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Polyphase deformation and metamorphism in the western Cariboo Mountains near Ogden Park, British Columbia Lewis, Peter D. 1987

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POLYPHASE DEFORMATION AND METAMORPHISM IN THE WESTERN CARIBOO MOUNTAINS  NEAR OGDEN PEAK, BRITISH COLUMBIA °y PETER D. LEWIS  B.S. (Stanford  University)  A THESIS SUBMITTED I N PARTIAL F U L F I L M E N T O F THE R E Q U I R E M E N T S F O R T H E D E G R E E O F MASTER OF SCIENCE  in T H E F A C U L T Y O F G R A D U A T E STUDIES Department of Geological Sciences  We accept this thesis as conforming to the required standard  THE UNIVERSITY O F BRITISH COLUMBIA September, 1987  ® Peter D. Lewis, 1987  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at The University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.  Department of Geological Sciences The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date: September, 1987  ABSTRACT  The boundary between the Omineca Belt and the Intermontane British  Columbia  represents  the  suture  between  Belt in Central  autochthonous  North  America  (Barkerville Terrane) and several allochthonous terranes accreted from the west In the Quesnel  Lake  region  allochthonous  sedimentary  and  volcanic  rocks  of Quesnellia  Terrane, accreted in the Jurassic, are in sharp tectonic contact with underlying siliclastic and carbonate  metasedimentary  rocks. The Ogden Peak study area is located 10 km  east of and structurally below this suture zone and is thus well situated for observing deformational styles within the autochthonous package. Rocks Snowshoe  exposed  Group  and  near  Ogden  Peak  local  diabasic  comprise  intrusions.  the  These  Hadrynian(?) rocks  record  to Paleozoic(?) a  deformational  history involving four phases of folding ( D - D ) and later brittle faulting (D ). Earliest x  recognizable transposed  structures  consist  of  recumbant  4  5  isoclinal  folds  with  a  well-developed  foliation. This foliation is tightly folded about northwest trending, southwest  verging second phase structures. Northwest trending third phase structures and northeast trending fourth phase structures occur as both crenulations and open buckles. Southeast dipping faults cut all earlier structures with tens of meters of normal offset Phase 1 and Phase 2 fold styles are compatible with a flattened mechanism contrasts  of formation, associated  across layering. Later fold  with  elevated  temperatures and  buckle fold  reduced viscosity  styles are controlled by higher viscosity contrasts  and detachment along layering. All  phases  of  deformation  are  dominated  by  semi-brittle  mechanisms  of  dislocation slip and glide, mechanical twinning, and microcracking. Temperature activated diffusional  creep  is only locally active and does not contribute  ii  appreciably to total  strain. The  mineral  assemblage  garnet- staurolite-kyanite  late in D . Metamorphic temperatures 2  defines  a  metamorphic peak  of approximately 530° C at 6.0 kb have been  determined using garnet/biotite geothermometry. Extensive retrograde metamorphism spans D  and D„, overprinting prograde  3  assemblages  and providing  evidence for  abundant  fluids late in deformation. Late phase 1 diabase dykes locally intruded an area to the southeast of Ogden Peak. Major  and trace element analyses of samples from  calc-alkaline, volcanic arc affinity.  i  iii  these intrusions suggest a  TABLE OF CONTENTS Abstract List of figures  ii .-.  vi  List of plates  viii  Acknowledgements  ..  ix  1. INTRODUCTION 1.1. Location 1.2. Previous work 1.3. Purpose  1 3 3 5  .  2. STRATIGRAPHY 2.1. Introduction 2.2. Snowshoe Group rocks 2.3. Intrusive rocks 2.4. Summary and discussion  ..  6 6 8 18 22  3. MAJOR AND TRACE ELEMENT GEOCHEMISTRY 3.1. Introduction 3.2. Major element geochemistry 3.3. Trace element geochemistry 3.4. Summary and discussion  24 24 26 29 32  4. STRUCTURE 4.1. Introduction 4.2. Mesoscopic structures, metasedimentary rocks 4.2.1. -D, - D Folding 4.2.2. D Faulting 4.3. Mesoscopic structures, intrusive rocks 4.3.1. Western dyke set 4.3.2. Eastern dyke set 4.4. Microscopic structures 4.4.1. Healed micTocracks 4.4.2. Extension fractures 4.4.3. Kink banding 4.4.4. Pressure solution features 4.4.5. Deformation twins 4.4.6. Recrystallization textures 4.5. Summary and discussion  34 34 35 35 58 59 59 64 68 68 69 72 76 76 76 81  4  5  5. METAMORPHISM 5.1. Introduction 5.2. Regional metamorphism Mj 5.2.1. Pelitic lithologies 5.2.2. Amphibole schist lithologies 5.2.3. Carbonate lithologies iv  ...»  87 87 89 89 101 103  5.3. Retrograde metamorphism M 5.4. Geothermometry 5.5. Summary and discussion  104 109 113  2  6. REGIONAL CORRELATIONS AND TECTONIC INTERPRETATIONS 6.1. Regional correlations 6.1.1. Stratigraphy 6.1.2. Structure 6.1.3. Metamorphism 6.2. Tectonic implications  115 115 116 117 119 122  7. REFERENCES  127  8. APPENDICES 8.1. Appendix 8.2. Appendix 8.3. Appendix 8.4. Appendix  1. 2: 3: 4:  Major and trace element analyses Axial dimensions of elongate pebbles Mineral abbreviations Electron microprobe analyses  v  133 133 135 137 138  List of Figures 1. Major tectonic belts of the Canadian Cordillera 2. Regional geology of the Quesnel Lake region 3. Map of the Ogden Peak area 4. Structural succession of the Ogden Peak area 5. Stratigraphic contact between unit 3 and unit 4 6. Lithologic variation in subunit 5a 7. Meta-diabase dyke intruding Snowshoe Group metasedimentary rocks 8. Distribution and surface traces of meta-diabase dykes 9. Alkaline/subalkaline discriminant diagram 10. A F M diagram 11. T i , Zr, Y ternary discriminant diagram 12. T i , Zr binary discriminant diagram 13. Phase 1 isoclinal folds 14. Phase 1 isoclinally folded quartz vein 15. Stereographic plot of D i data 16. Simple shear of S along Sj surfaces 17. Stereographic plot of D data 18. D folds in quartzite and marble 19. t versus a plots of phase 2 folds 20. D crenulations of biotite and muscovite 21. S muscovite growth 22. Quartz vein oriented along phase 2 axial plane 23. Stereographic plot of D data 24. Stereographic plot of D„ data 25. t versus a plot of phase 4 folds 26. Mesoscopic phase 4 buckle 27. Disharmonic phase 4 crenulation 28; Structural relationships of intrusive diabase dykes to country rocks 29. Diabase dyke of western set 30. Phase 2 fold of inuusive contact 31. Phase 1 isoclinal fold outlined by compositional layering within dyke 32. Contact between eastern set diabase dyke and metasedimentary country rock 33. Folds in metasedimentary rock along intrusive contact 34. Healed microcracks in quartz 35. Extension fractures in feldspar porphyroclasts 36. Kink bands in biotite porphyroblast 37. Subgrain developement in quartz 38. Deformation lamellae in quartz 39. Deformation twins in calcite 40. Quartz recrystallization texture 41. Recrystallized quartz mylonite 42. Summary of fold style and geometry, phase 1 - phase 4 43. Incremental strain ellipsoids showing phase 2 progressive deformation 44. Muscovite defining phase 1 and phase 2 foliations 45. Two stages of chlorite growth 46. Kyanite porphyroblasts growing across phase 2 crenulations 47. Sericitized staurolite growing across phase 2 crenulations 48. Helycitic inclusion trails in garnet 0  2  2  2  2  3  vi  2 4 7 9 13 15 19 20 .27 28 30 31 36 38 40 41 43 44 45 47 48 49 51 53 54 55 56 60 61 62 63 65 66 70 71 73 74 75 77 78 80 82 84 91 92 95 96 97  49. 50. 51. 52. 53. 54. 55.  A F M sketches showing stable mineral assemblages of pelitic zones Chlorite pseudomorphs of garnet flattened into phase four axial planes Quartz vein filling fracture along axial plane of mesoscopic phase 2 fold P - T diagram applied to pelitic rocks of the Ogden Peak area Garnet-biotite temperatures plotted against manganese concentration Mineral growth/deformation correlation chart Plate tectonic model for I M B / O M B boundary  vii  99 106 107 110 :. 112 114 125  LIST OF PLATES  Airp1alBS--aTe—included—in~me^ack—pocket- • -  1. PLATE I: Bedrock geology of the Ogden Peak area. 2. PLATE II: Cross section through the Ogden Peak area. 3. PLATE III: D  x  and D  2  structural elements, mineral lineations.  4. PLATE IV: D  3  and D  4  structural elements, faults.  viii  ACKNOWLEDGEMENTS  I am indebted to my thesis supervisor, Dr. J.V. Ross, for his continued support and advice throughout the course of this study. Valuable assistance in the laboratory aspects of this project was provided by C. Hickson,  S. Horsky, P. Michaels, and  M . Piranian. Innumerable  discussions with  S.  Garwin have contributed greatly to this project, and J.K. Russell, D. McMullin, D . Murphy, and J. Fillipone have helped clarify many issues. S. Sonnad provided able assistance in the field, and I am grateful to S. Taite for both moral support and assistance in the final preparation of this project Funding  for  field  and  laboratory  expenses  number 58-2134 to Dr. J.V. Ross.  ix  was provided by  NSERC  grant  1. INTRODUCTION  The Canadian Cordillera is composed of five major tectonic belts (Figure 1), and  numerous  study  discrete  in central  Omineca  Belt  tectono-stratigraphic  British  Columbia,  (OMB) and  the  near  terranes. In the Quesnel  Intermontane  Belt  Lake,  area  the  of interest  boundary  (1MB) represents  to this  between  the  contact  the of  autochthonous rocks of North America with allochthonous rocks of numerous displaced terranes  accreted  from  the  west  The  Omineca  Belt  here  (Barkerville Terrane)  is  dominated by siliciclastic and carbonate rocks of the late Proterozoic(?) to Paleozoic(?) Snowshoe Group (Campbell and Campbell, 1970). Allochthonous Intermontane  Belt rocks  include  has. been  the  late  Paleozoic(?) Crooked Amphibolite (Struik,  1986),  which  tentatively correlated with the Slide Mountain Terrane, and structurally overlying Triassic and  Jurassic  sedimentary  and  volcanic  rocks  assigned  to  the  Quesnellia  Terrane.  Extensive deformation and metamorphism of Jurassic age in both packages of rocks are believed to be related to the accretion of Quesnellia and more westerly terranes onto North  America  (Monger et  al., 1982). The  suture zone  between  the  characterized by an extensive mylonite zone that appears to be the  two belts is result of high  angle convergence (Ross et al., 1985). Figure 2 is a generalized geologic map showing the spatial distribution of lithologic units in the Quesnel Lake region.  1  INTRODUCTION / 2  Figure 1.  Major tectonic belts of the Canadian Cordillera and location of the Quesnel Lake area.  INTRODUCTION / 3 1.1.  LOCATION The Ogden Peak study area is located between the East Arm and North Arm  of  Quesnel  Lake, on the  western  flank of the  British Columbia (Figure 2). An area of 50 km the summer of 1985 at elevations between completely within the  2  Cariboo Mountains in  south-central  was mapped at 1:16,000 scale during  1,500 m and 2,500 m. The study area is  Omineca Belt, approximately  10 km east of the  Intermontane  Belt/Omineca Belt boundary. It is easily accessible by helicopter; lower elevations may be reached by boat from Quesnel Lake. Interconnected ridges allow easy travel through the area above timberline.  1.2. PREVIOUS WORK Western  Omineca Belt rocks in the  Quesnel Lake region were  first  mapped  north of the study area in the vicinity of Barkerville and Keithly Creek (Uglow, 1922; Lang, 1938; Holland, 1954; Sutherland Brown, 1957). Holland (1954) was first to assign these rocks to the Late Precambrian to Cambrian Snowshoe Formation of the Cariboo Group, with a type locality near Yanks Peak. Sutherland Brown (1957) described a 300 m thick section of Snowshoe Formation as forming the uppermost unit of the Cariboo Group, unconformably overlain by the Late Paleozoic Slide Mountain Group. Sutherland Brown outlined a structural history involving at least two phases of folding followed by brittle deformation. Based suggested  on  that  work  the  in the  Snowshoe  Quesnel  Lake area,  Formation  represents  Proterozoic Kaza Group. This revised Sutherland the  Kaza  mapping  Group at lower stratigraphic at  1:50,000 scale  by  Struik  a  western  Campbell (1970)  fades  Brown's interpretations  levels than (1982,  Campbell and  1983)  the  Snowshoe  resulted  of  the  late  which placed  Formation. Recent  in redefinition  of  the  INTRODUCTION / 4  Quesnellia Terrane UJ  m LU z  < 1-  NICOLA GROUP L. T r l » » » l c -  r£^j volcanlclastics  E. J u r a s s i c  Q U E S N E L RIVER GROUP  z o  {  ,'| black phylllta, argilllto  minor limsstona. volcanic*  2  GC HI  C R O O K E D AMPHIBOLITE L. Palaozoic(?)  E 3  metavolcanica. phyllrts  North A m e r i c a UJ  m < o UJ z i o Figure 2.  L. Osvonian E. Mlaaiaalpplan Hadrynian Palaozoic  ^  ['-. | granitic  gneiaa  S N O W S H O E GROUP  •  quartzofeldspathic schist snd gneiss, minor carbonsta  Regional geology of the Quesnel Lake area and location of map area. Late Paleozoic to Jurassic volcanic and phyllitic rocks of Quesnellia Terrane are tectonically juxtaposed against metasedimentary rocks and granitic gneiss of North America.  INTRODUCTION / 5 Snowshoe Formation as the Snowshoe Group, separated  from the more easterly  Kaza  Group along the Pleasant Valley Fault Detailed structural analyses of Omineca Belt rocks of the Quesnel Lake region by  Getsinger  (1985),  Montgomery (1985),  Fillipone  (1985),  and  Elsby  (1985)  have  delineated four widespread phases of folding in Snowshoe Group rocks and intrusive granitic gneisses. Ross et al. (1985) have related the distribution and geometry of some of these structures to the Jurassic accretion of Quesnellia onto North America.  1.3.  PURPOSE  The present students over  the  study  is one  last decade,  of a  with  the  series  of projects  involving  U B C graduate  overall objective of elucidating the  tectonic  processes related to convergence at the Intermontane Belt/Omineca Belt boundary. The Ogden Peak area is situated structurally well below the boundary, and thus spatially removed  from  the  zone  of  high  strain  concentrated  there.  This  location allows  observation of pre-accretion structures which have been only moderately overprinted by later deformation related to convergence. Overall objectives of this study are to provide a detailed structural and stratigraphic analysis of the Ogden Peak area in order to: 1. ) correlate Snowshoe Group stratigraphy with that described across the North Arm of Quesnel Lake by Getsinger (1985) and that described across the East Arm of Quesnel Lake by Montgomery (1985), and to 2. )  relate  the  structural  tectonic history, specifically North America.  and  metamorphic  those  events  developement  involving  the  of the  area  to  the  local  obduction of Quesnellia onto  2.  2.1.  STRATIGRAPHY  INTRODUCTION Rocks exposed  in the  Ogden Peak area consist of metamorphosed  siliciclastic  and carbonate rocks locally intruded by mafic dykes. Metasedimentary rocks in the area were first mapped by Campbell (1963) as part of the Hadrynian Snowshoe Formation, a  western  fades  of  the  Kaza  Group.  Regional  mapping  by  Struik  (1981,  1982)  culminated in the publication of a 1:50,000 scale geologic map of the Quesnel Lake region  in  which  he  demonstrated  that  the  Snowshoe  Formation  does  not  readily  correlate with strata described elsewhere as part of the Cariboo Group (Holland, 1954; Sutherland Brown, 1957). This has led to the elevation of the Snowshoe Formation to Group status (Struik, 1984). Struik separates it from the  more  easterly  Kaza  group  along the Pleasant Valley Fault (Struik, 1984; 1986a). The Snowshoe Group is included (by Struik) in the Barkerville Terrane, a subdivision of the Selkirk Terrane. Within the Selkirk Terrane, it is considered laterally equivalent to the Horsethief Creek Group as mapped by Pell (1984) east of Wells Gray Park (Struik, 1986b). Nine distinct lithologic units were mapped within the Snowshoe Group in the Ogden Peak area. Figure 3 shows the distribution of the major units across the area.  Complete  transposition  of  bedding  during polyphase  deformation  contacts between units, making estimates of original sedimentary Sedimentary transposed  structures,  when present, are  nature of these rocks, one  has  assume that the  obscured  thicknesses impossible.  in upright positions. However, due  cannot  map  to  the  complete  stratigraphic  below in  stratigraphic  succession is upright Snowshoe Group and  intrusive lithologies are  6  described  STRATIGRAPHY / 7  quartzite, schist units 5a, Sb. 5c  marble 1111111 ni • 1 1 1 1 1 1 1 1 1 unit 3 / q u a r t z o s e schist : - r - a » ~ - i amphibole schist unit 1c  marble, amphibolite  unit 1a  quartzite, schist  Ogdan Peak  Figure 3.  Map of Ogden Peak area showing distribution of major units. See figure 4 for lithologic types.  stratigraphic  STRATIGRAPHY / 8 order.  Stratigraphic interpretations  are  then  presented, along with possible correlations  with surrounding areas.  2.2. S N O W S H O E G R O U P ROCKS  A total present thickness of approximately 3,000 m of Snowshoe Group rocks is exposed  in the  Ogden Peak  pelitic and quartzose  area.  The  stratigraphy  schists, micaceous quartzites,  is characterized  by interlayered  amphibole schists, and marbles. A  generalized stratigraphic column of these lithologies is illustrated in figure 4. Unit 1 minimum thickness 1,500 m This series of interlayered pelitic to quartzose schists and feldspathic  quartzites  are the structurally lowest rocks of the study area. The unit can be divided into three parts, la, lb, and l c on the basis of lithological variation. The base of unit 1 is not observed in the mapped area. Subunit la minimum thickness 1,000 m Subunit l a consists of equal proportions of micaceous feldspathic quartzite and pelitic schists  alternating  in layers ranging  in thickness  quartzite layers crop out as prominent ledges  between  from  5 m to  areas of recessive  10 m. The topography  underlain by schist The grey weathering quartzite has well developed stratification 2 cm to 15 cm thick and a parallel foliation planar  alignment  of micaceous  minerals. Thin  defined  by elongate  discontinuous  marble  quartz  grains and  lenses crop  out  within the quartzite layers in the western map area, but are absent to the east Up to 20% mica and  feldspar  minerals may be  contained in the  quartzite. Grain size  STRATIGRAPHY  Unit  Lithology  Thickness  5c  ^> 1000 m  Quartzose schist,  5b  50 - 300 m  Micaceous quartzite, interlayered schist  0 - 100 m  Micaceous quartzite, schist, marble  50 - 300 m  Impure marble, interlayered schist, amphibolite lenses  150 m  Quartzose schist, thin quartzite layers  100 m  Amphibolite schist  1c  400 m  Thinly bedded quartzite, interlayered schist  1b  50 - 150 m  Quartzose schist, marble, amphibolite  1a  >  Quartzose schist, micaceous quartzite. marble  5a 4  3 2  Figure 4.  i' 3  i' i ' i ' i  1  S r  I I I  1000 m  Structural succession of Snowshoe Peak area.  quartzite  Group lithologies of the Ogden  / 9  STRATIGRAPHY / 10 varies from fine to medium, and large garnet porphyroblasts are typical of micaceous layers. Schist intervals have a distinctive platy appearance with yellow weathering. Thin quartzite  beds (0.3 cm to 0.5 cm) locally  constitute  up to 25% of the  succession.  Mineralogy is dominated by medium to coarse grained muscovite and biotite in roughly equal  proportions,  with  quartz,  feldspar,  and  metamorphic  garnet  making  up  the  remaining rock volume. Both  lithologic types  contain  abundant  quartz  veins crosscutting compositional  layering. The upper contact of this subunit is sharp and is defined by the appearance of abundant marble and amphibole schist layers indicative of subunit l b . Subunit l b variable thickness 50 m to 150 m Immediately overlying the interlayered schists and quartzites of subunit l a is a sequence of mixed lithologies including impure marble, micaceous quartzite, amphibole schist, and micaceous schist This poorly exposed sequence is usually recognizable by yellow  weathering  of the  marble  component  The base is sometimes  marked  by a  friable weakly foliated feldspathic quartzite up to 10 m thick. Overlying this is a platy to massive, tan weathering impure marble up to 50 m thick. Micaceous partings and occasional  quartz  or  amphibole  rich  horizons  define  compositional layering  medium grained carbonate. The marble marks the top of subunit l b in the part of the  study area,  while to the  east, additional interbedded  in  this  western  amphibole schists,  garnet bearing pelites, and marbles continues for up to 100 m. Amphibole schist layers here range in character  from fine grained hornblende-feldspar  gneissic schists to very  coarse grained strongly foliated schists composed exclusively of hornblende. The marble in this sequence is similar to the marble lower in subunit lb. The upper contact of  STRATIGRAPHY / 11 subunit lb is gradational and marked by the gradual disappearance of carbonate and amphibole schist layers. Subunit l c thickness 400 m The  uppermost  division of unit 1 is a thick interval of micaceous quartzite  with up to 30% pelitic schists. Alternation between  these lithologies occurs over as  little as 4 cm to 5 cm in the eastern part of the study area, increasing to 5 m in the west Medium grained schist is dark green and silver on fresh surfaces, weathering to a dark grey. It is more resistant steep slopes  and  cliffs.  Highly  than the schists lower in the section, forming  garnetiferous  intervals are  common, and  chlorite is  locally abundant Grey weathering quartzite has well developed stratification 2 cm to 8 cm thick. Thin mica partings define a foliation and commonly contain large euhedral garnets. Unit 2 variable thickness 50 m to 200 m The  top  of  subunit  lc  grades  abruptly  into  a  slope  forming  amphibole  schist/gneiss sequence. Theoe schists weather typically to dark brown, but local areas of high  carbonate  concentrations  weather  yellow.  Mineralogy  consists  hornblende, plagioclase, and carbonate, although the relative abundance  primarily  of  and grain size  of these components is highly variable. Plagioclase/hornblende ratios are highest in fine grained  rocks, and  grained rocks are  color banded homogeneous,  differentiated  layering is slightly  developed. Coarse  schistose, and composed of 90% to  100% euhedral  hornblende. Marble  lenses  up  to  2.0  m  thick occur at  all levels within  unit  2, and  carbonate content increases markedly in the western study area. With these lenses, 0.1  STRATIGRAPHY / 12 cm  to  1.0 cm thick amphibole/mica selvages  alternate with  much thicker  carbonate  layers. Quartz veins common to unit 1 are absent in the amphibole schist The upper contact with unit 3 is marked by the disappearence of amphibole schist and a return to pelitic lithologies. Unit 3 variable thickness 50 m to 300 m Above the amphibole schist is a resistant pelitic to quartzose schist of variable thickness.  The  bottom  3  m  is  a  very  fine  grained  fissile  schist  lacking  visible  metamorphic porphyroblasts. The remainder of the section consists of grey weathering, medium to coarse grained schist with porphyroblasts of garnet and.staurolite. Locally, up to 20% of this unit may be quartzite layers, and occasional discontinuous marble and amphibole rich horizons are intercalated within the schists in the western part of the study area. Unit 3 may contain up to 10% by volume of thin quartz veins cutting across foliation  at moderate  to high angles. A sharp transition to continuous marble  marks the upper contact with unit 4 (Figure 5). Unit 4 variable thickness 50 m to 300 m In marked contrast to underlying lithologies unit 4 consists primarily of marble, making it an amounts  important marker horizon for regional stratigraphic correlations. Lesser  of pelitic  schist,  quartzite,  and  amphibole  schist  form  discontinuous  lenses  within unit 4 in all parts of the study area. Schist and quartzite layers average 1 m to 2 m in thickness, and occur at all stratigraphic levels within the non-carbonates  marble. These  constitute up to 30% of the overall unit Relative abundances of rock  types follow no consistent pattern across the area. Characteristic yellow weathering of the carbonate  component facilitates easy identification of unit 4, although local areas  STRATIGRAPHY / 13  Figure 5.  Stratigraphic contact between units 3 and 4 north of peak 7570. Thin marble layer of unit 4 is interbedded with quartzite and schist of unit 3.  STRATIGRAPHY / 14 may  weather to dark brown or black. Lensoid, weakly foliated amphibolite boudins up  to 5 m long and with very sharp contacts to the surrounding rock are common to the  lower  part  of  unit  4  in  the  central  study  area.  Compositional layering in  surrounding rocks is parallel to boudin contacts. In hand sample, the marble is coarse grained and ranges in composition from pure  calcite  to  quartzose  marble  with  discrete  layers  of  mica  or  amphibole.  Compositionally distinct layers accompany a parallel penetrative  fissility. Unit 4 schists  have  to  an  unusually high proportion of calcite, and  weather  darker  yellow  than  similar rocks elsewhere in the area. The  upper  contact,  characterized  by  interfingering of marble with  siliciclastic  lithologies of unit 5, is mapped where rocks contain less than 10% marble. Unit 5 minimum thickness 1,400 m Forming  the  structurally highest rocks of the Ogden Peak succession is this  series of alternating schists and quartzites. Unit 5 is divided into three subunits on the basis of relative abundances of constituent lithologies. Subunit 5a variable thickness 0 m to 100 m Overlying the marble of unit 4 in most of the Ogden Peak area is a section of  mixed  section  is  pelitic  schists,  thickest  just  quartzites,  marble,  and  south  Ogden  Peak,  of  amphibole and  schists  thins  (Figure 6). This  rapidly  to  the  east,  disappearing completely over 2 km. Field evidence demonstrating either a structural or a  stratigraphic origin for this thinning is inconclusive. Quartzite and pelitic schist in  roughly  equal  abundances  are  the  dominant  lithologies in  subunit  5a,  with  lesser  amounts of amphibole schist and marble. These lithologic types alternate in layers 1 m  STRATIGRAPHY / IS  Figure 6.  Lithologic variation in base of unit 5a at location 591a. Stratigraphy consists of pelitic schist, quartzite, carbonate, and amphibole schist alternating in layers 1 m to 3 m thick.  STRATIGRAPHY / 16 to 3 m thick. Subunit 5a is overall slope forming, with quartzite forming resistant ledges. Less resistant schists and carbonates weather to tan or rust, and quartzites are typically  dark  discontinuous  grey boudins  in  outcrop.  within  Amphibole  the  marble.  schist  Near  forms  the  top  both of  discrete  the  unit  layers a  series  and of  repetitive marble and micaceous schist layers alternate over 5 cm to 10 cm. The top of  subunit 5a is highly gradational, and  marked as a gradual transition to  thickly  bedded quartzite and lesser pelitic schist lithologies. Subunit 5b variable thickness 50 m to 300 m Directly overlying the mixed lithologies of subunit 5a in the western study area and the marble of unit 4 in the quartzite  with  lesser  interbedded  eastern study area is a well exposed feldspathic  pelitic schist  The quartzite  has conspicuously thick  stratification of 10 cm to 1 m, weathers to a grey color, and crops out in rounded, cliff forming exposures. Visible mineralogy consists of medium to coarse grained quartz, feldspar, muscovite, and porphyroblastic garnet along micaceous partings. Pelitic schist is confined  to layers 0.5 m to 2 m thick, and constitutes up to 20% of subunit 5b.  Within the  schist, muscovite, biotite, and quartz are medium to coarse grained, and  garnet and staurolite porphyroblasts are  abundant  The upper  contact  of subunit 5b  occurs as a zone of increasing pelitic schist content The contact is arbitrarily chosen as the level at which rocks are composed of 30% to 40% schist and 60% to 70% quartzite. Subunit 5c minimum thickness 1,000^ m The series  structurally highest rocks of the Ogden Peak area comprise a repetitive  of feldspathic  quartzites  and  micaceous  schists.  Lithologically  these rocks  are  STRATIGRAPHY / 17 similar  to  those of subunit  5b, with  only  relative  abundances  of each  constituent  changing. In addition, alternation of lithologies is on a much larger scale, with schist layers 20 m to 40 m thick common. Just west of Ogden Peak a prominent 2 m to 3 m thick marker horizon of quartz-feldspar pebble conglomerate is exposed; this layer is  not  found  in the  eastern  part  of the  conglomerate is analyzed in a later section.  study  area.  The  strain  history of this  STRATIGRAPHY / 18 2.3. INTRUSIVE ROCKS  In  a  limited  portion  of  the  study  area  to  the  southeast of Ogden  Peak,  foliated amphibolite bodies occur within Snowshoe Group lithologies of subunit 5b. The resistant and dark weathering nature of these mafic rocks makes them readily visible both in the  field  and on aerial photographs  limited to an area of 1.5 km  2  presently  to  oriented  sub-parallel  where  (Figure 7). They are almost completely  they are clearly divisible into a western  compositional layering and  an  eastern set  set  sharply  truncating layering (Figure 8). In both, areas, they account for up to 20% of surface exposures. Both sets are medium grained and composed of at least  50% hornblende,  with biotite, muscovite, garnet, calcite, and plagioclase making up the remainder of the rock. A poorly to well developed foliation is defined by parallel alignment of mica and hornblende  and weak mineral segregations.  the amphibolites and the metasedimentary  Based on structural  relations  between  rocks, together with their composition, it is  inferred that they originated as diabasic intrusions. In the eastern set, dyke contacts  are planar on a large scale, although local  irregularites give them up to 1 meter of surface relief. The dykes are arranged in an en-echelon map pattern, and typical surface  exposures of a single body measure 3 m  to 20 m wide by 50 m to 150 m long. Mineral zonations occur adjacent to and parallel to the sharply defined contacts, often as a thin garnet rich band or a selvage of more coarsely crystalline hornblende. Angles between regional compositional layering and dyke contacts range from 50° to 9 0 ° . The dykes of the western set have irregular contacts, which are subparallel to compositional layering in the Snowshoe Group rocks. Thicknesses of individual  dykes  range from 1 m to 20 m; diffuse contacts and well developed foliation often  make  S T R A T I G R A P H Y / 19  Figure 7.  En-echelon diabase dykes intruding quartzite of unit 5b near location 459. Dike contacts truncate compositional layering at high angles.  STRATIGRAPHY  121 Figure 8.  / 20  45'  Map showing distribution and surface traces of diabase dykes. Dikes of western set are subparallel to compositional layering, dykes of eastern set truncate layering at high angles.  STRATIGRAPHY / 21 the  smaller  compositional  bodies layering  difficult defined  to  separate by  mineral  from  the  country  segregations  are  rock. much  Foliation more  and  strongly  developed here than in the eastern set No other intrusive rocks are found in significant volumes in the Ogden Peak area.  STRATIGRAPHY / 22 2.4. SUMMARY AND  DISCUSSION  Metasedimentary assigned to the  siliciclastic and carbonate  rocks of the  Downey and Ramos successions  (1984). This assignment  is based  of the  Ogden Peak area  Snowshoe Group by Struik  on similarities to rocks of the  rocks near Spanish Lake (Struik, 1983) and the Barkerville Gold Regional correlations of the Kootenay  Lake  (Schiarizza  and  Terrane,  (Read, Preto,  a group  1976) 1984)  and have  the led  of rocks extending  correlations with Arm  markers structural  Downey succession Belt (Struik, 1982).  Snowshoe Group with the Horsethief Creek Group near  within  of Quesnel Lake, Getsinger  its the  Bay  Formation  inclusion  (by  U.S. border  near  Adams  Struik) in the  inferred  to  Lake Selkirk  have  similar  .  the  successions  Eagle to  to  depositional and deformational histories. Continuous  are  Ogden  described  (1985)  Peak  succession  in adjacent  allow  stratigraphic  areas. Across the North  described a sequence of which  the  lowest  units appear to be equivalent to the highest levels in the Ogden Peak succession. This correlation necessitates a fault between the two areas downdropping the north side, the existence of which is corroborated by offset  in metamorphic zones (Campbell, 1970).  Stratigraphy south of Quesnel Lake described by Montgomery (1985) is similar to the lowest segment of the Ogden Peak succession. Rocks in the Niagara Peak region to the east lie structurally above those in the study area (Garwin, 1987). Ages of Snowshoe Group rocks are  poorly constrained. Microfossil  fragments  from the upper Snowshoe Group laterally equivalent to the Downey Succession have been identified as Early Paleozoic fauna (Struik, 1986). Upper age limits of Snowshoe Group rocks are approximately 340 Ma, provided by the emplacement of the Quesnel Lake Gneiss (Mortensen et al., 1987), and Early Permian, based on conodonts collected  STRATIGRAPHY / 23 from the upper Snowshoe Group (Orchard and Struik, 1985). The  quartzites,  marbles,  and  schists  of  the  Ogden  Peak  succession  are  interpreted to be metamorphic products of a series of clastic sediments, carbonates, and volcanic tuffs. Struik (1986) suggests a basalt flow protolith for some of the amphibole schists in the Downey Succession, however, the high carbonate content and preservation of relic bedding in the amphibolte schist of the study area are more indicative of a volcanic  sediment  or  dolomitic siltstone  protolith. This  sequence  of  lithologies is  consistent with the continental shelf depositional setting proposed for rocks in this area.  3. MAJOR AND  3.1.  TRACE ELEMENT  GEOCHEMISTRY  INTRODUCTION Geochemical analyses were completed for a group of intrusive rocks from the  Ogden  Peak area.  Samples were collected from  six meta-diabase  dykes  representing  both eastern and western sets at various distances from intrusive contacts. The study was conducted using the U B C Department of Geology X-ray fluorescence  spectrometer  with  results  pressed  powder  pellets  samples.  Analysis  procedures  and  test  are  summarized in Appendix 1, and sample locations are shown on Plate I. The chemical compositions of these rocks are used to characterize the igneous suites they  are  associated with.  Specifically,  the  trace  element  concentrations  of  the  dykes are used to infer their original tectonic environments using discriminant diagrams proposed by Pearce and Cahn (1973). A similar approach has been taken for previous workers in the Quesnel Lake region for the Quesnel Lake Gneiss and M L Perseus Gneiss (Montgomery, 1985) and the Takla Volcanics of Quesnellia Terrane (Bloodgood, 1987). Samples from Ogden Peak were analyzed in the present study in order to: 1.  characterize  dyke  rock  composition, and  determine  the  amount  of variation  between intrusive bodies, 2.  relate trace element abundances in dykes to tectonic setting, based on published discriminant diagrams, and  3.  compare the chemistry of these dykes to that of the Quesnel Lake Gneiss, the Boss  Mountain  relations  between  Gneiss,  and  the  the  intrusive  Takla  bodies  24  Volcanics are  to  the  south.  established  on  the  Petrogenetic  basis  of  this  MAJOR AND TRACE ELEMENT GEOCHEMISTRY / 25 comparison.  M A J O R A N D T R A C E E L E M E N T GEOCHEMISTRY / 26 3.2. M A J O R E L E M E N T G E O C H E M I S T R Y The makes  lack of relic igneous textures  classification schemes  based  in the  solely on  diabase  dykes near  whole rock  Ogden Peak  geochemistry  rather  than  i petrographic methods necessary. The dykes are classified using the classification scheme proposed  by Irvine and Baragar (1971). In this system, an initial  ( N a 0 + K 0 ) versus S i 0 2  2  2  plot of alkalies  allows differentiation between alkaline and sub-alkaline fields.  All dyke samples plot within the subalkaline field (Figure 9). An alternative dividing line determined from Hawaiian basalts by MacDonald (1968) places one sample near the boundary between fields. Within  the  sub-alkaline field,  assignment  to  either  tholeiitic or calc-alkaline  suites is based on enrichment trends best illustrated on ternary A F M plots. Tholeiitic suites tend to display strong iron enrichment followed by late stage alkali enrichment, whereas calc-alkaline suites have continuous and moderate samples  except  one  plot  in  Irvine  and  Baragar's  calc-alkaline  Assignment to the  calc-alkaline field  is tenuous,  as the  continuous  suite  enrichment  trends  igneous  differentiation  between  and  actual  calc-alkaline and  iron enrichment A l l dyke (Figure  10).  dykes do not represent are  tholeiitic fields is  section on the basis of trace element abundances.  field  not  observed.  made  in the  a  Further following  M A J O R A N D T R A C E E L E M E N T GEOCHEMISTRY  Figure 9.  / 27  Alkali-silica plot of diabase dyke samples with alkaline and sub-alkaline fields delineated. Dividing line of MacDonald (1986) is derived from Hawaiian tholeiitic and alkaline rocks, division of Irvine and Baragar (1971) is from analyses of alkaline, tholeiitic, and • calc-alkaline suites.  MAJOR AND TRACE ELEMENT GEOCHEMISTRY / 28  Figure 10.  AFM plot of dyke samples showing tholeiitic and calc-alkaline suites. (After Irvine and Baragar, 1971).  MAJOR A N D T R A C E E L E M E N T GEOCHEMISTRY 3.3. T R A C E E L E M E N T Trace  element  / 29  GEOCHEMISTRY abundances  in  igneous  rocks  have  been  shown  to  vary  systematically with tectonic environment (Pearce and Cann, 1973; Floyd and Winchester, 1975;  Pearce, 1984; Pearce et al., 1984; see Erdman, 1985 for review). Binary and  ternary discriminant diagrams showing this variation are constructed using trace element analyses of unaltered demonstrated  rocks from  known  tectonic settings.  As Ti, Zr, and  Y  have  low mobility at moderate metamorphic grades (Pearce and Cann, 1973;  Murphy and Hynes, 1986), diagrams using these elemtents as discriminators are used in classifying the altered diabase dykes. A ternary plot of Ti, Zr, and Y proposed by Pearce and Cann (1973) is used to differentiate  between arc related low-potassium tholeiites and calc-alkaline basalts,  within plate basalts, and ocean floor basalts (Figure 11). A l l analyses fall  within the  calc-alkaline basalt field, but several are in the region overlapped by the ocean-floor basalt and low-potassium tholeiite fields. An alternative plot with just Ti and Zr (after Pearce and Cann, 1973) shows five  analyses  in  the  calc-alkaline basalt  ocean-floor basalt field (Figure 12).  field,  and  one  analysis just  inside  the  MAJOR AND TRACE ELEMENT GEOCHEMISTRY / 30  Ti/100  Figure 11.  Discriminant diagram using Ti/100, Zr, and Y x 3- Fields different tectonic settings are defined by Pearce and Cann Calc-alkaline basalts plot in fields C and D, within plate field A, ocean floor basalts in field C, and low-potassium in fields B and C.  for (1973). basalts in tholeiites  M A J O R A N D T R A C E E L E M E N T GEOCHEMISTRY  / 31  15.000-  10,000Ti (ppm)  5,000-  i  50  100  150  200  Zr (ppm)  Figure 12.  Binary discriminant diagram using Ti and Zr. (After Pearce and Carm, 1973). Calc-alkaline basalts plot in fields A and B, low-potassium tholeiites in fields B and C, and ocean floor basalts in fields B and D .  M A J O R A N D T R A C E E L E M E N T GEOCHEMISTRY  / 32  3.4. S U M M A R Y A N D DISCUSSION The  chemical compositions of the  Ogden Peak dykes suggest  a calc-alkaline  affinity. These results are not conclusive however and several limitations are recognized: 1.  Amphibolite grade metamorphism has altered the mineralogical character of these rocks, and may have affected major and trace element abundances through fluid transfer  or  concentrations  diffusional between  different  positions  mobility  studies  processes.  The  samples from  within  dykes  different  suggests  indicating stable  • amphibolite grade  relatively small  metamorphism  variation  in  elemental  dykes and between samples  this  effect  concentrations (Murphy and  of  is  small.  Trace  Ti, Zr, and  Hynes, 1986)  Y  from  element even  also suggest  at the  trace element analyses are valid. 2.  Compositional fields on discriminant diagrams are empirical and are limited by available data from previous studies.  3.  Composition fields are  constructed  from  analyses of basic volcanic rocks, and  applications to intrusive dykes have not been demonstrated. 4.  Petrographic evidence confirming any interpretation is lacking due to overprinting of original mineralogical characteristics during amphibolite grade metamorphism. Petrogenetic  relationships  between  the  Ogden Peak  dykes and  other  igneous  rocks of the Quesnel Lake region are unclear. Studies of the Quesnel Lake Gneiss and M t Perseus Gneiss show calc-alkaline affinities and effects of crustal assimilation (Montgomery, much element studies  more  1985). Although mafic  abundances of the  than  either  bulk compositions of the the  closely resemble  Quesnel Lake  or  those  Mt  Takla Volcanics in the  of the  Ogden Peak Mount Perseus Perseus  samples  were  Gneiss, trace  Gneiss. Geochemical  Quesnel Lake area (Bloodgood, 1987) yielded  equivocal results, with characteristics of both tholeiitic and calc-alkaline suites. Structural  M A J O R A N D T R A C E E L E M E N T GEOCHEMISTRY evidence suggests a time of emplacement  / 33  similar to that of the Quesnel Lake and  Mount Perseus Gneiss (see section 4.2). Forthcoming zircon U - P b geochronometry on samples collected from the Ogden Peak area (Mortensen et a l , 1987) may clarify these genetic relationships.  4. STRUCTURE  4.1. INTRODUCTION Four  phases  of  folding  and  (Di-D«)  one  later  phase  of  localized brittle  deformation ( D ) are recognized within the Ogden Peak area. Assignment of mesoscopic 5  structures to specific deformational superposition structural  of  axial  elements.  deformation  surfaces,  episodes  was made in the  refolding  Snowshoe  Group  relationships,  rocks  record  and  field  on. the  relative  all  phases  within intrusive rocks is limited to developement  basis of  orientations of  of  deformation;  of foliation and minor  folds and warps of intrusive contacts. For simplicity, axial surfaces and axial directions are  referred  to  as  lineations designated  A1-A4 S1-S4  and  and  respectively,  FJ-FA  Li-L . 4  with  penetrative  foliations  and  The distribution and orientation of phase 1 and  phase 2 structures in the Ogden Peak area are presented on Plate II. Phase 3, Phase 4, and late brittle features are included on Plate III. Microcracks,  deformation  twins,  kink  bands,  and  recrystallization textures  are  observed on the microscopic scale within deformed crystals. Petrographic examination of deformation  fabrics  allows  correlation  of  these  microstructures  to  the  metadiabase dykes suggest  the  major  deformational episodes in the area. Structural during  D  x  features in and around  deformation,  metasedimentary  and  are  discussed  below  separately  from  emplacement  D j to  D  5  in  rocks. Kinematic significance of and relationships between all structures  are addressed in a concluding section.  34  S T R U C T U R E / 35 4.2. MESOSCOPIC  4.2.1.  D i  -  D  4  STRUCTURES, METASEDIMENTARY ROCKS  Folding  Phase 1 ( D O The earliest deformational event recognized in the study area is manifested in a regional penetrative occurs as  foliation and complete transposition of bedding. Associated folding  very tight  to  isoclinal  reclined or  recumbent  structures  in quartzite  and  marble lithologies and as isolated floating hinges outlined by dismembered quartz seams in schists. The absence of repetition of lithologic units and mappable  isoclinal  fold  closures indicates that phase 1 folds are limited to outcrop scale in the Ogden Peak area. However, the intensity of deformation and the abundance bedding indicate moderate  of isoclinal folds of  to considerable structural thickening of original  stratigraphy  accompanied this early folding event Evidence that compositional layering in the area is transposed includes isoclinal folding observed on outcrop scale and isolated hinges of dismembered isoclinal folds defined  by  segregations  quartz and  stringers. . Phase  1  parallel alignment  of  foliation  is  outlined  micas, amphiboles,  by  and  thin monomineralic elongate  quartz  and  calcite grains. No mineral lineation clearly associated with D j occurs in the study area, although F i axes are often parallel to D Dj  2  mineral lineations.  fold limbs are typically highly attenuated and accompanied by considerable  thickening of hinge regions (Figure 13). Extreme limb attenuation in schistose units has led to dismembered folds with floating hinge regions outlined by quartz  segregations  (Figure 14). Stereographic  projections  of structural  elements  related  to phase  1 folds are  S T R U C T U R E / 36  Figure 13.  a. ) Tight phase 1 fold of compositional layering in unit l c quartzite. b. ) Mesoscopic phase 1 isocline outlined by interlayered marble and schist, near location 591a.  STRUCTURE / 37  b.  S T R U C T U R E / 38  Figure 14.  Isoclinal hinge of dismembered phase 1 fold of quartz vein in pelitic schist, location 177.  S T R U C T U R E / 39 illustrated in figure 15. Axial surfaces are defined by a penetrative foliation (Si) which is everywhere parallel or subparallel to compositional layering (So), and dips gently to the northeast or northwest This surface will hereafter  be referred to as S / S i . F 0  x  fold  axes plunge gently to the northwest throughout the area. Vergence of D ! structures is equivocal, with fold sets asymmetric both east and west Offset of lithology along S i planes in an area where S angles  indicates  emplaced  early  east in  directed  shear  D i , indicate  (Figure  moderate  0  and Si are at moderate  16). Dismembered amounts  of  east  folded  quartz  veins,  directed  shear  along  compositional layering. Quartz  veins  formed  throughout  D i , most  abundantly  in schistose lithologies.  Those formed earliest are folded and transposed parallel to S]/S , while those formed 0  later  in  deformation  maintain  moderate  angles  preserved, are oriented perpendicular to vein walls.  to  foliation.  Quartz  fibres,  when  STRUCTURE / 40  Figure 15.  Equal area projections of phase 1 foliation and fold axis data. Contour intervals for S /S, plot are 1%. 3%, 5%. 7%, and 9%. 1.4% counting area determined using method outlined by Kamb (1959). 0  S T R U C T U R E / 41  Figure 16.  East directed offset of S surfaces along Si shear planes in unit 5a micaceous quartzite, near peak 7570. 0  STRUCTURE  /  42  Phase 2 (D ) 2  surfaces  S /Si 0  in all lithologies are folded about  phase 2 deformation. D  upright axial planes during  is the most pronounced phase of deformation in the Ogden  2  Peak area, with well developed structures documented in all locations. Fold scale ranges from microscopic crenulations to a map scale antiform-synform set in the eastern study area  outlined  outlined by  by  S /Si 0  the  unit  2  17. Fold  axes  northwest  Axial surfaces S  are  coaxial  folds  are  angles  to  D  fold  r  axes,  plunging  shallowly to  the  dip moderately to steeply to the northeast Angles measured and compositional layering  (See plate II for spatial distribution of Interlimb  A l l mesoscopic phase 2  structural elements are plotted on stereograms in figure  2  presently  axial surfaces  2  schist  surfaces.  Orientation data for D  between  amphibole  of D  2  folds  S /Si 0  are  -  S  2  (S /Si) 0  range from 10° to 80°  angles).  normal  to  tight  and  hinge  regions  are  subrounded to subangular. Marbles typically have tight angular hinges, while quartzose rocks have the most open, rounded geometries  (Figure 18). Hinge zones are always  thickened relative to limbs, giving most folds a "similar" shape. Graphs plotting limb dip against orthogonal layer thickness in different lithologies (after Ramsay, 1967) show clasr, 2 behavior in carbonates and schists and class l c forms in quartzite. (Figure 19). D of  2  folds are strongly asymmetric in almost all locations, with a westward sense  vergence  on all first  order  folds. Second and  third  order  folds show  expected  vergence changes with position on. larger structures. Diabasic intrusions have only weak phase 2 crenulations and no S and their intrusive contacts show evidence of D forms  and are  more abundant  2  deformation. D  in country rock surrounding the  2  2  folds have  foliation, tighter  intrusive units than  elsewhere in the area, possibly compensating for lesser amounts of strain in the more  STRUCTURE / 43  Figure 17.  Equal area projections of phase 2. axial plane and fold axis data.  Figure 18.  a) Normal D fold in unit 5b quartzite, near location 612. b) Tight D fold in unit 4 marble, location 293. Compositional layering is outlined by micaceous partings 2  2  STRUCTURE  /  class lb  Figure 19.  t' versus «< plot (Ramsay, 1967) of layer thickness as a function of limb dip. Marble and schist lithologies approach class 2 forms, quartzite displays class Ic behavior.  45  S T R U C T U R E / 46 competent dykes. D  crenulations  2  are  ubiquitous  in schistose  lithologies of the  study  area.  In  carbonates and quartzites, crenulation fabrics are developed only in pelitic horizons. Two types of axial planar crenulations  cleavage  have tightened  are  associated  with the  crenulations.  Most commonly,  such that one limb is parallel to the axial plane (Figure  20). This type is primarily found in rocks of very micaceous composition. Elsewhere, axial  planar  crenulated  growth  rocks  of muscovite  (Figure  21).  across  layering outlines a penetrative  Microscopic  folds  and  cleavage  are  not  cleavage in observed  in  quartzite and carbonate units, although mesoscopic folds are common. Linear  features  associated  with D  2  include mineral orientation  lineations  and  quartz rod lineations. Both of these lineations are penetrative and always occur parallel to F . Quartz rods are round or oval in cross-section, and up to 1 m long with 2  length-diameter  ratios often  exceeding  by amphibole, mica or deformed  10:1. Mineral orientation lineations are  defined  quartz and calcite grains. A pebble conglomerate in  subunit 5c has numerous quartz and feldspar clasts which are possibly deformed  and  now define a strong linear fabric parallel to 1^. Commonly associated with D  2  folds are planar quartz veins formed along axial  planes, especially in quartzose and schistose lithologies (Figure 22). These are composed of microcrystalline milky quartz and rare microcrystalline muscovite, and measure up to 20 cm thick and several meters in length.  S T R U C T U R E / 47  Figure 20.  D crenulations defined by muscovite and biotite in unit 3 schist, in sample 104. 2  S T R U C T U R E / 48  Figure 21.  Axial planar muscovite growth defining S  2  cleavage.  S T R U C T U R E / 50 Phase 3 (D ) 3  D Peak  3  is the least well developed phase of deformation in outcrop of the Ogden  area. Phase  mapped  in the  3 upright open warps with wavelengths of several kilometers are field  primarily by changes  responsible for the overall map pattern So/Sj  surfaces.  Mesoscopic folds are  Upright crenulations in D  3  in bedding  orientation. These  folds  are  and the great-circle stereonet distribution of  warps with  orientations are  "parallel" forms  and  open profiles.  found only in hinge zones of the  map  scale structures. related to D  Orientations of structural elements  3  folds are displayed in figure  2 3 . Fold axes are coaxial to those of D j and D , plunging shallowly to the northwest 2  with steeply dipping to vertical axial planes. Symmetric fold profiles preclude sense of vergence determinations. A fractures  spaced are  joint set  folded  during  is oriented D « but  perpendicular are  unaffected  to F by  3  axes  phase  association with D . No offset is observed along these fractures, 3  formation with respect to other D  3  features is inconclusive.  in outcrop. 2  folds,  These  suggesting  and their time of  S T R U C T U R E / 51  Figure 23.  Equal area projections of D  3  axial plane and fold axis data.  S T R U C T U R E / 52 Phase 4 (D ) 4  D,  crenulations and open warps refold earlier structures at nearly right angles.  Both crenulations and buckles occur in all parts of the study area; these structures are most strongly developed in schists surrounding the intrusive rocks. Kink bands coaxial with F  crenulations are believed to be related to this same deformational event  4  F or  fold axes have shallow to moderate  4  northwest  dipping axial  surfaces  northeast plunges and steeply southeast  (Figure  24), allowing  earlier folds. Axial surfaces are nearly at right angles to  easy  differentiation  Type III "dome and  S /Si. 0  basin" interference patterns (Ramsay, 1967) result from the superposition of D and D  3  from  4  on D  2  structures.  Hinge angles are open to normal on folds with wavelengths of less than 0.5 m and open on folds with greater wavelengths. In all lithologies, D  4  folds have "parallel"  class l b to l c profiles with little or no thickening in hinges, as illustrated by plots of layer thickness against bedding surfaces mesoscopic  F  4  limb  dip (Figure 25). Slickenside lineations may  at high angles to F buckle  folds  and  4  occur along  fold axes. These are only found on limbs of  probably  indicate  layer-parallel  movement  during  folding. Slip along layer boundaries may create mesoscopic disharmonic folds in areas (Figure 26). D  4  folds are symmetric with the  exception of parasitic structures  which show  appropriate vergence changes with position on larger structures. Where  D  4  crenulations  are  most  strongly  developed,  a  spaced  crenulation  cleavage is defined by the alignment of mica along fold limbs. Mica growth did not accompany the formation of this cleavage. In micaceous rocks, disharmonic crenulations often form as a result of slip along foliation planes during deformation (Figure 27). A joint set  developed during or after  D  4  dips steeply to the northeast and  STRUCTURE / 53  Figure 24.  Equal area projections of D axial plane and fold axis data. 4  S T R U C T U R E / 54  f  t' versus^, plot (Ramsay, 1967) of layer thickness as a function of limb dips for D folds. A l l lithologies display class l b to l c behavior. 4  STRUCTURE / 55  Figure 26.  Layer parallel detachment along mesoscopic phase 4 buckle in unit 1 micaceous quartzites, near location 391.  S T R U C T U R E / 56  Figure 27.  D disharmonic crenulation showing effects of layer-parallel slip during deformation, sample 523. 4  S T R U C T U R E / 57 southwest In the field, these joints are perpendicular to F  4  fold axes.  S T R U C T U R E / 58 4.2.2. D  5  Faulting  High  angle  designated D . s  easily  mapped  faults  offset  all  lithologies in the  Ogden  Peak  area  and  are  They strike north-northeast and dip steeply to the southeast, and are in  the  field  based  on  offset  of  stratigraphy  and  the  substantial  topographic expression associated with them. The most continuous faults occur with a regular spacing of 0.5 km to 1 km. Plate IV shows the locations and orientations of the major faults in the field area. Net slips on several faults were calculated using slip direction indicators and stratigraphic  offsets  measured  in  the  field.  Mullions  on  fault  surfaces  indicate  a  dominant down-dip component of slip, and later slickensides suggest minor strike-slip offset offset  Calculated net slip values of 20 m to 50 m are obtained assuming normal  S T R U C T U R E  /  59  4.3. MESOSCOPIC STRUCTURES, INTRUSIVE ROCKS  Meta-diabase  dykes  in  the  study  area  are  divided  into  a  western  set  sub-parallel to compositional layering in the country rock and an eastern set which truncates layering at high angles. Each set. has unique deformation features which will be  discussed separately  below. Figure 2 8 is an  interpretive  cross section illustrating  overall structural relationships of each set with the surrounding rocks.  4.3.1.  Western dyke set  Dikes of this set truncate  S /Si 0  surfaces  at low angles and dip shallowly to  the north (Figure 29). Intrusive contacts may be sharp or diffuse and gradational over 0.5 m, and are deformed by D  2  folds (Figure 30).  Structures internal to the dykes record a strain history similar to that of the surrounding Snowshoe Group rocks suggesting predeveloped penetrative grain  orientations  orientation  and  lineations  isoclines are  foliation, parallel to weakly  plunge  outlined by  developed  northwest  to syn- Dj emplacement  intrusive  contacts,  compositional  parallel  to  compositional layering, but  the  is outlined by mineral  layering.  Lj in  A well  the  Associated country  intrusive  mineral  rocks.  contacts  are  Rare not  likewise folded (Figure 31). Phase 2 folds of compositional layering within the dykes have wavelengths of up to 0 . 5 m and tight geometries.  STRUCTURE / 60  Figure 28.  Structural relationships of intrusive diabase dykes to surrounding country rocks. Dikes of western set are sub-parallel to compositional layering and folded during phase 2 deformation. Eastern set dykes are at high angles to compositional layering and intrusive contacts are not visibly deformed.  STRUCTURE / 61  Figure 29.  Diabase dyke of western set with sharp contact subparallel to compositional layering. Foliation within dykes is parallel to that in metasedimentary country rocks.  S T R U C T U R E / 62  Figure 30.  Phase 2 fold of intrusive contact in dyke of western set near location 591.  S T R U C T U R E / 63  Figure 31.  Phase 1 isoclinal fold outlined by compositional layering within dyke of western set, location 591.  S T R U C T U R E / 64 4.3.2. Eastern dyke set Dikes of the eastern set are large tabular bodies striking north-northwest  with  sub-vertical dips. Intrusive contacts are sharp, planar, and unfolded. Structures  in this set  of dykes indicate a strain history lacking  the  earliest  features found in the western set of dykes and the Snowshoe Group rocks. Oriented mineral  grains  and  weakly developed  foliation parallel to the high  angle  to  So/Si  compositional segregations  enveloping surfaces  intrusive contacts.  in adjacent  Amphibole grains  lying  northwest plunging mineral lineation, parallel to the L  2  define  a  penetrative  country rocks and at a  in the  foliation  outline a  mineral lineation in surrounding  country rocks. Folds internal to the  eastern set of dykes are limited to crenulations of the  dominant foliation within the outermost 20 cm to 30 cm. These folds have styles and orientations similar to D  2  stuctures in the adjacent country rock.  Metasedimentary rocks adjacent  to the  dykes contain structural  features unique  to this location. Figure 32 illustrates the style, orientation, and spatial distribution of these structures  along an  intrusive contact  S /S 0  x  surfaces  in the  country  rock  are  nearly perpendicular to dyke contacts, but may be folded into sub-parallelism with the dykes by folds with axial planes parallel to the intrusive contacts (Figure 33). A weak foliation  defined  by  oriented  biotite/chlorite aggregates may  form  across  the  S /Si 0  surface in a direction parallel to the dominant foliation in the dykes. A third planar surface defined by leucocratic seams crosscuts both of these foliations in an orientation parallel to the dyke contacts. Although the structure during  subsequent  metamorphism,  their  within these seams is obliterated  orientations  suggest  a  hydraulic  fracture  mechanism of formation synchronous with dyke intrusion. The present orientation of dyke contacts and the penetrative foliation within the  S T R U C T U R E  Figure 32.  /  65  Contact between eastern set diabase dyke and metasedimentary country rock at location 651c. Planar surfaces described in text are defined by: 1. S o / S j compositional layering in country rock, 2. Mica foliation crossing S / S i at low angles and parallel to foliation in intrusive rocks, and 3. leucocratic seams parallel to intrusive contacts. 0  S T R U C T U R E / 66  Figure 33.  Folds in metasedimentary rock along intrusive contact, eastern dyke set near location 582. Compositional layering is locally parallel to intrusive contact.  STRUCTURE / 67 dykes  suggest emplacement  and  subsequent  deformation  in a strain  field  similar in  orientation to that associated with the So/Sj foliation. Lack of transposition of intrusive contacts limits the possible time of formation to very late in Di, but prior to the onset of D . 2  S T R U C T U R E / 68 4.4. MICROSCOPIC  Textures which  STRUCTURES  observed  deformation  in thin section allow the  determination  was accomplished. Microstructures may be  phases of deformation  by their  orientations,  of mechanisms  correlated  relations to mesoscopic  by  with specific  fabrics, and  the  relative ages of metamorphic grains in which they occur. Earliest formed structures may be  overprinted  deformation  or  obliterated  mechanisms  temperature/pressure  by  later  operative  conditions  deformation  on  a  which  are  and  crystalline inferred  annealing. scale  to  Knowledge of  helps  verify  accompany  the  deformation.  Microstructures observed in rocks of the Ogden Peak area include healed microcracks, filled  microscopic  extension  fractures,  kink  bands,  deformation  twins  and  lamellae,  pressure solution features, and recrystallization textures.  4.4.1. Healed microcracks Microcracks form during deformation as microscopic planes of brittle extension. If  these cracks  diffusional  are  process  microcracks  may  limited as  be  in  outlined detected  extent, they by  in  may  Wanamaker crystals  as  undergo  and planar  later  Evans  healing  (1985).  arrangements  through  Partially of  a  healed  cylindrical  or  spheroidal pores. These pores represent gas filled inclusions which formed in response to lattice mismatch in the  healing crystal. Cylindrical inclusions formed  crack  divide into  healing process  may  isolated  spheroids  under  early in the  temperature induced  increased diffusion (Wanamaker and Evans, 1985). Cylindrical pore shapes, together with the  tendency  between  healed  for  inclusion  microcracks  planes and  to  cross  grain  "Boehm" lamellae  dislocation slip processes (Fairbairn, 1949).  boundaries,  allow  inclusion planes  differentiation  formed  through  S T R U C T U R E / 69 In rocks of the Ogden Peak area, healed microcracks commonly occur in quartz grains  and  microcracks  occasionally in feldspar filled  porphyroclasts  of feldspathic  quartzites. Unhealed  with foreign crystalline material are common in garnet, hornblende,  and feldspar, and are discussed in the 50% mica content  contain much higher  following section. Rocks with a greater than microcrack densities  than  do  more  silicious  rocks. Trails of spheroidal to cylindrical inclusions may be continuous through several adjoining show  a  quartz  grains  majority  (Figure  34). Orientation  of microcrack planes  dipping steeply  remainder randomly oriented. This preferred the  S /Si 0  measurements  foliation, and 50° to 70° from F  to  from  the  several  northwest,  samples with  the  orientation is always at a high angle to 2  and F  3  fold axes.  4.4.2. Extension fractures Mineral orientations  filled  during  extension fractures  deformation.  Infilled  may be used to determine mineral phases, if not  local strain axis  recrystallized, display  preferred growth orientations and reflect the stable mineral assemblage at the time of formation. Extension fractures are commonly observed in hornblende, in garnet, and in feldspar porphyroclasls. Garnet  porphyroblasts  are  fractured  along planes  foliation. Mica growth is common within fractures,  perpendicular  to  the  So/Sx  and later retrogression appears to  nucleate along them. Hornblende within the unit 2 amphibole schist is broken and extended along fractures perpendicular to  S /Si. 0  Fractures are infilled with equant quartz grains which  are presently randomly oriented but may have been elongate fibres at their time of formation. Feldspar porphyroclasts are dissected by extension fractures  infilled with equant  S T R U C T U R E / 70  Figure 34.  Healed microcracks in quartz defined by planar arrangements of elongate bubble inclusions, sample 447. Healed cracks are often continuous across several grains of different orientations.  STRUCTURE / 71  Figure 35.  Extension fractures in feldspar porphyroclasts of sample 188.  S T R U C T U R E / 72 quartz grains. These occur at moderate or high angles to S /Si  and do not continue  0  into adjacent  feldspar clasts (Figure 35). Fracture orientations are often sub-parallel to  healed microcracks in the feldspar and in surrounding quartz grains.  4.4.3. Kink banding Kink deformation  bands in mica and through  dislocation slip  sections cut normal to F at high angles to  S /Si 0  36). Cleavage planes surrounding  undulose  4  extinction in quartz  processes.  These  features  provide evidence for are  most  common in  fold axes. Biotite porphyroblasts have kink band boundaries  where they are deformed about phase 4 crenulations (Figure  within kink bands are rotated  crystal in a direction which  brings  up to 40°  them  closer to  with respect the  A4  to the  orientation.  Under higher strains grains may fail brittlely along kink band boundaries to form new separate grains. Undulose  extinction in  quartz  occurs  either  as  distinct  subgrain  regions of  slightly differing optical orientation or as a warping of the quartz structure distinct subgrain associated  boundaries  developed.  with subgrain developement  Rocks with  evidence  of high D  (Figure 37). Subgrains are  2  with no strain  equant or  are  elongate  parallel to kink band boundaries, and optical orientations are rotated less than 5° from adjacent subgrains. Undulose extinction without subgrain developement is characteristic of rocks deformed  dominantly by phase 4 folds. Narrow "Boehm" deformation lamellae  defined by changes in quartz relief and birefringence are re-oriented boundaries (Figure 38).  across subgrain  STRUCTURE / 73  Figure 36.  Kink bands in biotite porphyroblast deformed about a phase 4 microfold in sample 369. Kink band boundaries are subparallel to or symmetric about axial planes of folds.  S T R U C T U R E / 74  Figure 37.  Polygonization and subgrain developement in quartz, sample 463, evidence of diffusion climb deformation mechanism.  STRUCTURE / 75  Figure 38.  "Boehm" deformation lamellae in quartz, sample 130. Lamellae are re-oriented across kink band boundaries.  STRUCTURE / 76 4.4.4. Pressure solution features Sutured  grain  boundaries,  hydraulic  provide evidence of deformation  fractures,  and  quartz  by pressure solution processes  pressure  shadows  (Elliot 1973). Sutured  grain boundaries, common between quartz grains, occur in all orientations and cannot be positively correlated with any specific deformational quartz-filled  hydraulic fractures,  episode. However, mesoscopic  derived probably in part from pressure solution, are  correlated with all phases of deformation. Quartz pressure shadows about garnet and staurolite  porphyroblasts  indicate  pressure  solution  was  active  during  or  following  metamorphic mineral growth.  4.4.5. Deformation twins Several orientations of twin lamellae are observed in calcite grains of carbonate rocks. Twin lamellae are narrow relative to grain size, and are sharply bounded by planar surfaces  extending across the full  occur at all angles to the  width of the  host grain (Figure 39). They  foliation, and form irregularities in grain boundaries.  S /Si 0  Lamellae comprise between 10% and 40% of individual calcite grains.  4.4.6. Recrystallization textures Recrystallization textures are observed in quartzose lithologies where fine grained neoblasts  form  recrystallized  along  grain  grain  boundaries  boundaries  have  at  the  expense  irregularities  amplitudes. In one example recrystallization nucleates  with  of  larger  constant  grains. Scalloped wavelengths  and  along boundaries between highly  elongate quartz ribbon grains (Figure 40). This type of recrystallization is localized in a quartzose  segregation  mylonite  displays  forming the  similar  textures  core of a tight microscopic D (Figure  41)  where  original  4  fold. A  grains  have  quartzose partially  S T R U C T U R E / 77  Figure 39.  Deformation twins in calcite from location 261. Twin lamellae generate irregularities in grain boundaries  STRUCTURE /  Figure 40.  Quartz recrystallization texture in core of tight phase 4 microfold, sample 523. Fine grain neoblasts have nucleated along ribbon grain boundaries.  78  STRUCTURE  recrystallized  to small equant  / 79  shapes with equilibrium grain boundaries. Ribbon grains  are still visible in hand sample.  S T R U C T U R E / 80  Figure 41.  Recrystallization of ribbon grains in quartz mylonite, leading to equant, equigranular texture, sample 2401.  S T R U C T U R E  /  81  4.5. S U M M A R Y A N D DISCUSSION  A  structural  sequence  in  which  decrease over time is documented styles  accompanying  deformation  intensity  by structures are  of  folding  in the  strongly  and  ductility of rocks  Ogden Peak area. Structural  influenced  by  dependant mainly on lithologic type. Styles and geometries  rheologic  constraints  of folds representative  of  each deformational episode are illustrated in figure 42. Earliest  deformation  the  form  of a  regional  transposed  folds. Quartz veins initiated in D i are  mesoscopic isoclinal hydraulic fracture  is in  inferred  foliation  and  to form by a  mechanism fed by fluids derived from metamorphic dewatering and  pressure solution processes (Norris and Henley, 1976, Etheridge et al., 1984). Increasing metamorphic  grades are  implied  by mica foliation  growth and  continued  dewatering.  Sedimentary compositional differences were enhanced by dissolution and solution transfer processes  to  form  the  well  Dismembered folds of quartz shear along transposed  S /Si 0  into  developed  compositional  veins within the  transposed  layering  have a foliation parallel to  sub-parallel S /Si 0  tc  local  1972).  layering indicate substantial  surfaces. Diabase dykes which intruded during  orientations  (Durney,  D i  may have  been  compositional layering. Later dykes  in surrounding rocks, but contacts are not transposed.  This dyke foliation, together with S i mica growth across isoclinal fold hinges, suggests that high shear strains during early folding were followed by a flattening strain later in D i . This may be a consequence were  tectonically thickened.  of increased loading as higher structural levels  Folds formed  early  in  D  :  were  flattened  into present  isoclinal forms under conditions of high strain and low viscosity contrast Tight  class  lc  to  class  continuation of high temperature,  2 folds with  axial  planar  low viscosity contrast  mica growth  indicate  conditions during D  2  a  folding.  STRUCTURE / 82 M E S O S C O P I C  FOLD  D E V E L O P M E N T  SW  Phase 1:  SW  Phase 2:  SW Phase 3:  NW  Phase 4:  10 m  Figure 42.  Summary of mesoscopic fold style and geometry, phase 1 -  phase 4.  S T R U C T U R E / 83 Phase  1 folds were further  forms.  Phase  lc  to  during this event,  2 folds initiated as buckle or  viscosity contrasts class  tightened  across  class  2  layering and  forms  were  (Ramsay,  modifying them to isoclinal  flexural slip folds controlled by slight subsequently  1962).  The  flattened  extent  of  into their present  flattening  is  strongly  controlled by rock type, leading to tight class 2 folds in marble and schist and open class lc forms in quartzites. Consistant asymmetry of folds indicates non-coaxial strain with a component of west-directed simple shear during deformation. Deformed pebbles in one location and quartz rods throughout the area imply a constrictional component of  strain with  elongation  resolved in the  F  direction. This strain  2  history can  be  approximated by a series of incremental strain ellipsoids in which the flattening ( X - Y ) plane rotates away from the maximum compressive stress direction. If quartz rods and elongate clast axes truly represent the regional elongation direction, this rotation would be about the X strain axis, as illustrated in figure 43. Lesser  amounts  of  D  strain  2  in  meta-diabase  anomalously high strain in immediately adjacent  dykes  are  juxtaposed  against  country rocks. This suggests that the  dykes behaved more competently and controlled deformation in surrounding lithologies to allow for strain homogeneity on a large scale. Phase 3 broad buckles indicate a transition following D  2  to lower temperature,  higher viscosity contrast conditions of folding. Deformation was probably a continuum through phases 2 and 3, as D  2  folds were refolded coaxially about more upright D  3  axial planes. This refolding is slight and not easily discernible on stereonet projections of phase 2 data. Phase contrasts. mechanism  4  open  Detatchment dominated  (class  lb)  along  So/Sj  by  flexural  folds  imply  surfaces slip  on  between  continued all  folding  scales  buckled  at  indicate  layers.  high viscosity a  As with  deformation phase  2  Figure 43.  Incremental strain ellipsoids showing possible phase 2 progressive deformational history. Z and Y axes rotate about X axis in non-coaxial deformation.  S T R U C T U R E / 85 structures,  lesser amounts  of strain in dykes are reflected by high strains in adjacent  metasedimentary rocks. Latest deformation occurs as steeply dipping faults with no observed associated folding. Brecciation zones along faults indicate a majority of strain at this time was accommodated by brittle translation. The relations  formation  to  of  abundant  mesoscopic structures  quartz-filled  provides  hydraulic  fractures  evidence of ample  pore  with fluid  varying  availability  during all phases of deformation. Strain  was  accommodated  on  a  microscopic scale  through  ductile and semi-brittle mechanisms. The dominant deformation appear to vary in different  a combination of  mechanisms  operating  types of minerals. Within a given mineral species,  the  effects of various mechanisms are dependant on: 1.  The constitutive minerals of the overall aggregate, and relative proportions thereof,  2.  the relationship of the specimen observed to mesoscopic structures, and  3.  the timing of deformation within the specimen.  Quartz, mica, and calcite are the major mineralogical constituents rocks of the  study area, and thus accommodated  of  metasedimentary  a majority of the  strain in most  rocki. Quartz deformed through a combination of pressure solution, microcracking, and dislocation  glide.  Earliest  deformation  dislocation glide in quartzose rocks.  Strain  recrystallization  softening along  accommodated  dynamic  boundaries  has  recovery obscured  Preservation of bubbles along healed microcracks and later  intracrystalline diffusion  by  pressure  solution  and  rocks, with the addition of microcracking in micaceous  through  grain  was  is limited,  (polygonization) many  of  the  and  dynamic  earliest  features.  "Boehm" lamellae indicate that  and suggests recrystallization is accomplished  S T R U C T U R E / 86 through  grain  boundary  diffusion.  Later  deformation  (D ) 4  in quartz  is  mainly by  dislocation glide and kinking, and is limited to pelitic rocks. Recrystallization overprints phase 4 features only in regions of high D implies falling  4  strain, where the small size of neoblasts  temperatures and high differential  stresses (Carter,  1976). Thus, it is  inferred that temperature induced recovery mechanisms in quartz are unique to D i and D , 2  and only slight amounts of stress induced dynamic recrystallization are associated  with D . 4  Muscovite and biotite deform at all times through dislocation glide and kinking. Under  higher  strains  rotated  subgrains.  during D , kink  band  4  The  lack  of kink  banding  boundaries or  even  may  fail  undulose  brittlely to  form  extinction in mica  outlining phase 2 crenulations suggests recrystallized grains have replaced older strained grains. Carbonate minerals have been deformed dominantly by mechanical twinning. The narrow width and sharp  boundaries  of twin lamellae are typical of low strain, low  temperature conditions of deformation (Groshing, 1972; Nicolas and Poirier, 1976). Kink banding associated with dislocation glide would not be expected at the temperature and pressure conditions inferred to have accompanied deformation in the Ogden Peak area (see section 5.4). Deformational  episodes  are  more  specifically  related  growth and regional tectonic events in succeeding sections.  to  metamorphic  mineral  5. METAMORPHISM  5.1. I N T R O D U C T I O N The Ogden  Peak  area is located  on the  western  flank  of the  northwestern  extension of the Shuswap Metamorphic Complex (SMC), which is defined arbitrarily as a metamorphic and plutonic complex bounded by the sillimanite isograd (Reesor, 1970; Brown and Read, 1983). The northwestern early  Paleozoic paragneiss structurally  SMC is said to comprise late Proterozoic to  overlying the  Monashee  Decollement (Okulitch,  1984). Metamorphic peak conditions in the Quesnel Lake region range from sillimanite grade within the S M C to chlorite grade along the North Arm of Quesnel Lake and immediately adjacent to the I M B / O M B suture. The Ogden Peak area contains garnet to kyanite grade metamorphic  rocks situated  between  low grade rocks to the  west and  sillimanite grade rocks to the east Metamorphic zone boundaries within and adjacent to the area do not follow lithologic or structural controls. Pelitic rocks of the  Ogden Peak area contain indicator minerals typical of a  Barrovian-type metamorphic sequence of the middle amphibolite fades. Prograde mineral assemblages  have  been  replacement  of primary  subject  zone  +  an  porphyroblasts  mapped two metamorphic staurolite  to  extensive  retrograde  with chlorite  and  and  resulting  muscovite.  Campbell  in  the  (1971)  zones in the area based on first appearances of garnet and  kyanite in pelitic rocks. The present study  boundaries  event  furthur  staurolite and staurolite +  subdivides  his staurolite  locally redefines  +  kyanite  zone  Campbell's  into separate  kyanite zones.  Microscopic textures are used to establish the relative timing of mineral growth and  deformational  followed  by  events.  extensive  Metamorphic  retrograde  peak  conditions  metamorphism  87  were  through  D  attained 4  related  late to  in  D  2  waning  METAMORPHISM / 88 temperatures and abundant fluids. Metamorphic conditions during D to  poorly  developed  microstructures  analyses of garnet-biotite  related  to  this  deformational  3  are uncertain due event Microprobe  pairs allow determination of metamorphic temperatures and  pressures. Textures and timing of mineral growth are discussed separately below for each pelitic  metamorphic  geothermometry  and  zone  and  retrograde  for  each  non-pelitic  metamorphism  are  rock  addressed  type. in  Garnet-biotite later  sections.  Constitutive mineralogy typical of each metamorphic zone and lithology is summarized at the beginning of each section. Abbreviations of mineral names used in this chapter are listed in appendix 3.  M E T A M O R P H I S M / 89 5.2. REGIONAL METAMORPfflSM M , Amphibolite grade mineral assemblages in the Quesnel Lake area formed during a regional metamorphic event that was synchronous with accretion of Intermontane Belt terranes  in  mid-Jurassic  time  (Monger,  1982).  Pelitic,  carbonate,  and amphibolitic  lithologies of the Ogden Peak area each have unique mineral assemblages related to this event  5.2.1. Pelitic lithologies Three metamorphic zones are delineated in pelitic lithologies of the Ogden Peak area. These zones are defined by first appearences Individual staurolite  and kyanite occurences  bulk  and  composition,  Metamorphic  zone  identified on plate I.  these  boundaries  metamorphic and  sample  appear  of garnet, staurolite, and kyanite. to be largely controlled by local  zones locations  transect referred  major to  lithologic in  the  text  units. are  M E T A M O R P H I S M / 90 Garnet-biotite zone Q z - B t - M u - G t - P l - C h ± To, Sph, Op, Ap, Ru, Zr The garnet-biotite  zone is located in the most northwesterly part of the study  area, and is defined in pelitic rocks by the presence of garnet and biotite and the absence of staurolite and kyanite. Garnet chlorite  textures  knots.  range  from  Porphyroblasts  idiomorphic  truncate  the  poikiloblasts  to  foliation,  which  So/Si  highly  retrograded  may be slightly  deflected around the largest garnets. Planar quartz inclusion trails (Sp are subparallel to the  external  elongate  foliation. Quartz and chlorite pressure shadows  S /St 0  parallel to the  normal to the S„/Si  mineral lineation. Microcracking of garnet along  biotite  intergrown  several generations with  Later porphyroblastic biotite crosscuts kinked by D  4  fractures  foliation is common.  Textural evidence delineates reddish-brown  about garnet are  earliest  of biotite growth. Fine grained  muscovite  defines  the foliation and S  2  the  S /Si 0  crenulation planes  foliation. and is  crenulations.  Muscovite  growth  lasts  through  all early  phases  of  deformation.  Earliest  muscovite is present as a medium to fine grained phase outlining the So/Sj foliation. Syn-D  2  muscovite defines S  2  surfaces and may be crosscut by later randomly oriented  muscovite (Figure 44). Sericite is a common retrograde product of garnet Two  distinct  chlorite  textures  are  present  in  garnet  grade  rocks.  Coarse  unoriented blades of chlorite crosscut the So/Sj foliation defined by oriented biotite and muscovite.  Later  growth  includes retrogression  replacement of biotite by chlorite (Figure 45).  of garnet porphyroblasts  and mimetic  METAMORPHISM /  Figure 44.  Muscovite defining  S„/Si  and  S  2  foliations, sample 193  91  METAMORPHISM  /  92  Sketch of photomicrogaph showing two stages of chlorite growth in sample 527. Early chlorite is randomly oriented across the So/Si foliation. Later retrograde cholrite is a mimetic replacement of biotite.  METAMORPHISM / 93 Staurolite Zone Qz-E-t-Mu-Gt-St-Pl ± Ch, Sph, Op, Ap, Ru, Zr, To The staurolite zone occupies a narrow east-west trending area just south of the garnet  +  biotite zone. Indicator minerals are staurolite, garnet, and biotite, in the  absence of kyanite. Because occurences of staurolite are compositionally restricted to aluminous rocks which are spatially limited, the exact location and orientation of the boundary between staurolite and garnet + biotite zones is unknown. Staurolite forms 2 cm to 4 cm elongate porphyroblasts with long axes randomly oriented in the S /S] plane. Extensive retrogression of porphyroblasts makes textural 0  relationships to deformational fabrics and other minerals uncertain, but cross sections of partially preserved grains truncate the  S /Si 0  foliation. Sericite pseudomorphs of staurolite  mantle garnet porphyroblasts. A lack of pressure shadows or preferred alignment of elongate porphyroblasts indicates growth late or post- phase 2 deformation. Subidiomorphic  garnet  porphyroblasts  have  poikilitic  cores  surrounded  by  inclusion free rims, indicating changing chemical conditions during two stage growth. Inclusions of quartz and ilmenite in cores define a fabric which is weakly crenulated, and is discordant to the external foliation. Porphyroblasts truncate S„/S  u  and pressure  shadows of quartz and muscovite parallel to 1 indicate some garnet growth occured 2  pre-  or syn- D . 2  Biotite and muscovite exhibit similar textural relationships to those observed in the garnet + biotite zone. Sericite is an additional phase generated by retrogression of staurolite.  Chlorite  occurence  is  limited to  replacement  evidence for stability during peak metamorphic conditions.  of  other  phases,  with no  M E T A M O R P H I S M / 94 Staurolite + Kyanite Zone Qz-Bt-Mu-Gt-St-Ky-Pl  ±  Kspar, Ch, Sph, Op, Ap, Ru, Zr, To  The staurolite + kyanite zone covers most of the study area. Kyanite occurence is sparse within  the zone, and zone boundaries  are consequently  only approximately  located. Kyanite  occurs  in  two  distinct  settings.  Most  commonly  it  is  found  in  quartz-kyanite knots as 4 cm to 8 cm long randomly oriented blades. These knots are limited to pelitic schists, and minerals within them may be kinked by D  4  crenulations.  Kyanite also forms small porphyroblasts in muscovite schists. Extensive retrogression to sericite  makes  crosscuts  both  textural D  2  relationships  crenulations  and  uncertain, S  2  but  in  one  example  kyanite  muscovite (Figure 46). This latter  clearly  mode of  occurence is used in defining the staurolite + kyanite zone boundaries. Staurolite is texturally similar to that previously described in the staurolite zone, with long axes of porphyroblasts randomly aligned in the and  quartz  inclusions  are  abundant,  but  no  internal  So/Si  foliation plane. Sphene  fabric  is  defined.  Several  relationships suggest staurolite growth in part accompanied D . In one example where 2  staurolite elongate  mantles an earlier garnet, the  mineral pair has a quartz pressure shadow  parallel to 1 . Elsewhere, staurolite grew across phase 2 crenulations (Figure 2  47). Garnet  forms  idioblastic to  xenoblastic poikiloblasts with  varying degrees of  retrogression to chlorite. Two stage growth is indicated by inclusion free rims mantling poikilitic  cores. The  following  textural  relationships suggest garnet growth  throughout  phase 2 deformation: 1.  helycitic S^. quartz  inclusion  trails where  those in the surrounding rock (Figure 48),  crenulation fabrics are  subparallel  to  M E T A M O R P H I S M / 95  Figure 46.  Kyanite porphyroblasts growing across phase 2 crenulations, with later retrogression to sericite, sample 193.  METAMORPHISM / 96  M E T A M O R P H I S M / 97  Figure 48.  Helycitic inclusion trails in garnet, sample 293. S - crenulations are parallel to phase 2 crenulations in surrounding rock. z  M E T A M O R P H I S M / 98 2.  deflection of S  surfaces about garnet prophyroblasts, and  3.  pressure shadows about garnet aligned parallel to 1 lineations.  2  2  Biotite and muscovite textures are similar to those in other pelitic zones. No evidence  is  seen  for  stability  of  chlorite  in  the  prograde  assemblage  of  the  staurolite-kyanite zone. Discussion Pelitic assemblages indicator  rocks  of  the  Ogden  Peak  area  contains  mineral  of up to kyanite/staurolite grade. Reactions marking first appearances of  minerals  are  uncertain  due  to  strong  appearance and extensive retrogression of prograde may be modelled using observed system of A 1 0 , 2  approximate assemblages  Barrovian prograde  2  assemblages  that  they  2  are  2  derived  rather than reaction textures,  from  controls  reaction textures.  FeO, K 0 , H 0 , MgO, and Si0 .  3  in  stable  compositional  on  mineral  Possible reactions  and assuming a six component These  observed  generalized reactions  changes  in  stable  are  mineral  and microprobe analyses indicate significant  amounts of CaO and MnO are present (see section 5.4). The  first  appearance  of  staurolite  garnet-biotite± chlorite and garnet-biotite-staurolite  marks  the  boundary  between  stable assemblages, suggesting chlorite  may break down to form staurolite. A possible balanced reaction involving one change in A F M diagram topology (Figure 49) is propsed by Albee (1965): 95Gt(Al) + An  alternative  proposed  for  499Mu + 324Ch = 204St + 449Bt + 441Qz + 1194H 0 2  reaction not involving garnet is presented the  (Fillipone, 1985):  "staurolite  in" isograd to  the  south  by Hoscheck (1969) and is in the  Boss Mountain area  METAMORPHISM / 99  A  Staurolite - Kyanite  zone  AFM sketches showing stable mineral assemblages of pelitic metamorphic zones.  M E T A M O R P H I S M / 100 3Mu  + Ch = St +  3Bt + 7Qz + 14H 0 2  As garnet breakdown is not observed in the staurolite zone, the latter reaction is more viable. The transition to the staurolite +  kyanite zone is somewhat more problematic.  Formation of kyanite may have been at the  expense of staurolite, according to the  reaction: St + M u + Qz = Gt + Bt +  Ky +  H 0 2  (Carmichael, 1978). Extensive  retrogression  of  both  staurolite  and  kyanite  reaction uncertain. This reaction involves two changes  make  the  feasibility of  this  in A F M diagram topology in  which first the staurolite-chlorite tie line must be broken to form a biotite-ASK tie line (Figure 49). Alternatively, biotite, garnet, staurolite, and kyanite may all be stable phases of a seven or more component system as suggested by appreciable amounts of calcium and manganese in garnet (see appendix 4). The above generalized reactions should be considered speculative and lack firm supportive textural evidence.  M E T A M O R P H I S M / 101 5.2.2. Amphibole schist lithologies Hb-Bt-Qz-Ch-Pl-Mu +  Cc, II, Sid  Amphibole schists form all of unit 2, and occur occasionally as layers within other stratigraphic units. They are comprised of of 80% to 100% hornblende, except westernmost  exposures  of  unit  2  which  have  35%  to  40%  carbonate  minerals.  Hornblende forms large subidiomorphic grains which are mostly elongate in the S /S! 0  plane. It shows faint to moderate green pleochroism, and larger crystals are extremely poikilitic. Ilmenite and quartz inclusions in hornblende define an internal foliation (S.) which in elongate grains is subparallel to the external foliation. In equant grains S^. may  be slightly discordant to the dominant foliation. Pre- to syn- phase 2 growth is  indicated by porphyroblasts kinked about D  2  crenulations.  Biotite comprises up to 10% of the volume of amphibole schists. It occurs both as an alteration product of hornblende and as earlier prograde biotite growth. Earliest biotite may be completely enclosed by later hornblende porphyroblasts. Radiating fibrous chlorite is common both as alterations of biotite and hornblende and isolated knots within the quartz/feldspar matrix. Accessory minerals include clinozoisite, sphene, and rutile. Clinozoisite occurs as idiomorphic  fine grains within chlorite aggregates or as inclusions within  porphyroblasts.  Rutile  and  sphene  are  abundant  idiomorphic grains  with  hornblende long  axes  oriented in the dominant S /Sj foliation. They are commonly associated with chlorite, 0  but isolated grains may be completely enclosed by hornblende. Carbonate rich amphibole schists in the 30%  to 40% siderite, with  lesser amounts  western study area are composed of  of calcite. Siderite forms anhedral  grains  which surround more euhedral phases, and often have calcite rims. Hornblende has a higher inclusion density here than in non-carbonate  schists, and is also rimmed by  METAMORPHISM / calcite.  Clinozoisite  is more  abundant  than  in  non-carbonate  lithologies, and  102  forms  euhedral grains partially or completely enclosed in hornblende. Elongate clinozoisite is aligned within the So/Sj foliation and is bent about phase 2 crenulations.  M E T A M O R P H I S M / 103 5.2.3. Carbonate lithologies Cc-Bt-Par(?)-Ep-Qz ±  PI. Hb, Sph, II  Carbonate lithologies are limited to the east-west trending unit 4 marble and occasional lenses in siliciclastic units. Mineralogy consists of calcite, mica, epidote, quartz and hornblende. The marble occurs in both staurolite and staurolite + zones, but the distribution of mineral phases reflects  kyanite pelitic  compositional variations rather  than changes in metamorphic grade. Coarse grained calcite comprises 80% to 95% of all unit 4 carbonates. It forms a coarse granoblastic matrix with a weak foliation defined by elongate calcite grains. Dark green xenomorphic hornblende phenocrysts are aligned subparallel to the calcite foliation. sphene,  They  are poikilitic  and ilmenite,  with  and are  randomly  typically  oriented  embayed  inclusions of quartz,  by calcite. Hornblende  epidote, is most  abundant in the westernmost exposures of unit 4, where it makes up 10% to 20% of lithology. The  micaceous component of the carbonates consists of green to brown biotite  in hornblende bearing marbles and white mica in more pure carbonates. Both occur as small euhedral flakes aligned parallel to foliation, either completely enclosed by calcite or growing across grain boundaries. Fine grained epidote is commonly associated with small quartz rich pods in the marble.  It  also  occurs  rarely  as  isolated  inclusions in hornblende porphyroblasts.  grains  within  the  calcite matrix, or as  M E T A M O R P H I S M / 104 5.3. RETROGRADE METAMORPHISM  Rocks  of the  Ogden Peak  M  2  aiea have  been  subject  to a regional  retrograde  metamorphism evidenced by the replacement of prograde mineral assemblages by lower grade hydrous phases. Biotite  is replaced  by mimetic growth of chlorite and small  amounts of quartz. Original grain boundaries and intragranular kink bands are preserved throughout  chlorite growth. Garnet porphyroblasts are primarily replaced by unoriented  fibrous chlorite along rims with lesser sericite, quartz, and ilmenite concentrated  near  cores. Sericite pseudomorphs of staurolite have small amounts of chlorite and ilmenite restricted  to  core  zones  of pre-existing  porphyroblasts.  Kyanite is  replaced  by  a  randomly oriented matrix of sericite with rare larger muscovite grains. The completeness of retrogression is determined microscopic retrogression,  and  macroscopic  scales.  Porphyroblasts  commonly with complete  replacement  by local composition on both  in  pelitic  schist  show  of kyanite, staurolite,  greatest  and garnet  Retrogression is less complete in structurally lower pelitic rocks (unit la), and increases higher  in  the  succession.  Amphibole  schist  lithologies  lack  primary  kyanite  and  staurolite, but partial chloritization of biotite is common. Carbonate rocks and quartzites both lack retrograde On  textures.  a microscopic scale, the degree of retrogression is strongly determined by  the identity of the phases present  Kyanite and staurolite never have original growth  faces preserved, and are 60% to 100% replaced even when in contact with garnet only slightly mantled by chlorite. Garnet is anywhere from unaffected to 100% replaced, but is  never  replaced  to  a  greater  extent  than  adjacent  staurolite  and  kyanite  porphyroblasts. Likewise, biotite may be up to 100% replaced by chlorite, but never more than garnet staurolite, and kyanite in the same rock.  M E T A M O R P H I S M / 105 Retrograde textures are primarily developed in layers along the plane, occasionally resulting in a rock with alternating  retrograde  S /Si  and  0  foliation  non-retrograde  compositional layers. Timing constrained  by  parallel to D retain  of  4  original  retrograde  metamorphism  microscopic textures.  relative  Chlorite pseudomorphs  axial planes in a region of high D crystal  shapes  to  (Figure  50).  In  4  deformation of  garnet  strain where  another  example,  is  roughly  are  flattened  unaltered biotite  garnets  replacement  preferentially occurs along phase 4 crenulation axial planes.  Discussion Extensive retrograde  metamorphism in the Ogden Peak area indicates  abundant  fluids accompanied reduced temperatures and pressures (Turner, 1981). Prograde reactions in  underlying  transported  rocks  may  have  provided  a  source  for  fluids,  which  through regional advective flow coupled with local diffusion  were  then  (Mohr et al.,  1986). Local variations in completeness of retrogression appear to be controlled strongly by composition and may result from variable rates of advection and diffusion. Limited availability of fluids would have resulted in preferential porphyroblasts  which  would be  out  retrogression of higher grade  of equilibrium earliest,  and might  explain why  replacement of staurolite and kyanite is generally more complete than that of garnet and biotite. M  2  retrograde  continued through D  metamorphism closely followed 4  filled  extension fractures  mesoscopic folds (Figure 51). These fractures until D . The following 4  prograde  metamorphism  and  folding. Independent evidence for high fluid activity at this time  exists in the formation of quartz  field  Mi  speculative  retrogression sequence and observed textures:  along axial planes of D  2  would not have been in an extensional  reactions  are  consistent  with  the  proposed  M E T A M O R P H I S M / 106  Figure 50.  Chlorite pseudomorphs of garnet flattened into phase four axial planes, from sample 593.  M E T A M O R P H I S M / 107  Figure 51.  Quartz vein filling fracture along axial plane of mesoscopic phase 2 fold, near location 280.  M E T A M O R P H I S M / 108 Kyanite breakdown: 3Ky +  3Qz + 2 K  + 3H 0  +  2  = 2Mu + 2 H  +  Staurolite breakdown: St + 3Bt + 7Qz +  14H 0 = 3Mu + C h 2  (Hoscheck, 1969) Garnet breakdown: 4Alm + Bt + 12H 0 = C h + M u + 3Qz 2  (Fillipone, 1985) Biotite breakdown: Bt + H 0 + 2H 2  +  = Ch + Qz + II 4- 2 K  +  These are generallized reactions derived from observed mineral assemblages. In high grade pelites, excess K  +  by  the  kyanite  breakdown  in  ions generated from biotite breakdown may be consumed high  grade  pelites.  Electron microprobe  analyses  of  specimens might allow determination of exact balanced metamorphic reactions by which retrogression occurs.  M E T A M O R P H I S M / 109 5.4. G E O T H E R M O M E T R Y  Metamorphic temperatures area  from  experimental  Fe-Mg  have been calculated in rocks of the  partitioning  calibration of  between  Ferry  and  co-existing Spear  garnet/biotite  (1978).  Newton  and  Ogden Peak  pairs  using  the  Haselton (1981)  published a modification of the Ferry and Spear geothermometer to correct for mixing of Ca in garnet A n empirical model proposed by Ganguly and Saxena (1984) further corrects for both Ca and M n components in garnet In the present study, temperatures are calculated using the original Ferry and Spear calibration and both of the above correction models. Pressure  estimates  for  use  with  the  geothermometer  are  constrained  by  aluminosilicate stability fields (Holdaway, 1971) and the G R A I L geobarometer of Bohlen et al. (1983). The G R A I L geobarometer is based on the univariant reaction garnet  +  rutile = kyanite + quartz + ilmenite, which shifts to higher pressures with increasing almandine component in garnet garnet(Alm  77)  is  stable  in  The assemblage  kyanite  +  kyanite  staurolite  +  zone  quartz  +  ilmentite  +  rocks, indicating maximum  pressures of 6.5 kb in the kyanite stability field (Figure 52). Maximum pressures for a sample from the garnet + biotite zone are less well constrained. Pressure estimates for the Ogden Peak area of 7 kb (McMullin and Greenwood, 1986) determined using the Ghent  (1976)  geobarometer  fall  geobarometry, and may represent  outside  the  pressure  range  conditions earlier in the  indicated  by  GRAIL  metamorphic history. The  Ferry and Spear geothermometer has only a small pressure dependence ( 3 ° C to 4 ° C per kbar) and will not be notably affected by the above range of pressures. Elemental compositions of coexisting garnet-biotite pairs were obtained using the UBC  Department of Geology electron microprobe. Testing procedures and results are  M E T A M O R P H I S M / 110  500  600 Temperature  Figure 52.  700  800  f^c)  P - T diagram applied to pelitic rocks of Ogden Peak. (1) G R A I L geobarometer of Bohlen et al., modified for almandine(77); (2) from Hoscheck (1969). A S K stability fields of Holdaway (1971).  M E T A M O R P H I S M / 111 detailed in appendix 4, and sample locations are identified on plate I. Temperature estimates were determined using the Ferry and Spear geobarometer and the Newton and Haselton and Ganguly and Saxena calibrations. The calibration of Newton and Haselton consistently yielded temperatures geothermometers.  higher than either of the other  Although the Newton and Haselton calibration does not consider the  effects of manganese in garnet, the temperatures obtained appear to be independent of manganese Thus,  content  they  are  and  are  preferred  most  consistent  over temperatures  with  mineralogical assemblages  determined  from  other  observed.  geothermometers.  Temperatures determined from three pelitic schist samples are plotted as a function of manganese concentration in figure 53. Sample 598 from the garnet + 530 ±  24° C.  kyanite  +  from  This is almost identical to the  540 +  20° C temperature  staurolite zone (sample 233). A n anomalously low temperature  sample 447 may result  represents a retrograde 651c) yield  local chloritization of garnet  from  the  of 463° C  rims, and probably  Samples collected from the diabase dykes (651-2,  consistently higher  than  those  from  pelitic  rocks (562  ±  13° C).  summary,  metamorphic  from  temperature.  temperatures  23° C, 585 ± In  biotite zone yielded an average temperature of  kyanite  temperatures  of  grade  pelitic  rocks  of  approximately 540° C  at  the  Ogden  6 kbar.  Peak This  area  record  temperature  is  consistent with mineralogical assemblages and with temperatures determined by McMullin and Greenwood (1986) for the  same  area (545  ±  4°C). Retrograde  metamorphism  involving re-equilibration of garnet and biotite has reset temperatures in many rocks of the area.  M E T A M O R P H I S M / 112  Ferry-Spear  O  Newton- Haaetton  •  Ganguly-Saxena  A  600TI  9  550  IO I  CO CO CM  IOC0 CM  CM  co  a  00 CB IO  «2  O A  co IO  o a.  E  500-  A O  0  450-  o A  l 1.0  I  I 2.0  i  I i  3.0  Garn«t-Mn  Figure 53.  p » 6 kb  4.0  5.0  wt.%  Garnet-biotite temperatures from samples 447, 598, and 233 plotted as a function of manganese concentration in garnet  M E T A M O R P H I S M / 113 5.5. S U M M A R Y A N D DISCUSSION  Metamorphism in the Ogden Peak area ranges from chlorite grade to kyanite grade. A metamorphic peak of approximately 540° C at 6.0 kb was attained in kyanite grade  pelitic  schists late in or just  after  phase 2 deformation. Relative timing of  mineral growth and deformational episodes is summarized in figure 54. Mica foliation growth accompanied phase 1 and phase 2 deformation, but later  mineral' growth is  unoriented  except  for  between  deformation  and  mineral  mimetic growth  replacement are  textures.  inconclusive due  Relations to  the  lack  phase  3  of microscopic  structures. Complete retrogression of metamorphic porphyroblasts along with syn- and post metamorphic quartz vein intrusions provide strong evidence for abundant fluids at all stages of metamorphism. Fluids present during retrogression may have been  generated  at  overlying  presently  exposed  and  lower  structural  semi-impermeable rocks. Lithologic boundaries  levels  and  which project  trapped above  the  by  Ogden Peak  area and might have provided possible fluid traps include an Upper Snowshoe Group marble and the Omineca Belt/Intermontane Belt boundary. Ethoridge et al. (1983) propose that a fluid cap at shallow structural levels is generated as a natural consequence of regional prograde metamorphism. The cap would develop at the boundary between  hot rising metamorphic fluids and cooler meteoric  water, as mineral phases precipitated from the cooling metamorphic fluid into existing pore spaces, thereby reducing permeability.  METAMORPHISM / 114  Phase 1 syn  Phase 2  post  syn  post  Phase 4 pre  syn  post  Chlorite Muscovite Biotite Garnet Staurolite Kyanite  Retrograde  Prograde  constrained inferred  Figure 54.  Mineral growth / deformation correlation chart  6. REGIONAL CORRELATIONS AND  6.1. REGIONAL  . The  TECTONIC INTERPRETATIONS  CORRELATIONS  Intermontane  Belt/Omineca Belt  boundary  is  a  suture  zone  of crustal  proportions which strongly influences deformational and metamorphic styles in rocks of both  belts. Previous studies  in the  Quesnel Lake area  have  concentrated  on areas  either adjacent to and straddling the suture zone (Montgomery, 1978; Fillipone, 1985; Elsby, 1986; Bloodgood, 1987; Carye, 1985) or closer to the central Omineca Belt in high 1980;  grade Engi,  rocks of the 1984;  Shuswap  Getsinger,  Metamorphic Complex (Fletcher,  1985).  Regional  workers  have  1972;  described  Klepacki, a  general  stratigraphy comprising rocks of both belts (Campbell, 1972; Struik, 1984), but have not studied in detail the structural and stratigraphic progression eastwards from the margin. The current geologic studies of the Ogden Peak area allow correlation of structural styles and stratigraphy described along the suture zone with that to the northeast, as well as add detail to existing regional work. Additionally, metamorphic studies of the Ogden Peak area help constrain regional metamorphic styles. In this section, the stratigraphic succession and the progression of deformational and metamorphic styles eastward from the margin are described with specific references to the Ogden Peak area. A discussion of possible relations to the framework of the Intermontane and Omineca tectonic belts follows.  115  tectonostratigraphic  R E G I O N A L CORRELATIONS A N D TECTONIC INTERPRETATIONS / 116 6.1.1. Stratigraphy A  10 kilometer thick structurally continuous section of cratonic  rocks has been described from the accretion boundary/suture Metamorphic  Complex (Ross  et  al., 1987).  These  rocks  metasedimentary  eastward into the Shuswap comprise  members  of  the  Snowshoe Group, which ranges in age from Hadrynian to Early Paleozoic (Campbell, 1978;  Struik,  1983).  Upper  and  lower  successions  can  be  delineated  within  the  Snowshoe Group on the basis of lithology in the Ogden Peak area and in the Three Ladies  Mountain  siliciclastic  area  (Getsinger,  metasedimentary  metasedimentary  rocks.  1985). A n upper  The  lower  succession  succession of  is  siliciclastic  dominated and  by  carbonate  rocks is separated from the lower by major marker units of marble  and amphibole schist that occur close to its base and are traceable over a distance of 70 kilometers. No  evidence is seen for layer-parallel thusts within the sequence,  by Struik (1986a) from stratigraphic observations.  as inferred  R E G I O N A L CORRELATIONS A N D TECTONIC INTERPRETATIONS / 117 6.1.2. Structure Earliest recognizable structures  in all Snowshoe Group rocks of the  Quesnel  Lake region are mesoscopic isoclinal folds outlined by compositional layering. They are commonly rootless, and together with a strong axial planar foliation define a regional transposed foliation which outlines all later structures. Map scale features related to this deformation are not as yet documented in the Ogden Peak and surrounding areas. Second phase folds are Ogden Peak, but  westwards  west verging in the Ogden Peak area  from Ogden Peak,  closer to the  and east of  margin, second phase  folds have east vergent asymmetries. Temporal relations to metamorphic mineral growth and  other  deformational  episodes  suggest  throughout the region. East verging D  2  these  structures  formed  synchronously  folds are the oldest structures common to both  autochthonous and allochthonous packages. Phase throughout  three  upright  to  west  verging folds  are  the Quesnel Lake region, and associated  Amplitudes of major folds decrease eastward  syn-  to  the  earliest  structures  which  deform  metamorphic  strain increases toward the  west  from the suture zone while wavelengths  remain constant and related mesoscopic folds become less abundant are  post-  the  margin, and  are  Third phase folds responsible  for  the  present regional map pattern. Fold forms are controlled by contrasting rheology across the  IMB/OMB  suture.  Synforms are typically cuspate forms in which slivers of less  competent Triassic phyllite of Quesnellia are drawn down into shear zones within more competent  Snowshoe  Group rocks (Fillipone,  1985).  Lobate  antiforms  are  cored by  competent Snowshoe Group rocks. Late throughout  northeast the  trending  folds  (phase  4  at  Ogden  Peak)  are  ubiquitous  Quesnel Lake region, but at the margin are antedated by a fourth  northwest trending fold set absent in the Ogden Peak area.  R E G I O N A L CORRELATIONS A N D TECTONIC INTERPRETATIONS / 118 Post-folding  brittle faulting is cornrnon in the Ogden Peak area and to  the  northeast, but becomes increasingly less conspicuous nearer the suture zone. Absolute  ages  of  deformational  events  are  roughly  constrained  by  several  plutonic bodies in the Quesnel Lake region. The Boss Mountain Gneiss and Quesnel Lake Gneiss, deformed by all phases described above, yield zircon U - P b dates of 338 Ma to 375 M a (Mortensen et al., 1987). This is consistent with a zircon U - P b age of 335 M a to 450 M a on a  pre-Fi  dioritic gneiss in the Three Ladies Mountain area  (Getsinger, 1985). Phase 2 folds are believed to have formed during the accretion of allochthonous terranes of the Intermontane Belt onto North America (Ross et al., 1985). Stratigraphic evidence elsewhere indicates a Jurassic age for this event (Monger, 1982). Timing of convergence is constrained in the Kootenay Arc region, some 150 km south of Quesnel Lake, by syn- to post-  kinematic granitic plutons of 177 M a to 155 M a  which intrude both continental rocks and rocks of Quesnellia (Archibald et al., 1983). Third phase deformation follows obduction, but precedes emplacement  of the Hobson  Pluton which was dated using Rb-Sr whole rock analyses at 138 +  12 Ma and 163  ±  7 M a (Pigage,  1977). In  addition, the  Rb-Sr whole rock analysis at 104.3 ±  undeformed  Raft  Batholith, dated  using  33 Ma, cuts the suture between Omineca Belt  and Intermontane Belt rocks (Jung, 1986), although recent K - A r dates on this intrusion indicate a Jurassic age (R. L. Armstrong, oral comm., 1987). These constraints place the timing of phase 1 deformation at Late Paleozoic to Early Mesozoic, and the timing of phase 2 and phase 3 as Jurassic. However, the plutonic bodies used to constrain the age of phase 3 are located in areas where this deformational episode is not strongly developed and may not have affected a competent plutonic body. Thus, the above minimum age assigned D  3  is suspect  R E G I O N A L CORRELATIONS A N D TECTONIC INTERPRETATIONS / 119 6.1.3. Metamorphism Metamorphic sillimanite  grade.  rocks  in  the  Quesnel  Metamorphic zones  Lake  delineated  by  region  range  from  early  workers  chlorite  to  (Campbell, 1962;  Campbell & Campbell, 1972) have been shown to represent  in some cases isograds  marked  in  by  discontinuous  reactions,  and  elsewhere  changes  mineral  assemblages  resulting from variations in bulk composition (Getsinger, 1985; Fillipone, 1985; Fletcher, 1972). Sillimanite grade rocks are localized in three distinct nodes. Metamorphic zone boundaries about these nodes are extremely asymmetric, resulting in wide metamorphic zones  through  most  Belt/Intermontane Metamorphic  of the  area  but  very narrow zones  Belt  suture  and  along  Complex.  Zone  boundaries  the are  eastern  adjacent  boundary  broadly  folded  to  the Omineca  of  by  the  major  Shuswap phase  3  structures. The Ogden Peak area is located on an antiformal metamorphic culmination in  an area of relatively wide metamorphic zones. Most parautochthonous  chlorite grade,  but  staurolite and  garnet  zone boundaries  rocks are  locally crosscut the  suture  zone in the Eureka Peak area. Metamorphic zones are sharply offset across the North Arm of Quesnel Lake northwest of the study area where a probable late brittle fault places sillimanite grade rocks against chlorite grade rocks. Metamorphic textures, including porphyroblastic inclusion trails, pressure shadows, and  kinked  grains, as well  as the  above  map  scale  relations  have  been  used  to  determine the relative timing of metamorphism and deformational events. Metamorphic grade increased through phase 1 and phase 2, peaking late in or following phase 2 but prior to the onset of phase 3. Absolute timing of metamorphism has been inferred from  cooling ages in several locations. Sphene  Isoceles  Peak  yields a  U - P b date of 174±4  from  the  Quesnel Lake Gneiss near  M a for cooling  through  isotherm (Mortensen et al., 1987). A less reliable date of 114 M a to  the  500° C  117 Ma is  R E G I O N A L CORRELATIONS A N D TECTONIC INTERPRETATIONS / 120 determined from monazite from the Boss Mountain Gneiss, and may represent cooling through a lower temperature  (Mortensen et al., 1987). A n anomalously young 83 M a  K-Ar  a  age  determined  from  muscovite/plagioclase pegmatite  in the  Three Ladies  Mountain area (Getsinger 1985) probably represents cooling through 400° C. It is not clear whether Lake  peak  region  metamorphic conditions were reached  simultaneously,  and  the  above  range  everywhere in the Quesnel of  cooling  ages  suggests  metamorphism may have been diachronous through the region. Widespread hydrothermal retrogression observed in rocks around Ogden Peak is also documented to the northwest in the Three Ladies Mountain Area (Getsinger, 1985) and  along the  East Arm of Quesnel Lake near  Isoceles Peak (Montgomery, 1985;  McMullin, oral comm., 1987). These three areas outline a northwest trending zone of retrogression which roughly follows stratigraphy and the suture zone but cuts sharply across metamorphic zone boundaries. Synmetamorphic veins, especially common in high grade rocks, have composition and  structural  relations which  during dewatering of the  indicate a hydraulic fracture  mechanism  of formation  sedimentary pile (Garwin, 1987; Ross et al., 1987). These  veins, together with the asymmetry of metamorphic zones about thermal nodes, suggest that advective heat transfer the  played a strong role in influencing metamorphic styles in  Quesnel  Lake  region. The  superposition  of  metamorphic  zones  is  of  across, zone  Thompson,  1984).  directional  fluid  evidence  Advective permeability,  heat  advection transfer  which  would  would be  retrograde  be  metamorphism boundaries  prominent  localized  in  according  on  (England zones to  of  wide and high  pre-existing  structural or lithologic anisotropics. Distribution of retrograde metamorphism in a single continuous zone suggests fluids ponded in that area below a semi-impermeable barrier and were present while temperatures  and pressures waned following metamorphic peak  REGIONAL CORRELATIONS AND TECTONIC INTERPRETATIONS / 121 conditions. Continuous  carbonate  units in the Upper  Snowshoe Group  and the  OMB/IMB suture zone both project above the region of retrogression and dictate a geometry that may have provided such a barrier.  REGIONAL CORRELATIONS  AND  TECTONIC INTERPRETATIONS / 122  6.2. TECTONIC IMPLICATIONS  Observations of structural and metamorphic styles in the Ogden Peak area add detail  to  existing models  which  outline the  geologic evolution of the  Intermontane  Belt/Omineca Belt boundary in central British Columbia. Prior to the accretion of allochthonous terranes from the west, siliciclastic and carbonate  sediments had accumulated along the western shore of North America in a  marginal  basin  or  shelf  setting  (Struik,  1982).  Sediments  comprising the  Snowshoe  Group included siliclastic and volcanic sediments, as well as carbonates. Granitic bodies now forming the Quesnel Lake and Boss Mountain gneisses intruded into this package during the Devonian and Mississippian. Volcanic  and  sedimentary  rocks  of  Quesnellia Terrane  formed  in  the  Late  Paleozoic to Jurassic in a volcanic arc setting off the coast of North America (Monger, 1977). It is unclear whether represent  oceanic  basement  mafic and ultramafic rocks of the Crooked Amphibolite to  this  arc,  or  whether  they  are  part  of a separate  Earliest recognizable structures  (Di)  occur only in the autochthonous rocks, and  tectono-stratigraphic terrane.  are  thus  thought  to  be  associated  with  deformation  prior  to  or  very  early  in  convergence. During phase 1 deformation, Snowshoe Group and intrusive granitic rocks underwent dewatering and mesoscopic folding at the greenschist grade of metamorphism. The earliest structures  common to both allochthon and autochthon  easterly verging folds concentrated the  margin and  related  to  craton.  Rocks at  along the suture zone. These folds do not deform  decrease in intensity away  Jurassic convergence the  and  margin and  consist of  from it, and are  subsequent overthrusting along several  detachment  thus believed to  of Quesnellia onto surfaces  higher  in  be the the  R E G I O N A L CORRELATIONS A N D TECTONIC INTERPRETATIONS / 123 allochthon are strongly mylonitized during this thrusting. Fold styles are controlled by lithology and position within the structural succession. In the allochthon, folds are tight to isoclinal at the margin and open upwards, and axial planes are marked by pressure solution and slaty cleavage developement  In rocks of the  Snowshoe Group tight to  isoclinal folds are accompanied by discrete zones of mylonitization and brittle faulting immediately below the suture (Fillipone, 1985), but at deeper levels brittle surfaces  are  lacking. Phase  detachment  1 folds in Snowshoe Group rocks are tightened  during  initial convergence. Obduction underlying inferred  of  Snowshoe  to occur at  Quesnellia resulted Group  in  elevated  rocks, contributing  this time. Present  to  exposures  temperatures  the  increased  and  pressures in  metamorphic  grade  of the suture zone near Crooked  Lake suggest a minimum of 70 km to 80 km of shortening  by overthrusting. The  absence of easterly verging folds in the Ogden Peak area suggests that either: 1) the thrust surface  has ramped high above present exposures or 2) overthrusting is much  less than that observed at Crooked Lake, and the suture did not extend above the Ogden Peak area. Easterly  verging folds  and  the  suture  zone  itself  are  deformed  by westerly  verging folds following initial obduction. These structures indicate continued convergence which is no longer taken up by movement along the tectonic boundary. West verging map  scale folds of the  viscosity contrast  boundary  have  forms  which  between allochthonous and autochthonous  zones riddled with quartz filled hydraulic fractures for  advective  are  heat flow  into higher  level  strongly controlled by  the  rocks. Synclines are cuspate  and may have served as conduits  rocks during metamorphism  (Ross et al.,  1985). The absence of these cuspate zones around Ogden Peak is again evidence that the area is structurally far removed from the zone of convergence.  R E G I O N A L CORRELATIONS A N D TECTONIC INTERPRETATIONS / 124 Several  models have  verging structures  been  proposed  to  explain the  to later west verging structures  change  from  early east  (Ross et a l , 1985; Brown  et al.,  1986). A simple model proposed by Ross et al. relates the change in vergence to a switch in subduction direction (Figure 55). Following initial obduction, the oceanic slab carrying Quesnellia is subducted beneath the leading edge of North America, producing the observed change to westerly vergences. This model requires that west verging phase 2  folds  situated  structurally  well  below  the  margin  (near  synchronously with phase 3 folds at the margin, with the metamorphic  peak  conditions are  also attained  later  to  Ogden  Peak)  formed  attendant implication that  the  east  An  east-stepping  metamorphic front would be expected with thrusting induced tectonic loading occuring later to the east A followed  recent by  west  model  proposed  directed  by  "back  Brown  thrusting"  et from  al. (1986) the  has  craton,  initial  with  convergence  associated  west  verging folds. This model may not apply to the Quesnel Lake region, where detailed mapping has not shown the existence of back thrusts. However, the back thrust model is attractive in that it allows contemporaneous metamorphic peak conditions and phase 2 folding throughout the area. A  third  possibility  is  that  east  directed  subduction  occurs  throughout  convergence, and that obduction of Quesnellia represents a short lived accretion event in which high level volcanic and sedimentary rocks are decoupled from the subducting slab. East verging folds would be concentrated along the presently exposed suture zone in  this  model, and  west  verging  folds  would  package at all stages of convergence. Additional  form  throughout  study of the  the  autochthonous  nature of mafic and  ultramafic sequences exposed along the margin will help in evaluating this proposition. Regional models proposed by Monger et al. (1982) involve large scale lateral  R E G I O N A L CORRELATIONS A N D TECTONIC INTERPRETATIONS / 125 1) P r e - J u r a s s i c Snowshoe Group sediments  3)  Figure 55.  L a t e J u r a s s i c (?) r e v e r s a l  Plate tectonic model for evolution of I M B / O M B boundary region. Modified from Dewey (1976), Ross et al. (1985).  R E G I O N A L CORRELATIONS A N D TECTONIC INTERPRETATIONS / 126 translation in addition to and synchronous with convergence. A l l deformation associated with convergence in the Quesnel Lake region indicates movement at a high angle to the  suture  manifested faulting.  zone. in the  Minor  translation  Ogden Peak  area  parallel as  to  later  the  zone  of  phase 4 folding  convergence or phase  may  be  5 brittle  7. REFERENCES  Archibald, D . A., Glover, J. K., Price, R. A., Farrar, E., and Carrnichael, D. M . 1983. Geochronology and tectonic implications of magmatism and metamorphism, southern Kootenay Arc and neighbouring regions, southeastern British Columbia. Part I: Jurassic to mid-Cretaceous. Canadian Journal of Earth Sciences, 20, pp. 1891-1913. Albee, Arden L. 1965. A petrogenetic grid for the F e - M g American Journal of Science, 263, pp. 512-536.  silicates of pelitic schists.  Bloodgood, M . A. 1987. Deformational history, stratigraphic correlations and geochemistry of eastern Quesnel Terrane rocks in the Crooked Lake area, east central British Columbia, Canada. Unpublished M.Sc. thesis, University of British Columbia, Vancouver, British Columbia. 165 p. Bohlen, S. R., Wall, V. J., and Boettcher, A. L. 1983. Experimental investigations and geological applications in equilibria of the system F e O - T i 0 - A l 0 - S i 0 - H 0 . American Mineralogist, 68, pp. 1049-1058. 2  2  3  2  2  Brown, Richard L., Journeay, J. M . , Lane, L. S., Murphy, D. C , and Rees, C. J. 1986. Obduction, backfolding, and piggyback thrusting in the metamorphic hinterland of the southeastern Canadian Cordillera. Journal of Structural Geology, 8, pp. 255-268. Brown,  R.  L and Read, P. B. 1983. Shuswap Terrane of mesozoic "core complex". Geology, 11, pp. 164-168.  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Mixing properties of aluminosilicate garnets: constraints from natural and experimental data, and applications to geothermo-barometry; American Mineralogist 69, pp. 88-97.  Garwin,  S.  L. 1987. Deformation and metamorphism in the northern Shuswap Metamorphic Complex, western Cariboo Mountains, British Columbia. In: Geological Society of America, Abstracts with programs, Cordilleran Section annual meeting, Hilo, Hawaii, 19.  Getsinger, J. S. 1985. Geology of the Three Ladies Mountain/Mount Stevenson area, Quesnel Highlands, British Columbia. Unpublished PhD. thesis, University of British Columbia, Vancouver, British Columbia. Ghent,  E.  D. 1976. Plagioclase-garnet-Al Si0 -quartz: a potential geothermometer. American Mineralogist 61, pp. 88-97. 2  5  geobarometer-  Groshong, R. H . Jr. 1972. Strain calculated from twinning in calcite. Geological Society of America Bulletin, 83, pp. 2025-2038. Hickson,  C. J. and Juras, S. J. 1986. 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Chemical processes and migration of elements during retrogression of a staurolite zone assemblage in western North Carolina. Contributions to Mineralogy and Petrology, 92, pp. 400-411. Monger, J. W. H. 1977. Upper Paleozoic rocks of the western, Canadian Cordillera and their bearing on Cordilleran evolution. Canadian Journal of Earth Sciences, 14, pp. 1832-1859. Monger, J. W. H., Price, R. A. and Templemen-Kluit D. 1982. Tectonic accretion and the origin of two major metamorphic and plutonic welts in the Canadian Cordillera. Geology, 10, pp. 70-75. Montgomery, J. R. 1985. Structural relations of the southern Quesnel Lake Gneiss, Isoceles Mountain area, central British Columbia. Unpublished MSc. thesis, University of British Columbia, Vancouver, British Columbia. Montgomery, S. L. 1978. Structural and metamorphic history of the Dunford Lake area, Cariboo Mountains, British Columbia. Unpublished M.S. thesis, Cornell University, Ithaca, New York. Mortensen, J. K., Montgomery, J. R. and Fillipone, J. 1987. U-Pb zircon, monazite and sphene ages for granitic orthogneiss of the Barkerville Terrane, east-central British Columbia. Canadian Journal of Earth Sciences 24, pp. 1261-1266. Murphy, J. Brendan and Hynes, A. J. 1986. Contrasting secondary mobility of Ti, P, Zr, Nb, and Y in two metabasaltic suites in the Appalachian. Canadian Journal of Earth Sciences, 23, pp. 1138-1144. Newton,  R. C. and Haselton, H. T. 1981. Thermodynamics of the garnet— plagioclase- Al Si0 geobarometer; in: Thermodynamics of Minerals and Melts, ed. R. C. Newton, A. Navrotsky, and B. J. Wood; New York, 2  2  REFERENCES /  131  Springer-Verlag, pp. 131-147. Nicoloas, A . and Poirier, J. P. 1976. Crystalline plasticity and solid metamorphic rocks. John Wiley and sons, London. 444 p.  state flow in  Norris, R. J. and Henley, R. W. 1976. Dewatering of a metamorphic pile. Geology, 4 , pp. 333-336. Orchard, M . J. and Struik, L. C. 1985. 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In: Structure of the Canadian Cordillera, editor J. O. Wheeler. Geological Association of Canada Special Paper 6, pp. 73-86. Ross, J. V., Fillipone, J. A., Montgomery, J. R., Elsby, D . C. and Bloodgood, M . A. 1985. Geometry of a convergent zone, Central British Columbia, Canada. Tectonophysics 119, pp. 285-297. Ross, J. V., Lewis, P., and Garwin, S. 1987. Geology of the Quesnel Lake Region, central British Columbia: Geometry and implications. In: Geological Society of America, Abstracts with programs, Cordilleran Section Meeting, Hilo, Hawaii, 19. Schiarizza, P. and Preto, V . A . 1984. Geology of the Adams Plateau-Clearwater area. British Columbia Department of Energy, Mines, and Petroleum Resources, preliminary map 56. Struik, L. C. 1982. Snowshoe Formation, central British Columbia. In Current Research, part B. Geological Survey of Canada, Paper 82-IB, pp. 117-124.  REFERENCES / 132 Struik,  L. C. 1983. Bedrock geology of Spanish Lake and parts of adjoining map areas, central British Columbia. Geological Survey of Canada, Open File map 920.  Struik, L. C. 1984. Geology of the Quesnel Lake and part of Mitchell Lake map area, central British Columbia. Geological Survey of Canada, Open File map 962. Struik, L. C. 1986a. Imbricated terranes of the Cariboo Gold Belt with correlations and implications for tectonics in Southeastern British Columbia. Canadian Journal of Earth Sciences, 23, pp. 1047-1061. Struik, L. C. 1986b. A regional east dipping thrust places Hadrynian onto probable Paleozoic rocks in Cariboo Mountains, British Columbia. In Current Research, part A . Geological Survey of Canada, Paper 86-IA, pp. 589-594. Sutherland Brown, A . 1957. Geology of the Antler Creek area, Cariboo District, British Columbia. British Columbia Department of Mines, Bulletin 38. Thompson, A. B. 1976a. Mineral reactions in pelitic rocks: I. Predictions of P - T - X (Mg-Fe) phase relations. 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Geological Assodation of Canada, Spedal Paper 11, pp. 1-81.  8. APPENDICES  8.1. APPENDIX 1. MAJOR AND TRACE ELEMENT ANALYSES Major  and  trace element  concentrations  were analyzed for the  samples listed  below using the U B C Department of Geology X-ray fluorescence spectrometer. powder pellets were prepared using a tungsten-carbide  Pressed  ring mill and agate mortar to  minimize contamination introduced during sample preparation (Hickson and Juras, 1986).  Samples analyzed Meta-diabase dykes: 442j 444 297 293b 459 591 Metasedimentary Rocks: 246n (quartzite) 372 (pelitic schist) 188 (feldspathic quartzite) 340 (amphibole schist) 293a (marble)  133  APPENDICES / 134  T A B L E 1: M A J O R E L E M E N T CONCENTRATIONS  442-J 444 297 293-b 459 591  Si0 57.46 53.05 59.76 59.05 58.83 55.63  A1 0 17.38 18.26 16.63 16.55 17.01 16.91  FeO 8.13 10.44 7.63 7.66 9.08 8.39  MgO 4.01 3.78 2.82 . 2.53 3.26 4.50  CaO 7.58 8.44 6.86 7.62 5.50 8.26  Na 0 3.15 3.99 3.69 4.66 4.21 3.15  K 0 1.34 0.92 1.17 0.39 1.09 2.05  Ti0 0.47 0.18 0.65 0.66 0.61 0.53  MnO 0.12 0.15 0.11 0.11 0.17 0.12  P0 0.36 0.16 0.66 0.79 0.25 0.45  246-n 372 188 340 293a  93.95 66.55 86.05 55.78 5.65  3.11 17.03 8.41 12.90 2.90  0.56 4.74 1.13 9.35 1.08  0.47 1.91 0.58 9.00 2.92  0.41 0.54 0.23 10.22 85.07  0.10 0.59 1.42 0.75 1.25  1.19 7.95 2.00 0.65 0.65  0.06 0.48 0.10 0.86 0.06  0.00 0.09 0.02 0.14 0.07  0.16 0.13 0.05 0.35 0.38  2  2  3  2  2  T A B L E 2: T R A C E E L E M E N T CONCENTRATIONS  442-j 444 297 293-b 459 591 372 246-n 188 340 293a BDL =  Cr 26 28  Rb BDL BDL 15 BDL 10 47  36  Nb 6 6 6 7 3 6  36 15 12 879 67 Below  180 17 6 9 BDL BDL 87 38 47 42 detection limits  -37  Sr 811 537 477 . 820 412 586 111 9 BDL 126 3130  V 233 319  275  Y 24 21 26 24 22 23  Zr 72 155 102 105 90 78  82 60 23 239 25  17 17 BDL 35 40  198 41 31 276 104  -307  2  2  :  APPENDICES / 135  8.2. APPENDIX 2: AXIAL DIMENSIONS OF ELONGATE PEBBLES  Dimensions of elongate quartz and feldspar clasts were measured in the field at location  602.  Measurements  were  taken  on  surfaces  parallel  to  foliation  and  perpendicular to 1 lineation. Long and intermediate axes were measured on foliation 2  surfaces, short  axes on lineation-normal surfaces.  In each case, the  largest  10% of  clasts in a defined area were recorded: The arithmetic mean of each group is plotted on a Flinn diagram in figure 23.  APPENDICES / 136  Long axes (nun) Quartz 56 46 22 32  Feldspar  11 9 13 8  Intermediate Axes (mm) Quartz 7 6 11 12 Feldspar  9 5 2 3  Short Axes (mm) Quartz 2 1 2 3  Feldspar  3 4 4 3  26 18 23 18  38 15 39 17  31 21 18 24  20 18 32 16  17 22 28 29  21 18 10 11  9 12 11 17  5 8 11 22  12 9 6 13  12 9 8 15  6 6 3 3  4 7 3 7  7 7 3 8  8 7 4 3  8 5 2 5  9 5 7 5  5 6 2 4  3 3 3 3  4 5 7 4  5 4 6 6  3 3 3 1  2 2 2 2  2 3 2 3  2 2 3 3  3 4 4 2  2 3 3 3  3 3 2 4  4 4 3 3  6 3 3 2  4 5 4 3  .  APPENDICES / 8.3. APPENDIX 3: MINERAL ABBREVIATIONS  An Ap Aim Bt Cc Ch Cz Ep Gt Hb 11  Kspar Ky Mt Mu Op Par PI Qz Ru Sid Ser Sill Sph St To Zo Zr  Andalusite Apatite Almandine Biotite Calcite Chlorite Clinozoisite Epidote Garnet Hornblende Ilmenite Potassium Kyanite Magnetite Muscovite Opaques Paragonite Plagioclase Quartz Rutile Siderite Sericite Sillimanite Sphene Staurolite Tourmaline Zoisite Zircon  APPENDICES / 138  8.4. APPENDED 4: ELECTRON MICROPROBE ANALYSES Microprobe analyses of garnet and biotite were completed using the C A M E C A SX-50 microprobe at the U B C Department of Geology. Five samples were collected from pelitic schists and meta-diabase  intusions in garnet  +  biotite and staurolite  +  kyanite metamorphic zones in the Ogden Peak area. Operating conditions were similar for all analyses: Accelerating potential = 15kV Specimen current = 50 nanoamps Counting time =  10 seconds  Beam diameter = 10-15 microns  Garnet and biotite were analyzed separately and the microprobe was recalibrated for  each mineral species. Standards used consisted of natural and synthetic minerals  from the U.B.C. Department of Geology collection (table 1). This microprobe.  work  represented  the  initial  use  of  the  newly  installed  CAMECA  APPENDICES /  T A B L E 1: STANDARDS FOR G T - B T  Element  Standard  GARNET Si Al  GE07HERMOMETRY  Locality  UBC id no.  Pyrope  Victor Mine, S. Africa  G278  Pyrope  Victor Mine, S. Africa  G278  Fe  Fayallite  Synthetic  O250  Mg Mn Ca Ti  Pyrope  Victor Mine, S. Africa  G278  Pyroxmangite  Shidara-Machi, Japan  P245  Pyrope  Victor Mine, S. Africa  G278  Hornblende  Kakanui, New Zealand  A229  Si Al  Hornblende Orthoclase  Kakanui, New Zealand  A229  Ti Mg Fe Mn Ca Na  Hornblende Forsterite Fayallite Pyroxmangite Hornblende Albite  St. Lawrence. N. Y. Kakanui, New Zealand San Carlos, Arizona  F96 A229 0275  Synthetic Shidara-Machi. Japan Kakanui, New Zealand Langlois, Orezon  O250 P245 A229 F20  BIOTITE  139  APPENDICES / 140  T A B L E 2: SAMPLE  LOCATIONS  Number 233  Latitude (N). 52° 35' 38"  Longitude (W) 120° 43' 23"  Rock type St + Ky pelitic schist  447  52° 36' 36"  120° 46' 19"  St + Ky pelitic schist  zone  598  52 - 37' 23"  120° 48' 28"  Gt + Bi pelitic schist  zone  651-2  52° 36' 31"  120° 46' 39"  St + Ky meta- diabase  zone  651-c  52  120  St + Ky meta-diabase  zone  a  :  36' 29"  3  46* ^2"  .  zone  APPENDICES / 141  Sample  851-c 651C-3  651C-4  651C-6  651C-7  37 . 4 7  Garnet S10.  37.  10  37 . 6 0  36 . 9 3  A l .0,  21 . 10  2 1.23  2 1 . 38  2 1 .05  MgO  1 . 98  2 .05  2.17  2.20  MnO  0. 6 7  0 . 79  0. 69  0.65  CaO  6.08  6 .34  6.43  6.39  T1O1  0.08  0.03  0.04  0.01  Total  99 . 46  100.08  99.40  99 .42  Biotite S10,  34 . 8 0  36 . 57  35 . 78  46 . 53  A l ,0.  18  18 . 6 5  17 . 7 6  15.80  T10,  1 .53  2 .08  1  MgO  9 . 30  10.08  10.61  23  19.86  43  1 .62 8 . 77  FeO  2 1 . 20  19 . 5 6  17  MnO  0. 13  0.06  0.03  0.02 0.02  20  CaO  -  0.04  0. 05  Na.O  0.03  0.03  0.02  -  K,0  8 . 73  9.16  8.81  7.14  3.86  4 OO  3 . 90  4 . 25  97.80  100.54  97 . 96  101.60  H't  0  Total  APPENDICES /  Sample  447 447-1  Garnet SlOr  37.62  &l>Oi  21.34  FeO  34.52  MgO  2.40  MnO  0.36  CaO  4.70  TIOi  0.04  Total  IOO.96  B l o t 1te S10i Al  .0,  36 . 73 17 . 97  TIOi  1 . 76  MgO  12.80  FeO MnO  16.83 0.05  CaO  0.01  Na.O  0.17  K,o  9.17  HiO  4.01.  Total  99 . 49  142  APPENDICES /  TABLE 3: SAMPLE COMPOSITIONS Sample -  Garnet Si0 A1 0 FeO MgO MnO CaO Ti0 Total 2  2  3  2  Biotite Si0 A1 0 Ti0 MgO FeO MnO CaO Na 0 K 0 H 0 Total 2  2  3  2  2  2  2  233 233-2  233  37.24 21 . 4 8 32.36 3.42 1 .38 2.53  36.68 20.99 32.06 3.21 2.31 3.61  37.16 21.11 31.70 2.99 3.00  4a  233  4b  233-5  233-6  3.91  37.05 21.06 31.29 3.20 4.32 2.64  98.88  99.87  99.63  20.54 20.79 32.31 3.46 1.31 3.55 0.07 98.44  33.20 18.26 1 .30 14.41 1 7.97 0.04  35.64 18.68 I. 32 I I . 78 17.49 0.09  6.70 3.86 95.80  0.08 8.21 3.95 97.92  37.38 19.07 1.42 13.73 14.59 0 . 10 0.01 0.20 9.44 4.08 100.01  34.77 18.39 1.34 12.78 18.56 0.15 0.02 0.05 8.04 3.92 98.02  -9 8 . 4 1  -0 . 0 6  34.04 19.24 0.94 13.80 18.45 0.10 0.04 7.43 3.94 97.97  143  APPENDICES 7 144  Sample  59S 1  598-  598 - 2  598-3  37.23  Garnet S iO»  36 . 3 6  37  A 1 , 0i  2 1.07  J 1 17 .  2 1 . 38  FeO  30.81  3 1  30 . 88  MgO  2 .09  1 3 3.  1 .82  MnO  2 . 30  1  79  3 . 00  23 ;  29  CaO  6  18  6 6 0  6 . 27  TiO,'  0 . 12  C 03  0.07  Tota 1  98 . 9 3  •00.60  1 0 0 . 10  36 . 70  B i o t i t e S  IO,  35 8 5  36 . 46  18.12  17  1 8 . 55  TiO,  1 . 74  1 . 60  1 . 49  MgO  9 . 89  9.21  10.  FeO  19.01  17 . 3 6  18 . 46  Al  , 0 ,  MnO  0 . 10  CaO  60 '  25  0 . 06  0 . 10  0  0.03  03  Na,0  002  0.03  0.04  K,0  9 . 55  9 36  9 . 98  H,0  3  . 95  3 . 85  3  Tota 1  99  9 6 . 54  99 . 32  07  96  Saapla 681-2 6512-1  6512-2a  6512-2b  6512-3  6512-5  6512-6a  6512-6b  6512-7  Garnet SIOi  35.05  36.10  36 55  36.38  36.67  36.48  35.81  35.57  AliO.  21.17  21.21  21.79  21.31  2.1.50  21 . 2 3  21 . 6 0  2 1 . 16  FeO  30.94  31.64  31.77  30.42  31.66  31 .45  31 .34  31 .84  MgO  2 .64  2.05  2.35  2.02  2.26  2.35  2 :33  2.27  MnO  0 . 77  O 66  0.67  0.69  0 73  0.66  0.65  0.67  CaO  5.79  6.37  6.26  7.01  6.23  6.46  6.33  6.07  TIOi  0.05  0.01  0.05  0.01  O 04  0.05  0.01  Total  97.02  96.04  99.04  97 92  99.05  98 . 5 6  99.05  97.58  SIOi  35.50  34.46  32.85  34.65  34 57  34.61  35.62  38 .52  A 1,01  17 40  17.87  18.37  17.18  17.31  18.11  17.53  16 .89  TIOi  1.91  1.84  1.51  1.97  1.17  1 .50  1.51  1 .22  MgO  9.70  9.91  10.61  9.28  10.40  9.54  9.59  9.61  19.49  B l o t 1te  FeO  19.75  21.02  20.90  20 89  21.08  20.63  MnO  0.06  0 . 09  0 . 08  0.05  O.06  0.05  19.31 0.03  CaO  O 02  O 06  O.14  0.06  0 . 05  0.01  0.05  0.03  Nai0  O.03  0.03  0.02  0.03  0.03  0.02  0.02  0.04  K10  9  30  8.57  6.84  8.66  7.67  8.97  9.68  7.64  H.O  3.66  3.85  3.77  3 . 80  3.80  3.84  3.85  3.93  Total  97.53  97.70  95.10  96.55  96.10  97 . 27  97.35  97.20  Compositions Gt  X-Mg  Gt  X-Fe  Gt  X-Ca  Gt  X-Mn  Temperatures  Bt  X-Mg  Bt  X-Fe  F  &  5  N  &  H  G  ft  233-2  0  8240  4 . 3740  0  43SO  O  1890  3. 3380  2 . 3360  49 t  520  466  233-3  0. 7490  4 . 34 3 0  O. 7 4 6 0  0  2430  2 . 7 BOO  2 . 9800  596  646  592  233-4  0. 7770  4 . 3490  0  6280  0  31 B O  2  8350  2. 2200  408  548  499  233-4  O . 7 170  4 . 2600  0. 6720  O. 4 0 9 0  3 .0  too  1 .7 9 5 0  424  464  426  233-5  0 . 7 7 10  4  2 180  O  4560  O  5900  2  9 120  2 . 3720  526  556  519  233-6  0 . 7.590  4 . 3300  0  6840  0  2940  3  1350  2  3510  490  534  485  233-7  O . 8380  4 . 3850  0  6170  0  18 10  3  O 1 10  1 7250  444  482  425  65 1 C - 3  O. 4 7 7 0  4  3750  1 0500  0  0920  2  1550  2 . 7580  507  575  544  651C-4  0. 4900  4 . 2830  1 0860  0  1070  2 . 2510  2: 4880  480  550  515  651C-6  0. 5220  4 . 27BO  1  1 IOO  0  0940  2 . 4330  2  5170  480  550  5 10  65 t C - 7  0 . 5280  4 . 2550  1  10OO  o.  0890  1 .8 4 7 0  2 .0320  501  572  53 1  6512-1  0. 2800  2 . 1500  0. 5400  0. 0500  2 . 2450  2 . 5660  526  596  553  6512-2  O . 2799  2  0. 5200  0 . 10O0  2 . 2990  2  73BO  539  607  569  6512-2  0. 4990  4 . 3 3 10  1. 1 I S O  0  0 9 10  2  5150  2 . 7BOO  482  553  5 16  65 1 2 - 3  0. 5370  4  1. 0 8 7 0  o  1050  2 . 1800  2 . 7530  559  634  589  65 12-3  0  4 . 1510  1 2330  0  0950  3  1 170  3  6 130  501  582  540  6512-5  0. 5440.  4 . 2790  •V. 0 7 9 0  0  0990  2 . 4 370  2  7770  518  588  546  G  0  54 10  4 . 27 4 0  1  1240  0  0 9 10  2  2230  2  6970  535  609  566  65 12-6  0  5670  4  1  1060  0. 0900  2  2224  2  5370  531  603  557  6512-7  o.  5480  4 . 3260  1. 0 9 6 0  o.  0960  2  2280  2 . 3800  498  568  527  65 12-7  O 5580  4  3880  1 :0 7 10  o  0930  2 . 1860  2 . 4650  5 15  583  542  447-1  0. 2800  2 . 3000  0 . 40OO  0. 0200  2 . 7860  2 . 2020  414  463  432  598- 1  0. 2500  2 . lOOO  0  5400  o.  2 . 2380  2  4 140  484  552  522  6512  4900  1400  0860  2750  16O0  598-2  0  2300  2 . 1000  0  5700  0 . 1200  1 3200  1 4 IOO  460  531  502  598-3  0. 2200  2 . 0700  0. 5400  0. 2000  2 . 3140  2 . 3390  439  506  484  

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