a white groundmass a l l occurred i n one hand specimen. The groundmass of the breccia i s extremely fine and somewhat altered. Nothing to suggest i t s original nature was seen. The jumbled arrangement of the fragments, presence of fragments which could not withstand long transport i n a stream, paucity of matrix and preponderence of fragments of volcanic origin BUggeBt that the rock was deposited quickly under turbulent conditions. Whether i t i s of pyroclastic, turbidity current or mixed origin remains uncertain. f. Limestone. Limestone interbedded with a r g i l l i t e occurs as interbeds i n the lenticule arenite-volcanic arenite breccia unit. It crops out a few feet south of the arenites i n the railway cut 9,700 feet northeast of Kidd. In the creek valley 1,000 feet south of the micro-volcanic outcrops, limestone i s the westermost outcrop. On a weathered surface, the limestone i s dark gray; on a freshly 20. "broken surface, dark gray-brown. It reacts vigorously with dilute hydro-chloric acid releasing a large insoluble residue content. In plane light, a thin section of this rock i s dark "brown. Under polarized light, sutured carbonate crystals cut by a reticulate network of carbonate veinlets are seen. The rock consists essentially of medium to coarse grained calcite crystals which enclose much argillaceous material. Rounded zones i n the limestone which consist of calcite with a core of quartz or argillaceous material are thought to be remnants of crinoid columnals. Chert nodules which are irregular i n outline range up to three inches i n long dimension and comprise 30 to 40$ of the rock. The distribution of the limestone remains somewhat uncertain because i t was seen i n only two outcrops. Its relation, i f any, to the eastern limestone pods i s not known. Evidence for age determination i s lacking because no positive f o s s i l identification T*as possible. g. Ribbon Chert. Six thousand feet northeast of Kidd, overlooking the highway i s a low bluff composed of ribbon chert. It i s white weathering but pale gray when freshly broken. Ribbons in this chert are continuous over tens of feet and sli g h t l y crenulated. No inter-ribbon argillaceous material i s present although the chert i t s e l f i s slightly argillaceous. Overburden surrounds the bluff. C. Volcanic Rocks. Intercalated volcanic and granitic rocks crop out from 4,000 f e e t northeast to 1,000 f e e t southwest of S i n c l a i r . V o l c a n i c rocks predominate and the granitic ones are thought to be imbricate s l i c e s a s s o c i a t e d w i t h 21. the fault which "bounds the crystalline rocks on the west. (Figure 3, Section E-E>). a. Altered Diabase. Adjoining the highway 4,000 feet northeast of Sinclair, massive-looking olive green rock with numerous nearly "black, lustrous, serpentine-coated sl i p surfaces crops out. The rock i s very fine grained. The green color of the rock results from extensive saussuritization of the abundant feldspar laths. Augite, which has been p a r t i a l l y altered to serpentine alone cleavages, occurs as subhedral laths. Although rendered uncertain by alteration, the rock appears to have a sub-ophitic texture. As well as replacing augite, serpentine forms thin coats on slip faces. Also cutting the rock are veinlets of stubby, radiating prehnite crystals. Occasional carbonate crystals are intergrown with this prehnite. In places, these veinlets comprise as much as 15$ of the rock. A thousand feet southward along the highway, rock i s exposed which i s almost indistinguishable from the diabase i n hand specimen. In thin section, however, this rock i s seen to be fragmental. Altered diabase, augite crystal, volcanic quartz crystal, dark brown devitrified volcanic glass and feldspar porphyry fragments l i e i n a dense, altered groundmass. No shards were found but the nature and diversity of fragments suggests that the rock i s a tuff. b. Volcanic Porphyries. Porphyritic volcanic rocks crop out intermittantly along the 22. British Columbia Electric Railway tracks from 2,500 feet northeast to 1,000 feet southwest of Sinclair. Exposures of brecciated to mylonitized granitic rocks also crop out within this predominantly volcanic area. The porphyries have been subjected to variable cataclasis. Tension cracks p a r t i a l l y or wholly quartz-filled are prominent. The ground-mass of the porphyries varies from pale to dark gray or green and contains white to pale gray phenocrysts. Quartz, which occurs as clean, embayed crystals and/or plagioclase laths with composition near Angg comprise the phenocrysts. Phenocrysts occupy 10 to 40$ by volume of the rocks. The groundmass, where i t i s not obscured by c a t a c l a s i B and alteration, con-sists of a mosaic of tiny, sutured quartz and oligoclase crystals. K-Peldspar was not found and the rocks would be called oligoclase bearing dacite porphyries. Even i n the porphyries least affected by cataclasis phenocrysts are bent and broken (Plate 11). In the more strongly affected rocks, the matrix i s extremely fine grained and phenocrysts are reduced to scattered crystal fragments. Mylonite zones are common and appear as dense, iso-tropic, foliated zones with scattered, tiny crystal fragments. Prehnite occurs both as veinlets comprised of stubby prisms and as scattered grains in mylonitized areas. It i s widespread and occasionally comprises 5$ of the rock. Some of these porphyries are similar to that which underlies the western sediments. No basis other than physical and mineralogical similarity exists but i f these porphyries correlate i n part with the porphyry from the western sediments, some of them are very probably older. 23. More extensive exposure i s the "basis of this suggestion. D. Crystalline Rocks. As used here, crystalline rocks refers to araphioolites, epidote -amphibole schists and gneisses, amphibole and epidote - amphibole mica schists and granitic rocks. These rocks form a northeast trending unit which i s roughly a mile wide and comprises much of the western flank of Vedder Mountain. a. Metamorphic Rocks. The non-granitic components of the crystalline rocks have mineral assemblages which are typical of the regional metamorphic Aimandine-Amphibolite Facies of Turner and Verhoogen (i960). According to these authors, coexisting epidote and plagioclase in the range Ang5 *° A n 4 5 indic-ate: conditions of high load pressure. Further, they suggest that the mineral assemblages formed between 550 and 700 degrees Centigrade and 4,000 to 8,000 bars water pressure. Typical minerals from the Vedder Mountain metamorphic rocks include: hornblende, actinolite, white mica, almandite, epidote and oligoclase with accessory sphene and pyrite. By comparing mineral assemblages and textures, i t seems clear that the amphibole schists and gneisses, garnet amphibole schists, mica amphibole and garnetiferous mica amphibole schists which crop out on Vedder Mountain were formed under conditions of f a i r l y high temperature and pressure, presumably at consider-able depth within the crust. i . Hornblendite. Hornblendite i s relatively rare on Vedder Mountain. It was found 24. n one locality fonly am, about half a mile northeast of Vedder Mountain Station i n a railway cut. Hornblende, which i s pleochroic i n browns and green, occurs . as medium grained subhedral laths with irregular borders. No pronounced fabric was present, although they were poorly aligned. Sphene i s accessory. Hornblende has been bleached and/or iron stained along a series of cracks which cross the rock. i i . Amphibolite. Amphibolite i s not prominent among the metamorphic rocks. Only one loc a l i t y has been verified by thin section work, that being a small quarry alongside the highway l/4 mile northeast of the railway crossing northeast of Yarrow. From hand specimen study, i t i s suggested that amphibolite also occurs interlayered with the schists and epidote amphibolites which are well exposed i n road cuts around the north end of the Mountain. Hornblende, which i s the predominant amphibole comprises 50 to 80$ of the rock. Feldspar i s oligoclase near A n 3 Q . Foliation, as defined by segregation of light and dark minerals and parallelism of the elongated amphibole laths, varies from weak to very strong. Where fol i a t i o n i s well developed, the texture of the rocks i s gneissic. Quartz in the rocks usually occurs i n thin stringers parallel to the foli a t i o n , i i i . Epidote Amphibolite. Most prominent by far among these metamorphic rocks are epidote amphibolites. Outcrops of these rocks are well exposed in many road cuts around the north end of the Mountain. These medium grained rocks are usually f a i r l y well banded. Hornblende or actinolite occur as stubby 1 laths which, combined with mineral segregation, outline the fol i a t i o n . In these rocks, amphiboles seldom exceed 50$ and usually range from 35 to 45$. Epidote, usually elinozoisite with minor' amounts of zoisite, occurs as equant to slightly elongated, usually somewhat rounded grains. Often these grains are i n subparallel alignment. Epidote comprises 10 to 30$ of the rock. OligoclaBe, usually An_K to An , occurs as i n t e r s t i t i a l , equant, <>o 35 somewhat sutured grains. Twins are rare. Sounded equant quartz grains occur i n t e r s t i t i a l l y with the oligoclase grains. Quartz varies from less than 5$ up to a 1:1 ratio with the feldspar. Sphene occurs both as elongated prisms with rounded corners and as stubby prisms with rounded corners. Cross sections are equant to roughly diamond-shaped. Sphene comprises up to 3$ of the rock. Pyrite cubes are rare accessories (Plate 12). Along the Cultus Lake highway several hundred feet northeast of the turnoff to the Watermanship Training Area, a rock which was mapped as pseudo-serpentinized greenstone crops out. Just out of the map area, a similar rock i s exposed in a quarry a few hundred feet northeast of the bridge across the Vedder River near Vedder Crossing. Mineralogically, however, the rock was found to be an epidote amphibolite. Serpentine, which appeared prominent in the f i e l d was found only as thin layers on joint surfaces i n thin section. Foliation was not apparent i n hand speci-men but pronounced mineral alignment was visible in thin section. The outcrops of this rock are adjacent to the eastern bounding fault of the crystalline rocks which further clouded positive identification of the rock. Clearly, however, this pseudo-serpentinized lava i s actually a medium grade metamorphic rock. i v . Foliated Garnet White Mica Hornblende Quartz Feldspar Rock. 26. Although not abundant, foliated garnetiferous amphibole-rich rocks are widespread throughout the metamorphic rocks. The most accessible exposure of these rocks i s 200 feet east of the railway crossing northeast of Yarrow. Several other good exposures occur along the road around the north nose of Vedder Mountain at altitude 500 feet. The rock i s usually banded with thin, white discontinuous, B l i g h t l y undulatory stringers in a dark green medium grained matrix. Garnets, ranging from l/8 to 3/8 inches diameter, comprise 10 to 20$ of the rock. The fo l i a t i o n bends around the garnet crystals (Plate 13). Even in hand specimen, brecciation of the garnet crystals i s apparent. White mica plates l i e i n the plane of foliation. Mica comprises roughly 10$ of the rock. Hornblende, which i s pleochroic from green to brown, forms aligned, ragged laths. The isotropic garnet i s near almandite i n com-position. Crystal edges are rounded with numerous embayments and quartz, feldspar and epidote occur abundantly within crystal boundaries. White mica cross sections are elongated and taper out gently at both ends. Quartz and plagioclase, most of which i s albite, Aiig to An^Q, are inter-s t i t i a l . Crystals of these minerals tend to be elongated par a l l e l to the foliation. Elongated prisms of sphene with rounded corners and scattered anhedral medium grained pyrite crystals are accessory. Often, the pyrite has been p a r t i a l l y altered to hematite; v. Garnet Sphene Schist. Porphyroblasts of pale red-brown garnet ranging up to 3/8 incheB i n diameter and sphene which i s very nearly the same color but occurs as 27. porphyroblasts which are commonly l/8 inch i n diameter l i e i n a crinkled, foliated irregularly banded green matrix. This matrix consists of a frame-work of elongated, sutured quartz grains with i n t e r s t i t i a l albite, A I I I Q _ I 5 I and irregular discontinuous layers consisting of bent, contorted white mica plates. Much of the quartz displays undulatory extinction. The almandite crystals are intimately brecciated,Kave embayed edges and often contain quartz crystals. Quartz, mica and feldspar f i l l the embayments. Sphene usually occurs as roughly diamond-shaped crystals. They are often ragged and i n places have been broken with fragments spread out along the f o l i a t i o n (Plate 14). Most of these crystals are brecciated and white mica occupied the cracks in one. What appear to be polysynthetic twins are prominent in some of the sphene crystals. Also present i n the rock are pale green, f a i n t l y pleochroic chlorite and a few ragged epidote crystals. An average mode for this rock i s as follows; Almandite Garnet 18$ Sphene 13$ White Mica 32$ Feldspar 10$ Quartz 25$ Chlorite < 2$ Epidote Trace b. Granitic Rocks. Granitic rocks within the crystalline s l i c e predominate southeast of Sinclair. These rocks are thought to be magmatic i n origin. Dykes of 28. light colored d i o r i t i c rock cutting darker d i o r i t i c rock have "been Been (Plate 15). Border phase pegmatitic zones are thought to represent late stage fluids derived from the magma during crystallization. A melanocratic border phase separates the granitic rocks from the metamorphics and inferred contacts suggest intrusive relationships with the metamorphic rocks. i . Foliated Quartz Diorite. Foliated quartz diorite occurs i n minor amounts within the diorites which are the predominant granitic rocks. These quartz-rich bodies are of very limited extent and their textures vary radically over short distances. For instance, i n a highway cut just north of the micro-volcanic arenite outcrops which are within the western sediments, fine grained quartz diorite and quartz diorite gneiss with prominent stringers of quartz occur within a few feet of one another. The gneisB i n this instance appears to be of cataclastic origin. Contacts were not exposed i n the outcrop so relation--ship8 between the two rock types could not be determined. Many of the quartz diorites are gneissic and in these rocks, quartz i s very prominent. It occurs in discontinuous stringers with maximum width l/lO inches which comprise up to 40$ of the rock. Grayish white quartz which occurs as large, elongated, sutured grains comprises the stringers. Most of these grains exhibit pronounced undulatory extinction (Plate 16). Stringers of pale green chlorite which are sub-parallel to the quartz stringers comprise roughly 15$ of the rock. The matrix contains a mixture of albite, zoisite and sericite. Prior to alteration, the matrix was medium grained plagioclase. Where rocks of this group are poorly foliated, the mineralogy i s 29. roughly the same "but the stringers are thinner and not well aligned. In a l l instances, however, quartz i s very prominent. The relationship of these quartz d i o r i t e s to the d i o r i t e s i s un-certain. Their l o c a l l i z e d nature and high quartz content suggest that they may "be l a t e stage magmatic intrusions cutting the d i o r i t e s . Their gneissic textures may be a function of their positions, since they commonly occur near the f a u l t which bounds the c r y s t a l l i n e s l i c e . Mylonitized zones are common and perhaps cataclasis associated with emplacement resulted i n mobilization and r e c r y s t a l l i z a t i o n of the quartz. i i . D i o r i t e s . Most of the c r y s t a l l i n e rocks which comprise the southwest flank of Vedder Mountain are f o l i a t e d d i o r i t e s . P r i o r to ubiquitous, intense saussuritization, these rocks consisted e s s e n t i a l l y of hornblende and plagioclase, i n the r a t i o of 2:8. S e r i c i t e , a l b i t e and z o i s i t e now form pseudomorphs after the plagioclase. Hornblende has withstood a l t e r a t i o n f a i r l y w e l l although i t has been bleached and c h l o r i t i z e d f o r short distances out from fractures. The d i o r i t e s are uniformly medium grained and commonly show mineral alignment. This alignment i s s o l e l y of the elongated hornblende lathes. P y r i t e , p a r t i a l l y altered to hemfttite, i B a common accessory mineral (Plate 17). Composition, color index, grain s i z e and texture of these rocks t a l l y with these features as described f o r t y p i c a l d i o r i t e s i n Williams, Turner and Gilbert (1955, p. 106). Consequently, the name d i o r i t e has been assigned to these rocks despite destruction of the plagioclase. Numerous quartz-albite and prehnite v e i n l e t s cut the d i o r i t e s . 30. Both quartz and albite i n these veinlets occur as tiny sutured grains which can be distinguished only by r e l i e f . Prehnite prisms vary from stubby to elongated. They are clear in thin section and often display so-called bow tie structure. Most of these prisms are roughly at right angles to the veinlet walls (Plate 18). In one hand specimen, white, vitreous prehnite f i l l e d a l/4 inch veinlet and occurred as interlocking prisms with cocks-comb texture. A second hand specimen had an open tension crack, the walls of which were covered by a felted mass of tiny, transparent, colorless prehnite needles. i i i . Mixed Rocks and Pegmatites. Near the contacts with the medium grade metamorphic rocks, mixed rocks crop out which are characterized by the same alteration and minerals as the diorites but with much higher color index than the diorites. Typical color indices for this rock range between 60 and 70 (Plate 19). They are also slightly finer grained than typical diorites. Foliation i s usually well defined i n these rocks, perhapB i n part as a result of their higher hornblende content and hence higher color indexes. Since these rocks occur near contacts, i t seems reasonable to suggest that they represent the basic border phase of the diorite intrusion. Poor outcrop renders the extent and detailed distribution of this "border phase" uncert-ain. Pegmatites, consisting of albite, again with superposed saussurite alteration, and clots of hornblende or actinolite crop out i n the same general area as the mixed rocks. These are thought to becferived from late stage fluids derived from crystallization of the diorite. Contact relations 31. of these pegmatites were not determined during the f i e l d work and have been inferred. The granitic rocks have been interpreted as being of magmatic origin. Misch, (personal communication with Armstrong), however, suggests that they are of metamorphic origin. His interpretation i s based on thin section analysis of samples taken by Armstrong and a f i e l d trip to Vedder Mountain. Several features are l e f t unanswered i f the crystalline rocks of Vedder Mountain are a l l of metamorphic origin. Among these are the dikes, the mixed rocks and pegmatites and the fact that f o l i a t i o n i n the granitic rocks i s not related to that from the obvious medium grade meta-morphic rocks. c. Diorite Cutting the Eastern Sediments. Four hundred feet east of Vedder Peak, a narrow, steeply dipping northeast trending body of diorite cuts the eastern sediments (Figure l ) . Its outcrop pattern suggests that i t parallels bedding in the sediments. The diorite superficially appears altered and sheared. In thin section, intense alteration i s seen to have destroyed plagioclase i n the rock, as i s typical of the diorites. Unlike the other diorite specimens, zoisite in this specimen has reached such a size that i t can be easily disting-uished under low power. Clots of hornblende crystals contain individual crystals which have been p a r t i a l l y chloritized and closely broken. Fragments of these crystals were subsequently drawn out by differential movement. Many of the hornblende crystals p o i k i l i t i c a l l y enclose rounded quartz and feldspar grains which are spread out along cleavage directions and appear i n part to replace the host. 32. A network of mylonite zones into which prehnite has been intro-duced comprise up to 30$ of the rock. Prehnite i n these zones i s equant and very fine grained. A further 15$ of the rock consists of quartz-prehnite veinlets i n which prehnite occurs as elongated to blocky prisms arranged roughly at right angles to the walls of the veinlets. These veinlets cross-cut the mylonite zones and probably represent tension gash f i l l i n g s . No chilled zone was seen at the borders of the diorite body and the adjoining sediments are massive, unaltered and not mylonitized. The data presented suggests that the diorite was emplaced i n the solid state along a fault; presumably i t i s a slice separated from the crystalline rocks to the west. d. Epidote Amphibolite Cutting the Western Sediments. Epidote amphibolite of unknown extent crops out within the western sediments i n a railway cut about 800 feet northeast of the ribbon chert outcrop. In hand specimen, foliation i s obscure; in thin section, i t i s seen to be well developed. Numerous polished, slickensided faces cross the rock. Hornblende, elinozoisite, oligoclase, quartz and some white mica comprise the rock. Thin crush and comminute zones along which quartz, plagioclase and carbonate bearing veinlets have been introduced are common. The rock is of metamorphic origin and would be classified as an epidote amphibolite. Despite the relatively small amount of cataclasis observed, i t i s suggested that the rock was emplaced along a fracture and was derived from the crystalline rocks to the east (Section C-C1, Pigure 3). 33. e. Serpentinite. Small, poorly exposed serpentine bodies crop out intermittently along the fault which bounds the crystalline slice on the east. Five serpentinite bodies were located during the f i e l d work but none was well enough exposed to be mapped in detail. Numerous highly polished, often striated joint faces characterize the serpentine outcrops. These faces are often pale green but the serpent-ini t e i s dark green to black on a freshly broken face. Serpentine i n these serpentinite bodies i s commonly fine grained; remnant pyroxene crystals on the other hand range from very fine to coarse grained. In polarized light a thin section from the serpentinite shows a mesh-like, subrectangular network of bladed antigorite crystals. Openings in the mesh are f i l l e d by massive antigorite (Plate 20). Tiny needles of a pale green, high r e l i e f mineral are common and project into the massive antigorite at right angles to be bladed antigorite walls (Plate 21). Pyroxene remnants are predominantly augite, although enstatite with clinopyroxene intergrowths occurred in one specimen. Most of these grains are rounded and many have been serpentinized for short distances out from the cleavage traces. During serpentinization, excess iron from the olivine was expelled from the serpentine crystals and tended to gather along what appear to be former olivine crystal boundaries. If this inter-pretation i s correct, olivine i n the rock was sub - to euhedral. These serpentinite bodies, which are thought to be ellipsoidal, crop out along the eastern bounding fault of the crystalline body and were presumably brought up along the fault from great depth, possibly the 34. earth's mantle. Section III - STRUCTURE. Vedder Mountain contains well consolidated eugeosynclinal sediments which were folded and sheared during emplacement of a slice of crystalline rocks i n the solid state. This slice, which trends northeast, i s hounded hy steep southeast dipping faults. On the eastern flank of the mountain, the sediments were deformed average into a syn ; f o r m . Thetaxis of this fold plunges less than one degree toward the northeast (Figure 3, Section E-E'). Its axial plane trends northeast and dips 75 degrees southeast. Along the western edge of the mountain, the sediments form an overturnedl?),southeast dipping monocline (Pigure 3, Section C-C). A second period of deformation affected "both the sediments and the crystalline rocks. Warping of the limbs of the synfor.m; resulted i n places and i s best displayed near the southwest end of the map-area near the crest of the mountain. The western sediments appear to occupy'a fold embayment in the crystalline rocks formed during this second period of deformation. The overturned^monocline was folded about a steep southeast plunging axis. . Axial planes of folds formed during the second deformation trend^lSO degrees and are vertical. The plunge of the fold axis was controlled by the dip of the bed being folded. Within the crystalline slice, only mesoscopic folds were seen and were confined to the medium grade metamorphic rocks. Crinkles are common 35. in the fol i a t i o n of these rock types. In the pseudoserpentinized lava especially,small scale faults at right angles to the fo l i a t i o n offset i t as much as l/4 inch. Openings formed during movement have subsequently been f i l l e d with what are now horsetail carbonate stringers. Folding and cri n k l -ing of the foliation took place under f a i r l y high grade metamorphic con-ditions and was similar i n nature. In the f i e l d , thickening at fold crests support this conclusion (Plate 22). In thin section, bending, rather than breaking of the crystals comprising crinkles support this conclusion. In one case, actinolite crystals were bent \- .. . ^ to outline a microscopic S-shaped fold without breaking (Plate 23). The absence of stress twins i n plagioclase also indicate folding under f a i r l y high grade metamorphic conditions. A. Faults Bounding the Crystalline Slice. On the basis of f i e l d and laboratory work, i t i s suggested that the crystalline rocks are bounded by steep southeast dipping faults. Early workers thought that they comprised an altered s i l l or altered volcanic rocks but the most recent work done by the Geological Survey of Canada favors bounding faults (Armstrong, 1956). Adjacent to the crystalline rocks are sediments which are essent-i a l l y unmetamorphosed. If the crystalline rocks were an altered s i l l , one would expect to find thermal metamorphic effects. The trace of the eastern boundary of the crystalline rocks, when stratum contoured, indicates a 75° southeast dip for i t . Bedding and fo l i a t i o n measurements (Figure l ) strike into the boundary, suggesting that an unconformity exists. From the cross sections (Figure 3), i t i s evident that a fault best explains this uncon-Figure 4 Poles to Bedding - Eastern and Western Sediments N S • 2 - 3 % 1X3 3 - 4 % LZ3 > 4 % 36. formity. Serpentinite bodies along this contact also suggest that a fault of considerable magnitude exists. The western boundary of the crystalline rocks also crosscuts foliation and to a lesser extent bedding planes. Imbricate slices of d i o r i t i c and volcanic rocks with numerous mylonite zones (Plate 24) i n each crop out near Sinclair (Pigure 3, Section E-E'). In the railway cut in which the contact between the western sediments and the diorites i s exposed, both sediments (Plate 25) and crystalline rocks (Plate.26) have been sheared and are now cataclasites. There are no thermal metamorphic effects at the contact. Consequently, i t seems reasonable to suggest that the western contact i s also a fault. Non-coring diamond d r i l l holes i n Sumas Valley showed that Tertiary bedrock i s as much as 1,100 feet below the valley floor (Armstrong, 1959). It i s probable that movement along the (Moan, WbZ) western bounding fault activated during the late- Pliocenelvorogenytdown-dropped these Tertiary sediments. B. Phase I Folding. The axial trace of the synform' which comprises much of the eastern side of Vedder Mountain, crops out just east of the crest of the mountain and parallels the trace of the fault which forms the eastern boundary of the crystalline slice. The^fold axis plunges less than 1 degree toward the northeast. The axial plane strikes N50°E and dips 75° SE, except where disrupted by later deformation. Fold limbs are almost planar with steep dips but the hinge zone i s rounded. Where the fold i s l i t t l e influenced by later deformation, the apical angle varies between o Figure 5 Minor Folds from the Sedimentary Rocks N 37. 50 and 70 degrees. Near the International Border (Figure 3, Sections A-A', B-B') the limbs of the major synlbrm are almost para l l e l with the eastern limb over-turned. The contact with the crystalline rocks swings southward near the Border and this swing may have led to a concentration of force which in turn led to the overturned nature of the fold. In the argillaceous rocks at the north- tip of Cultus Lake, minor folds are similar i n nature. However, since minor folds were developed only i n the argillaceous zones they shed no light on the style of folding in the more competent rocks. Several features, when taken together, suggest that the competent beds were concentrically folded. F i r s t , they are unmeta-morphosed. Second, cleavage i s at best poorly developed. Third, no optical alignment of quartz grains or other evidence of strong shearing were seen. Fourth and less decisive are concentrations of poles to joints which seem to represent a-c and a conjugate set of shear joints related to the f i r s t period of deformation. If these joints are i n fact related to the early deformation, then the folding must have been concentric. LesB decisive s t i l l are concentrations of striae which nearly coincide with the inter-section of these shear joints. If these concentrations are associated with shear joints formed during phase I folding, the folding must have been concentric. Interpretation of the major synform as a syncline i s based primarily on the hypothesis that the sediments were pushed aside and folded during emplacement of the crystalline slice. Tops from one cross bedded outcrop support this interpretation but data are insufficient to prove i t . Figure 6 Minor Folds from the Metamorphic Rocks Lid Poles to Axial Planes 38. On the "oasis of t h i s hypothesis, i t i s suggested that the western sediments are overturned. F o l l o w i n g emplacement of the c r y s t a l l i n e s l i c e , the western sediments are thought to have comprised a steep, southeast d i p p i n g homocline which was subsequently f o l d e d during phase I I deformation. Tops determinations from the western sediments could not be used t c t e s t the s t r u c t u r a l i n t e r p r e t a t i o n . Minor f o l d s w i t h t i g h t l y oppressed limbs are present w i t h i n the sediments and because outcrop i s poor, they cannot be traced. Consequently, the l o c a t i o n s of the tops determinations w i t h respect to the limbs of the minor f o l d s could not be determined. Without t h i s knowledge, the s i g n i f i c a n c e of the tops determinations was rendered u n c e r t a i n . a. Minor F o l d s . In t o t a l , only 26 minor f o l d s were seen during the f i e l d work; of these 16 were from the metamorphic rocks and the r e s t from the a r g i l l a c -eous sediments. Axes p l o t t e d from the metamorphic rocks tended to l i e i n the southeast quadrant of the p r o j e c t i o n , although s e v e r a l l a y i n the northeast quadrant ( F i g u r e 6). Spread f o r these p o i n t s was considerable. Although they might p o s s i b l y represent a conjugate set of f o l d s a s s o c i a t e d w i t h shear j o i n t s , i n s u f f i c i e n t data i s a v a i l a b l e to define the s i g n i f i c a n c e of these minor f o l d s . Axes from the sediments show s l i g h t l y d i f f e r e n t but e q u a l l y d i v e r s e spread. Whether they represent a conjugate set of f o l d s cannot be determined from present data (Figure 5). C. Phase I I F o l d i n g . When p l o t t e d on a lower hemisphere equal area p r o j e c t i o n , p o l e s to Figure 7 Poles to Cleavage Planes 39. bedding clearly show spreading as a result of the second period of deformat-ion (Figure 4). From f i e l d work, i t i s evident that the axial planes for phase II folds trend from 090 to 140 and are vertical. It i s thought that axes for these folds vary in- accordance with the dip of the bed being - folded. In support of this idea i s the extreme variation i n trend of minor fold axes measured (Figures 5 and 6). Near the International Border (Figure 1), i t appears that the limbs of the overturned syncline were refolded during phase II deformation. From Figure 12, considerable scatter of poles to bedding i s evident. From the geologic map, axial plane 140°/vertical and fold axis 140°/60° are indicated for the phase II folds. With three notable exceptions, poles to beds f a l l roughly on a conic surface with fold axis II as inferred from •field work as i t s axis. The exceptions are poles to beds with southeast trend and steep northeast dips. The r e l i a b i l i t y of these readings i s doubtful because the banding which they represent was observed i n intensely brecciated dark colored chert i n which banding i s often disrupted. If one accepts that the poles to bedding are conically distributed about fold axis, II, then the apical angle of the phase II fold can be estimated by measuring the extent of the spread of the poles to bedding. This spread indicated that the southwestern limbs of the syncline were moved 46° and the north-eastern limbs 24° (Figure 12). Because these angles represent the move-ment of these beds from the planar condition, the apical angle of the f o l d i s 180° - their sum. That i s , the apical angle i s 110°. a. Foliation from the Granitic Rocks. It was possible to measure foliation planes at only 32 outcrops Figure 8 Poles to Foliation in Granitic Rocks nj 6 - 8% 8-10% EZJ > i o % 40. within the granitic rocks of the crystalline slice. When poles to these planes were plotted (Figure 8), the resulting concentrations were found to l i e roughly along a great c i r c l e whose pole trends 097°/08°. From this distribution, i t i s concluded that foliation i n the granitic rocks prior to phase II folding was planar. During phase II deformation, poles to f o l i a t i o n would then he spread out to their present positions. If, as has been postulated, the granitic rocks are of magmatic origin, the fo l i a t i o n would l i k e l y be a result of flow within the magma. Such flow would l i k e l y result i n a simple planar pattern and i s consistent with the interpretation of Figure 8. b. Foliation from the Metamorphic Rocks. Foliation i s well developed i n the metamorphic rocks but exposure i s limited so only 50 foliation planes were measured during the f i e l d work. Poles to these planes are very nearly conic i n distribution with axis 120°/88° (Fi gure 9). Consequently, i t would appear that the metamorphic rocks were refolded during phase II deformation about a near-vertical axis. Distribution of the foliation prior to phase II deformation remains uncertain. As previously mentioned, minor folds from the metamorphic rocks SynkitiemaVic indicate that they have undergone aiee*£ -f ec<-ys+alliration.However, distribution of these folds suggest nothing of the attitudes or extent of any large scale folds which may have been present. Since evidence 'suggesting high temperature and/or pressures after emplacement of the crystalline slice i s mi nor lacking, i t seems probable that the ataML folds formed prior to this event. c. Deformation of the Crystalline Rocks. Both axial planes and fold axes of folds developed during phase II Figure 9 Poles to Foliation in Metamorphic Rocks N T s I I 4 - 6 % 6 - 8% EZ3 > 8% 41. deformation are different for the metamorphic and granitic rocks. If, as has been postulated, phase II fold axes have been controlled by the attitude of the plane being folded, granitic f o l i a t i o n trended N7°E/Q8°SE prior to phase II deformation. Similar reasoning suggests that the majority of the metamorphic fo l i a t i o n planes were steeply dipping to nearly vertical prior to phase II deformation. Variations i n the attitude of the axial planes and the trend and plunge of fold axes from the metamorphic and granitic rocks are thought to have resulted from differences i n attitude of the foliation planes prior to phase II folding. C. Joints from the Sedimentary Rocks. Joints as used here refers to fracturesin the rock which are more than l/8 inch apart. In the f i e l d , only well developed joints up to a maximum of four per outcrop were measured. Using this approach, i t was biased r e s v » l f s . hoped to avoid m t Poles to the 357 joints measured concentrated near the periphery of the projection, indicating that steeply dipping joints predominate (Pigure l l ) . Joints with f l a t to intermediate dip are not well developed i n the map-area. a. Phase I Joints. In Pigure 11, concentrations of poles near 285° and 350° l i e 36° and 30° respectively away from the pole to the axial plane of the major syncline. These concentrations may represent a conjugate set of shear joints formed during the f i r s t period of deformation. In support of this con-clusion are offset joints i n a r g i l l i t e of the western sediments along the railway tracks near the southern contact with the crystalline rocks-Figure 10 Striae on Joint Faces CZD 2 - 3 % ESJ 3 - 4 % EZZ3 > 4% 42. ( H a t e 6 ). P o l e s to these o f f s e t j o i n t s l i e w i t h i n the mamma near 285°. Strong concentrations of po l e s near 230° and 050° l i e on the a x i a l plane of the s y n c l i n e and are steep d i p p i n g . These are thought to represent a-c j o i n t s formed d u r i n g phase I f o l d i n g . b. Phase I I J o i n t s . A weak c l u s t e r of p o i n t s near 260° may represent shear j o i n t s formed during phase I I f o l d i n g . The angle "between t h i s c l u s t e r and the p o l e to the average a x i a l plane I I i s 40°. No f i e l d evidence was found i n support of t h i s c o n c l u s i o n . C l u s t e r s at 130° and 310° probably represent a ~ c j j j o i n t s since they l i e along the average a x i a l plane. High concentrations of poles spread from 210° to 230° and from 015° to 040°. These a r e thought to represent a - b j j j o i n t s . The spread may be a r e s u l t of e a r l i e r a-c^ j o i n t s which would act as zones of weakness and cause the l a t e r j o i n t s to migrate from t h e i r t h e o r e t i c a l l o c a t i o n . V a r i a t i o n s i n the trend of the a x i a l planes of the phase I I f o l d s might a l s o cause t h i s spread. c. Concentrations of P o l e s of J o i n t s w i t h U n c e r t a i n S i g n i f i c a n c e . Concentrations of po l e s near 090° and 100° do not appear to be r e l a t e d to e i t h e r p e r i o d of deformation. Their s i g n i f i c a n c e i s u n c e r t a i n . d. Cleavage. A r b i t r a r i l y , i f fractures i n the rock vrere l e s s than l / 8 i n c h apart they were c a l l e d cleavage. During the f i e l d xirark, only 46 cleavage measure-ments were made. When p l o t t e d , p o l e s to these planes formed concentrations near 350° (Pigure 7). The two maxima appear to l i e along a great c i r c l e whose po l e plunges 28° toward 077°. Figure II Poles to Joints in Sedimentary Rocks 1 1 I " 1.5% EZ3 1.5-2% CZZ3 2.-2.5% 1=1 2.5-3% ES3 3-3.5% [ -i > 3.5% 43. If the planes measured represented axial plane cleavage formed during phase I deformation, their poles would concentrate at a point which would he the pole to axial plane I prior to phase II deformation. That i s the . cleavage would i n i t i a l l y he parallel to the axial plane. During phase II deformation, the poles to cleavage would then he expected to he rotated about fold axis II. Consequently, they should l i e along a great c i r c l e whose pole i s this fold axis. However, no evidence to suggest a fold axis trending.077°/28° was found during the f i e l d or subsequent laboratory work. On Figure 12, concentrations of poles to joints which are thought to represent a conjugate set of shear joints formed during phase I deformat-ion occur at 350°. These concentrations are very close to those for poles to cleavage planes. Consequently, i t i s concluded that the planes which were mapped as cleavage were i n fact closely spaced shear joints associated with phase I folding. e. Slickensides on Joint Faces. Striae from 219 slip faces were plotted to give Figure 10. A pronounced, somewhat skew concentration of points was found near the center of the projection. A second, less pronounced, concentration occurs in the northwest quadrant near the edge of the projection. The Bteeply dipping striae probably formed during phase I deformat-ion. Within the sediments, bedding plane slippage i n the units which folded concentrically would account for part of the concentration. Within the crystalline rocks, small scale faults and slips p a r a l l e l to the bounding faults would account for the remainder of the concentration. Since phase II folding was concentric i n nature, slippage between Figure 12 Poles to Bedding from the Eastern Sediments near the International Boundary 44. beds would occur during deformation. Since this slippage would occur at right angles to the fold axis, i t would give rise to predominantly north-west trending striae with shallow dipB for the steeply southeast plunging fold axes. From these considerations i t seems reasonable to correlate the concentrations of striae i n the northwest quadrant with phase II deformation. Section IV - DISCUSSION OF THE AGE RELATIONSHIPS OF VEDDER MOUNTAIN ROCK UNITS. A. Eastern and Western Sediments - Other Workers. Daly (1912) relegated both eastern and western sediments to the Chilliwack group which he suggested was of Carboniferous age. Crickmay (1930) showed only the eastern sediments on his geological map. He placed them i n the Slollicum Series of Upper Triassic age. Mi sen (1955, personal communication with Armstrong) f e l t that the volcanic rocks which crop out near Sinclair could be correlated with the Nooksackvolcanics of northern Washington, which are of Jurassic age. Later in the communication he suggested that the eastern sediments also correl-ated with the Nooksack Group. Hillhouse (1956) correlated the eastern sediments with the Upper Jurassic to Lower Cretaceous Nooksack Group of northwestern Washington. His correlation was based on personal communication with Misch and Armstrong. Moen (1962), who worked on the portion of Vedder Mountain which extends into the United States, mapped the extension of the eastern sediments as Chilliwack Group. He redefined the Chilliwack Group and suggested that the sediments were deposited during Late Palaeozoic time. 45. B. C r y s t a l l i n e Rocks - Other Workers. Daly (1912) p l a c e d the c r y s t a l l i n e rocks i n the C h i l l i w a c k Group w i t h the sediments. He c a l l e d them the Vedder Greenstone and thought the c r y s t a l l i n e body was a s i l l . Crickmay (1930) thought that the c r y s t a l l i n e rocks were a l t e r e d v o l c a n i c rocks of T r i a s s i c age. He suggested that they were conformably u n d e r l y i n g the eastern sediments. Armstrong (1956) l i s t e d the c r y s t a l l i n e rocks as h i g h l y metamor-phosed rocks of u n c e r t a i n age on the P i t t Lake sheet. Moen (1962) r e f e r s to s i m i l a r rocks i n the Van Zandft quadrangle and compares them to c r y s t a l l i n e rocks exposed i n the San Juan I s l a n d s . Banner (1957) showed t h a t the San Juan I s l a n d rocks were pre-Devonian i n age. Moen thought t h a t the c r y s t a l l i n e rocks which he mapped were a l s o pre-Devonian and r e f e r s to them as upthrust basement s l i c e s . C. Eastern and Western Sediments - Present Work. In the east, the conglomerate, which i s the o l d e s t u n i t exposed sometimes contains numerous g r a n i t i c pebbles. The s i g n i f i c a n c e of these pebbles i s not c e r t a i n . G r a n i t i c rocks were supposedly not prominent u n t i l J u r a s s i c time so the conglomerate might be p o s t - J u r a s s i c i n age. Hoitfever, the pre-Devonian g r a n i t i c rocks which crop out i n the San Juan I s l a n d s cast doubt upon t h i s i n t e r p r e t a t i o n . No f o s s i l s were found i n the eastern sediments d e s p i t e the presence of a r g i l l i t e , limestone pods and chert beds which were p o t e n t i a l l y f o s s i l -i f e r o u s . Consequently, no p o s i t i v e age can be assigned to these rocks. Prom the western sediments, r a d i o l a r i a n b earing chert fragments 46. were found in the chert lenticule arenite and the chert arenite breccia. probably Since the radiolaria found*originated during Devonian time and range to (pan"««". personal cjmmunic.a+"" ') the presentf, i t i s possible to say only that the western sediments contain probab'y fragments which aretpost-Siiurian in age. However, since the radiolaria probably involved^originated during Devonian time and since they are contained within fragments of the rock i n which they were deposited, i t seems l i k e l y that the sediments are post-Devonian i n age. The eastern and western sediments cannot be correlated directly from lithologic or palaeontologic evidence. However, correlation on the basis of lithology has been attempted i n a tentative way (Figure 2). In this correlation, i t has been suggested that the limestone-bearing horizons are equivalents. The volcanic rocks near Sinclair are thought to correlate i n part with the oldest member of the western sediments, the quartz plagioclase porphyry. This suggestion i s based on the lithologic similarities between the porphyry and some of the rocks near Sinclair. Since the rocks are more extensive near Sinclair, i t seems l i k e l y that they are in part older than the porphyry and hence the western sediments as a whole. D. Crystalline Socks - Present Work. The crystalline rocks are believed to have been emplaced along steep, southeast dipping faults, presumably from great depth. Metamorphic components are from the regional metamorphic Almandite-Amphibolite Facies and were derived from basic and p e l i t i c rocks. Their absolute age i s unknown. Since they have pushed aside the sediments i t i s probable that the crystalline rocks are older. 47. The granitic components of the crystalline complex appear to intrude the metamorphic components. Consequently, they would he younger than the date of metamorphism. Within the granitic rocks themselves, the quartz diorites and pegmatites appear to he younger than and to intrude the diorite. The time lapse between formation of the metamorphic rocks and intrusion of the granitic rocks i s not known; nor i s the time between intrusion o f the granitic rocks and emplacement of the crystalline com-plex. It seems probable, however, that the granitic rocks were solid prior to emplacement of the slice, since no contact metamorphic effects were present i n the sediments. a. Emplacement of the Crystalline Slice. Moen indicates a fault along the southwest margin of the United States extension of Vedder Mountain. This fault affects sediments which he assigns to the Chilliwack Group and uplifted them with respect to upper Eocene continental sediments. He suggests that what i s now Sumas Valley originated as a result of this late Pliocene (?) block faulting. In Canada, Armstrong (1959) reports that Tertiary bedrock i s as much as 1,100 feet below the valley floor. This fault i s the western bounding fault of the crystalline s l i c e in the map-area. Although movement occurred along this fault during the late Pliocene(?)orogeny, i t i s unlikely that the crystalline complex was emplaced at that time. If i t had been emplaced then, the Tertiary contin-ental rocks and western sediments should have acted as a structural unit. Ho\<rever, the block faulting bypassed the western sediments and down-dropped the Tertiary rocks with respect to them. The age of emplacement of the crystalline s l i c e can only be bracketed as post-sediment, pre-Tertiary at 48. t h i s time. Section V - SUMMARY OF GEOLOGIC HISTORY. P e l i t i c sediments and basic volcanic rocks were deposited-fre^^a* ftBtHttaq With time these rocks were buried and eventually subjected to metamorphism of the Almandite Amphibole Facies. Amphibolites, hornblend-i t e , epidote amphibolite, epidote and amphibole white mica schists, and garnetiferous amphibole and mica schists and gneisses formed. Since foldB i n the metamorphic rocks are outlined by the f o l i a t i o n , i t follows that deformation post-dates formation of the f o l i a t i o n . Minor folds within these rocks have been subjected to rheid deformation since f o l d crests are much thickened and limbs thinned. Evidence from thin section examination suggests that deformation was synkinematic. From t h i s data i t seems l i k e l y that the metamorphic rocks were subjected to rheid deformation during metamorphism but before they were cooled, that i s , folding probably occurred under roughly the same pressure and temperature conditions at which the minerals formed. Lack of retrograde metamorphic effects despite r e c r y s t a l l i z a t i o n during folding further supports this hypothesis. Some time after t h e i r formation, the metqmorphic rocks were intruded by d i o r i t e . Along the contact • • • • the d i o r i t e was f a i r l y quickly cooled and more basic mixed rock resulted. Subsequently, small bodies of quartz d i o r i t e and pegmatite derived from the c r y s t a l l i z i n g parent magma intruded the d i o r i t e . . Whether they intrude the metamorphic rocks also was not determined from the f i e l d work. A l l phases of the g r a n i t i c intrusion are characterized "by extensive saussuritization of the plagio-clase. Presumably, this alteration resulted from late stage deuterie solutions within the crystallizing bodies since the metamorphic and sedi-mentary rocks are not saussuritized. Post-Devonian(?)sedimentation resulted i n what are now referred to as the eastern sediments. The base upon which they were deposited i s not exposed. Judging from the nature of the pebbleB to cobbles of the oldest unit exposed, the chert, volcanic granitic pebble to cobble conglomerate, the source area probably had interlayered chert and volcanic rocks cut by granitic bodies. The conglomerate has plagioclase volcanic arenite both as interbeds and as i t s matrix. The relationship of well rounded, mature cobbles with angular immature matrix components and interbeds i s easily visualized i f the rocks are turbidites. As time went on, conglomeratic material became scarce and arenite rna+ertal 5 t o p P « J b«i«q supplied- +o fVu. icpo-sit-ionol ar<M-more prominent. Eventually, conglomeratictMHHBffiBHBMBMl About that time, argillaceous interbeds began to appear in the arenite. The arenite, unit, which i s capped i n places by a r g i l l i t e was succeeded by micro-volcanic arenite. A r g i l l i t e , plagioclase volcanic arenite and chert inter-beds are common within the micro-volcanic arenite. One 1 band \, which has been used as a marker, consists of impure si l i c i o u s a r g i l l i t e which con-tains pods of impure crystalline limestone. At the northeast end of the map-area, considerable thicknesses of chert were being deposited while the micro-volcanic arenite predominated to the southeast. Micro-volcanic arenite i s the uppermost exposed unit of the eastern sediments. Prom the conglomerate to the top of the plagioclase volcanic 50. arenite, i t seems l i k e l y that the sediments were deposited from turbidity currents. Graded beds, sole marks, current marks and other typical features of turbidites were lacking. The constitution of the rocks i s the funda-mental reason for suggesting that they were deposited from turbidity currents. Whether the micro-volcanic arenites are turbidites remains i n doubt. Mineralogically, they are nearly identical to the plagioclase volcanic arenites but are much finer grained. The marker horizon represents a period of slow introduction of argillaceous material which mixed with s i l i c a to form an impure gel. The limestone pods represent local high concentrations of carbonate i n the water. Whether the carbonate and s i l i c a to form the cherty and limy deposits resulted from vulcanism outside the area of deposition of the eastern sediments i s not known. If vulcanism did supply these substances, the limy horizon would correlate with the limy horizon from the western sediments which i s underlain by volcanic rocks and probably resulted from emanations associated with the vulcanism. At some time before, during or after the eastern sediments were deposited, sediments of post-Devonian$age which are now referred to as the western Bediments were l a i d down. Vulcanism apparently preceeded sedi-mentation but how important i t was i s uncertain. Diabase and porphyritic dacite predominate. Argillaceous sediments followed by micro-volcanic arenite overlie the volcanic rocks. It i s possible that pyroclastic activity was the source of breccias which overlie the arenite. These breccias include chert lenticule arenite and volcanic chert lenticule arenite breccia. Chert from these breccias contains radiolaria which have 51. long ranges but originated during Devonian time. Whether these rocks are of pyroclastic, sedimentary or turbidity current origin i s not certain. A limestone horizon within the breccia unit suggests water with high calcium carbonate content which might have resulted from volcanic emanations. At the same time, the jumbled arrangement of some of the fragments from these rocks suggest turbulent,, perhaps turbidite, deposition. The question of origin cannot be answered from present data. Introduction of clastic material into the area decreased and a f a i r l y thick a r g i l l i t e unit was deposited upon the breccias, later, deposition of clastic material almost stopped and sli g h t l y argillaceous ribbon chert formed. This ribbon chert i s the youngest unit of the western sediments which i s exposed. After both eastern and western sediments were deposited, tectonic a c t i v i t y caused a s l i c e of the underlying, more deeply buried, crystalline and medium grade metamorphic rocks to move up along bounding faults which dip steeply toward the southeast. As the "basement" s l i c e pierced the sediments, i t pushed them aside and caused what i s now referred to as phase I folding. The eastern sediments were primarily deformed into a syncline with i t s f o l d axis plunging less than 1° toward the northeast and axial plane trending 050/75 SE. While the incompetent a r g i i l i t e s were folded similarly, the more competent conglomerates, arenites and chertB were folded concentrically. The western sedimentB were pushed up by the s l i c e to form an overturned monocline with steep southeast dip. A second period of deformation affected both the sediments and the crystalline rocks, Folds produced during this deformation have ver t i c a l axial planes which trend between 090° and 140°. Fold axes vary widely i n 52. plunge and trend. Since folding during phase II deformation was concentric, the axes and to a lesser extent the axial planes of the folds depend on the strike and dip of the plane being folded. Most of the beds and fo l i a t i o n planes were steeply dipping after phase I deformation and the introduction of the crystalline s l i c e so most of the axes of phase II folds plunge steeply. During Tertiary time, continental sedimentation occurred i n what i s now Sumas Valley. Movement along the western bounding fault of the crystalline s l i c e which Moen suggests occurred during Upper Pliocene$time i s thought by him to have caused Sumas Valley to form. Armstrong (1959) reports that d r i l l i n g reveals these Tertiary sediments 1,100 feet below the present valley floor. Unfortunately, rotary, non-coring d r i l l s were used so no information on the attitude of these rocks i s available (Armstrong, personal communication). Since the western sediments are s t i l l exposed, i t seems l i k e l y that the embayment which they occupy i n the crystalline rocks caused the Tertiary block faulting to occur along their western edge rather than following the crystalline rock - sediment contact. Field evidence to support this speculation i s lacking since the probable locus of this fault zone i s covered by overburden. During the Pleistocene epoch,the map-area was covered by an ice sheet which was of continental proportions. Scour by the ice streamlined the mountain and gouged out softer rocks to some extent. Glacial erratics on the mountain were dropped as the ice retreated and i t s sides were plastered with Surrey t i l l (Armstrong, 1959), Since the ice retreat, Vedder Mountain has been much as i t i s today, although incised hy several important and numerous small intermittant streams. Suhaerial erosion primarily through plant and water action tinues. SELECTED BIBLIOGRAPHY Amstrong,. J.B.,"Surficial Qeology of the Sumas Map-Area, B.CV' Geological Survey of Canada Paper 59-9j 1960i "~ '.Crickmay> C i H i , "The Structural Connection Between the Coast Range of  British Columbia and the Cascade Range of Washington," Geological Magazinej v* 67, 1930* Dalyj R.A., "Geology of the North American Cordillera at the U9th Par- a l l e l j " Geological Survey of Canada, Memoir 3b", 1912 i Dannerj W.Ri, "A Stratigraphic Reconnaissance in the Northwestern Cas- cades Mountains and the San Juan Islands of Washington," PhD/Thesis, Washington University(Seattle), 1957. Hillhouse, D.N., "Qeology of the Vedder Mountain-Silver Lake Area." Unpublished MiSc* Thesis, University of British Columbia, 1956. Folk! R.L., "Petrology of Sedimentary Rocks," The University of Texas, Hemphill's, Austin, Texas, 1961. Moen, W.S., "Geology and Mineral Deposits of the North Half of the Van  Zandt Quadrangle, Whatcom County," State of Washington Department Conservation Division of Mines and Geology, Bulletin 50, 1962 i Ricker, W.E., "Physical Characteristics of Cultus Lake," Journal of the Biological Board of Canada, 3(U) 1937, 363-ii02. Turner*and•VerhoogenV "Igneous and Metamorphic Petrology," Second Edition McGraw-Hill, New York, I960. ."' '"v'" H. F-J- CM-Williams?, Turnerfand Gilbert*, "Petrography," W.H. Freeman, San Francisco 1955. Plate 1 Photomicrograph showing well-rounded granitic and volcanic peb-bles i n plagioclase volcanic arenite matrix i n which the frag-ments are angular (plane light, x20). Plate 2 Photomicrograph of immature plagioclase volcanic arenite contain-ing a dark colored lens-like a r g i l l i t e fragment (plane light, x20). Plate 3 Hand specimen of color banded argillaceous chert showing intense brecciation and disruption of the banding. The scale divisions are millimeters. Plate 4 Hand specimen of brecciated argillaceous white chert. The scale divisions are millimeters. Plate 5 Photomicrograph of micro-volcanic arenite. Quartz, feldspar and • volcanic fragments predominate. The matrix i s argillaceous (plane light, x55). Plate 6 A hand specimen of a r g i l l i t e from the western sediments i n which steps resulting from movement along shear joints are preserved. The scale divisions are millimeters. Plate 1 Plate 2 •9. Plate Plate 6 Plate 7 Photomicrograph of rounded radiolaria from an argillaceous chert fragment i n radiolarian chert lenticule arenite. The texture of the radiolaria i s similar i n appearance to the surface of a golf h a l l (plane light, x50). Plate 8 Photomicrograph of cigar-shaped radiolaria with rounded cross section from a chert fragment i n radiolarian chert lenticule arenite. The longitudonal section i s similar i n appearance to a cob of corn (plane light, x85). Plate 9 Photomicrograph of lawsonite from the matrix of radiolarian chert lenticule arenite. The mineral has fibrous habit (plane light, x60). Plate 10 Hand specimen of radiolarian chert arenite breccia showing the jumbled distribution of the fragments. The scale divisions are millimeters. Plate 11 Photomicrograph of quartz feldspar volcanic porphyry with strained and broken phenocrysts (crossed Nicols, x25). Plate 12 Photomicrograph of foliated epidote amphibolite. Hornblende, epidote, quartz and feldspar predominate (crossed Nicols, x30). Pla;te 13 Photomicrograph of foliated garnet white mica hornblende quartz feldspar rock showing bending of the f o l i a t i o n around the garnet porphyroblasts (crossed Nicols, x20). Plate 14 Photomicrograph of garnet sphene schist..Garnet i s black, em-bayed; sphene roughly diamond-shaped and strung out parallel to the metamorphic f o l i a t i o n . White mica outlines the foliation (crossed Nicols, x20). Plate 15 Dike of lighter colored diorite cutting darker colored diorite. Note unevenness of the border of the dike but the definite crack-f i l l i n g offset from the dike. The scale divisions are m i l l i -' meters. Plate 16 Photomicrograph of foliated quartz diorite in which the quartz stringers are characterized by pronounced undulatory extinction (crossed Nicols, x20). Plate 17 Photomicrograph of foliated diorite i n which feldspar has "been completely saussuritized (plane light, x20). Plate 18 Photomicrograph of thin prisms of prehnite from a veinlet which crosses foliated diorite. Many of the prisms are roughly perpen-dicular to the veinlet w a l l B (crossed Nicols, x30). Plate 19 Photomicrograph of basic mixed rock with very high hornblende content. Peldspar has been completely saussuritized (plane light, x20). Plate 20 Photomicrograph of a subrectangular mesh comprised of blade-like antigorite crystals with i n t e r s t i t i a l massive antigorite (crossed Nicols, x20). Plate 21 Photomicrograph of tiny, pale green, needle-like crystals which project from the "walls" of the bladed antigorite meshwork into the massive antigorite seen i n plate 20 (plane light, x2l0). Plate 22 Hand specimen of epidote amphibolite containing a minor fold i n which the crests are thickened and the limbs are thinned. The scale divisions are i n millimeters. Plate 23 Photomicrograph of a minor fold formed under synkinematic con-ditions and outlined hy elongated prisms of actinolite which were "bent hut not broken during the deformation (crossed Nicols, x60). Plate 24 Photomicrograph showing a mylonite zone crossing granitic rocks near the southwest contact with the western sediments (plane light, x25). Plate 25 Photomicrograph of cataclasite derived from quartz plagioclase porphyry at the southwest contact of the western sediments block with the granitic rocks (plane light, x20). Plate 26 Photomicrograph of cataclasite derived from granitic rock at the southwest contact of the western sediments block (crossed Nicols, x20). 59. 2000 Figure 3. VEDDER MOUNTAIN CROSS SECTIONS FOR LOCATIONS AND LEGEND SEE FIGURE I SCALE 1000 2000 3000 4000 5000 Geology of Vedder Mountain Figure I. LEGEND Western Sediments Ribbon Chert Cherty Argillaceous Cryitalllne Limeetone Volcanic Radiolorian Chert Arenite Breccia and Radiolarian Chert Lenticule Arenite Micro-volcanic Arenite 1 I Argillite Altered Dlaboee and Tuff < i I Quartz Plagioclase Porphyry, Dacite Porphyry Eastern Sediments 2 L_—I Mlcro-volconic Arenite I 1 Siliceous Argillite with Limestone Pods I I Massive, Nodular and Ribbon, Chert and Jasper I 1 Argillite ond Phyllite I I Plagioclaee Volcanic Arenite I I Plagioclase Volcanic Arenite with Conglomerate Interbeds Conglomerate with Plagioclase Volcanic Arenite Interbeds Crystalline Rocks Serpentinite > UJ I I O I I Diorite, Foliated Quarti Diorite, Mixed Rocks i and Pegmatite Hornblendite, Amphibolite, Epidote Amphibolite, Garnet Mico and Garnet Sphene Schiet Outline of mapped outcrop / / / / , Bedding - upright, overturned . . iii Metamorphic and Igneous foliation ' Cleavage •* I'" Fault - defined, approximate, inferred / / / movement - U,up - D.down Axial plane of minor fold Fold axis of minor fold Axial trace - antiform, synform / / Highway or good gravel road = Dirt road passable with two wheel drive . . . Railway , , , International boundary Intermittent stream Contours - interval 500 feet . . . . Approximate magnetic declination 22° 39'east (1965) onnuol change 3.5'west SCALE 1000 2000 3000 feet 4000 5000 

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