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Geochemistry of igneous rocks from the southern coast belt plutonic complex, southwestern British Columbia Cui, Yao 1993

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GEOCHEMISTRY OF IGNEOUS ROCKS FROM THE SOUTHERN COAST BELT PLUTONIC COMPLEX, SOUTHWESTERN BRITISH COLUMBIA By YAO CUI M.Sc., Chengdu College of Geology, Sichuan, P.R. China, 1988 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA October, 1993 © Yao Cui, 1993  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.  (Signature)  Department of  ^e..,9/0//GeZZ  The University of British Columbia Vancouver, Canada  Date  DE-6 (2/88)  at /3014, /993  ABSTRACT Source materials and magmatic differentiation have been constraint by Nd, Sr and Pb isotopic analyses and major, trace and rare earth element data for calc-alkaline plutonic and volcanic rocks collected along a 180 km transect from Vancouver to Anderson Lake in the southern Coast Plutonic Complex (CPC), southwestern British Columbia. The southern CPC comprises mainly Jurassic to Tertiary plutonic rocks, ranging in composition from granite, tonalite, quartz diorite, diorite to gabbro, with an average composition of quartz diorite. Subordinate Permian to Quaternary metamorphic and volcanic rocks make up the remainder of the southern CPC. Nd, Sr, and Pb isotopic data suggest that plutonic and volcanic rocks from the southern CPC consist mainly of mantle-derived materials with little or no involvement of old continental crust. Plutonic and volcanic rocks have initial E Nd of +5.0 to +9.8 and initial 87 Sr/86 Sr ratios of 0.70244 to 0.70483. Values of Pb isotopic ratios for the suite range from 18.30 to 19.03 for  206 Pb/204 Pb,  15.43 to 15.67 for 207pbp°4 Pb and 37.64 to  38 . 30 for 208pb/2o4pb . 208pb/204Pb rises slightly with decreasing age for a subset of volcanic rocks. Examined against position along the transect, the isotopic compositions are uniform along the transect from Vancouver to Pemberton, except for a subtle rise in E Nd  values for plutonic rocks. Northeast of Pemberton, a rise in initial  the NE end is defined by volcanic rocks.  207 pb/2°4 Pb  87 Sr/ 86 Sr  towards  ratios for plutonic rocks drop at  Pemberton and then rise toward the NE margin of the southern Coast Belt. The isotopic variations with distance probably suggest either an important tectonic boundary near Pemberton (e.g., west margin of the Wrangellia terrane) or differences in source region characteristics. Based on the Nd and Pb isotopic data three different origins are proposed for igneous rocks of the southern CPC: 1) partial melting of mantle wedge, 2) anatexis of juvenile terranes (e.g., Wrangellia), and 3) combinations of 1 and 2.  ii  Geochemical characteristics and magmatic differentiation of plutonic rocks from this transect in the southern CPC are further examined by mineralogy and chemical analysis. Based on petrography the calc-alkaline plutons are divided into two compositional suites: (1) a mafic suite comprising tonalite, quartz diorite, diorite and gabbro with abundant hornblende and little or no K-feldspar and (2) a felsic suite of plutons comprising granite, granodiorite, tonalite and quartz diorite with K-feldspar as an important phase and rare hornblende. Two fractionation hypotheses are proposed to explain the chemical variations for these two suites of plutonic rocks: sorting of plagioclase + hornblende + biotite ± titanite ± apatite for the mafic suite and sorting of plagioclase + biotite + K-feldspar titanite ± apatite for the felsic suite. Pearce element-ratios were employed to discriminate the mineral assemblages and to test these two hypotheses on samples from this transect. The tests demonstrate that these two hypotheses can explain the chemical variations. The importance of intercepts on Pearce element ratio diagrams was explored in testing the comagmatic hypothesis, distinguishing source regions and discriminating magma batches. The variation pattern of intercepts against distance is similar to that of Nd, Sr and Pb isotopic compositions and incompatible element ratios for plutonic rocks from this transect area. This similarity suggests that the intercepts can be used to discriminate source regions for plutonic rocks. Therefore, two distinct source regions for plutonic rocks along the transect is confirmed by intercepts: one SW of Pemberton and another NE of Pemberton. Different source regions may reflect a tectonic boundary between Wrangellia terrane SW of Pemberton and other inner terranes NE of Pemberton, or a broad geochemical difference between NE and SW of Pemberton, an important conclusion also suggested by isotopic systematics. Based on intercepts of Pearce element-ratio diagrams, 6 magma batches are also recognized for this suite of plutons across the southern Coast Belt. Magma batch grouping is important in further discussion of the chemical affinity of the source materials for the plutonic rocks  iii  TABLE OF CONTENTS ABSTRACT ^  ii  TABLE OF CONTENTS ^  iv  LIST OF FIGURES ^  vi  LIST OF TABLES ^  viii  ACKNOWLEDGMENTS ^  ix  1. INTRODUCTION ^  1  1.1 SCOPE OF RESEARCH ^  4  1.2 ACCESS OF STUDY AREA ^  5  1.3 TECTONIC SETTING ^  6  2. Nd, Sr AND Pb ISOTOPIC SYSTEMATICS ^  8  2.1 INTRODUCTION ^  8  2.2 GEOLOGY AND AGE SUMMARY ^  8  2.3 ANALYTICAL TECHNIQUES ^  12  2.3.1 Rb-Sr chemistry ^  12  2.3.2 Sm-Nd chemistry ^  13  2.3.3 Pb chemistry ^  14  2.4 RESULT ^  14  2.4.1 Nd and Sr isotopes ^  14  2.4.2 Pb isotopes ^  19  2.5 DISCUSSION ^  22  2.5.1 Crustal contamination effects ^  22  2.5.2 Nature of source regions ^  23  2.5.3 Tectonic implications ^  25  2.6 CONCLUSIONS ^  29  iv  3. PETROGENESIS OF CALC-ALKALINE PLUTONIC ROCKS ^ 31 3.1 INTRODUCTION ^  31  3.2 GEOLOGY AND PETROLOGY OF PLUTONIC ROCKS ^ 31 3.3 ANALYTICAL METHODS ^  35  3.4 GEOCHEMICAL CHARACTERISTICS ^  37  3.5 MAJOR ELEMENT VARIATIONS AND IMPLICATIONS ^ 61 3.5.1 Magmatic differentiation: application of Pearce element-ratios ^ 61 3.5.1.1 Testing the PHB hypothesis ^  63  3.5.1.2 Testing PBK hypothesis ^  71  3.5.2 Source materials: importance of Pearce element-ratio intercepts ^ 76 3.6 CONCLUSION ^  81  4. CONCLUSION ^  84  REFERENCES ^  87  LIST OF FIGURES Figure 1.1 Generalized tectonic map of the Canadian Cordillera ^  2  Figure 1.2 Generalized terrane map of the Canadian Cordillera ^  3  Figure 1.3 Terrane map of the southern Coast Belt ^  7  Figure 2.1 Geological map of the southern Coast Belt with sample locations for isotopic study ^ 9 Figure 2.2 E Nd vs. 87 Sr/86 Sr for plutonic and volcanic rocks ^ 17 Figure 2.3 Nd, Sr and Pb isotopic compositions vs. age and distance along the transect from Vancouver to Anderson Lake for plutonic and volcanic rocks from the southern CPC 18 Figure 2.4 Initial 206Pb/204Pb vs. 208 Pb/204 Pb and vs. 207Pb/204Pb for plutonic and volcanic rocks ^ 21 Figure 2.5 Stylized tectonic cross-section of the southern Canadian Cordillera ^ 25 Figure 2.6 Initial E Nd vs. age for plutonic and volcanic rocks ^  29  Figure 3.1 Geological map of the southern Coast Belt with sample locations for petrogenesis study ^ 32 Figure 3.2 Na 2 0 + 1(2 0 vs. Si0 2 diagram for plutonic rocks ^  43  Figure 3.3 AFM diagram for plutonic rocks ^  44  Figure 3.4 Harker variation diagrams of oxides for plutonic rocks ^ 45 Figure 3.5 Chondrite normalized REE discrimination diagrams for Late Jurassic plutonic rocks ^ 50 Figure 3.6 Chondrite normalized REE discrimination diagrams for Cretaceous plutonic rocks ^ 51 Figure 3.7 Chondrite normalized REE discrimination diagrams for Bralorne Diorite ^ 52 Figure 3.8 Chondrite normalized REE discrimination diagrams for volcanic rocks ^ 53 Figure 3.9 Rb vs. Y + Nb tectonomagmatic discrimination diagram for plutonic and volcanic rocks ^ 56  vi  Figure 3.10 Primitive mantle normalized abundance patterns for moderately to highly incompatible elements for Late Jurassic plutonic rocks ^ 57 Figure 3.11 Primitive mantle normalized abundance patterns for moderately to highly incompatible elements for Cretaceous plutonic rocks ^ 58 Figure 3.12 Primitive mantle normalized abundance patterns for moderately to highly incompatible elements for volcanic rocks ^ 59 Figure 3.13 Sr and Nb (ppm) vs. distance position for plutonic and volcanic rocks ^ 60 Figure 3.14 PHB element-ratio diagram for plutonic rocks from Soo River ^ 64 Figure 3.15 PHB element-ratio diagram for plutonic rocks from Spetch Creek ^ 65 Figure 3.16 PHB element-ratio diagram for plutonic rocks from Mt. Rohr ^ 66 Figure 3.17 PHB element-ratio diagram for plutonic rocks from Bendor  68  Figure 3.18 PHB element-ratio diagram for plutonic rocks from Cloudburst ^ 69 Figure 3.19 PHB element-ratio diagram for plutonic rocks from Ashlu Creek ^ 70 Figure 3.20 PBK element-ratio diagram for felsic rocks from Ashlu Creek. ^ 72 Figure 3.21 PBK element-ratio diagram for plutonic rocks from Sechelt ^ 73 75  Figure 3.22 PBK element-ratio diagram for Squamish ^  Figure 3.23 Intercepts, model lines and associated uncertainties for mafic suite of plutonic rocks plotted on PHB diagram to group magma batches ^ 79 Figure 3.24 Isotopic ratios, PHB intercepts and incompatible element ratios vs. ages and geographic positions for plutonic rocks from the southern CPC ^ 80  vii  LIST OF TABLE TABLE 2.1 Sample locations for plutonic and volcanic rocks from the southern Coast Plutonic Complex for isotopic study ^ 10 TABLE 2.2 Sm-Nd and Rb-Sr data ^  16  TABLE 2.3 Pb isotopic data ^  20  TABLE 3.1 Sample locations for plutonic and volcanic rocks from the southern CPC for 33 petrogenesis study ^ TABLE 3.2 Primary mineralogy of plutonic rocks ^  36  TABLE 3.3 Major and trace element composition of plutonic rocks ^ 38 TABLE 3.4 Major and trace element composition of volcanic rocks ^ 41 TABLE 3.5 Rare earth element composition of plutonic rocks ^  47  TABLE 3.6 Rare earth element composition of volcanic rocks ^  49  TABLE 3.7 Comparative statistics on model intercepts on Pearce element-ratio diagrams 77 for plutonic rocks ^  viii  ACKNOWLEDGMENTS I wish to express my sincere appreciation to my first supervisor, the late Professor Richard Lee Armstrong, for inspiring and initiating this line of research before he passed away in 1991. I thank J.K. Russell for his kindness of letting me continue this project. I also thank him for excellent supervision and discussion throughout this study. All isotopic analyses were performed at The University of British Columbia (UBC) in the Geochronology Laboratory established by R.L. Armstrong. Laboratory procedures used in isotopic analyses were implemented by D. K. Ghosh. D.K. Ghosh instructed me in performing Nd, Sr and Pb isotopic analyses and S. Horski helped me in XRF measurements. Isotopic data are reduced by modified programs provided by D.K. Ghosh. Error propagation for Pearce element-ratios was performed by a modified Turbo Pascal program "PRATIO" provided by Professor J. Nicholls of The University of Calgary. This thesis was greatly benefited from critical comments from R. M. Friedman, D. K. Ghosh, J. B. Mahoney, J. K. Mortensen, Dita Runkle, J.K. Russell and C. R. Stanley although any remaining inconsistencies belong to the author. Discussions with D.K. Ghosh, R.M. Friedman and J.K. Mortensen helped to improve this manuscript. Fellow graduate students at UBC, particularly A.R. Calderwood, Xiaolin Cheng, B.R. Edwards, B. James, Peiwen Ke, Bo Liang, J.B. Mahoney and Min Sun gave moral support and valuable discussions. UBC technicians M. Baker, B. Cranston and Y. Douma are also thanked for technical advice. Special thanks go to my wife, Meiying, for her patient and encouragement. Financial support was provided by NSERC operating grants J.K. Russell and R.L. Armstrong. This research was also funded in part by a UBC Graduate Fellowship and funding from the Dean of the Faculty of Science at UBC.  ix  1. INTRODUCTION The Coast Plutonic Complex (CPC) is an integral part of the Canadian Cordilleran orogen and makes up a volumetrically substantial portion of the Coast Belt, one of the five morphogeological belts in the Canadian Cordillera (Fig. 1.1). It is situated along the tectonic boundary between Alexander and Wrangellia terranes in the Insular Belt to the west and the Stikinia, Cache Creek, Quesnel, and Yukon-Tanana terranes in the Intermontane Belt to the east (Fig. 1.1 and 1.2; Wheeler and McFeely, 1991; Monger and Journeay, 1992). The CPC comprises mainly Jurassic to Tertiary calc-alkaline plutonic rocks, ranging in composition from granite, tonalite, quartz diorite and diorite to gabbro, with an average composition of quartz diorite (Roddick, 1983; Armstrong, 1988). Subordinate Permian to Cretaceous metamorphic rocks and Cretaceous to Quaternary volcanic rocks make up the remainder of the Coast Plutonic Complex. The Jurassic to Tertiary magmatism within the Coast Belt coincided with accretion of arc-type terranes (e.g., Wrangellia and Stikinia terranes) against the North American craton (Monger, 1984). From a tectonic perspective, the CPC is a critical component of the Canadian Cordillera because it masks the relationships between terranes of the Insular and Intermontane Belts. For example, in the southern CPC the suture between Wrangellia and other inner terranes in the eastern Coast Belt terranes (Fig. 1.3) is completely obliterated by plutons. A complete tectonic model for the Canadian Cordilleran orogen should include not only the timing and style of terrane accretion, but also the style and character of plutons which intrude and weld these terranes. Despite the dominance and tectonic importance of the plutons within the CPC there have been few comprehensive studies on their nature, origins and magmatic evolution. To date most geochemical research has concentrated on the northern CPC (e.g., Arth et al., 1990; Barker and Arth, 1988; Barker et al., 1986; Samson et al., 1990, etc.) and little is known about 1  13.;  \ 1 25•  65•  -11 0 73 P1  0  12 0•  4  z  rn  0  o  NZ)Ei  ALBERTA------  ---i-^  0  -A^ )^ VI^ .. -)3^  \  60.  \  1 T. 4 LZ1 , 0^Pi , z I4 r-.... ....A^ --A^ , E  H  :---4  1--^ 40 Crk^Ca t  0^  -Z.^ 0  (J  37 lil  )  ..--.1^  ''ZI.^ '.. ,......,  o  CA \ 0 1 1-"" \ C", \ -73^;  \ \II- 1 \ i \'!‘0e, ! ■ 0  55" -  I^\ 4" :. <S3^ ,... ci)^ ‘,.r. .\ 1 \ --- ^ -^  c") •  C." 3  4  ■ 4  200  300 km  )  50' -  CANADA 120•^  115•  Fig. 1.1. Generalized morphogeological map of the Canadian Cordillera (after Wheeler and McFeely, 1991)  2  ^  CRATON North American ^ Craton I 65.  -^TERRANES NORTH AMERICAN BASEMENT?  Monashee DISPLACED CONTINENTAL MARGIN  Cassiar Nisling PERICRATONIC  Kootenay  ACCRETED TERRANES Iniermontone Superterrane  Slide Mountain  OMB MEM MN= 1•1•11•1 ..1=•1111 '11■.^IMICIN1 '.1111IM^'IMMIS -Num 111. , 111M111  Dorsey Quesnellio Cache Creek  VICIMEN, 111,"■IIIMM '411=t  Stikinia Terrones of the Coast Belt  CD Cadwallader Bridge River Insular Superterrane  AX  Alexander Wrangell is  Outer Terrones  Chugach Yakutat  BATHOLITHS  CPC  Coast Plutonic Complex  100^200^300 km  Fig. 1.2. Generalized terrane map of the Canadian Cordillera (after Wheeler and McFeely, 1991).  3  the mineralogy and geochemistry of the plutonic rocks in the southern CPC on a regional scale. The plutons found throughout the southern Coast Plutonic Complex were emplaced into a unique tectonic environment because accreted terranes are isotopically primitive, comprising mainly mantle-derived arc-type volcanic rocks. This assemblage of terranes lack significant contamination from the pre-existing old continental crust (Samson et al., 1989 and 1990; Cui and Russell, in prep.). The southern Coast Belt Plutons, themselves, are also isotopically (Nd, Sr, Pb) primitive, indicating that these rocks consist mainly of mantle-derived materials with little or no involvement of old continental crust (Cui and Russell, in prep.). In contrast, plutonic rocks from the northern Coast Belt represent a mixture of juvenile, mantle-derived material and sediments showing in part Early Proterozoic isotopic signatures (Samson et aL, 1991). 1.1 SCOPE OF RESEARCH The research results in this thesis are presented in two parts which address, firstly, isotopic geochemistry and, secondly, petrogenesis of the plutonic rocks. The first part presents Nd, Sr and Pb isotopic data for plutonic and volcanic rocks collected along a 180 km transect across the southern CPC (Fig. 1.3). The systematics of these three isotopes are used to constrain the origins of granitic and volcanic rock bodies within the CPC by characterizing the nature of their source regions and the extent and nature of crustal contamination. The igneous rocks comprising this transect completely span the southern Coast Belt and most are well dated. This has allowed us to create a comprehensive picture of the isotopic diversity within the southern CPC in space and time. The isotopic data, presented in this thesis, provide a means of characterizing the nature of Late Jurassic to Quaternary magmatism  4  within the southern CPC. In conclusion, these data elucidate the magmatic and tectonic evolution of the southern CPC. The second part of this thesis presents mineralogical and chemical data on the same plutonic and volcanic rocks along this transect of the southern CPC. These data are used to further constrain the magmatic origins of these rocks. Petrographic study and chemical analyses of major, trace element and rare earth elements are used to characterize the nature and geochemical phenomenon for this suite of plutonic and some volcanic rocks. Data from four plutons, namely Squamish, Sechelt, Bendor and Mt. Rohr, previously studied by Michael and Russell (1989), are also incorporated into this study. Rare earth elements (REE) and incompatible element abundance patterns are used to quantify differences within and between plutons. Pearce element ratios are employed to examine the effects of magmatic differentiation and evaluate differences in source regions for each plutonic suite.  1.2 ACCESS OF STUDY AREA  The study area comprises a 180 km transect across the southern Coast Belt from Vancouver to Anderson Lake (Map sheets of 92G and 92J), in southwestern British Columbia. Access is mainly via Highway 99 and occasionally via logging roads. The transect lies within the south end of the Coast Mountains which is characterized by immense relief and rugged topography. Elevations range from sea level to 3000 meters above sea level .  1.3 TECTONIC SETTING  The Canadian Cordillera orogen has two distinct parts. To the west, the orogen is dominated by accreted arc-type terranes, whereas to the east the orogen comprises 5  Precambrian North American craton (Coney et al. 1980). It is suggested that the Coast Plutonic Complex is a Jurassic to Tertiary Andean-style magmatic arc built across terranes above an east-dipping subduction zone on the west margin of North America (Monger et al., 1972).  Currently, the timing and mechanism of accretion of the Insular Belt to the  Intermontane Belt are a matter of debate. Recently proposed models include: i) Middle Cretaceous amalgamation and closure of a Bridge River ocean (Monger et al.,, 1982), ii) Farly Cretaceous accretion (Armstrong, 1988), iii) pre-late Jurassic accretion followed by northward translation during Late Jurassic-Early Cretaceous time (McClelland and Gehrels, 1990; McClelland et al. , 1992), iv) Middle Jurassic amalgamation with closure of a Jura-Cretaceous intra-arc rift basin in mid-Cretaceous time (van der Heyden, 1992). While the history of amalgamation is controversial, all workers agree that the southern Coast Plutonic Complex is a compound suite of subduction-related intrusions ranging from Middle Jurassic to Tertiary in age which intrudes and obscures the contact between the Insular and Intermontane Belts. The eastern portion of the southern Coast Belt consists of a number of Devonian to Jurassic, arc-related terranes, (e.g., Methow, Harrison, Cadwallader; Fig. 1.3). The Bridge River terrane is an exception; it comprises Mississippian to late Middle Jurassic oceanic rocks (Cordey, 1988). The western portion of the southern Coast Belt comprises arc-related volcanic and sedimentary rocks including Lower to Middle Jurassic Bowen Island Group and the Early to mid-Cretaceous Gambier Assemblage. All terranes across the eastern and western portions of the southern Coast Belt were stratigraphically linked by mid-Cretaceous time (Garver, 1992). The youngest rocks within the southern Coast belt are Cenozoic volcanic rocks.  6  ^  V V V V V V V  ^  V  V V  V  V  V  V  V  V  V  V  V  V  V  V  V  V  V  V  V  V  V  V  V  ^  V  ^  V  V  ^  ^  V  V  ^  V V \^V V V V V  0 50 100 km  ^  V V V V  MF_A\-\0\ti SAACN\  \.A`mcc\ QAYQ s\ ,  ? u() 6 Q u7w \%)k ,  ,  Fig. 1.3. Terrane map of the southern Coast Belt (after Wheeler and McFeely, 1991) with the transect area of this research.  7  2. Nd, Sr AND Pb ISOTOPIC SYSTEMATICS 2.1 INTRODUCTION Nd, Sr and Pb isotopes were analyzed on representative plutonic and volcanic rocks collected along the 180 km transect across the southern CPC from Vancouver to Anderson Lake (Fig. 2.1 and Table 2.1). These three isotopes are used to constrain the origins of these calc-alkaline plutonic and volcanic bodies within the southern CPC by characterizing the nature of their source regions and the extent and nature of crustal contamination. In evaluating the extent of crustal contamination and source materials, model mixing calculation is done by using Nd isotopic composition and Nd concentration. An isotopically-constrained view of the plutonism within the southern CPC is also present. 2.2 GEOLOGY AND AGE SUMMARY A brief geology about the southern CPC and age summary for samples collected along the transect are given here (Table 2.1). More detailed petrographic descriptions for these samples are given in next chapter. The southern Coast Plutonic Complex comprises a nearly continuous suite of Middle Jurassic to Early Tertiary calc-alkaline plutons that intruded the allochthonous terranes accreted to North America. Within this transect of the CPC (Fig. 2.1), these plutons are neither well-divided nor consistently named. Based on recent U-Pb zircon dating work of Leitch (1989), Parrish and Monger (1992) and Friedman and Armstrong (1993) and several earlier K-Ar age determinations (Caron, 1974; Miller, 1979; Green et al., 1988), four suites of plutons are differentiated (Table 2.1): Late Jurassic (153-  145 Ma), Early Cretaceous (128-113 Ma), mid-Cretaceous (103-101 Ma) and Late 8  0.  4  MORPHOGEOLOGIC MAP  49' N  +41  Southern Coast Plutonic Complex (CPC)  Cenozoic sediments AAAAA  AA  AAAAA, "Ann  AA AAA  A A A A  90 1^A A 9011^A 4^AA 9011A 9012^AAA AAA 09 AA  9  Tertiary plutons Late Cretaceous plutons  ++  ..I90a -, A A AA  007^ ^  Cenozoic volcanic rocks  AA  A A  A A  + + + + + + 44 . 4  +  Mid–Cretaceous plutons Early Cretaceous plutons Later Jurassic plutons Gambier Assemblage Bowen Island Group Cayoosh Assemblage Cadwallader Group Bridge River Group Bralorne–East Liza Complex Chism Creek Schist  Undivided gneiss and ^ metamorphic rocks  Figure 2.1. Generalized terrane map and geological map of the southern Coast Belt (after Wheeler and McFeely, 1991; Journeay, 1990; Journeay and Northcote, 1992; Journeay et al., 1992; Monger and Journeay, 1992). Numbers denote sample locations (90x x) and individual igneous bodies: 1-Cypress intrusion; 2-Sechelt pluton; 3-East Sechelt pluton; 4-Newman Creek intrusion; 5-Porteau pluton, 6-Squamish pluton; 7-Ashlu Creek intrusions; 8-Cloudburst pluton; 9-Whistler intrusion; 10-Callaghan Creek intrusion; 11-Soo River intrusion; 12-Pemberton Diorite Complex; 13-Spetch Creek pluton; 14-Mt. Rohr; 15-Bendor intrusions. 9  TABLE 2.1. SAMPLE LOCATIONS FOR THE PLUTONIC AND VOLCANIC ROCKS FROM THE SOUTHERN COAST PLUTONIC COMPLEX Rock Type  Age (Ma)  122 °29.38'  Diorite  284 ± 20 (K-Ar, Hbl)'  123 °7.70' 123 °7.70' 123 °7.70' 123 °9.23' 123 ° 9.23' 123 °9.23'  Aplite Tonalite Tonalite Quartz diorite Granodiorite Mafic dike  147 ± 0.5 (U-Pb) h 147 ± 0.5 (U-Pb)h 147 ± 0.5 (U-Pb)h 147 ± 0.5 (U-Pb) h 147 ± 0.5 (U-Pb) h <147  123 ° 13.60' 123 ° 18.90' 123 ° 18.90' 123 ° 18.90'  Granodiorite Tonalite Tonalite Hbl diorite  145 + 12/ -3 (U-Pb)c 145 + 12/ - 3 (U-Pb)c 145 + 12/ - 3 (U-Pb)c 145 + 12/ - 3 (U-Pb)c  50 °5.60'  123°0.80'  Diorite  151 + 2 (U-Pb)c  50 ° 13.40' 50 ° 13.40' 50 ° 13.40'  122 °52.70' 122 °52.70' 122 °52.70'  Diorite Diorite Diorite  151 ± 2 (U-Pb)c 151 ± 2 (U-Pb)c 151 ± 2 (U-Pb)c  9001  49 °21.50'  123 ° 12.80'  Granodiorite  125 + 5/ - 7 (U-Pb)c  9002  49 °25.25'  123 ° 14.00'  Gabbro  119 ± 8 (K-Ar) d  Callaghan Creek intrusion 9020  50 ° 6.75'  123°7.00'  Hbl diorite  128 ± 8 (K-Ar, Hb)e  Squamish pluton Spetch Creek pluton  9004 9005 9032  49 °41.30' 49 °41.30' 50 °25.70'  123 ° 8.73' 123 ° 8.73' 122 °41.70'  Leuco-granite Aplite Tonalite  101 ± 2 (U-Pb)f 101 ± 2 (U-Pb) f 103 + 5/ - 3 (U-Pb) c  Late Cretaceous suite  Bendor intrusions  9040  50 °39.35'  122 °24.85'  Tonalite  64 + 11/ - 2 (U-Pb) c  Volcanic rocks  Cadwallader Group  9030 9033 9037  50 °22.16' 50°27.58' 50 °32.62'  122 °43.13' 122 ° 38.54' 122 °29.38'  Andesitic tuff Andesite Ultramafic rock  Late Triassicg Late Triassicg Early Permian'  Cayoosh Assemblage  9039  50 °37.97'  122 °26.35'  Andesitic tuffite  Middle Jurassic h  Gambier Assemblage  9003  49 °25.25'  123 ° 14.25'  Tuff  Early Cretaceous h  Cenozoic volcanic rocks  9009  49 ° 49.26'  123 °7.70'  Tuff  Late Tertiary to Quaternary'  Sample  Latitude  Bralorne Complex  9038  50°33.72'  Cloudburst pluton  9006 9007 9010 9011 9011A 9012  49 °49.26' 49 °49.26' 49 °49.26' 49 °51.60' 49 °51.60' 49 °51.60'  Ashlu Creek intrusions  9013 9014 9015 9016  49 °52.60' 49 ° 54.70' 49 °54.70' 49 °54.70'  Whistler intrusion  9021  Soo River intrusion  9022 9022A 9023  Cypress intrusion Newman Creek intrusion  Rock Unit  Longitude  Plutonic rocks  Early Permian suite Late Jurassic suite  Early Cretaceous suite  Mid-Cretaceous suite  Note: Numerical ages are radiometric ages. Method of determination is given in parenthesis. Qtz and Hbl denote to quartz and hornblende, respectively. a Leitch (1989). b Parrish and Monger (1992). c Friedman and Armstrong (1993). d Caron (1974). e Miller (1979). f Armstrong and Shore, The Unicersity of British Columbia unpublished data. g Church and others (1988) and Rusmore (1985). bMonger and Journeay (1992). 1 Green and others (1988).  10  Cretaceous (86-64 Ma). In general, the plutons are younger towards the NE end of the transect (Fig. 2.1). Late Jurassic intrusions comprise the major part of the southern CPC. Representative Late Jurassic plutons in this study include Ashlu Creek, Cloudburst, Soo River and Whistler. Table 2.1 lists U-Pb zircon ages for each intrusion (Parrish and Monger, 1992; Friedman and Armstrong, 1993). Typically the plutons are northwest elongate and the dominant rock types include granodiorite, tonalite and diorite. Early Cretaceous plutons include Cypress, Newman Creek and Callaghan Creek intrusions (Table 2.1). The Cypress intrusion is a small, granodiorite to tonalite stock on the western margin of the CPC with an U-Pb zircon age of 125 +5/-7 Ma (Friedman and Armstrong, 1993). Newman Creek is a gabbro and has been dated previously by K-Ar at 119 + 8 Ma (Caron, 1974). The Callaghan intrusion is a diorite stock dated at 128 + 8 Ma by K-Ar (Miller, 1979). The Squamish and Spetch Creek plutons represent the mid-Cretaceous plutonic suite and contain granite and tonalite, respectively (Table 2.1). The Squamish has an U-Pb zircon age of 101 + 2 Ma (Friedman and Armstrong, 1993) and a Rb-Sr whole rock age of 101 + 30 Ma (Armstrong and Shore, The University of British Columbia unpublished data) whereas Spetch Creek is 103 +5/-3 Ma based on U-Pb zircon (Friedman and Armstrong, 1993). The Late Cretaceous suite is represented by the Bendor intrusions (Table 2.1) which occur mainly as tonalite stocks aligned or oriented in a northwest direction. The Bendor intrusion has a U-Pb zircon age of 64 +11/-2 Ma (Friedman and Armstrong, 1993). The oldest plutonic rock in the southern CPC has not been included in the above intrusive suites. The Bralorne diorite intrusion outcrops in the eastern part of the southern CPC. It is part of the Bralorne Complex and radiometric age determinations  11  include a minimum U-Pb zircon date of 270 Ma (Leitch, 1989) and a hornblende K-Ar date of 287+20 Ma (Leitch, 1989). 2.3 ANALYTICAL TECHNIQUES  Fresh whole-rock samples weighing approximately 3-4 kg were reduced to roughly 3 cm rock chips with a hydraulic splitter. Weathered surfaces were removed. Rock chips were further reduced to <0.5 cm chips in a steel-faced jaw crusher and then taken through a sample splitter with multiple passes. Half of each sample was powdered to about 100 mesh using a tungsten carbide shatter box and then ground to about 200 mesh in a motor-driven agate mortar. For Sr, Nd, and Pb isotopic analyses, each unspiked whole-rock sample was dissolved in a HF-HNO 3 mixture using Teflon dissolution bombs (Krogh, 1973) at 195200 ° C for a minimum of 24 hours. The entire solution was centrifuged and the residue, which consisted mainly of fluorides, was used for separating Sr and Nd. Pb was separated from the supernatant. Both residue and supernatant were dried on a hot plate and treated with concentrated HNO 3 to drive off remaining HF and to convert fluorides to nitrates.  2.3.1 Rb-Sr chemistry  Rb and Sr concentrations were determined on pressed powder pellets by X-ray fluorescence in the Department of Oceanography at UBC. The estimated precision for Rb and Sr concentrations is 5%, based on duplicate analyses of 16 samples. Separation of Sr and rare earth elements (REE) was done on 100-200 mesh 8 x 50W Dowex (Hform) cation exchange resin columns (the first column). After Sr was stripped with 2.5 N HC1, the REE fraction was eluted with 4 N HC1. 12  The dried Sr fraction was dissolved in water and loaded on a single Ta-filament with Ta oxide as the emission base. The Sr isotopic measurement was carried out on a VG Isomass 54R mass spectrometer automated with a Hewlett-Packard HP-85 computer. The Sr standard NBS 987 runs (N = 9) return an averaged 87Sr/86Sr ratio of 0.71010 + 0.00001 (2a m ). Measured ratios have been normalized to a  86 Sr/ 88 Sr  ratio  of 0.1194. A Rb decay constant of 1.42 x 10 -11 a-1 (Steiger and Jager, 1977) was used for calculation of initial ratios. 2.3.2 Sm-Nd chemistry  Sm and Nd concentrations were measured by an Elan-5000 ICP-MS at the University of Saskatchewan. Analytical precision for Sm and Nd concentrations is <5%. After initial separation of REE on cation exchange resin columns (see Sr separation above), further purification of REEs and separation of Nd from Sm were done with Teflon columns containing 4 cm of powdered Teflon, treated with HDEHP (Di-2-ethylhexyl orthophosphoric acid) and capped with 0.5 cm of anion exchange resin. Nd was stripped with 0.25 N HC1. The dried Nd fraction was loaded with water on the Re side filament of a double-filament assembly. Measured ratios were normalized to a 146Nd/144Nd ratio of 0.7219 (O'Nions et al., 1979) and adjusted so that our in-house Nd oxide strandard yielded a  143 Nd/ 144 Nd  ratio of 0.511544 +  0.000024 (la), the best value on this in house Nd standard in the Geochron Lab -  at UBC. The La Jolla standard runs (N = 4) yield a  143Nd/144Nd  ratio of 0.511847 +  0.000014 (2a m ). Averaged in-house Nd oxide standard runs (N = 5) returned a 143 Nd/ 144 Nd  ratio of 0.511495 + 0.000016 (2a m ). A Sm decay constant (146s m ) o f  6.54 x 10 12 (Lugmair and Marti, 1978) has been used to calculate the initial Nd isotopic compositions. 13  2.3.3 Pb chemistry U and Th concentrations were measured by instrumental neutron activation at Chemex Labs Ltd. (Vancouver). Pb concentrations were measured by XRF in the Department of Oceanography at UBC. The supernatant portion of the sample dissolution, prepared for Rb-Sr and SmNd analysis, was used for Pb separation. Pb was initially separated using the Ba(NO 3 ) 2 co-precipitation method. Pb was then further purified by passing the solution through 100-200 mesh, chloride form anion exchange resin. The dried fraction was dissolved in H2O and loaded onto a Re single filament with silica gel. Pb isotopic compositions were measured at a filament temperature of 1250 ° C, and were corrected for mass fractionation of 0.14 + 0.02% per amu as determined by replicate analysis of the NBS 981 common Pb standard (absolute values from Todt et al., 1984). Replicate analyses of Pb standard NBS 981 (N = 21) yielded 207pb/204Pb =  206 Pb/ 204 Pb  = 16.8951 + 0.0044 (26 m ),  15.4316 + 0.0038 (26 in ) and 208 Pb/ 204 Pb = 36.5089 + 0.0108 (26 in).  Pb procedural blanks averaged <2 ng, representing less than 1% of the estimated total Pb in the samples; therefore, no blank correction was made. 2.4 RESULTS  2.4.1 Nd and Sr isotopes  Twenty-five samples of plutonic and volcanic rocks from the southern CPC were selected for Nd and Sr isotopic analysis. Nd and Sr isotopic ratios and E Nd values are given in Table 2.2 and shown graphically in Figs. 2.2 and 2.3. The plutonic rocks have initial E Nd values ranging from +5.0 to +9.0 and initial 87 Sr/ 86 Sr ratios ranging from 0.70244 to 0.70433. With the exception of one 14  sample, both initial E Nd and 87 Sr/ 86 Sr ratios appear to be independent of rock type. The most mafic plutonic rock, a gabbro from the Newman Creek intrusion, has the lowest initial 87 Sr/ 86 Sr ratio of 0.70244. Samples from the Ashlu Creek intrusions have initial  ENd  values (+6.0 to  +7.0) and Cloudburst pluton (+6.2 and +8.0). Sample 9012 represents a mafic dike intruding the 147 Ma Cloudburst Pluton. The dike has a present-day E Nd value of +6.1 or a maximum initial E Nd value of +6.9, using the age of the pluton as a limit. The highest initial 87 Sr/ 86 Sr value (0.70433) comes from the Bendor intrusion and the lowest value (0.70244) is from the Newman Creek gabbro. Samples from the Cloudburst and Ashlu Creek intrusions show very small ranges in initial  87 Sr/ 86 Sr:  0.70336 to 0.70356 and 0.70359 to 0.70332, respectively. The volcanic rocks have initial E Nd values ranging from +5.6 to +9.8, showing much greater isotopic variation than seen in the plutonic rocks. The initial 87 Sr/ 86 Sr  values for the same volcanic rocks range from 0.70329 to 0.70483, again  showing far less homogeneity than the plutonic rocks. Figure 2.3a to Figure 2.3g illustrates the Nd and Sr isotopic variations of plutonic and volcanic rocks within the southern CPC against their ages and geographic position (e.g., along the transect). The upper left portion of Figure 2.3 (a, b) maps initial E Nd and 87 Sr/ 86 Sr against age. Both Nd and, especially, Sr isotopic data show significant dispersion where plotted against time. Indeed neither isotope defines a coherent trend for data sets comprising plutonic, volcanic or both rock types. The upper right graphs in Figure 2.3 (f, g) illustrate variations in Nd and Sr isotopic data from SW-NE along the transect. In these graphs there is less apparent dispersion in the isotopic data and, although weak, there are some apparent trends. Firstly, the initial E Nd values show a weak increase from SW-NE which is crudely supported by both plutonic and volcanic rock types. Secondly, although the initial 87 Sr/ 86 Sr  values show more scatter than do the Nd isotopes, there may be a subtle 15  TABLE 2.2. Sm-Nd AND Rb-Sr DATA FOR SAMPLES FROM THE SOUTHERN COAST PLUTONIC COMPLEX  ^6  Rock Unit  Sample  147s m b Age Sm a Nd a 144 Nd (Ma) (ppm) (ppm)  I43Nd c 144 Nd  6 NC1 (°)d  e^f (pRpbm8 (pSprtn I Nd(t) (liDM vI a)^  (measured)  ur e 8 s8 Sr  )  87Sr s  Srb h 8876R  Sr (measured)  (initial) 0.70251 0.70301 0.70356 0.70336 0.70356 0.70336 0.70302 0.70331 0.70332 0.70296 0.70307 0.70323 0.70320 0.70347 0.70244 0.70331 0.70324  Plutonic rocks  Early Permian suite Late Jurassic suite  Late Cretaceous suite  9038 9006 9007 9010 9011 9011A 9012 9013 Ashlu Creek intrusion 9014 9015 9016 Soo River intrusion 9022A 9023 Cypress intrusion 9001 Newman Creek intrusion 9002 Callaghan Creek intrusion 9020 Squamish pluton 9004 9005 9032 Spetch Creek pluton Bendor intrusions 9040  Volcanic rocks  Cadwallader Group  Early Cretaceous suite Mid-Cretaceous suite  Bralorne Complex Cloudburst pluton  Cayoosh Assemblage Gambier Assemblage Cenozoic volcanic rocks  9030 9033 9039 9003 9009  284 147 147 147 147 147 147 145 145 145 145 151 151 125 119 128 101 101 103 64 230 230 178 135 2.3  1.07  8.41  0.0771  0.51284±5 4.0±1.1  +6.2  2.38  12.50  0.1153  0.51297±6 6.4±1.1  +8.0  5.43 2.03 4.84 4.46 3.03 2.42 5.23 2.34  21.20 11.53 20.68 22.99 12.52 12.51 28.31 12.88  0.1549 0.1062 0.1416 0.1172 0.1464 0.1167 0.1117 0.1098  0.51295±7 0.51286±3 0.51291±4 0.51290±4 0.51295±8 0.51295±8 0.51298±3 0.51283±4  6.1±1.4 4.3±0.6 5.3±0.8 5.1±0.8 6.1±1.5 6.1±1.5 6.6±0.5 3.8±0.9  +6.9 +6.0 +6.4 +6.5 +7.0 +7.6 +8.3 +5.2  4.84 2.47 4.00 2.37  21.68 12.51 13.89 11.66  0.1351 0.1196 0.1741 0.1231  0.51284±3 4.0±0.7 0.51291±9 5.3 ±I.7 0.51300 ± 7 7.1 ± 1.3 0.51305±9 8.6±1.7  +5.0 +6.2 +7.4 +9.0  2.77 4.21  10.62 15.63  0.1574 0.1630  0.51308±5 0.51295±3  8.7±0.9 6.2±0.7  +9.8 +7.2  3.09 3.15  12.84 13.29  0.1456 0.1433  0.51289 ±9 5.0 ±1.7 0.51292±6 5.5 ±1.2  +5.9 +5.6  2.5 250^45.7 14.0 393^17.8 155^14.4 157^23.0 286^20.5 288^13.4 317^39.6 264^49.4 258^23.8 184^7.9 135^15.7 334^45.5 3.7 423^14.9 255^68.7 237 -^42.7 32.4  172 132 878 800 574 783 449 767 392 323 380 669 548 393 65 964 127  0.042 1.00 0.046 0.064 0.072 0.085 0.132 0.050 0.292 0.443 0.181 0.034 0.083 0.334 0.174 0.045 1.57  0.70268±7 0.70511±2 0.70366±9 0.70350±5 0.70371±7 0.70354±4 0.70329±4 0.70342±5 0.70392±9 0.70387±1 0.70344±7 0.70330±8 0.70338±5 0.70407±9 0.70277±6 0.70339±8 0.70550±2  568 625  0.218 0.150  0.70358±5 0.70326 0.70447±5 0.70433  -^19.4 324^16.4 21.4 372^8.2 304^5.4  241 444 243 832 804  0.234 0.107 0.255 0.029 0.020  0.70405±1 0.70468±7 0.70547±3 0.70372±4 0.70339±3  Note: Reported errors are 2a on the mean. ° Analytical precision for Sm and Nd are < 5 %. b Analytical precision for 147 Sm/ 144 Nd are < 7 %. Ratios normalized to 146 Nd/ 144 Nd = 0.7219 and adjusted so that UBC in-house Nd oxide standard yields 143 Nd/ 144 Nd = 0.511544 ± 0.000024 (la). 143 Nd/ 144 Nd = 0.511847 ± 0.000014 (ta m ) for the La Jolla Nd standard during period of study (N = 4). d^ = r ( 143 1-,4 di ENclk",^144Nd) pie(0)/(143Ndi 144Nd)CHURP 1] x 104 using (143Nd/ 144Nd)CHURM = 0.512638 and ( 146 Sm/ 144 Nd) 0 = 0.1966. ory( 143 Nd/^7) [( 143 Nd/ I44 Nd)^i) ^(^1] e Nd (T) - x 10 4 . 144Nd).CHURsf Depleted mantle ages based on the model of DePaolo (1981). CT4^g Analytical precisions for Rb and Sr are 7 % and 8 % respectively. h Analytical precisions for 87 Rb/ 86 Sr are < 10 %. Ratio normalized to 86 Sr/ 88 Sr = 0.1194. 87Sr/ 86 Sr = 0.71010 ± 0.00001 (ta m) for Sr standard NBS 987 during period of study (N = 9).  0.70329 0.70433 0.70483 0.70366 0.70339  14 12  I^'^I^I^I^'^I^I  MORB^  10  el  Cypress  •  Squamish  ^  Cloudburst Ashlu Creek  -14-^Callaghan Creek  8  •  Soo River  A^Spetch Creek  6  A^Cenozoic  Nd 4  ▪  Gambier  •  Cadwallader  2 0 -2 -4 -6 0.702 0.703 0.704 0.705 0.706 0.707 0.708 0.709 "Sris6 Sr  Figure 2.2. Initial e Nd vs. 87Sr/ 86 Sr for plutonic (open symbols) and volcanic (filled symbols) rocks from the southern CPC. Comparative fields include modern midoceanic ridge basalts (MORB) (Hawkesworth et al., 1979; Cohen et al., 1980; Cohen and O'Nions, 1982; Jahn et al., 1980 and White and Hofmann, 1982), oceanic island basalts (OIB) (Zindler and Hart, 1986), island-arc volcanic rocks (IAV) (Samson et al., 1989). Also shown for comparison are the fields for Wrangellia (after Andrew et al., 1991; Samson et al., 1990) and Stikinia terranes (after Samson et al., 1989).  17  ^ ^  Vancouver  12 10 8 E Nd  6 4 2  -  I  '  I  •  I  • •  1  .  I^.^I^.  I  O o •0 0  i  1  i •  1^1^1^1  Pemberton  f  ^ ^8 o 0 i^ 0 O•^ • o -  ,Y  0.704  •  )  0.703  1 AZ 38.5  0.  I  I  I  I  b-  0 I^1^I^i  I  1  _  —  38.0  •  4.8 ®  •  •  •  0 oo  0  I  r•■ •^0 tg,  8^  R  • 0  I 15.7 15.6 15.5 15.4 15.3 19.5 N  19.0  Q_ 18.5  S  18.0 17.5  I  1  I •  • _ _ 1  0_  I  -•  'III  _ -•  •  •  I^I^I^1 o i • oo o 0 ^o  ,  1  ,  0  1  • _  d_ 1^1111 I _ 0 0 ., g  I  I  1^.^1^,  0  _ a e^-1 .  -  •  1  1  1  11111111  - o•^o^0 _ ^8 t o 11111111111 h  11+11 , • o^oc o^_ 11111  ^  _  t _4^ o^8 0 o^ o o -^  0 • _  • 0^-  37.5 ^37.5  C  Anderson Lake  -  1g AI ^•• • o 0.705  ^  12  •  _ 1 _ CI^1 1 _  ^  F11111111 -i - '4^@ o g^t^ _-O  -  1  ^I^I^I I^I^I^I^1^I^I  -j - o  _^  6 E Nd  4 2  0.705  0.703  38.5^zw a_ 38.0  ^  A.. 0_  ^c.,  •  • O  • • ^o  -  15.7 15.6  .0  15.5 15.4 15.3  IIIII -  • o^0^-  ■1,1.1,1.1,1,1.  19.5 19.0 18.5  —  18.0  -  17.5  300^250^200^150^100^50^0^20 40 60 80 100 120 140 160  Age (Ma)  Z3  0.704  1111  8 € - •^0^CI ')^2^opt 0^,  10 8  Distance (km)  Figure 2.3. Initial isotopic ratios vs. age and distance along the transect from Vancouver to Anderson Lake for plutonic (open circles) and volcanic (filled circles) rocks from the southern CPC.  18  .0 .P-  a  o  decrease in the Sr initial ratio over the first 120 km. This NE-decreasing trend is terminated by a significant increase in initial 87 Sr/ 86 Sr values for both plutonic and volcanic rocks. The sole exception is the Bralorne diorite which has a very low initial 87 Sr/ 86 Sr  value. The volcanic rocks defining this abrupt rise in initial Sr isotopic ratio  include rocks from the Cadwallader Group and Cayoosh Assemblage. 2.4.2 Pb isotopes  Pb isotopic compositions were determined for 24 whole rock samples. The results are reported in Table 2.3 and plotted in Figs. 2.3 and 2.4. The total variation in Pb isotopic ratios for plutonic rocks is 18.30-19.03 for 206pb/204Pb, 15.43 to 15.64 for 207pb/204Pb and 37.64 to 38.30 for  208 Pb/ 204 Pb.  and the central CPC show little variation in  Samples from Squamish, Ashlu Creek  207 Pb/ 204Pb  (from 15.55 to 15.60) and  2osph/2o4ph (from 37.92 to 38.30). The Cloudburst pluton has a wider range of 2o7phi2o4ph (15.47 to 15.64) and 208Pb/204Pb (37.64 to 38.24). The mafic dike within the Cloudburst pluton has lower 207 Pb/ 204 Pb (15.47) as well as lower 208 Pb/ 204Pb (37.74). Samples from the Bralorne Complex and Spetch Creek pluton have very nonradiogenic 207 Pb/ 204 Pb ratios which is consistent with the Nd-Sr isotopic systematics of these bodies discussed above. In general the Pb isotopic ratios for the volcanic rocks lie within the range established for the plutonic suite. The exception is  207pb/204  Pb which for the volcanic  rocks ranges from 15.47-15.67, with the highest ratios obtained from Cadwallader Group volcanic rocks. The Pb isotopes show no correlation with rock type or age (Fig. 2.3), except that 208 Pb/ 204Pb ratios for volcanic rocks increase slightly towards present day. In examining Pb isotopic data against geographic position, 207 Pb/ 204 Pb shows some variation along the transect. From Vancouver to Pemberton, 207phi204ph i s very 19  TABLE 2.3. Pb ISOTOPIC DATA FOR IGNEOUS ROCKS FROM THE SOUTHERN COAST PLUTONIC COMPLEX Initial  Measured Rock Unit  Plutonic rocks Early Permian suite Late Jurassic suite  Bralorne Complex Cloudburst pluton  Ashlu Creek intrusion  Whistler intrusion Soo River intrusion  Early Cretaceous suite Mid-Cretaceous suite  Newman Creek intrusion Callaghan Creek intrusion Squamish pluton  Late Cretaceous suite  Spetch Creek pluton Bendor intrusions  Volcanic rocks  Cadwallader Group Cayoosh Assemblage Gambier Assemblage Cenozoic volcanic rocks  Sample  207 pb  208 pb  2°4 Pb  2°4 Ph  (ppm)  Th (ppm)  Pb (ppm)  2°6Pb 2e4 Pb 18.35 19.06 18.60 18.61 18.83 18.46 18.71 18.84 18.90 18.83 18.67 18.93  15.46 15.58 15.56 15.64 15.59 15.47 15.61 15.61 15.59 15.58 15.57 15.60  Age  U  (Ma) 9038 9006 9010 9011 9011A 9012 9013 9014 9015 9016 9021 9022A 9023 9002 9020 9004 9005 9032 9040  284 147 147  0.1 10.2 0.8  0.5 25.0 4.0  147  0.6  4.0  147 147 145 145 145 145 151 151  1.2 0.2 1.0 0.8 1.6 1.0 2.6 1.8  3.0 0.5 1.0 2.0 3.0 2.0 5.0 6.0  6.5 21.0 6.7 12.0 7.5 9.9 9.3 7.4 7.4 9.3 12.0 5.5  151 119 128 101 101 103 64  1.0 0.1 0.4 2.0 5.6 1.4 1.4  1.0 0.5 0.5 14.0 24.0 3.0 2.0  5.6 6.7 9.3 9.8 16.0 9.0 10.9  18.49 19.05 18.61 18.83 19.07 18.64 18.74  9030 9037 9039 9003 9009  230 290 178 135 2.3  0.6 0.1 1.4 0.4 0.4  1.0 0.5 3.0 0.5 1.0  10.3 1.5 9.7 9.4 9.3  18.68 18.85 18.90 18.56 18.62  206 pb  207 pb  2°8Pb  204 pb  2°4 Pb  204pb  37.61 38.21 38.18 38.35 38.20 37.76 38.28 38.43 38.41 38.28 38.18  18.30  15.46  18.34  15.54  37.54 37.64  18.43  15.55  37.89  18.54 18.59 18.43 18.55 18.69 18.59 18.68 18.35  15.64 15.58 15.47 15.60 15.60 15.58 15.57 15.55  38.19 38.01 37.74 38.23 38.30 38.23 38.17 37.98  15.59 15.58 15.58 15.58 15.64 15.44 15.56  38.46 38.11 38.22 38.21 38.31 38.50 37.85 38.27  18.44 18.23 19.03 18.55 18.62 18.72 18.48 18.66  15.58 15.58 15.58 15.57 15.57 15.62 15.43 15.55  37.92 38.02 38.19 38.18 37.83 38.00 37.74 38.24  15.57 15.68 15.56 15.56 15.63  38.03 38.12 38.25 38.11 38.24  18.55 18.65 18.64 18.50 18.62  15.56 15.67 15.55 15.56 15.63  37.96 37.80 38.07 38.08 38.24  Note: All errors are 2 S.E. Measured Pb isotopic compositions were corrected for mass fractionation of 0.14 ± 0.02 % per a.m.u., determined by the average deviation of NBS 981 (21 runs) from its absolute value (Todt et al. 1984). Replicate analyses of NBS 981 (N = 21) yielded 206Pb/2°4Pb = 16.8951 ± 0.0044, 2°7Pb/ 204Pb = 15.4316  ± 0.0038 and 2°8 Pb/ 2°4Pb = 36.5089 ± 0.0108. The within-run precision averages ± 0.2 % for all measured Pb isotopic ratios.  39.00  Pacific sediments VVrangellia  38.50  ±2a  38.00  Newman Creek  37.50  -2(-^Callaghan Creek +  Whistler  Bendor^ 37.00  ^  Pacific sediments  15.70  S^• g A  •  Cayoosh Assemblage  ^VVrangellia HFtL  CS  15.60  -  Bralorne  15.50 SMT 15.40  15.30^' 17 50  /±2a  MORB  I^I  18.00  1^I  ^1^1  19.00  18.50 206  I^1^1^1^1^I^1^1^1^1  Pb/  204  19.50^20.00  Pb  Figure 2.4. Initial 2o6pb/204pb vs. 208 Pb/ 204 Pb and vs. 207 Pb/ 204 Pb for igneous rocks from the southern CPC. Symbols as in Figure 2.2. Comparative fields, recalculated back to 150 Ma, are MORB (Church and Tatsumoto, 1975; Br6vart et al., 1981; Vidal and Clauer, 1981), northeast Pacific Ocean seamounts (SMT) (Church and Tatsumoto, 1975; Hegner and Tatsumoto, 1987), Pacific sediments (Church, 1976; Vidal and Clauer, 1981; Sun, 1980), and Wrangellia terrane (Andrew and Godwin, 1989a and 1989b). NHRL and S & K denote the Northern Hemisphere reference line of Hart (1984) and the reference growth curve of Stacey and Kramers (1975).  21  uniform (Fig. 2.3). At NE near Pemberton (130 km on the transect; Fig. 2.3), 207pb/204pb for plutonic  rocks drops and then rises toward the northeast margin of the  southern CPC. 2.5 DISCUSSION  2.5.1 Crustal contamination effects  The igneous rocks of the northern CPC may have been contaminated by ancient continental crust (Samson et al., 1991). Nd, Sr and Pb isotopic data allow us to evaluate possible crustal contamination of igneous rocks in the southern CPC. The initial ENd vs. 87 Sr/ 86 Sr ratios from the southern CPC are plotted on Figure 2.2. The fields for modern mid-ocean-ridge basalts (MORB), oceanic island basalts (OIB) and island-arc volcanic rocks (IAV) are shown for reference. Also shown for comparison are the fields for Wrangellia and Stikinia terranes with all data recalculated to 150 Ma (the approximate median age of igneous rocks from the southern CPC). The igneous rocks from the southern CPC plot within the field of modern uncontaminated IAV and at the lower end of the MORB field (Fig. 2.2). Only the Cadwallader Group volcanic and Spetch Creek plutonic rocks plot outside the field of OIB. A limit on the extent of crustal contamination was set by considering mixing between end members with MORB and upper crustal characteristics. The calculations were done using E Nd of +8.5 for and 10 ppm Nd for MORB and E Nd of -14 and 31 ppm Nd for old crustal material (DePaolo, 1981, 1991). The results indicate that for southern CPC igneous rocks the maximum permissible crustal contamination is < 6% with a mean value of 2.6%. The 207 Pb/ 204 Pb ratios for the same suite of rocks define a field which partially overlaps fields for MORB, seamounts (SMT) and Pacific sediments (Fig. 2.4). The 22  most striking feature of the Pb isotopic data for the southern CPC is the slightly elevated 207Pb/204 Pb ratios with respect to MORB (Fig. 2.4). The Newman Creek intrusion shows both high 207Pb/204Pb an d 206pb/204Pb ratios, but still plots within the SMT field. Most of  207 Pb/ 204 Pb  ratios lie above the Northern Hemisphere Reference  Line (NHRL) of Hart (1984) suggesting an apparent Dupal anomaly (Dupre and All6gre, 1983). However, in Figure 2.4, the  208 Pb/ 204 Pb  ratios for these same rocks  plot within the fields established for MORB and SMT and along the NHRL. These characteristics, together with the Nd and Sr isotopic data, demonstrate that the igneous rocks from the southern CPC have not been contaminated significantly by old continental material. The elevated  207Pb/ 204 Pb  ratios for these igneous rocks probably  result from the introduction of oceanic sediments through subduction. 2.5.2 Nature of source regions  Various source materials are suggested for the CPC. Monger et al. (1982) proposed that Alexander-Wrangellia and Stikinia terranes were the two main components of the source materials to the CPC. Barker et al. (1986) also invoked two source region components: mantle-derived melts and material derived from the accreted terranes. They suggested that the latter contribution could have been introduced either as assimilated material or as anatectic melts of the crust. Samson et al. (1991) suggested a mixture of Early Proterozoic crust and juvenile, mantle-derived material as source to the northern CPC. They envisaged the old crustal material as Yukon-Tanana terrane and the juvenile component as mantle-derived melts or anatexis of the surrounding terranes In this study, three different sources and petrogeneses for the igneous rocks in the southern CPC are recognized: 1) partial melting of mantle wedge beneath accretionary terranes, 2) anatexis of the accretionary terranes, and 3) combinations of 23  the above two processes (Fig. 2.5). These scenarios are based mainly on the Nd and Pb isotopic data and comparisons between these data and isotopic characteristics of MORB, Pacific sediments and Wrangellia and Stikinia terranes. Below, the details of each scenario are elaborated. Plutons with more material from mantle source include Cloudburst and Soo River intrusions. These rocks have very high E Nd values (+7.6 to +8.3) and have Nd depleted-mantle model ages (t DM ages; 135 to 184 Ma, Table 2.2) that are very close to the crystallization ages (147 to 151 Ma). These plutons are the best candidates in the southern CPC for magmas derived from mantle sources (the first type as shown on Fig. 2.5). Mixing calculations were made using MORB and Wrangellia terranes as end members with E Nd values of +8.5 vs. +5.1 and Nd concentrations of 10 vs. 16 ppm, respectively (e.g., Andrew et al., 1991 and Samson et al., 1990). For these intrusions, the calculated maximum amount of contamination by Wrangellia-like material is less than 20%. Calculations using model values for Stikinia of E Nd of +4.1 and 16 ppm Nd (e.g., Samson et al., 1989) yield similar results. Igneous rocks with more terrane materials contain samples from the Early Cretaceous magmatic suite, including Cypress and Callaghan intrusive rocks and Gambier volcanic rocks in the southern CPC. This magmatic suite has the lowest initial E Nd from +5.0 to +5.9. Crystallization ages range from 125 to 128 Ma in contrast to calculated t DM ages of 334 to 423 Ma (Table 2.1). The mean difference in ages is on the order of 250 m.y. Based on material balance arguments (as above) calculations permit more than a 60% contribution from Wrangellia to this set of igneous rocks. A representative Cenozoic volcanic rock (2.3 Ma) also yields an older, depleted-mantle model age (304 Ma). Material balance calculations would permit up to 80% input from a Wrangellia-like source. For this suite of southern CPC rocks, at least, it appears that anatexis of juvenile accreted terranes could have played an important petrogenetic role (the second type as shown on Fig 2.5). 24  Wrangellia Terrane^:;,:;;;;;i:::. Deformed rocks 1^V,  AN-. • 4'1N  Stikine Terrane North American craton  Oceanic sediments, modern accretionary complex  r.11  Partial melt Plutonic rocks  Figure 2.5. Stylized tectonic cross-section of the southern Canadian Cordillera (after Monger et al., 1985; Green et al., 1990). Numbers in circles denote magmas derived from (1) mainly mantle melting, (2) mainly anatexis of juvenile terranes and (3) combinations of 1 and 2.  25  Other igneous suites in the southern CPC are more or less a combination between more mantle derived material and anatectic terrane materials (third type as shown on Fig. 2.5), including the Late Jurassic intrusions of Ashlu Creek, Whistler, and the mid-Cretaceous intrusions include most of the plutons in the southern CPC and are characterized by lower initial E Nd values. The initial E Nd for the Late Jurassic intrusions ranges from +6.4 to +7.4. Crystallization ages of the plutons range from 145-151 Ma compared to the older t DM ages of 237-317 Ma. The mid-Cretaceous intrusions have initial E Nd values ranging from +6.2 to +7.4. The crystallization age of 101 Ma is younger than the calculated t DM ages (235 to 255 Ma). The difference between tDM ages and crystallization ages for both Late Jurassic and mid-Cretaceous intrusions is about 130 m.y. This difference, however, is not as great as that for the Early Cretaceous magmatic suite. Therefore, this result suggests that these Late Jurassic and mid-Cretaceous intrusions result from mixing between mantle-derived melts and either anatectic melts or assimilated material from juvenile terranes (e.g., Wrangellia or S tikinia). In each of the three scenarios discussed above, the incorporation of oceanic sedimentary material cannot be ruled out. Most southern CPC rocks plot within fields established for MORB or Wrangellia on the 206pb/2o4pb vs.  208  Pb/ 204Pb diag ram (Fig.  2.4). In contrast, on the 206pb/204pb vs. 207pb/204pb diagram (Fig. 2.4) most data lie outside and above the MORB field. Generally the data are dispersed across the fields for Pacific sediments and Wrangellia. Plotted on  207 Pb/ 204 Pb  diagrams the effects of  even small amounts of contamination by oceanic sediments are discernible. This may explain the Pb isotopic character of three samples including: a Cenozoic volcanic rock, an ultramafic rock from the Cadwallader Group and a plutonic rock from the Cloudburst pluton. The Soo River intrusion, based on Nd isotopic data, appears to be derived mainly from mantle material although in Fig. 2.4 there is a suggestion that it may also have suffered some contamination by subducted oceanic sediments. 26  2.5.3 Tectonic implications  Nd, Sr and Pb isotopic varaitions against distance (Fig. 2.3) suggest an important tectonic boundary near Pemberton. It could be the west margin of the Wrangellia terrane, or the thrust belt between the Wrangellia terrane and other inner terranes in the southern Coast Belt. This study combined with previous research (e.g., Andrew et al., 1991; Andrew and Godwin, 1989a and 1989b; Samson et al., 1989; Samson et al., 1990) allows construction of an integrated, isotopically-constrained view of plutonism within the southern CPC. Igneous rocks from Wrangellia (Andrew et al., 1991; Samson et al., 1990) and Stikinia terranes (Samson et al., 1989) show a correlation between E Nd and crystallization ages (Fig. 2.6). There appears to be a decrease in E Nd values at about 185 Ma, which corresponds to the time when terranes began to accrete to the North American craton. Thus, the 185 Ma magmatism which is characterized by relatively lower initial E Nd values may reflect crustal contamination of mantle-derived magmas caused by crustal thickening by juvenile accretionary terranes. The slightly lower initial E Nd values at Eocene time may reflect the introduction of additional continental material as terranes continued to accrete onto North America. Based on the occurrence of magmatic epidote in plutons in the central portion of the southern CPC (Cui and Russell, 1993) the depth of emplacement for these plutons could be 25 to 30 km (Zen, 1985). The present crust thickness in the southern CPC is about 35 km (Iwasaki and Shimamura, 1990; Thybo, 1990). Therefore, if we ignore increases in crust due to underplating over the past 150 Ma, the crust at the time of plutonism could be very thick. Parrish (1983) suggested that the Coast Belt has been uplifted 4 km during the last 40 Ma which might suggest a total uplift over 150 Ma of 15 km. If this uplift has been isostatically compensated then the crustal thickness at 150 Ma may be close to 4045 km. 27  This thickness of crust would be capable of depressing lower crustal rocks and forcing the oceanic lithospheric mantle (above the subduction zone) into the asthenosphere thereby inducing partial melting (Fig. 2.5). Subsequent devolatilization of the underlying subducted oceanic slab and the concomitant release of fluids (Wyllie, 1982) would enhance partial melting processes. Within this scenario three different petrogenetic styles for igneous rocks from the southern CPC are recognized (Fig. 2.5). Some CPC magmas (e.g., Spetch Creek intrusion) have isotopic characteristics consistent with primary magmas derived from the mantle. Other plutons (e.g., Cypress intrusion) represent magmas derived from anatexis of juvenile terranes. Thirdly, combinations of these two processes have contributed to the majority of plutonic rocks comprising the southern CPC. The interaction between the fluids emanating from the subducted oceanic slab and the source regions may have been critical to initiating partial melting in the above scenarios. 2.6 CONCLUSIONS The southern Coast Plutonic Complex consists mainly of abundant, large granitic plutons and small volumes of volcanic rocks. The Nd, Sr and Pb isotopic studies demonstrate that the igneous rocks comprise largely juvenile, mantle-derived materials. Nd and Sr isotopic data show that any amount of old continental crust incorporated into the primitive magmas is very small ( < 6%). The Pb isotopic data suggest that any contamination affecting Pb is likely due to the incorporation of subducted oceanic sediments. This is in contrast to plutonic rocks from the northern CPC, which derive from combinations of juvenile material and old, recycled crustal material (Samson et al., 1991).  28  12  •  10 8  GL.  •  DM  0^©  Sit^::, A^ 1 A^ 00 '46 0, 0^A —•  ••  6  RA IA 0 0 ‘-'^  ■  •  4  A  8A  —  2  E  Nd 0  CHUR  -2 — Southern CPC  -4 —  o Plutonic rocks • Volcanic rocks  -6 —  Wrangellia 6. Plutonic rocks A Volcanic rocks  Stikine ^ Plutonic rocks ■ Volcanic rocks  -8 — -10 — -12 —  1.8 Ga  Proterozoic CrUst  -14 — - 16 500^400^300^200^100^0 Age (Ma)  Figure 2.6. Initial ENd vs. age for plutonic (open symbols) and volcanic (filled symbols) rocks from the southern CPC, Wrangellia terrane and Stikinia terranes. Data sources for Wrangellia and Stikinia terranes are from Samson et al. (1989, 1990) and Andrew et al. (1991). Also shown is the depleted mantle curve of DePaolo (1981).  29  Along the 180 km SW-NE transect across the southern CPC, Nd, Sr and Pb isotopic data show no evident systematic correlation with rock type. The only variation between isotopic data and radiometric ages of igneous rocks is in  208Pb/204 Pb  ratios of  volcanic rocks that show a slight rise with decreasing age. It appears that, during the 180 Ma of magmatism which characterizes the southern CPC, the source regions had similar Pb isotopic ratios although the extent to which oceanic sediments were involved in CPC magmatism may have risen slightly with time. The isotopic data examined against transect distance are also uniform except for a rise in the initial 87 Sr/ 86 Sr ratios of volcanic rocks from the NE end of the transect. An isotopically-constrained view of the plutonism within the southern CPC for the last 180 Ma is present. In this scenario, the North American craton acted as a barrier to further eastward transport as terranes were accreted. Further accretion of terranes, therefore, caused the stacking and thickening of crustal rocks. This thickening was responsible for inducing partial melting of lithospheric mantle or anatexis of crustal rocks.  30  3. PETROGENESIS OF CALC-ALKALINE PLUTONIC ROCKS 3.1. INTRODUCTION  Concentrations of major, trace and rare earth elements were measured by X-ray fluorescence spectrometry (XRF) for plutonic and volcanic rocks collected along the 180 km transect across the southern Coast Plutonic Complex from Vancouver to Anderson Lake (Fig. 3.1 and Table 3.1). Rare earth elements (REE) were also analyzed on representative sample within this suite of igneous rocks by ICP-MS. These analytical data are used to characterize the nature of this suite of plutonic rocks and to constrain their origins.  3.2 GEOLOGY AND PETROLOGY OF PLUTONIC ROCKS  Samples from a series of intrusions were collected along a 180 km transect from Vancouver to Anderson Lake (Fig. 3.1), spanning the entire southern Coast Plutonic Complex. Many of the intrusions making up the CPC are neither well-divided nor named consistently. Based on recent U-Pb zircon dating (Table 3.1) of Friedman and Armstrong (1993), Parrish and Monger (1992) and several early measured K-Ar hornblende ages, plutonic rocks along the transect are grouped into four age series (Table 3.1): Late Jurassic (153-145 Ma), Early Cretaceous (128-113 Ma), mid-Cretaceous (103101 Ma) and Early Cretaceous (86-64). Compositionally, the plutonic suites range from leucocratic granite to hornblende gabbro (LeMaitre, 1989). Primary minerals consist of plagioclase (P1) + biotite (Bt) + hornblende (Hbl) + quartz (Qtz) + zircon (Zrn) + apatite (Ap) K-feldspar (Kfs) titanite (Ttn) epidote (Ep) + Fe-Ti oxides (mineral abbreviations after Kretz, 1983). Visually estimated mineral modes are listed in Table 3.2.  31  1 20' w  MORPHOGEOLOGIC MAP VaR Ak\F_S VikAVAIM  \ CAD% tAIMAR ,isws,c3cst.  C..AC1r\E_ CREEK MIN AU S1.\1\CSAN \AMMON 49'N^Nk\F\011 ^ v\\C\k" Southern Coast +J Plutonic Complex (CPC)  -'Pemberio ++  + *9024A + + + 4  +  + + + + + + + + + + + + ++ +. +.+ + ++  Cenozoic sediments AA AAA A AAA A A  AAAAA AAAAAt AAAnn  901^ 9011  .  381? +, A,,  AAA A A A  ovum A  .009 -, A A '9006^AAA', 90 9 7 AAAAAAAA  Cenozoic volcanic rocks Tertiary plutons  + + + +  Late Cretaceous plutons Mid—Cretaceous plutons  AA AA  •  T  + +++ . -L^_L  Early Cretaceous plutons Later Jurassic plutons Gambier Assemblage  +  + +  + +.+ ++ ++  Bowen Island Group +  Cayoosh Assemblage •:  Cadwallader Group Bridge River Group Bralorne—East Liza Complex Chism Creek Schist  101111WWWWIMAI 1 ,140.11.11  Undivided gneiss and metamorphic rocks  Fig. 3.1. Generalized terrane map and geological map of the southern Coast Belt (after Wheeler and McFeely, 1991; Journeay, 1990; Journeay and Northcote, 1992; Journeay and others, 1992; Monger and Journeay, 1992) showing sample locations (90x x) and individual igneous bodies: 1-Cypress intrusion; 2-Sechelt pluton; 3-East Sechelt pluton; 4-Newman Creek intrusion; 5-Porteau pluton, 6-Squamish pluton; 7-Ashlu Creek intrusion; 8-Cloudburst pluton; 9-Whistler intrusion; 10-Callaghan Creek intrusion; 11-Soo River intrusion; 12-Pemberton Diorite Complex; 13-Spetch Creek pluton; 14-Mt. Rohr pluton; 15-Bendor intrusions. 32  TABLE 3.1. SAMPLE LOCATIONS FOR PLUTONIC AND VOLCANIC ROCKS FROM THE SOUTHERN COAST PLUTONIC COMPLEX Rock Unit (abbreviation)  Age (Ma)  Label  Latitude  Longitude  Rock Type  Plutonic rocks  Early Permian suite Late Jurassic suite  Bralorne Complex (BR)  284 ± 20 (K-Ar, Hbl)•  9038  50°33.72'  122 °29.38'  Diorite  Sechelt pluton (SE)  153 ± 3 (U-Pb)b  SE-19A* 49 °25.25' SE-19*  123 ° 14.00'  Aplite Granodiorite  Cloudburst pluton (CB)  147 ± 0.5 (U-Pb) b  9006 9007 9010 9011 9011A 9012  49°49.26' 49°49.26' 49°49.26' 49°51.60' 49 °51.60' 49°51.60'  123'7.70' 123 ° 7.70' 123 °7.70' 123 °9.23' 123 °9.23' 123 °9.23'  Aplite Qtz diorite Tonalite Tonalite Granodiorite Mafic dike  Ashlu Creek intrusion (AC)  145 + 12/ -3 (U-Pb)°  9013 9014 9014A 9015 9016 9017  49°52.60' 49°54.70' 49 °54.70' 49°54.70' 49°54.70' 49°54.65'  123 ° 13.60' 123 ° 18.90' 123 ° 18.90' 123 ° 18.90' 123 ° 18.90' 123 ° 17.35'  Qtz diorite Qtz diorite Qtz diorite Tonalite Hbl diorite Hbl diorite  <147  Whistler intrusion (WH)  151 ± 2 (U-Pb)°  9021  50°5.60'  123°0.80'  Diorite  Soo River intrusion (SR)  151 ± 2 (U-Pb)°  9022 9022A 9023  50°13.40' 50 ° 13.40' 50°13.40'  122 °52.70' 122 °52.70' 122 °52.70'  Diorite Diorite Diorite  125 + 5/ - 7 (U-Pb)°  9001  49°21.50'  123 ° 12.80'  Granodiorite  Newman Creek intrusion (NC)  119 ± 8 (K-Ar) d  9002  49°25.25'  123 ° 14.00'  Hbl gabbro  Callaghan Creek intrusion (CA)  128 ± 8 (K-Ar, Hbl)°  9020  50°6.75'  123 °7.00'  Hbl diorite  Pemberton Diorite Complex (PD)  113 ± 2 (U-Pb) b  9024A  50 ° 13.40'  122 °52.70'  Hbl diorite  Squamish pluton (SQ)  101 ± 2 (U-Pb) f  49°41.30' 49°41.30'  123 °8.73' 123 °8.73'  Spetch Creek pluton (SC)  103 + 5/ - 3 (U-Pb)°  9004 9005 S-12* S-10A* 9031 9032  50°23.10' 50°25.70'  122 °41.90' 122 °41.70'  Leuco-granite Aplite Granodiorite Aplite Tonalite Tonalite  Mt. Rohr pluton (RO)  86 + 2 / - 2 (U-Pb)° 64 + 11/ - 2 (U-Pb)°  49°25.25' 50°39.35'  123 ° 14.25' 122 °24.85'  Early Cretaceous suite Cypress intrusion (CP)  Mid Cretaceous suite -  Late Cretaceous suite  Bendor intrusions (BD)  R-5* 9040 B-1* B-8*  Diorite Qtz diorite Diorite Tonalite  33  TABLE 3.1 (Continued)  Volcanic rocks Cadwallader Group (CD)  Cayoosh Assemblage (CY) Gambier Assemblage (GB)  Cenozoic volcanic rocks (CV)  Late Triassicg  9028 9029 9030 9033 9034 9035 9036 9037 9039 Middle Jurassic' Early Cretaceous' 9003 9018 9019 9024 9025 9026 9027 Late Tertiary to Quaternaryi 9008 9009  50°22.16' 50°22.16' 50°22.16' 50°27.58' 50°32.91' 50°33.03' 50°32.62' 50°32.62' 50°37.97' 49°25.25' 50°10.90' 50°8.5' 49°49.26' 50°17.72' 50°17.82' 50°17.87'  122°43.13' 122 °43.13' 122 °43.13' 122 °38.54' 122 °33.13' 122 °31.42' 122 °29.38' 122°29.38' 122 °26.35' 12.3 ° 14.25' 123 °9.90' 123°7.75' 123 ° 7.70' 122 °41.40' 122 °41.90' 122°42.40'  Andesitic tuff Andesite Andesitic tuff Andesite Quartzite Andesite Semischist Ultramafic rock h Andesitic tuffite Tuff Tuff Tuff Tuff Tuff Tuff Tuff  49°49.26' 49°49.26'  123 °7.70' 123 °7.70'  Tuff Tuff  Note: Numerical ages are radiometric ages. Method of determination is given in parentheses. Hbl denotes hornblende. Samples from Michael and Russell (1989). a Leitch (1989). b Friedman and Armstrong (1993). Parrish and Monger (1992). d Caron (1974). e Miller (1979). f Armstrong and Shore, The University of British Columbia unpublished data. g Church et al. (1988) and Rusmore (1985). h Early Permian (Leitch, 1989). i Monger and Journeay (1992). Green et aL (1988).  34  Magmatic epidote occurs in most intrusive bodies but is more abundant in plutons in the central part of the southern Coast Belt. Based on petrography, including description from Michael and Russell (1989), the southern CPC plutonic rocks are grouped into two compositional suites: one suite of intrusions tends to be more mafic (ranging in composition from tonalite to gabbro) and another suite of intrusions is more felsic (ranging in composition from leucocratic granite to tonalite). The more mafic suite includes most intrusions in the southern CPC, including the Cloudburst, Newman Creek, Soo River, Whistler, Callaghan, Pemberton, Spetch Creek, Mt. Rohr, Bendor and some rocks from Ashlu Creek. This suite comprises tonalite, quartz diorite, diorite and gabbro. The primary mineralogy for this suite always contains PI + Hbl + Bt + Qtz + Zrn + Ap and commonly contains Ttn + Fe-Ti oxides ± Ep. Texture suggests an approximate crystallization sequence of Hbl > PI > Ep > Ttn > Bt > Ap > FeTi oxides followed by Qtz. This suite of plutons is further distinctive in that they contain virtually no K-feldspar (Kfs) and any that is present is very late in the crystallization sequence. The more felsic suite includes the Sechelt, Squamish and Cypress intrusions and some phases of the Ashlu Creek intrusion. This suite comprises granite, granodiorite and tonalite. The primary mineralogy for this suite always contains PI + Bt + Qtz + Kfs Hbl + Zrn + Ap and commonly contain Ttn + Fe-Ti oxides ± Ep. Texture suggests an approximate crystallization sequence of P1 > Ep > Ttn > Bt > Ap > Fe-Ti oxides followed by Qtz and Kfs. K-feldspar is an important phase whereas hornblende is rare in this suite.  3.3 ANALYTICAL METHODS  Fresh whole-rock samples, approximately 3-4 kg, were cut to roughly 3 cm rock chips with a hydraulic splitter. Weathered surfaces were removed. Rock chips were further  35  TABLE 3.2. PRIMARY MINERALOGY (VOLUME PERCENT) OF PLUTONIC ROCKS FROM THE SOUTHERN COAST PLUTONIC COMPLEX Suite  Pluton  Sample  PI  Hbl  Bt  Qtz  Kfs  Ttn  Ep  Ap  Late Jurassic  Cloudburst  9006 9007 9010 9011 9011A 9013 9014 9014A 9015 9016 9017 9021 9022 9022A 9023 9001 9002 9020 9024A 9004 9005 9031 9032 9040  25 72 60 65 65 70 68 75 60 68 72 75 75 75 75 60 65 70 65 22 tr 60 70 70  5  tr 9 15 8 5 8 11 15 10 5 5 10 10 2 5 4 5 5 5 3 tr 2 5 5  65 18 25 20 20 20 18 8 23 4 5 15 15 15 10 20 2 5 5 50 75 28 20 18  20 tr tr  1 tr tr tr tr tr tr tr tr tr tr tr tr tr  tr tr 2 tr tr tr tr tr tr tr tr tr tr tr  tr tr 1  tr tr 1  tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr  Ashlu Creek  Whistler Soo River  Early Cretaceous  Mid Cretaceous -  Cypress Newman Creek Callaghan Pemberton Squamish Spetch Creek  Late Cretaceous  Bendor  Mineral abbreviations is after Kretz (1983) tr: volume of mineral < 1 %.  2 2 2 2 23 18 8 10 6 28 20 25  10 5 2  10 1 5 tr tr -  10 25 25 tr 3  tr tr tr tr  Fe-Ti oxides tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr tr  reduced to <0.5 cm chips in a steel-faced jaw crusher and then taken through a sample splitter with multiple passes. Half of each sample was powdered to about 100 mesh by a tungsten carbide shatter box and then finely ground to about 200 mesh in a motor-driven mortar. Major elements were measured on ground fused glass pellets by a Philips PW1410 XRF in the Department of Geological Sciences at The University of British Columbia (UBC). Trace elements were performed on pressed powder pellets by a Philips PW-1400 XRF in the Department of Oceanography, UBC. For major and trace elements, analytical uncertainties are estimated by duplicate analyses performed on randomly chosen rock samples within these plutonic and volcanic rocks from the southern Coast Belt. Rare earth elements (REE) were measure by an Elan-5000 inductively coupled plasma mass spectrometer (ICP-MS) in the Department of Geological Sciences at the University of Saskatchewan, following the procedure described by Jenner et al. (1990). Precision is better than ± 5 % for all REE, according to replicates.  3.4 GEOCHEMICAL CHARACTERISTICS  Major element data from this study are reported in Table 3.3 and Table 3.4. All plutonic rocks plot in the subalkaline field (Fig. 3.2). Plotted on an AFM diagram (Fig. 3.3) the southern CPC plutonic rocks are strongly calc-alkaline (Fig. 3.4). Plotted on Harker diagrams (Fig. 3.4), CaO, MgO, FeO (T), Al 2 0 3 , TiO 2 and P 2 0 5 show continuous and negative correlation with Si0 2 , except for the Newman Creek hornblende gabbro and the Bralorne diorite. However, K 2 0 shows positive correlation with Si0 2 . Na2 0 is scattered, correlating poorly with Si0 2 . Compositions reflect the rock types and do not separate plutons or vary systematically with age or geographic position. However, the Al 2 0 3 content of volcanic rocks decreases from west to east and increases from 300 Ma to present. 37  TABLE 3.3. Major (wt %) and trace element composition of plutonic rocks from southern Coast Plutonic Complex measured by XRF with calculated normative mineralogy Pluton body Sample No.  SiO 2 TiO 2 Al 20 3 Fe2 O 3 FeO MnO MgO CaO Na2 O K2 O P 2O5 Total LOI  CP 9001  NC 9002  9004  9005  9006  9007  CB 9010  62.88 0.40 18.57  47.17 0.16 19.96 4.42 0.11 9.90 17.62 0.69 0.03 0.19 100.26 1.59  73.54 0.17 13.96 2.39 0.05 0.62 1.49 5.27 2.78 0.04 100.20 0.00  75.42 0.05 12.90 1.85 0.02 0.57 0.70 5.35 3.54 0.02 100.41 0.00  70.23 0.05 12.94 1.83 0.03 0.59 6.11 5.43 3.40 0.02 100.63 0.05  64.49 0.41 17.56 3.14 0.09 1.59 3.79 7.92 0.92 0.20 100.10 0.14  63.79 0.58 17.59 0.49 2.89 0.12 1.91 3.86 6.72 1.05 0.21 99.20 0.56  67.10 0.49 16.05 1.30 1.16 0.07 1.64 3.23 7.46 1.32 0.06 99.87 0.43  64.80 0.45 16.04 0.05 4.26 0.13 1.62 3.23 7.44 1.33 0.24 99.58 0.72  8.99  11.29  6.22  6.26 57.31 14.86 2.52  7.81 63.19 6.43 7.25  7.89 63.21 6.48 6.78  1.07  0.78 0.47  7.75 0.72 1.11 0.50  1.89 0.93 0.14  7.93 0.07 0.86 0.57  5 73 5 878 14 8 48 6 9 49 32 917  4 87 5 800 18 7 64 6 11 61 16 973  5 78 7 783 23 7 63 14 14 92 38 857  4 66 3 574 14 12 31 2 10 3 73 925  4.15 0.10 2.09 3.71 5.00 2.46 0.15 99.51 0.05  SQ  9011A  9011  CIPW normative mineralogy Qtz Cor Or Ab An Di Wo Hy 01 Mt Il Ap  10.54 1.30 14.61 42.51 17.51 12.41 0.76 0.36  0.18 5.82 51.15 27.88 1.31 12.91  26.44 16.38 44.45 6.21 0.77 5.33 -  0.30 0.45  0.32 0.09  27.38 20.84 45.08 0.73 2.21 3.62 0.09 0.05  16.42 19.97 45.65 0.89 9.38 7.55  4.27 5.43 66.94 9.64 6.54 5.93  0.09 0.05  Trace elements (ppm) Nb Zr Y Sr Rb Pb Zn Ni Co V Cr Ba  7 94 12 393 45 8 38 10 11 79 32 860  4 16 3 63 4 7 24 163 29 119 801 66  5 80 17 127 69 10 13 5 6 9 20 1055  8 73 45 9 100 16 6 15 4 <3 20 81  8 47 8 132 46 21 10 5 7 10 72 946  38  TABLE 3.3 (Continued) Pluton Sample No.  SiO 2 TiO2 Al 2 05 Fe2O3 FeO MnO MgO CaO Na2O 1(20 P2 O5 Total IADI  AC 9013  9014A^9014  9015  9016  9017  63.00 0.38 17.63 0.42 3.53 0.12 2.36 4.49 6.79 0.78 0.20 99.71 0.53  63.57^63.37 0.35^0.76 17.09^17.09 0.41^4.11^4.46 0.13^0.10 2.00^2.00 3.92^3.92 6.64^6.65 1.14^1.15 0.20^0.19 99.57^99.70 0.77^0.19  64.79 0.59 16.24  53.21 1.30 18.38 0.54 8.23 0.19 4.92 7.22 4.56 0.98 0.22 99.77 1.43  56.90 0.65 19.34 0.39 5.24 0.16 4.24 6.73 5.23 0.84 0.24 99.96 0.45  CIPW Qtz Or Ab An Di Hy 01 Mt II Ap  6.57 4.62 57.62 15.38 4.68 9.33 -  0.61 0.72 0.48  -  4.43 0.09 1.74 3.07 6.46 1.55 0.16 99.11 0.00  54.34 0.90 18.97 1.09 6.53 0.15 4.67 6.95 5.17 0.78 0.35 100.64 1.50  WH 9021  64.00 0.47 16.71  -  4.62 0.15 2.56 3.57 6.38 1.25 0.20 99.92 2.54  normative mineralogy  7.68^7.26 6.77^6.82 56.43^56.44 13.53^13.43 3.93^4.04 9.94^10.11  10.06 9.24 55.14 10.84 2.92 10.29  -  -  0.60^0.67^1.45 0.48^0.45  -  -^  CA 9020  1.13 0.38  -  5.81 38.68 26.86 6.30 8.80 9.78 0.78 2.47 0.52  0.40 4.97 44.27 26.83 4.11 17.07 0.57 1.23 0.57  4.55 43.15 25.90 4.82 13.91 3.62 1.56 1.69 0.82  4 61 11 811 15 6 76 19 19 192 45 487  4 92 10 964 15 9 103 26 30 191 49 598  -  8.25 7.39 54.03 13.28 2.61 13.07  -  0.89 0.47  Trace elements (ppm) Nb Zr Y Sr Rb Pb Zn Ni Co V Cr Ba  6 70 9 767 13 9 57 11 13 81 31 706  5^4 190^247 26^25 511^392 39^40 4^7 62^54 11^13 16^13 62^97 60^36 773^890  3 224 17 323 49 7 43 9 9 69 33 900  3 86 20 380 24 9 91 22 37 265 40 358  7 112 12 494 30 12 80 8 10 103 27 1170  39  TABLE 3.3 (Continued) Pluton Sample No.  Si0 2 Ti02  Al 20 3 Fe2 03 Fe0 Mn0 Mg0 Ca0 Nap  1( 20  P2 0 5 Total LOI  9022A  57.83 0.39 18.04 1.31 3.74 0.09 4.55 7.70 5.60 0.35 0.17 99.78 0.54  SR 9022  9023  57.76 0.46 18.06  56.43 0.79 18.66  5.11 0.23 4.55 7.71 5.56 0.35 0.30 100.08 0.07  6.46 0.15 3.95 6.68 4.96 1.01 0.26 99.34 0.24  PB 9024A  55.59 0.69 19.47 0.99 5.12 0.13 4.37 5.51 5.73 0.97 0.23 98.70 0.50  SC 9031  67.99 0.50 16.51 4.54 0.13 2.43 4.17 2.21 1.28 0.14 99.90 0.27  9032  66.25 0.62 17.19 0.39 4.14 0.13 2.65 4.01 2.78 1.56 0.28 100.00 0.27  BR 038  BD Analytical 9040 Error (la)  47.38 0.17 18.88  65.88 0.49 16.84  4.52 0.10 10.31 16.46 0.99 0.04 0.22 99.08 0.91  3.29 0.07 1.67 3.04 7.00 1.22 0.19 99.69 0.28  10.25  0.18 0.01 0.09 0.02 0.08 0.02 0.33 0.09 0.18 0.10 0.03  CIPW normative mineralogy Qtz Cor Or Ab An Di Hy 01 Mt II Ap  1.73 2.07 47.49 23.11 11.37 11.18 1.90 0.74 0.40  0.31 2.07 47.00 23.27 10.66 15.12 0.87 0.71  0.56 6.01 42.24 25.84 4.82 18.41 1.51 0.62  6.97 50.34 23.39 2.18 3.42 10.40 1.45 1.32 0.55  13.82  29.40 4.31 9.22 23.52 18.07 13.10  0.95 0.33  0.57 1.18 0.66  0.24 8.45 47.40 26.88 3.06 13.13 0.33 0.53  5 96 7 568 43 9 53 22 14 102 66 699  3 20 5 172 3 6 24 142 34 125 678 76  34.58 4.25 7.57 18.72 19.79  7.23 59.41 10.97 2.43 8.33 0.93 0.45  Trace elements (ppm) Nb Zr Y Sr Rb Pb Zn Ni Co V Cr Ba  6 110 9 669 8 6 25 10 8 83 26 880  4 62 12 659 3 10 67 77 29 258 276 104  5 96 16 548 16 6 51 22 29 231 54 692  3 59 12 600 10 8 47 31 21 239 66 408  2 109 17 253 25 5 99 17 13 123 40 499  4 96 6 625 32 11 63 5 9 57 32 572  Major elements were measured with a Philips PW-1400 XRF Spectrometer on ground fused glass pellets. Trace elements were measured by a Philips PW-1410 XRF Spectrometer on pressed powder pellets. FeO was determined volumetrically. Precision estimates are calculated according to Thompson (1978) and Thompson and Howarth (1973, 1976 and 1977) based on duplicate measurements on samples.  40  TABLE 3.4. Major (wt. %) and trace element composition of volcanic rocks from southern Coast Plutonic Complex measured by XRF Volcanic unit Sample No.  Si0 2 TiO2 Al 2 0, Fe2O 3 FeO MnO MgO CaO Nap KO P 2 0, Total LOI  CV 9008  9009  48.60 1.26 19.21 2.62 13.00 0.23 4.38 5.36 4.60 1.26 0.35 100.87 1.50  51.15 0.83 21.45 0.16 6.17 0.18 5.14 9.25 4.75 0.41 0.38 99.87 2.14  CB 9012  48.72 2.02 17.65 2.47 7.53 0.25 4.71 7.12 7.93 0.98 0.55 99.92 2.75  9003  54.18 1.00 21.39 5.64 0.14 3.82 6.77 6.19 0.44 0.29 99.88 2.26  9018  52.81 1.13 20.05 2.95 5.87 0.20 5.65 8.16 2.33 0.79 0.30 100.24 2.79  GB 9019 9025  62.84 0.68 18.26 5.57 0.13 3.75 1.96 4.14 2.35 0.11 99.78 1.61  9026  9027  9.16 0.10 4.20 4.37 4.32 1.61 0.24 99.76 2.36  56.20 0.80 17.46 8.38 0.15 4.95 5.45 5.78 0.08 0.22 99.46 2.38  48.76 0.90 19.80 9.84 0.11 6.00 13.30 0.47 0.08 0.30 99.56 5.84  3 101 17 493 22 10 80 51 34 24 162 88 1109  4 89 14 530 4 8 82 54 28 24 207 84 166  3 60 10 1105 3 9 84 158 30 45 295 46 76  55.16 0.68 19.92  Trace elements (ppm) Nb Zr Y Sr Rb Pb Zn Cu Ni Co V Cr Ba  6 95 17 648 16 6 208 47 29 19 296 88 962  5 65 12 804 5 9 90 30 22 33 229 39 381  9 151 27 449 21 10 113 36 23 25 270 67 354  7 89 17 832 8 9 72 240 25 21 214 69 466  4 125 26 299 16 19 141 85 56 36 216 39 214  4 78 12 363 55 5 74 85 29 17 165 108 1373  41  TABLE 3.4 (Continued) Volcanic unit Sample No.  SiO2 TiO 2 Al 2 02 Fe2 O3 FeO MnO MgO CaO Na2O  K2 O  P2O5  Total LOI  9028  9029  9030  9033  CD 9034  50.03 1.29 16.01 0.16 14.49 0.20 5.19 4.55 7.19 0.09 0.24 99.43 0.43  50.35 0.67 20.84  56.01 0.81 17.17  67.91 0.50 13.75  90.92 0.13 4.79  8.31 0.16 4.78 7.83 5.56 0.86 0.20 99.55 0.85  13.05 0.17 3.77 5.58 2.59 1.15 0.19 100.48 0.00  5.04 0.08 1.39 1.61 8.67 0.40 0.12 99.47 0.05  2.58 0.02 1.14 0.43 0.56 0.54 0.02 101.11 0.69  9035  9036  9037  CY 9039  51.86 1.56 17.94 0.36 9.61 0.15 5.97 7.73 4.16 0.63 0.27 100.23 7.91  63.30 0.51 15.82 2.40 4.50 0.12 2.08 3.20 5.98 1.37 0.16 99.44 3.27  44.39 0.03 1.33 8.50 3.81 0.18 41.07 0.43 0.49 0.02 0.01 100.24 12.95  62.43 0.81 16.21 0.15 6.13 0.13 2.89 1.12 8.31 0.67 0.13 98.97 2.00  4 92 10 403 39 14 61 64 35 18 94 142 489  3 10 <2 8 <2 <3 29 157 2418 124 30 3140 66  5 102 12 243 21 10 74 21 23 17 159 64 369  Trace elements (ppm) Nb Zr Y Sr Rb Pb Zn Cu Ni Co V Cr Ba  5 88 26 141 2 7 93 100 27 45 258 100 52  4 48 10 242 22 10 67 78 39 31 261 105 307  2 79 22 241 19 10 78 85 31 32 274 111 288  10 148 31 444 16 9 109 33 20 23 271 64 338  3 28 2 21 21 5 24 7 6 7 17 32 490  6 93 24 148 18 11 98 78 103 42 272 356 408  42  16 Permian Bralorne diorite  14 - 0 12 10  Late Jurassic Early Cretaceous  O A  Mid-Cretaceous  Alkaline  Late Cretaceous  GZD^0^0  A 0^  8  —  Subalkaline  co 0  6  a^  4 2 0  1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1^1  45^50^55^60^65 Si02( Wt  ^  70  ^  75  ^  %)  Fig. 3.2. Na2 0 + K2 0 vs. Si0 2 diagram (Irvine and Barager, 1971). All plutonic rocks plot as subalkaline.  43  80  FeO*  Tholeiitic  0  ?al 00  Calc-Alkaline  Na20 + K20  MgO  Fig. 3.3. AFM diagram for plutonic rocks. Symbols are shown as in Fig. 3.2.  44  20  _ +o  1.5  16 ^Ti02 Ca0  ^0  12  1 .0  8  0  00^(3D 0 0  4  0  •  00 A0 0  0 ^0  45  50  55  60  65  70  0. 0  0  75  80  12  0  0  0.5  8  00 0 PO "'00  ^ 0  ^10  45^50^55^60^65^70^75^80  12  10  10  Mg0  8  8  6 00  4 2  6 00 6)  '6 'o,,®^ a A0  4  0  2  - ,,  P  0  0  0  45^50^55^60^65^70^75^80^45^50^55^60^65^70^75^ 10  6  1 0  8  Fe0(T) 4  6 . e 1. 0 0 0  et  4  2  °O 0  2  0  0  0  0  0  45^50  55^60^65^70^75^80^45^50^55^60^65^70^75  22 20 18 16  80  80  0.4 -  +  0  Al2 0 3  ^  0  0.3  ^ 0 0^^ 0 OCO 0 ,D A  0.2  6 o°  14  0^—  0  12  ^  - ^  0  0 ^ 0^0  v11.  0^0 0  0.1 0  0  45^50^55^60^65^70^75^80 Si02  P205 0  p^i0  0.0  45^50^55^60^65^70^75^80 Si02  Fig. 3.4. Harker variation diagrams of oxides for plutonic rocks from the southern Coast Plutonic Complex. Symbols are shown as in Fig. 3.2.  45  Rare earth element data are listed in Table 3.5 for plutonic rocks and in Table 3.6 for volcanic rocks. Corresponding chondrite normalized REE discrimination patterns are plotted on Figures 3.5, 3.6 and 3.7 for plutonic rocks and Figure 3.8 for volcanic rocks. On the REE discrimination diagrams, REE data are normalized by using chondrite REE values from Boynton (1984). In Table 3.5 and 3.6, FREE, La N/SmN, LaN/Yb N and Eu/Eu* are as defined by Taylor and McLennan (1985). The shaded field on Figure 3.5 and 3.6 is the REE pattern for typical intermediate volcanic rocks from Late Triassic Cadwallader group and Middle Jurassic Cayoosh Assemblage (data from Table 3.6, shown on Fig. 3.7). This field is plotted as reference to show the similarities and differences between plutonic rocks and representative volcanic rocks. Plutonic rocks of the Late Jurassic suite (Cloudburst, Ashlu Creek, Sechelt and Soo River) have similar REE patterns, with slightly enriched LREE, less enriched HREE and no Eu anomaly (Figure 3.5). Among these intrusions, tonalite and diorite show negative LREE fractionation and very little variation in HREE while granodiorites have greater fractionation between LREE and HREE. In the Cloudburst body, granodiorite and aplite show positive HREE fractionation (Fig. 3.5a). Among different rock types, granodiorite shows the highest fractionation within LREE (LaN/SmN = 6.51) and between LREE and HREE (La N/Yb N = 25.36). The fractionation is caused by relative enrichment of LREE and depletion of HREE in the granodiorite. The Ashlu Creek intrusion contains the most primitive plutonic rocks. Hornblende diorite shows almost the same REE pattern as the volcanic rocks (Fig. 3.5b). Quartz diorite is more enriched in REE (ZREE = 62.10 ppm) than its tonalite and hornblende diorite varieties. Quartz diorite also shows a negative Eu anomaly (8Eu = 0.78). Tonalite has a more fractionated REE pattern (LaN/YbN = 8.54) which is probably caused by depletion of the HREE. The Sechelt pluton is more felsic in composition. The analyzed granodiorite from this pluton shows a pronounced REE fractionation between LREE and HREE (La N/YbN = 14.18; Fig. 3.5c).  46  TABLE 3.5. Rare earth element compositions (ppm) of plutonic rocks from the southern Coast Plutonic Complex measured at the University of Saskatchewan with an Elan-5000 ICP-MS. CP 9001  NC 9002  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  14.17 27.69 3.23 12.88 2.34 0.70 2.25 0.30 1.88 0.40 1.29 0.22 1.43 0.21  0.30 0.92 0.168 1.19 0.43 0.27 0.69 0.125 0.85 0.173 0.50 0.076 0.40 0.068  EREE 8Eu SCe  68.99 0.92 0.95 6.68 3.81  6.17 1.53 0.97 0.50 0.44  Pluton Sample No.  LaN/YbN LaN/SmN  CB  SQ 9005  S-10A  S-12  14.76 28.62 3.30 12.51 2.47 0.34 2.40 0.38 2.74 0.57 1.80 0.31 2.25 0.35  11.44 27.75 3.53 13.89 4.00 0.038 4.67 0.89 6.78 1.50 4.97 0.86 6.22 1.01  31.23 63.94 7.37 26.79 4.76 0.23 4.63 0.75 5.47 1.20 4.07 0.70 5.09 0.82  13.68 27.25 3.25 12.90 2.60 0.53 2.60 0.42 3.04 0.65 2.08 0.34 2.46 0.40  72.81 0.42 0.95 4.42 3.75  87.53 0.027 1.04 1.24 1.80  57.06 0.15 0.98 4.14 4.13  72.19 0.62 0.95 3.75 3.30  9004  9007  9011  5.58 14.31 1.97 8.41 1.70 0.44 1.41 0.20 1.29 0.26 0.91 0.19 1.56 0.27  9.48 22.37 3.17 13.82 2.54 0.77 2.12 0.22 1.21 0.24 0.62 0.090 0.62 0.080  10.01 21.15 2.84 12.50 2.38 0.80 1.97 0.26 1.67 0.35 1.01 0.166 1.10 0.167  18.65 34.34 3.86 13.64 1.80 0.58 1.11 0.122 0.73 0.141 0.40 0.071 0.50 0.092  38.50 0.84 1.04 2.42 2.06  57.35 0.99 0.98 10.31 2.35  56.37 1.10 0.94 6.13 2.64  76.02 1.16 0.93 25.36 6.51  9006  9011A  TABLE 3.5 (Continued) Pluton Sample No.  SE SE-19 SE-19A  9013  AC 9014  9016  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  12.12 23.28 2.79 11.53 2.03 0.67 1.81 0.23 1.54 0.31 0.95 0.148 0.96 0.144  14.09 32.34 4.43 20.68 4.84 1.26 5.01 0.73 4.81 0.93 2.72 0.39 2.51 0.35  9.46 20.55 2.71 12.52 3.03 1.05 3.27 0.52 3.51 0.71 2.07 0.30 2.08 0.32  8.71 17.45 2.09 8.21 1.32 0.37 1.02 0.123 0.74 0.129 0.33 0.047 0.41 0.060  EREE 5Eu 5Ce  58.512 1.05 0.93 8.54 3.76  95.11 0.78 0.98 3.78 1.83  62.10 1.10 0.97 3.06 1.96  41.01 0.93 0.96 14.18 4.15  LaN/YbN LaN/SmN  4.98 6.68 0.51 1.41 0.21 0.097 0.171 0.022 0.140 0.030 0.128 0.019 0.24 0.064 14.70 1.52 0.82 13.75 14.97  CA 9020  SR 9022A  12.42 28.63 3.96 17.81 3.56 1.06 2.98 0.39 2.42 0.47 1.39 0.196 1.27 0.198  14.40 27.33 3.16 12.51 2.42 0.72 2.12 0.30 2.06 0.42 1.34 0.21 1.46 0.24  76.76 0.97 0.98 6.60 2.19  68.67 0.95 0.94 6.67 3.75  SP 9032  BR 9038  6.41 14.22 2.01 9.83 2.32 0.76 2.29 0.36 2.39 0.48 1.49 0.23 1.49 0.21  10.65 21.57 2.80 11.66 2.37 0.70 2.07 0.28 1.70 0.31 0.95 0.147 0.90 0.143  0.30 0.87 0.170 1.10 0.42 0.190 0.65 0.121 0.86 0.189 0.49 0.079 0.48 0.071  44.49 1.00 0.95 2.91 1.74  56.25 0.95 0.93 8.01 2.82  5.98 1.11 0.91 0.42 0.45  PD 9024A  47  TABLE 3.5 (Continued) Pluton Sample No.  RO R-5  9040  BD B-1  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  8.92 19.81 2.72 12.08 2.73 0.76 2.66 0.37 2.34 0.46 1.35 0.19 1.29 0.21  9.92 21.58 2.91 12.59 2.69 0.79 2.15 0.26 1.40 0.24 0.58 0.089 0.57 0.080  13.69 28.16 3.79 17.38 3.74 1.11 3.49 0.50 2.98 0.53 1.66 0.21 1.31 0.22  12.36 25.42 3.37 14.66 3.00 0.90 2.68 0.37 2.24 0.42 1.15 0.170 1.08 0.174  EREE 8Eu 6Ce  55.90 0.86 0.96 4.67 2.05  55.82 0.97 0.96 11.76 2.32  78.77 0.93 0.93 7.05 2.30  67.99 0.96 0.93 7.71 2.59  LaN/YbN LaN/SmN  B-8  48  TABLE 3.6. Rare earth element compositions (ppm) of volcanic rocks from the southern Coast Plutonic Complex measured at the University of Saskatchewan with an Elan-5000 ICP-MS. Rock unit Sample No.  003  GB 9003*  9003*  CV 9009  CB 9012  CD 9030  9037  CY 9039  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  8.59 19.29 2.68 12.92 3.00 1.05 3.21 0.46 3.01 0.60 1.77 0.27 1.80 0.27  8.66 19.13 2.67 12.84 3.09 1.09 3.23 0.48 3.16 0.62 1.85 0.29 1.93 0.29  8.66 19.07 2.78 12.93 3.15 1.02 3.13 0.47 3.18 0.62 1.81 0.27 1.98 0.27  7.82 18.29 2.70 13.29 3.15 1.03 3.05 0.41 2.67 0.53 1.53 0.24 1.45 0.23  11.85 29.42 4.29 21.20 5.43 1.85 5.95 0.88 5.93 1.20 3.48 0.50 3.44 0.51  5.96 14.18 2.09 10.62 2.77 0.84 3.43 0.53 3.77 0.78 2.43 0.38 2.43 0.36  0.21 0.29 0.027 0.094 0.018 0.026 0.005 0.004 0.033 0.007 0.024 0.002 0.056 0.004  10.34 22.06 3.00 13.20 2.98 0.86 2.98 0.43 2.87 0.57 1.71 0.26 1.66 0.27  FREE OEu SCe  58.91 1.02 0.96 3.22 1.80  59.34 1.05 0.95 3.03 1.76  59.31 0.98 0.93 2.96 1.73  56.38 1.05 0.96 3.63 1.56  95.93 1.10 0.86 2.05 1.36  50.57 0.83 0.97 1.65 1.36  0.80 6.38 0.79 2.54 7.40  63.20 0.87 0.94 4.21 2.18  LaN/YbN LaN/SmN  *Replicate.  49  100  100  =^I^I  Ashlu Creek intrusion  Cloudburst pluton  U CC  9006: Aplite 9013: Tonalite  9007: Tonalite  1  a:  9011A: Granodiorite  9016: Hbl diorite  b  0.1  0.1  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 100  =  9014: Qtz diorite  9011: QC diorite  =  I  I  Sechelt pluton  100 e^  —E— SE-19: Granodiorite  F  ^ SE-19A: Aplite  10  0 0  0  Soo River intrusion CC  :7-^---*-- 9022A: Qtz diorite  C^  0.1  11111111111111  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  0.1  d  I^I^[III^I^I^I  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  Fig. 3.5. Chondrite normalized REE discrimination diagrams for representative samples from Late Jurassic plutonic rocks, compared against typical REE patterns for older volcanic rocks (Fig. 3.8) along the same transect (shaded area).  50  100  I^I^I^I^I^I^I^I^I^I^I^I^I^–  Early Cretaceous suite  I  Li  10  O  _c  ri^ Cypress: Granodiorite  0^1  —0— Newman Creek: Hbl gabbro  ^  _a  Callaghan Creek: Hbl diorite  -^Pemberton: Hbl diorite^–  1^I^I^I^I^I^I^I^I^I^I^I^I^I  0.1  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 100 Mid-Cretaceous suite  –  . !•. . , , 1  A  2E-, 10  . ■^  –a = . a 2 A 1^.  :-.;----v--10*Z-----;---Z  Nuf 11 ^/ ^  O  -C  0  1  —3  Squamish 9004: Granite _  I^  O  ^  cc  \ I - –0.-- Squamish 9005: Aplite  1  b 0.1  g  ___e_ Squamish S-12: Granodiorite_, 7^  _ Squamish S-10A: Aplite^_  )(^ Spetch Creek: Tonalite II^II^[Ill]^!^II  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 100  III^I^I^1^I^I^I^I^f^I^I  La te Cretaceous suite .  a) c 10 O  _c  X X X X  A^Mt. Rohr. Diorite cc  1  x  Bendor 9040: Qtz diorite --v-- Bendor B-1: Diorite C^X^Bendor B-8: Tonalite  0.1  I  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  Fig. 3.6. Chondrite normalized REE discrimination diagrams for representative samples from Cretaceous plutonic rocks. REE patterns for older volcanic rocks are shown as before (shaded area).  51  10  1  0.1  La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  Fig. 3.7. Chondrite normalized REE discrimination diagrams for Bralorne Diorite.  52  100  Volcanic rocks =  10 A^  - 0- -4. -  -O a  -  •  0  —0--  Cenozoic volcanic rock Cloudburst: mafic dyke Gambier Assemblage Cayoosh Assemblage Cadwallader Group Cadwallader ultramafic rock  re  0.1  0.01 La Co Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  Fig. 3.8. Chondrite normalized REE discrimination diagrams for representative Late Triassic to Quaternary volcanic rocks.  53  The aplite is even more depleted but has positive HREE fractionation and a positive Eu anomaly (8Eu = 1.52). Qtz diorite from Soo River shows slight fractionation between LREE and HREE (LaN/YbN = 6.67), a small enrichment in LREE and depletion in HREE (Fig. 3.5d) The REE discrimination patterns for Early Cretaceous intrusions are shown on Figure 3.6a. The Newman Creek hornblende gabbro shows a very primitive pattern REE = 6.17 ppm). LREE's have positive fractionation (La N/SmN = 0.44) and there is a positive Eu anomaly (8Eu = 1.53). There is no significant fractionation of HREE's, but they are overall depleted. Hornblende diorite from Pemberton and Callaghan Creek show similar HREE patterns but Callaghan Creek is more enriched and has more LREE fractionation. The granodiorite from the Cypress pluton is also remained primitive (FREE = 68.99 ppm) and less fractionated (LaN/YbN = 6.68). The mid-Cretaceous suite includes plutonic rocks from Squamish and Spetch Creek. The leucocratic plutonic rocks from Squamish have the most evolved REE discrimination patterns among igneous rocks from the transect. Both aplites show very similar LREE patterns and enrichment but differ in Eu anomaly and HREE enrichment (Fig. 3.6b). One aplite has a small negative Eu anomaly (8Eu = 0.15) showing positive fractionation but is less enriched in HREE; it is very similar to the host granite. The other aplite has a very large Eu anomaly (8Eu = 0.027) and also shows positive HREE fractionation but has very high HREE enrichment. Granodiorite has the highest LREE enrichment among these samples and also shows a negative Eu anomaly (8Eu = 0.42). The REE pattern for tonalite from Spetch Creek is the same as that from other plutons, showing depleted HREE. The Late Cretaceous suite contains Mt. Rohr pluton and Bendor intrusions. Diorites from both Mt. Rohr and Bendor are very similar, with flat REE patterns and little fractionation within and between LREE and HREE (Fig. 3.6c). In the Bendor intrusions  54  quartz diorite is slightly more enriched than diorite in both LREE and HREE The tonalite Bendor is depleted in HREE. Diorite of the Early Permian Bralorne Complex has very low TREE (5.98 ppm) and shows a depleted and primitive REE pattern, with a positive LREE trend, flat HREE and a very small positive Eu anomaly (Fig. 3.7). As predicted, all plutonic rocks plot in the field for volcanic arc granites (VAG) in Figure 3.9. This tectonic setting reflects the geochemical nature of the source materials for plutonic rocks from the southern Coast Belt. The incompatible trace element distributions (Tables 3.3, 3.4, 3.5 and 3.6) are typical of arc rocks, having high LILE/HFSE ratios. Figures 3.10 and 3.11 show primitive mantle normalized abundance patterns for moderately to highly incompatible elements for representative plutonic rocks from the southern Coast Belt. Normalization values of primitive mantle are from Sun and McDonough (1989). The high LILE/HFSE ratios for plutonic rocks reflect either inheritance of arc-type source materials or are the result of new magma input from the subducted slab. The enrichment of Pb and depletion of Nb are pronounced for both plutonic and volcanic rocks. The high LILE/HFSE ratios are trace-element attributes for Phanerozoic calcalkaline and shoshonite arc magmas, and reasons of HFSE depletions continue to be a subject of debate (Briqueu et al., 1984; Arculus and Powell, 1986; Hildreth and Moorbath, 1988; Drummond and Defant, 1990; McCulloch and Gamble, 1991). It is generally accepted that HFSE and HREE remain immobile during slab-fluxing processes and are, thus, derived from the mantle wedge without additional enrichment from the slab. In contrast, enrichment of LILE, such as Rb, Cs, Ba, Sr, Pb, U and LREE's (i.e., La, Ce) in island-arc basalts (IAB) are consistent with slab involvement (McCulloch and Gamble, 1991). This relative enrichment is inferred to result from a combination of high rock-melt incompatibility and slab-"fluid" mobility (McCulloch and Gamble, 1991).  55  ^  1 00 0  1 00  L7  -  • 10  VAG  0^0 0 4- 60 GD 0^1° 0 O• _ A i OA 0 0 0^l" 0 0 •  6 •'  • 0^• 0 • 0  1  o Plutonic rocks ♦ Volcanic rocks  •  ^Ai Jill  ^  ORG  10^ Y + Nb (ppm)  1^1^I^  ►  100  ^  1 000  Fig. 3.9. Rb vs. Y + Nb tectonomagmatic discrimination diagram for plutonic and volcanic rocks from southern CPC (after Pearce et al., 1984), showing volcanic arc granite (VAG) affinity.  56  1000  1000  100  100 A  10 O  0.1 Rb Ba K Nb La Ce Pb Sr Nd P Sm Zr Eu Ti Ho Y Yb  0.1 ^  1000  Rb Ba K Nb La Ce Pb Sr Nd P Sm Zr Eu Ti Ho Y Yb  1000 Soo River intrusion 100  100 a)  w  C  "C  7-  10  3 10 0  O  0.1  0.1 Rb Ba K Nb La Ce Pb Sr Nd P Sm Zr Eu Ti Ho Y Yb Rb Ba K Nb La Ce Pb Sr Nd P Sm Zr Eu Ti Ho Y Yb  Fig. 3.10. Primitive mantle normalized abundance patterns for moderately to highly incompatible elements for representative samples from Late Jurassic plutonic rocks, compared against typical patterns for older volcanic rocks (Fig. 3.12) from the same transect, shown as shaded area. Symbols as in Fig. 3.5.  57  1000 Early Cretaceous plutonic suite 100  1  0.1 Rb Ba K Nb La Ce Pb Sr Nd P Sm Zr Eu Ti Ho Y Yb 1000 Mid-Cretaceous plutonic suite 100  1  0.1 Rb Ba K Nb l.a Ce Pb Sr Nd P Sm Zr Eu Ti Ho Y Yb 1000 Late Cretaceous plutonic suite  E  100  10 O  1  0.1 Rb Ba K Nb La Ce Pb Sr Nd P Sm Zr Eu Ti Ho Y Yb  Fig. 3.11. Primitive mantle normalized abundance patterns for moderately to highly incompatible elements for representative samples from Cretaceous plutonic rocks, compared against typical patterns for older volcanic rocks (Fig. 3.12) from the same transect, shown as shaded area. Symbols as in Fig. 3.6. 58  1000  100  10  1  0.1  0.01  Rb Ba K Nb La Ce Pb Sr Nd P Sm Zr Eu Ti Ho Y Yb  Fig. 3.12. Primitive mantle normalized abundance patterns for moderately to highly incompatible elements for select volcanic rocks. Symbols as in Fig. 3.8.  59  Pemberton  Vancouver  Anderson Lake  1200 ^ 1000 —  0 v  800 — •  Sr  600 — _ 400  • 0 0 0 0 0  0  0  0  0^  0 • 0 o^•  o -  0  0  0  •.^ • • .0 .  ^  200 — . I^  0 1^ I  I  2 0  I^  0^Volcanic rocks 0  0 0  8  4  0^Plutonic rocks  81  10  Nb 6  .  0 0  0 .)  —0  0^.g 0  0  0^• .0^0 • 0 o • 0. o • • •  0  • •t  •  lb  1^I^I,^i^I^1^I^1^1^I^1^I  0 20 40 60 80 100 120 140 160 180  Distance (km) Fig. 3.13. Sr and Nb (ppm) vs. geographic position for plutonic and volcanic rocks, showing slightly decreasing Sr and Nb concentrations from SW toward NE.  60  Both plutonic and volcanic rocks show Y anomalies (Figs. 3.10, 3.11 and 3.12). Y enrichment might reflect breakdown of a large amount of amphibole in the subducted oceanic slab or in the mantle wedge, since amphibole is enriched in Y (Green, 1980). One controversy is that volcanic rocks from the southern Coast Belt show a decrease in both Sr and Nb components from SW to NE (Fig. 3.13). If input from the subducted slab increases, Nb should decrease and Sr should increase. The observed Sr decrease away from the subduction trench maybe a result of preferential breakdown of Srrich carbonate phases in the slab (McCulloch and Gamble, 1991) at shallower depth, near the subduction trench.  3.5 MAJOR ELEMENT VARIATIONS AND IMPLICATIONS  3.5.1 Magmatic differentiation: application of Pearce element-ratios  Based on mineralogy, there are two different plutonic suites from the southern Coast Belt, namely the more mafic and the more felsic suites. On the basis of this observation, two fractionation hypotheses are proposed to explain chemical variations within these plutonic rock bodies. These are: (1) sorting of Pl, Hbl and Bt vs. (2) sorting of P1, Bt and Kfs. To test these hypotheses, Pearce element-ratios (Pearce, 1968; Russell and Nicholls, 1988, Ernst et al., 1988, Russell et al., 1990) are used. Two pairs of Pearce element-ratios are formulated by designing assemblage test diagrams following the techniques described by Stanley and Russell (1989): X 1 = [0.8571Si - 0.1429 (Fe + Mg) + 1.2857Ca + 1.85741(]/Z Y 1 = (1.1428Ti + Al + Fe Mg + Ca + 1.5714Na + 0.4762P)/Z, and X2 (2Ti + Al + 3.3333 P)/Z  61  Y2 = (2Ca + Na + K)/Z  with Z (the denominator) representing a conserved element. The first pair (X 1 , Y 1 ) accounts for the stoichiometry of sorting of Pl, Hbl and Bt as well as Ttn and Ap and are named PHB axes. The second pair (X2 , Y2 ) accounts for the stoichiometric effects of fractionation of Pl, Bt, Kfs and Ep as well as Ttn and Ap: named PBK axes. Zirconium was chosen as the denominator Z. Geochemically, Zr is an incompatible element in most magmatic processes. Zircon occurs as inclusions in biotite. In this suite of plutonic rocks, biotite in the mafic suite doesn't include zircon. In more leucocratic rocks, zircon occurs only within the margins of some biotite. The non-zero intercepts for Pearce element ratio plots of petrologically meaningful numerators with Zr as the denominator are consistent with Zr not being affected by the fractionation process characterizing these intrusive bodies (Nicholls, 1988). Chemical data for plutonic rocks from the southern Coast Belt transect are plotted on PHB or PBK diagrams depending on the observed mineral assemblages. Results are shown on Figure 3.14-22. On each diagram vectors are plotted indicating the chemical trends expected from sorting of various minerals. The norms to these phase displacement vectors are calculated based on 8 oxygens, which makes the phase displacement more realistic and comparable with each other. The chemical data are plotted with 1a error ellipses. For each suite of plutonic rocks a model line with unit slope (referred to as model line hereafter) is fit to the data. This line represents ideal chemical trend associated with sorting of the restricted phase assemblage (PHB or PBK) within a closed chemical system (e.g., a single uncontaminated magma batch). The shaded bar represents la error due to analytical uncertainty on the model line. In discussing the petrogenesis of these plutonic rocks I used the following definitions:  62  Cogenetic association: a suite of rocks derived from a single magmatic system that behaves as an open or closed system. There may be no conserved element. Comagmatic association: a suite of rocks derived from a single magmatic system that behaves as a closed system for at least one component. There must be at least one conserved element. Discussion progresses from analysis of the mafic suites to the felsic suite and from simple cases to more complicated cases. In this study, data from four plutons within the transect area (Sechelt, Squamish, Mt. Rohr and Bendor) are taken from Michael and Russell (1989).  3.5.1.1 Testing the PHB hypothesis  Two plutons, Soo River and Spetch Creek, with relatively little internal petrologic variations are chosen to test the MB hypothesis first. All three samples from the Soo River intrusion plot on the model line of slope 1 (Fig. 3.14). The best fit model line has an intercept of -284 ± 141 and R 2 of 0.9998. The two samples from Spetch Creek also plot on the model line (Fig. 3.15), with best fit line having an intercept of -3753 ± 289, the smallest along the transect across the southern Coast Belt. The fact that all samples from the Soo River and Spetch Creek intrusions plot directly on the model lines developed for the PHB hypothesis suggests that this hypothesis is a viable mechanism to explain the chemical variation within in these plutons. The Mt. Rohr pluton contains more mafic intrusive rocks and their leucocratic varieties. On the PHB diagram (Fig 16), all data fall on the model line of slope 1, with the more mafic rocks (3 samples) plotting up the trend and the leucocratic rocks (2 samples) plotting at lower values. The intercept to the fit is -2773 ± 239 with R 2 equals to 0.9920. For this pluton, the PHB hypothesis is consistent with the observed variations (e.g., sorting of P1 f Hbl Bt t Ap f Ttn). 63  18000 16000 14000 12000 10000 8000 6000  Soo River intrusion Intercept = - 284 ± 150 R 2 = 0.9998  4000 2000 2000  4000 6000 8000 10000 12000 14000 16000 18000  [0.8571Si-0.1429(Fe+Mg)+1.2857Ca+1.8574K] / Zr Fig. 3.14. PUB element-ratio diagram for plutonic rocks from Soo River for sorting of ideal mineral components Ab f An ± Hbl f Bt Ep Ttn f Ap. Ed denotes to edenite.  64  18000 16000 14000 12000 10000 8000 6000 4000 2000 2000 4000 6000 8000 10000 12000 14000 16000 18000  [0.8571Si-0.1429(Fe+Mg)+1.2857Ca+1.8574K] / Zr Fig. 3.15. PUB element-ratio diagram for plutonic rocks from Spetch Creek.  65  4000^6000^8000^10000^12000^14000  [0.8571Si-0.1429(Fe+Mg)+1.2857Ca+1.8574K] / Zr Fig. 3.16. PHB element-ratio diagram for plutonic rocks from Mt. Rohr.  66  The Bendor intrusions comprise more mafic and felsic rock types. Among 7 analyzed samples, B-1, B-2 and B-9 are the more mafic varieties and B-7, B-10 and B-12 are the leucocratic varieties. B-8 is an intermediate composition. To test the PHB hypothesis, all data from Bendor plot on the PHB diagram (Fig. 3.17). Among these rocks, samples B-1 and B-10 do not fall on the model line of slope 1. Five other samples fall on the best fit model line and have an intercept of -1767 ± 203 and R 2 of 0.99997. Sample B-10 is a marginal phase and is strongly foliated, which means that this sample could have been contaminated by another batch of magma or materials from the wallrocks. Pyroxene included in Hbl in the more mafic varieties might also have an effect on the fractionation trends, as shown by sample B-1: note that clinopyroxene sorting causes trends that lie between PHB and Kfs with a slope of 0.7. From this test we can see that the PHB hypothesis can explain several samples from Bendor intrusions. The PBK hypothesis is not realistic for the Bendor intrusions because Hbl is abundant in the mafic rock types and is also present in the felsic rocks. Data from Cloudburst are plotted to test the PHB hypothesis. Three samples define a best-fit model line of slope 1, with an intercept of -1807 ± 256 and R 2 of 0.9528 (Fig. 3.18). A single granodiorite sample (9011A) is also plotted. This sample was collected from a cross-cutting dike and was expected to be cogenetic with the pluton. Figure 3.18 clearly suggests otherwise that this rock is from a different batch of magma. An alternative is that Zr is no longer conserved in 9011A which happens to be relatively leucocratic sample. For plutonic rocks from Ashlu Creek, Pearce element-ratios are used to test whether these rocks are comagmatic and hence a single pluton, and to test the PHB hypotheses. This suite includes three mafic rocks (9013, 9016 and 9017) and three felsic samples (9014, 9014A and 9015). Kfs is present in samples 9014 and 9015. The mafic suite and felsic suite are different in petrography. In the mafic samples 9016 and 9017, both fresh plagioclase and slightly altered plagioclase are present. The fresh plagioclase 67  18000 16000 14000 12000 10000 8000 6000 Intercept = - 1767 ± 203 R 2 = 0.99997  4000 2000 2000  4000 6000 8000 10000 12000 14000 16000 18000  [0.8571Si-0.1429(Fe+Mg)+1.2857Ca+1.8574K] / Zr Fig 3.17. PUB element-ratio diagram for Bendor intrusion.  68  18000 16000 14000 12000 10000 8000 6000 4000  Intercept = - 1807 ± 256 R 2 = 0.9528  2000 2000 4000 6000 8000 10000 12000 14000 16000 18000  [0.8571Si-0.1429(Fe+Mg)+1.2857Ca+1.8574K] / Zr Fig. 3.18. PHB element-ratio diagram for Cloudburst.  69  18000 16000 14000 Hbl Ab An Bt Ep  12000  /Ttn Ed  10000 8000  Ap  Ashlu Creek intrusions 0 Intercept = 586 ± 156  6000  C Intercept = - 215 ± 205 Intercept =- 760 ± 65  4000  C) Intercept = - 1639 ± 272  Fig. 3.19. PHB element-ratio diagram for plutonic rocks from Ashlu Creek, illustrating that the more mafic and felsic rocks are not comagmatic. For the mafic rocks, magmatic differentiation trend accounts for sorting of Ab + An + Hbl + Bt + Ep Ttn Ap. In felsic rocks, Kfs may be involved along with Ab + An + Hbl + Bt + Ep f Ttn f Ap.  70  grains do not show zoning and are An y) . The slightly altered plagioclase grains showing zoning usually have a calcic core (An 60 ) and sodium margin (An 45 ). The change from core to margin is abrupt with a very clear boundary. Therefore, magmatic differentiation for this more mafic suite of rocks is fractional crystallization. In the more felsic samples, plagioclase is commonly zoned with calcic cores changing continuously and gradually to sodium margins, an indicator of equilibrium crystallization for magmatic differentiation. Three more mafic samples, 9013, 9016 and 9017, should fall on a single model line if they are comagmatic. The test indicates that they are not comagmatic, as illustrated by Figure 3.19. Instead, they are probably three separate suites of intrusions. The model lines have intercepts of 586 ± 156, -215 ± 205 and -1639 ± 272 for sample 9016, 9017 and 9013, respectively. The more felsic rocks, 9014, 9014A and 9015, plot at the lower left of the diagram and are not simply felsic varieties of the more mafic rocks of sample 9013, 9016 and 9017. The more felsic rocks appear, themselves, although the presence of Kfs in samples 9014 and 9015 invalidates the PHB hypothesis. This suite of rocks should be used to test the PBK hypothesis.  3.5.1.2 Testing PBK hypothesis  The PBK hypothesis can potentially explain the chemical diversity of the felsic rocks from Ashlu Creek and two other felsic plutons: Sechelt and Squamish. As shown on Figure 3.20, samples 9014, 9014A and 9015 from Ashlu Creek fall on the model line within analytical uncertainty. The best fit line has an intercept of 72 ± 31 and R2 of 0.9967. This test demonstrates that these rocks are comagmatic and the PBK hypothesis can explain the chemical variation for this suite of rocks. Data for granodiorite, tonalite and quartz diorite from the Sechelt intrusion are plotted on Figure 3.21. Also plotted is an aplite sample (SE-19A). Most data fall on the 71  (2Ti + Al + 3.3333P) / Zr Fig. 3.20. PBK element-ratio diagram for felsic rocks from Ashlu Creek. This diagram accounts for sorting of plagioclase, biotite, K-feldspar, titanite and apatite.  72  6000  5000  Kfs, Ab An Hbl  Ed  Ttn^Ep  4000  3000  2000  Sechelt pluton Intercept = - 214 ± 60 R 2 = 0.9897  1000 1000  2000^3000^4000^5000  6000  (2Ti + Al + 3.3333P) / Zr Fig. 3.21. PBK element-ratio diagram for plutonic rocks from the Sechelt pluton. This diagram accounts for sorting of plagioclase, biotite, K-feldspar, titanite and apatite.  73  best-fit model line within analytical uncertainty. Two samples, SE-19 and SE-24, are off the model line. SE-19 and SE-24 are extremely leucocratic granitic rocks. The large flakes of biotite in SE-19 and SE-24 contain zircon crystals, which means that if biotite is fractionated, Zr will not be conserved. The best fit model line for all other samples has an intercept of -214 ± 60 and R 2 of 0.9897. It has a statistically significant non-zero intercept within analytical uncertainties. Both biotite and K-feldspar could have been sorted, thus, the data distribution along the model line does not have a unique intersection. The point for aplite (SE-19A) is meaningless because Zr is likely no longer conserved. The low R 2 value and two samples (SE-19 and SE-24) off the model line may be caused by local, small scale assimilation, as abundant mafic inclusions exist in this pluton. Data from Sechelt are plotted in a PHB diagram. All data fall on a trend (not exactly a straight line) between the vector for Kfs and the vectors for Ab, Hbl, An, Bt, Ep, Ttn and Ap (not shown). This suggests that sorting of Kfs plays a role for the geochemical variation in this pluton. Thus, the PBK hypothesis can explain the general geochemical variation for Sechelt pluton with the exception of the leucocratic late phases of SE-19A, SE-19 and SE-24. The Squamish is the most felsic pluton along this transect. Data from this pluton are used to test both the PBK and PHB hypotheses and neither of them are satisfied. However, the PBK axes work better than the PUB axes. On the PBK diagram (Fig. 3.22), 4 of the 7 data define a model line of slope 1 with an intercept of -233 ± 71 and a poor R 2 of 0.8724. Using the data to test the PUB hypothesis, the data points are plotted along a trend between the vector for Kfs and the vectors for Ab, Hbl, An, Bt, Ep, Ttn and Ap (diagram not shown). Thus, the PBK hypothesis might be generally accepted and the PHB hypothesis should be rejected. Aplite has the highest Pearce element ratio, which is caused by de-conservation of Zr at the final stage of fractionation.  74  4000  3000  2000  Squamish pluton Intercept = -292 ± 70 R 2 = 0.7160  10 00 1000  2000^3000  4000  (2Ti + Al + 3.3333P) / Zr Fig. 3.22. PBK element-ratio diagram for Squamish pluton.  75  Some of the scatter in the data plotted on the PBK diagram could result from Zr no being totally conserved (Ernst et al., 1988), because in the felsic rocks zircon could have fractionated. In conclusion, Pearce element-ratios work successfully for the more mafic suite of plutonic rocks based on the application of Pearce element-ratios on plutonic rocks from the southern Coast Belt. For the more felsic suite of rocks, caution should be taken, as in the more felsic rocks incompatible elements may be no longer as conserved as in the more mafic rocks. 3.5.2 Source materials: importance of Pearce element-ratio intercepts  The slopes and intercepts of the model fractionation trends on Pearce elementratio diagrams account for the stoichiometry of differentiation process and the initial magma composition of the system, respectively (Nicholls and Russell, 1991; Stanley and Russell, 1989). The intercept remains invariant during differentiation and the compositions of samples from the same magma-batch will have the same intercept within analytical uncertainty (Pearce, 1968; Nicholls, 1990; Nicholls and Russell, 1991). If the assemblage being fractionated remains the same, that slope is preserved. Differences in intercepts between trends may indicate a difference in the original melt composition. This difference could be caused by differences in partial melting or difference in the composition of source materials. Nd and Pb isotopic data and incompatible element ratios (P/K and Ti/K, as used here) can show differences of the source materials, no matter the degree of partial melting. By comparing intercepts with isotopic data and incompatible element ratios, we could further explore the importance of intercepts in discriminating magma batches and elucidating differences in source materials for plutonic rocks. As discussed above, we can distinguish samples formed by one magma batch from the others. The leucocratic dike from the Cloudburst intrusion is singled out by its different intercept (Fig. 3.18). The rocks collected from Ashlu Creek are actually formed 76  TABLE 3.7. Comparative statistics on model intercepts on Pearce element-ratio diagrams for plutonic rocks from the southern Coast Plutonic Complex Pluton Sechelt Squamish Ashlu Creek: felsic suite Cypress Cloudburst Ashlu Creek: 9016 Ashlu Creek: 9017 Ashlu Creek: 9013 Callaghan Whistler Soo River Pemberton Spetch Creek Mt. Rohr Bendor  Samples 9 6 3 1 3 1 1 1 1 1 3 1 2 5 7  Diagram type I (intercept) PBK PBK PBK PHK PHB MB PHB PHB PHB PHB PHB PUB MB PHB PHB  -214 -292 72 -342 -1807 586 -215 -1639 593 -1419 -284 689 -3753 -2773 -1767  a(I, data) 76 168 41 254  59 71 239 168  47 (I, a.u).  60 70 31 78 256 156 205 272 146 157 150 234 347 230 203  R2 0.9897 0.7160 0.9967 0.9528  0.9998 0.9920 0.99997  standard deviation of data a(1 a.u).•• analytical uncertainty CV data ):  77  from three different magma batches. They are recognized by three different intercepts (intercepts for Ashlu Creek 9013, Ashlu Creek 9016 and Ashlu Creek 9017, as listed on Table 3.7). From Fig. 3.23, a minimum of 6 magma batches are recognized. Plutons from every magma batch are not necessarily comagmatic or linked in some way, but they probably share similar attributes of chemical characteristics and/or partial melting processes. Thus, magma batch grouping can be further used to discuss the geochemical characteristics of the source materials for the plutonic rocks. This topic is out of the scope of this paper and won't be addressed in detail in this report. There is no systematic correlation of intercepts, isotopic data and incompatible element ratios against ages (Fig. 24a to Fig. 24g). Extent of magmatic differentiation does not correlate with geographic position, however, the intercepts of PHB diagrams for the more mafic plutons show a rise from SW to NE. Indeed, the trend changes abruptly at Pemberton (Fig. 24/). The intercepts drop NE of Pemberton and rise again near the NE end of the transect at Anderson Lake. Figure 24h to Figure 247/ also show ENd, 87 Sr/ 86 Sr, 208pbpo4pb an d 207pb/204 Pb isotopic compositions (Cui and Russell, 1993b, in prep.; P.J. Michael's unpublished Nd and Sr isotopic data for the Mt. Rohr and Bendor intrusions) and incompatible element ratios of Ti/K and P/K against the position for plutonic rocks from the same transect. Along the Vancouver to Pemberton transect, E Nd values for plutonic rocks increase from SW to NE. Initial  87 Sr/86 Sr  ratios are more scattered and a  rise NE of Pemberton is evident. Pb isotopes are more uniform from Vancouver to Pemberton. However, both 207Pb/204Pb and 208 Pb/ 204 Pb ratios decrease at Pemberton and 207pb/204Pb ratios rise again toward the NE end of the transect. Both P/K and Ti/K incompatible element ratios systematically increase from SW to NE and the increasing trend is abrupt at Pemberton. From Pemberton to the NE margin of the southern Coast Belt, these two ratios have low values and show no variation. Based on the similar variation pattern against distance between Pearce elementratio intercepts, isotopic data and incompatible element ratios, it appears that the 78  20000 18000 16000 14000 12000 10000 8000 6000  1. Pemberton 2. Callaghan 3. Ashlu Creek: 9016 4. Ashlu Creek: 9017 5. Soo River 6. Whistler 7. Ashlu Creek: 9013 8. Bendor 9. Cloudburst 10. Mr. Rohr 11. Spetch Creek  4000 2000  0 -2000 -4000  0 2000 4000 6000 8000 10000 12000 14000 16000 18000  [0.8571Si-0.1429(Fe+Mg)+1.2857Ca+1.8574K] / Zr Fig. 3.23. Model lines and associated uncertainties (shaded bars) for more mafic suite of plutonic rocks are plotted on PHB diagram. Intercepts on this diagram are indicative of source region differences and suggest that a minimum of 6 magma types are separated to explain these plutonic rock suites (see text).  79  ^  •  Pemberton I^I Anderson Lake .'  Vancouver  12  ^'  ^I^'^1^'^-I-^'^1^• 10 -^ • 8  ENd  6 4 2  0.7045 0.7040  co  0.7035  a -  •  ^I^•^_ •• • -^ •_ _ -^ IIIIIIII# -^• •_•  - •^  ••^•.:  •  -  C1") 0.7030 cr-8^0.7025 •  0_ Csi  CL  CO  -^•^• 1^1^is^I^;I'll 38.8 38.4 38.0  a.^  15.7  03  a-  -  15.3  -  0.7 0.6 0.5 0.4 0.3 CL 0.2 0.1 0.0 0.8 0.6  •  -  -^•  _  _  _  IIIIII^IIIII1,  15.4  1000 0 -1000 -2000 -3000 -4000  rts.1  -  • - if •^••^•^• -^•  15.6 15.5  •  -^• -^me^•^•^• -1:^•  _ _^•^• _•^s ^• _• IIIIIIIIIII _.• • :^ • p -  -  •  -  a4 0.2 0.0  _  -  _  -  d -  -^• _  _ -  z^iff 7  I^I I  I^I^&III^riI  -^•^ •-  ,_^•^• -^ •• • • ••: _^•8 1; ^• -•^  •  g  .  •^•  -^ • "_.^. •j^ •^• •  -  7  -  _ _  I^i^I^I^I^I^I^I^I  -^•  ic  7 7 .I  f a•_  •ID,:  11,..^1^.^I^,^■^.^I^,  2  s^_  •  • :  I • :  • •  :  • •  •  :•  i •  s  •  • •  I 11^I^I I  a . I I^•^I  10 8  E Nd  0.7045 0.7040 F . 0.7035  _ 0.7030 (./3 - 0.7025 c°  j_  I  -  1  IIII. • -  , _ . -  k • • -  38.8 38.4 38.0 37.6 37.2 15.7 15.6 15.5 15.4 15.3  IIIIIIIIIII I IIII.  I  e  6 4  1^I^1^I 1 I^1^i 1^I 1 i 1^I 1^i^I  11111IiIiiIII  7z I^  12  h_ • _ • _  I^I^o^I • 1^■^1 i I I I olif^•  37.6  CV^37.2  •  -  1000  : 0 .  a I  i^= I^= ... 1 I^i 1 I I^I I^I^I  -1000 -2000 -3000 -4000  N co  a.  -  -  •  /11-  ••t_  0.5 0.4  0.3 • • 0.2 • • I • . •• _41 0.1 • 1^I^I^I t 1^II 4^I s I • I i^1^s . .: • n7 0.8  _ -  -•  • • 1^.^II.  •  • • •  • •• 1.^1.^1  _, • --  0.6 0.4  • .^• ..., 0.2 . I.^1.^1. - 0.0 •  160^140^120^100^80^60 0^20 40 60 80 100 120 140 160 180  ^ Age (Ma)  Distance (km)  Fig. 3.24. Isotopic ratios, PBB intercepts and incompatible element ratios are plotted  against ages and geographic positions for granitic rocks from the southern CPC. Note the variations between plots from 0 - 120 km (SW of Pemberton, see Fig. 3.1) and 120 - 180 km (NE of Pemberton, see Fig. 3.1).  80  intercepts are sensitive to different source materials. Thus, they can be used to discriminate source regions for plutonic rocks. The implication of intercepts for plutonic rocks from the southern Coast Belt is that magmas for these plutonic rocks originated from two distinct source regions along the transect: one SW of Pemberton and one NE of Pemberton. The boundary of source regions may reflect the difference of source materials from Wrangellia terrane SW of Pemberton and other terranes NE of Pemberton. Indeed, the Wrangellia terrane comprises mainly island arc-related volcanic and sedimentary rocks. The terranes NE of Pemberton consist of very complicated materials, including arc- and back-arc-type volcanic rocks, volcanic, carbonate, pelitic and plutonic clastic rocks. Furthermore, the Bridge River terrane NE of Pemberton, contains oceanic rocks of pelagic facies (radiolarian chert) and clastic rocks (Monger and Journeay, 1992). From the above discussion, we can see that the intercepts on Pearce element-ratio diagrams can be used to discriminate the source materials and magma batches for plutonic rocks.  3.6 CONCLUSIONS  The southern Coast Plutonic Complex comprises mainly Jurassic to Tertiary calc-alkaline plutonic rocks, ranging in composition from granite, tonalite, quartz diorite, diorite to gabbro, with an average composition of quartz diorite. The magmatic origins of plutons from the southern CPC are constrained by petrographic study and chemical analysis, including major, trace and rare earth element data, on rocks collected from a 180 km transect across the southern Coast Belt from Vancouver to Anderson Lake. Plutonic rocks are divided into two groups based on petrography: a more abundant suite of mafic plutons and a suite of felsic plutons. The more mafic suite comprises mainly tonalite, quartz diorite and diorite and has little K-feldspar and abundant hornblende. The 81  primary mineral assemblage for this suite is plagioclase + hornblende + biotite + quartz ± K-feldspar + zircon + apatite ± titanite + Fe-Ti oxides ± epidote. The more felsic suite of plutons comprises mainly granite, granodiorite, tonalite and quartz diorite. The primary mineral assemblage for this suite is plagioclase + biotite + quartz + K-feldspar hornblende + zircon + apatite ± titanite + Fe-Ti oxides ± epidote. K-feldspar is an important phase and hornblende is rare in these rocks. Both felsic and mafic rocks are present in some weakly zoned plutons. The plutonic rocks have incompatible traceelement abundances characteristics of arc rocks. This is consistent with their source materials being mantle-derived magmas or being arc-type volcanic rocks from terranes in the southern Coast Belt, or the combination of both of them. Pearce element-ratios are demonstrated to be a powerful tool in testing petrological hypotheses including identification of source regions, crystal sorting and comagmatic suites. On the basis of petrographic study, two different mineral assemblages are proposed as having controlled fractionation: (1) An + Ab + Hbl + Bt f Ep f Ttn t Ap for more mafic plutons and (2) Ab + An + Bt + Kfs Ttn Ap for more felsic plutons. To test this hypothesis, two sets of axes for Pearce element-ratio diagrams are formulated (PHB and PBK). The PHB accounts for mafic plutons and PBK for felsic plutons. The tests indicate that we can not reject the proposed fractionation hypotheses. Phase displacement vectors are calculated by using 8 oxygens. This makes the phase displacement vectors more realistic and comparable with each other. This study demonstrates that Pearce element-ratios work successfully for testing the PHB hypothesis for the more mafic suite of plutonic rocks. However, for the more felsic suite of rocks, incompatible elements may be no longer conserved, so caution should be taken with using Pearce element-ratios. The importance of intercepts from Pearce element-ratio diagrams is explored in testing comagmatic hypotheses including discrimination between magma batches and source materials for plutonic rocks. A leucocratic late stage dike from the Cloudburst 82  intrusion was considered to be comagmatic with the Cloudburst intrusion itself. The test indicates that dike is actually from a different batch of magma. The rocks from Ashlu Creek were originally considered to be part of a single intrusion. The test indicates that the rocks are not comagmatic. Rather, they are from three different intrusions. To discriminate the source regions, the intercepts of PUB diagrams for the more mafic suite of plutons are plotted against pluton's position and variation of intercepts is compared with Nd and Pb isotopic data and incompatible element ratios. The intercepts show a rise from southeast to northwest until Pemberton, where the trend is terminated. The intercepts drop northeast of Pemberton and rise again toward the northeast end of the transect. This variation pattern against distance for intercepts is similar to that of the Nd, Pb isotopic data and incompatible element ratios of Ti/K and P/K for plutonic rocks from the same transect. The similarity between Pearce element-ratio intercepts, isotopic data and incompatible element ratios suggests that the intercepts are sensitive to the difference of source materials, thus they can be used to discriminate source regions for plutonic rocks. Implication of intercepts for plutonic rocks from the southern Coast Belt is that magmas for these plutonic rocks originate from two distinct source regions along the transect: one on the SW of Pemberton and the other to the NE of Pemberton. The boundary of source regions may reflect the difference of source materials between the Wrangellia terrane to the SW of Pemberton and other inner terranes on NE of Pemberton. Intercepts can also be used to group magma batches based on their chemical affinity. For plutonic rocks from the southern CPC, six batches of magma are recognized. Magma batch grouping is important in further discussion of the geochemical characteristics of the source materials for the plutonic rocks.  83  4. CONCLUSIONS A suite of plutonic and volcanic rocks were collected along a 180 km transect across the southern CPC from Vancouver to Anderson Lake. This transect spans the entire southern Coast Belt. Geochemical data reported in this thesis include major and trace element analyses, rare earth element measurements, and Nd, Sr and Pb isotopic analyses on representative samples. Nd, Sr and Pb isotopic studies suggest that the igneous rocks comprise largely juvenile, mantle-derived materials. The effects of subducted oceanic sediments are indicated by slightly elevated  207 Pb/204 Pb  isotopic ratios for some samples. The primitive  nature of the southern CPC contrasts with plutonic rocks from the northern CPC, which are derived from combinations of juvenile material and sediments with Proterozoic isotopic signatures (Samson et al., 1991). Along the 180 km transect in the southern CPC, Nd, Sr and Pb isotopic data show no evident systematic correlation with rock type. The only correlation between isotopic data and radiometric ages of igneous rocks is in 208Pb/204 Pb ratios of volcanic rocks, which show a slight rise with decreasing age. It  appears that during the 180 Ma of magmatism which characterizes the southern CPC the source regions had similar Pb isotopic ratios although the extent to which oceanic sediments were involved in CPC magmatism may have risen slightly with time. The isotopic data are also examined against transect distance. Along the transect southwest of Pemberton, isotopic compositions are also uniform except a subtle rise in E N d values. At Pemberton, 207Pb/204 Pb ratios for plutonic rocks drop and then rise toward the northeast margin of the southern CPC. Initial 87 Sr/ 86 Sr ratios for volcanic rocks also show a rise toward the northeast end of the transect. Pemberton appears to be an important tectonic boundary, as indicated by these isotopic variations. The magmatic origins of plutons from the southern CPC are constrained by petrography and chemical analysis. Plutonic rocks are grouped into two compositional 84  suites based on petrography: a more abundant suite of mafic plutons and a suite of more felsic plutons. The more mafic suite comprises mainly tonalite, quartz diorite and diorite and has little K-feldspar and abundant hornblende. The primary mineral assemblage for this suite is plagioclase + hornblende + biotite + quartz ± K-feldspar + zircon + apatite ± titanite + Fe-Ti oxides ± epidote. The more felsic suite of plutons comprises mainly granite, granodiorite, tonalite and quartz diorite. The primary mineral assemblage for this suite is plagioclase + biotite + quartz + K-feldspar ± hornblende + zircon + apatite ± titanite + Fe-Ti oxides ± epidote. K-feldspar is an important phase and hornblende is rare in these rocks. The plutonic rocks have incompatible trace-element abundances typical of arc rocks, suggesting inheritance of their source materials either from mantle derived magmas in a subduction-related arc-type tectonic environment or form the arc-type volcanic rocks of terranes in the southern Coast Belt, or a combination of both of them. Pearce element-ratios are demonstrated to be a powerful tool in testing petrological hypotheses involving differentiation by crystal sorting, comagmatic relationships and source region discrimination for plutonic rocks. On the basis of petrography, two different mineral assemblages are proposed as having controlled chemical variation in these suites: (1) fractionation of An + Ab + Hbl + Bt ± Ep ± Ttn ± Ap for more mafic plutons and (2) fractionation of Ab + An + Bt + Kfs ± Ttn ± Ap for more felsic plutons. Two diagrams are derived (PUB, PBK) to test the proposed fractionation hypotheses against the observed chemical compositions. The tests indicate that these fractionation hypotheses can explain the chemical variations. Phase displacement vectors for all pertinent phases are calculated using an 8 oxygen basis. This makes the phase displacement vectors more realistic and comparable with each other. The importance of intercepts from Pearce element-ratio diagrams is explored for testing the comagmatic hypothesis and discriminating between magma batches and source materials for plutonic rocks. To discriminate the source regions, the intercepts for the more mafic suite of plutons are plotted against pluton's position and the variation of 85  intercepts is compared with Nd and Pb isotopic data and incompatible element ratios. The variation pattern against distance for intercepts is similar to that of the Nd, Pb isotopic data and incompatible element ratios of Ti/K and P/K for plutonic rocks from the same transect. The similarity between Pearce element-ratio intercepts, isotopic data and incompatible element ratios suggests that the intercepts are sensitive to the difference of source materials, thus they can be used to discriminate source regions for plutonic rocks. The implication of the Pearce element-ratio intercepts for plutonic rocks from the southern Coast Belt is that magmas for these plutonic rocks originated from two distinct source regions along the transect: the one southwest of Pemberton and the other northeast of Pemberton. The boundary of the source regions may reflect the difference of source materials from the Wrangellia terrane southwest of Pemberton and other inner terranes northeast of Pemberton. Based on Pearce element-ratio intercepts, six batches of magma are recognized along the transect through the southern CPC. 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