Nd ISOTOPIC SIGNATURES AN]) STRATIGRAPIIIC CORRELATIONS: EXAMPLES from WESTERN PACIFIC MARGINAL BASINS and MIDDLE JURASSIC ROCKS of the SOUTHERN CANADIAN CORDILLERA

Nd ISOTOPIC SIGNATURES AN]) STRATIGRAPIIIC CORRELATIONS: EXAMPLES FROM WESTERN PACIFIC MARGINAL BASINS AND MIDDLE JURASSIC ROCKS OF THE SOUTHERN CANADIAN CORDILLERA by J. Brian Mahoney B.S., University of Wisconsin-Madison, 1983 M.S., Idaho State University, 1987 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY 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 August, 1994 © J. Brian Mahoney, 1994 ______________________________ In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Bntish Columbia, I agree that the Ubrary 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 éZ)Lc2tcr <_tG’CL The University of British Columbia Vancouver, Canada ci Date ‘‘ U ‘ld?,EYL DE-6 (2/88) ABSTRACT The purpose of this investigation is twofold: 1) to evaluate the applicability of Nd and Sr isotopic analyses of fine grained clastic sediments to basin analysis and stratigraphic correlation; and 2) to document the lithostratigraphic, biostratigraphic, geochemical and isotopic characteristics of Lower to Middle Jurassic strata in tectonostratigraphic terranes of the southern Canadian Cordillera in order to evaluate potential terrane linkages. Isotopic analyses of Neogene strata from three western Pacific marginal basins (Shikoku Basin, Sea of Japan, Sulu Sea) permit evaluation of isotopic analyses to basin discrimination and stratigraphic correlation. The isotopic signatures of the Sulu Sea and Sea of Japan demonstrate that modern marginal basins have an isotopic signature that varies within limits defined by the geology of its source regions. The highly evolved (ENd < (-8)) isotopic signature of the Shikoku Basin, however, strongly overlaps that of the Sea of Japan, and contrasts with the juvenile character of the crustal domains on the basin margins. This anomalous signature is interpreted to be the result of cratonal2aeolian influx. Temporal isotopic fluctuations in the Shikoku Basin are roughly synchronous across 5600 of basin floor, and the pattern of isotopic fluctuations can therefore be used to correlate strata throughout the basin. Isotopic fluctuations are interpreted to result from changes in the relative contribution of each crustal domain within the source region to the basins’ total sediment budget, which is a function of tectonism, volcanic episodicity, climatic factors, and basin hydrology. Isotopic fluctuations in a stratigraphic sequence may therefore prove to be important as both tools for stratigraphic correlation and as a monitor of basin evolution. Lithostratigraphic data indicate that Lower to Middle Jurassic strata of the Harrison, Cadwallader, Bridge River, and Methow terranes each contain six strikingly similar, regionally consistent lithostratigraphic variations. Biostratigraphic data indicate that each terrane contains Aalenian to Bajocian strata with identical mixed fauna of Boreal, East Pacific and Tethyan faunal realms. Isotopic data indicate that the Harrison, Cadwallader, and Methow terranes contain coeval isotopic fluctuations of similar magnitude. Volcanic 11 geochemical data indicate that the Harrison and Methow terranes constitute separate volcanic arc systems flanking a basin containing back arc basin basalts. In addition, volcanic geochemistry and isotopic data suggest that the Harrison terrane represents the youngest eastern fades of the eastward migrating Bonanza- Harrison arc system, which provides an Early Jurassic link between Wrangellia and Harrison terranes. Results of this investigation strongly suggest that Lower to Middle Jurassic strata of the Wrangellia, Harrison, Cadwallader, Bridge River, and Methow terranes comprise a single marginal basin floored by trapped oceanic crust of the Bridge River terrane, and flanked by volcanic arc systems to the east and west. Wrangellia, Harrison, Cadwallader, Bridge River, and Methow terranes were amalgamated by the Early Jurassic, and have behaved as a coherent crustal block since that time. II’ TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iv LIST OF FIGURES vii LIST OF TABLES x LIST OF PLATES Xi DEDICATION xii ACKNOWLEDGMENTS xiii 1. INTRODUCTION 1 1.1 OBJECTIVE AND METHODS 6 A. Lithostratigraphy 6 B. Biostratigraphy 7 C. Volcanic Geochemistiy 7 D. Isotopic Characterization of Fine-Grained Sedimentaiy Rocks 7 E. U-Pb Zircon Analyses 9 1.2 GOALS 9 1.3 PRESENTATION 10 2. ISOTOPIC FINGERPRINTING OF FINE-GRAINED CLASTIC SEDIMENTS: A CASE STUDY OF WESTERN PACIFIC MARGINAL BASINS 2.1 iNTRODUCTION 13 2.2 BASiN DESCRIPTION 15 A. SeaofJapan 17 B. Shikoku Basin 19 C. SuluSea 21 2.3 METHODS 22 A. Sample Selection 22 B. Age Control 24 C. Analytical Procedures 24 a. Rb-Sr 25 b. Sm-Nd 25 D. Data Presentation 26 2.4 RESULTS 27 2.5 DISCUSSION 35 A. Interbasinal Isotopic Signatures 35 B. Intrabasinal Isotopic Signatures 39 2.6 CONCLUSIONS 41 3. REGIONAL GEOLOGIC SEllING 3.1 TERRANE DESCRIPTIONS 46 A. Wrangellia 46 B. Harrison 48 C. Bridge River 49 D. Cadwallader 51 E.Methow 52 iv F Cache Creek 54 G. Quesnellia 56 3.2 STRUCTURAL SET1TNG 57 3.3 PLUTONIC SETrING 60 4. EVOLUTION OF A MIDDLE JURASSIC VOLCANIC ARC: STRATIGRAPHIC, ISOTOPIC AND GEOCHEMICAL CHARACTERISTICS OF THE HARRISON LAKE FORMATION, SOUTHWESTERN BRITISH COLUMBIA 4.1 INTRODUCTION 64 4.2 GEOLOGIC SETTiNG 64 4.3 PREVIOUS WORK 67 4.4 STRATIGRAPHY 67 A. Celia Cove Member 68 B. Francis Lake Member 70 C. Weaver Lake Member 72 D. Echo Island Member 75 4.5 AGE CONSTRAINTS 77 A. Biostratigraphic Data 77 B. U-Pb Geochronology 78 4.6 STRUCTURAL DEFORMATION 82 4.7 GEOCHEMISTRY 83 4.8 Nd-Sr ISOTOPIC SYSTEMATICS 93 4.9 ALTERATION 98 4.10 MINERALIZATION 98 4.11 EVOLUTION OF HARRISON LAKE FORMATION 99 4.12 MODEL FOR VOLCANIC ARC DEVELOPMENT 102 4.13 CONCLUSIONS 103 5. EARLY TO MIDDLE JURASSIC VOLCANISM ON WRANGELLIA: EVOLUTION OF THE BONANZA-HARRISON ARC SYSTEM 5.1 INTRODUCTION 107 5.2 GEOLOGIC SETTING 109 5.3 TERRANE STRATIGRAPHY 111 5.4 LOWER TO MIDDLE JURASSIC STRATA 114 5.5 AGE CONSTRAiNTS 116 5.6 GEOCHEMISTRY 117 A. Major and Trace Element Geochemistiy 124 B. Rare Earth Elements 131 5.7 ISOTOPIC SIGNATURE 136 5.8 CONSTRAINTS ON ARC CORRELATION 141 A. Lithostratigraphic Considerations 141 B. Temporal Considerations 143 C. Geochemical Considerations 144 D. Isotopic Considerations 145 E. Structural Considerations 145 5.9 CONCLUSIONS 147 6. REGIONAL TECTONOSTRATIGRAPHIC CORRELATIONS IN THE SOUTHERN CANADIAN CORDILLERA: IMPLICATIONS FOR JURASSIC TERRANE LINKAGES AND BASIN EVOLUTION 6.1 INTRODUCTION 149 6.2 GEOLOGIC SETTING 151 A. Terrane Distribution 152 6.3 STRATIGRAPHIC CHARACTERIZATION 156 A. Harrison Terrane 156 V a. Terrane Description 156 b. Lithostratigraphy 157 c. Biostratigraphy 159 d. Volcanic Geochemistry 160 e. Isotopic signature 160 f Depositional Environment 165 B. Cadwallader Terrane 166 a. Terrane Description 166 b. Lithostratigraphy 167 c. Biostratigraphy 170 d. Volcanic Geochemistry 171 e. Isotopic signature 172 J Depositional Environment 172 C. Bridge River Terrane 175 a Terrane Description 175 b. Lithostratigraphy 177 c. Biostratigraphy 181 d. Volcanic Geochemistry 183 e. Isotopic signature 186 f Depositional Environment 189 D. Methow Terrane 191 a. Terrane Description 191 b. Lithostratigraphy 192 1. Boston Bar Formation 192 2. Dewdney Creek Formation 195 c. Biostratigraphy 198 d. Volcanic Geochemistry 199 e. Isotopic signature 201 f Depositional Environment 203 6.4 STRATIGRAPHIC CORRELATIONS 207 A. Lithostratigraphic Correlations 207 B. Biostratigraphic Correlations 212 C. Volcanic Geochemistiy Correlations 213 D. Isotopic Signatures 216 6.5 BASIN EVOLUTION MODEL 220 7. CONCLUSIONS 230 a. Tectonic Implications 234 8. REFERENCES 238 APPENDICES 254 APPENDIX A - ANALYTICAL TECHNIQUES 254 APPENDIX B - ANALYTICAL PRECISION 258 APPENDIX C - SAMPLE LOCATIONS 264 APPENDIX D - TIHN SECTION DESCRIPTIONS 277 APPENDIX E - CURRENT RESEARCH PUBLICATIONS 291 El. Mahoney, 1991 292 E2. Mahoney, 1992 298 E3. Mahoney and Journeay, 1993 308 E4. Journeay and Mahoney, 1994 318 vi LIST OF FIGURES Figure 1.1 - (a) - Morphogeologic map of the Canadian Cordilera; (1,)- Schematic terrane map of the Canadian Cordillera 2 Figure 1.2 - Schematic terrane map of the southern Canadian Cordillera 4 Figure 2.1 - Geographic map of western Pacilic marginal basins, with crustal isotopic domains 16 Figure 2.2 - Schematic stratigraphic sections of Neogene sediments in western Pacific marginal basins 18 Figure 2.3 - Schematic stratigraphic sections of Neogene Shilcoku Basin sediments 20 Figure VS. 87SrI86Sr 2.4 - Nd isotopic diagram for three western Pacific marginal basins 28 Figure 2.5 - Depth vs. ENd for drill holes in the Shikoku Basin 32 Figure 2.6 - Age vs. ENd for drill holes in the Shikoku Basin 33 Figure 2.7 - Age 87Sr/86Sr for drill holes in vs the Shikoku Basin 34 ..jSm/Nd Figure 2.8 vs. ENd for samples from the Shikoku Basin and Sea of Japan 33 Figure 3.1 - Geographic location map of the southwestern British Columbia 45 Figure 3.2 - Generalized geologic map of southwestern British Columbia 47 Figure 4.1 -Schematic terrane map of the southern Canadian Cordillera and generalized stratigraphic

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