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Paleomagnetism of the Mesozoic in Alaska a H PALEOMAGNETISM OF THE MESOZOIC IN ALASKA A H DISSERTATION c~: Presented to the Faculty of the * University of Alaska in Partial Fulfillment " *-'*U of the Requirements for the Degree of t , DOCTOR OF PHILOSOPHY CD by - Duane R. Packer Ci College, Alaska uL May 1972 PALEOMAGNETISM OF THE MESOZOIC IN ALASKA APPROVED: Chairman APPROVED: DATE: Dean of the College of Earth Sciences and Mineral Industry Vice President for Research and Advanced Study I/ ABSTRACT Over 400 oriented cores of Permian, Triassic, Jurassic, and Cretaceous sedimentary and igneous rocks were collected from 34 sites at 10 areas throughout southern Alaska. After magnetic 'cleaning' in successively higher alternating fields 179 samples were considered to be stable and to give statistically consistent results within each site and age group. Due to the lack of a sufficient number of stable samples, the results from Permian, Triassic, and Cretaceous rocks were inconclusive. The nine remaining Jurassic sites represent 100 samples from three general areas in southern Alaska. The mean paleomagnetic declinations calculated with respect to the present, Carey's model, and Grantz's model are not significantly different from one another and do not show a systematic change along the strike of the orocline. The paleomagnetic poles for the Jurassic from southern Alaska and North America are separated in the opposite direction to be explained by the Alaskan orocline. The Alaskan orocline as Carey defined it, therefore, does not appear to be a valid concept. The southern Alaskan Jurassic paleomagnetic pole is significantly different from the North American Jurassic pole. This suggests that since the Jurassic, southern Alaska must have moved approximately 18 degrees north and rotated 52 degrees clockwise to reach its present position. Tectonic interpretation of these results give a possible explanation for many of the geologic features observed in southern Alaska. hrVT, 71 ACKNOWLEDGEMENTS I would like to acknowledge with sincere gratitude and indebtedness the continual guidance, support, and encouragement offered by Dr. David B. Stone, who suggested this research topic originally and who was always more than willing to discuss its many aspects at length. I would also like to thank Dr. Douglas K. Bingham for "initiation" into the practical intricacies of paleomagnetic collection and data refinement. For invaluable support in many ways while in the field and for other assistance I offer sincere thanks to Dr. R. B. Forbes of the Geophysical Institute and to J. W. Deininger of the Geology Department, University of Alaska; D. H. Richter, N. A. Matson, and F. R. Weber of the Alaska Branch, United States Geological Survey; and B. Bender of the Columbia-Ward Cannery at Chignik, Alaska. I also thank G. W. New- man of Humble Oil and Refining Co., for field support and joint collection and analysis of results. A special tribute is due to Genevieve Edsall for the myriad of top-quality paleomagnetic measurements she conducted and for her close attention in completing the numerous other details of the work. Thanks are due to Pat Kirton for typing the preliminary draft. I would like also to thank LuAnne, my wife, for her typing and editing of the first drafts, and for her patience with long hours. This work was supported by a National Defense Education Act, Title IV, fellowship through the Geology Department, University of Alaska; and by grants GA 1216 and GA 12014 from the National Science iv Foundation, Geophysics and Earth Science Section, grant NGL-02-001-063 from the National Aeronautics and Space Administration, and State of 'laska funds through the Geophysical Institute, University of Alaska. V TABLE OF CONTENTS Page ABSTRACT ACKNOWLEDGEMENTS iv TABLE OF CONTENTS vi LIST OF ILLUSTRATIONS viii LIST OF TABLES xi CHAPTER I. ARCUATE TECTONIC FORM OF ALASKA 1 Topographic expression 1 Geologic expression 2 Discussion of origin 7 CHAPTER II. PALEOMAGNETIC APPROACH 17 Remanent magnetization 17 Paleomagnetism 19 Techniques 21 Application to structural problems 23 CHAPTER III. MESOZOIC PALEOMAGNETIC RESULTS FROM ALASKA 25 Alaska Peninsula 25 Geologic setting of the Alaska Peninsula 25 Sites on the Alaska Peninsula 31 Chignik Lake (CHL) 31 Chignik Lagoon (CHG) 41 Puale Bay (PLB) 42 Cape Kekurnoi (CPK) 45 vi P'age Katmai area (KTM) 50 Tuxedni Bay (TXD) 57 Southcentral Alaska 66 Geologic setting of the Upper Matanuska Valley 66 Sites in the Upper Matanuska Valley 70 Sheep Mountain (SHP) 70 Geologic setting of the Mentasta Mountains 73 Sites in the Mentasta Mountains 74 Mentasta (MNT) 74 Nabesna area (NBS) 75 Whitehorse, Canada 83 Geologic setting of the Whitehorse area, Canada 83 Sites near Whitehorse, Canada 87 Whitehorse, Canada (WTH) 87 CHAPTER 1l. ALASKAN MAGNETIC DECLINATIONS AND VIRTUAL GEOMIAGNETIC POLES 91 Alaskan orocline 97 Alaskan paleomagnetic poles 101 Polar wandering curves 104 CHAPTER V. TECTONIC IMPLICATIONS OF ALASKAN PALEOMAGNETIC DATA 126 Summary and Conclusions 126 Tectonic implications 127 Speculative reconstruction 127 Recommendations for future work 133 APPENDIX 135 REFERENCES 154 vii LIST OF ILLUSTRATIONS Figure Page 1-1 Major fault trends in Alaska and northwestern Canada. 4 1-2 Alaskan orocline and Arctic sphenochasm. 8 1-3 Correlation of tectonic elements between Alaska and Siberia in mid Paleozoic time. 13 3-1 Location map for place names and sampling localities on the Alaska Peninsula. 26 3-2 Paleomagnetic data for CHL-1, Chignik Lake, Alaska. 36 3-3 Paleomagnetic data for CHL-2, Chignik Lake, Alaska. 37 3-4 Paleomagnetic data for CHL-3, Chignik Lake, Alaska. 38 3-5 Paleomagnetic data for CHL-4, Chignik Lake, Alaska. 39 3-6 Paleomagnetic data for CHL-5, Chignik Lake, Alaska. 40 3-7 Paleomagnetic data for CHG, Chignik Lagoon, Alaska. 44 3-8 Paleomagnetic data for PLB, Puale Bay, Alaska. 47 3-9 Paleomagnetic data for CPK, Cape Kekurnoi, Alaska. 49 3-10 Paleomagnetic data for KTM-1, Katmai area, Alaska. 53 3-11 Paleomagnetic data for KTM-2, Katmai area, Alaska. 54 3-12 Paleomagnetic data for KTM-3, Katmai area, Alaska. 55 3-13 Paleomagnetic data for TXD-1, Tuxedni Bay, Alaska. 61 3-14 Paleomagnetic data for TXD-2, Tuxedni Bay, Alaska. 62 3-15 Paleomagnetic data for TXD-3, Tuxedni Bay, Alaska. 63 3-16 Paleomagnetic data for TXD-4, Tuxedni Bay, Alaska. 64 3-17 Location map for place names and sampling localities in central Alaska. 67 viii Figure Page 3-18 Paleomagnetic data for SHP, Sheep Mountain area, Alaska 72 3-19 Paleomagnetic data for MNT, Mentasta, Alaska. 77 3-20 Paleomagnetic data for NBS-1, Nabesna area, Alaska. 80 3-21 Paleomagnetic data for NBS-2, Nabesna area, Alaska. 81 3-22 Paleomagnetic data for NBS-3, Nabesna area, Alaska. 82 3-23 Location map for place names and sampling locality in the Whitehorse area, Canada. 84 3-24 Paleomagnetic data for WTH, Whitehorse area, Canada. 89 4-1 Mean VGP's for Triassic and Permian sites. 93 4-2 Mean VGP's for Jurassic sites. 94 4-3 Mean VGP's for Cretaceous sites. 95 4-4 Magnetic declinations from Alaska for the Triassic, Jurassic, and Cretaceous. 98 4-5 Magnetic declinations for Alaskan Jurassic results showing present position, Carey's model, and Grantz's model. 100 4-6 Selected North American paleomagnetic poles and Jurassic results from southern Alaska. 102 4-7 Permian paleomagnetic poles from North America. 107 4-8 Permian paleomagnetic poles from Asia. 108 4-9 Permian paleomagnetic poles from Europe. 109 4-10 Triassic paleomagnetic poles from North America. 110 4-11 Triassic paleomagnetic poles from Asia. 111 4-12 Triassic paleomagnetic poles from Europe. 112 4-13 Jurassic paleomagnetic poles from North America. 113 4-14 Jurassic paleomagnetic poles from Asia. 114 4-15 Jurassic paleomagnetic poles from Europe. 115 ix Figure Page 4-16 Cretaceous paleomagnetic poles from North America. 116 4-17 Cretaceous paleomagnetic poles from Asia. 117 4-18 Cretaceous paleomagnetic poles from Europe. 118 4-19 Polar wandering curve for North America. 121 4-20 Polar wandering curve for Asia. 122 4-21 Polar wandering curve for Europe. 123 4-22 Schematic representation of polar wandering curves for North America, Asia, and Europe. 125 x LIST OF TABLES Table Page 3-1 Paleomagnetic directions and pole positions for Chignik Lake, Alaska. 33 3-2 Paleomagnetic directions and pole positions for Chignik Lagoon, Alaska. 43 3-3 Paleomagnetic directions and pole positions for Puale Bay, Alaska. 46 3-4 Paleomagnetic directions and pole positions for Cape Kekurnoi, Alaska. 48 3-5 Paleomagnetic directions and pole positions for Katmai area, Alaska. 52 3-6 Paleomagnetic directions and pole positions for Tuxedni Bay, Alaska. 59 3-7 Paleomagnetic directions and pole positions for Sheep Mountain area, Alaska. 71 3-8 Paleomagnetic directions and pole positions for Mentasta, Alaska. 76 3-9 Paleomagnetic directions and pole positions for Nabesna area, Alaska. 79 3-10 Paleomagnetic directions and pole positions for Whitehorse area, Canada. 88 4-1 Paleomagnetic directions and pole positions for Triassic, Jurassic, and Cretaceous sites. 96 4-2 Mean paleomagnetic pole positions for North America, Asia, and Europe. 119 xi I. ARCUATE TECTONIC FORM OF ALASKA The arcuate form of Alaskan topography and tectonics has been a topic of speculation for many years, especially since the accep- tance of continental drift ideas spurred real interest in global geology. TOPOGRAPHIC EXPRESSION Besides the southern shoreline, the most obvious topographic feature in Alaska with an arcuate form is the Alaska Range, which is a part of the Cordillera that bounds the western edge of the Americas. The trend traced by the Coast Mountains of Canada, the Alaska Range and the Aleutian Range curves approximately 75 degrees in mid-Alaska. The Tanana River and the Kuskokwim and Nushagak Rivers create a lowland to the north that parallels the Alaska Range.
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