The Stratigraphy and Geochemistry of the Crescent Formation Basalts and the Bedrock Geology of Associated Igneous Rocks Near Bremerton, Washington
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Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship Winter 1989 The trS atigraphy and Geochemistry of the Crescent Formation Basalts and the Bedrock Geology of Associated Igneous Rocks Near Bremerton, Washington Kenneth P. Clark Western Washington University, [email protected] Follow this and additional works at: https://cedar.wwu.edu/wwuet Part of the Geochemistry Commons, and the Geology Commons Recommended Citation Clark, Kenneth P., "The trS atigraphy and Geochemistry of the Crescent Formation Basalts and the Bedrock Geology of Associated Igneous Rocks Near Bremerton, Washington" (1989). WWU Graduate School Collection. 652. https://cedar.wwu.edu/wwuet/652 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. MASTER'S THESIS In presenting this thesis in partial fulfillment of the requirements for a master's degree at Western Washington University, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of this thesis is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without mv written permission. Signature MASTER’S THESIS In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Western Washington University, I grant to Western Washington University the non-exclusive royalty-free right to archive, reproduce, distribute, and display the thesis in any and all forms, including electronic format, via any digital library mechanisms maintained by WWU. I represent and warrant this is my original work, and does not infringe or violate any rights of others. I warrant that I have obtained written permissions from the owner of any third party copyrighted material included in these files. I acknowledge that I retain ownership rights to the copyright of this work, including but not limited to the right to use all or part of this work in future works, such as articles or books. Library users are granted permission for individual, research and non-commercial reproduction of this work for educational purposes only. Any further digital posting of this document requires specific permission from the author. Any copying or publication of this thesis for commercial purposes, or for financial gain, is not allowed without my written permission. Kenneth P. Clark February 20, 2018 THE STRATIGRAPHY AND GEOCHEMISTRY OF THE CRESCENT FORMATION BASALTS AND THE BEDROCK GEOLOGY OF ASSOCIATED IGNEOUS ROCKS NEAR BREMERTON, WASHINGTON by Kenneth P. Clark Accepted in Partial Completion of the Requirements for the Degree Master of Science Dean of Graduate School /y Advisory Committee Chair THE STRATIGRAPHY AND GEOCHEMISTRY OF THE CRESCENT FORMATION BASALTS AND THE BEDROCK GEOLOGY OF ASSOCIATED IGNEOUS ROCKS NEAR BREMERTON, WASHINGTON A Thesis Presented to The Faculty of Western Washington University In Partial Fulfillment of the Requirements for the Degree Master of Science by Kenneth P. Clark January 1989 ABSTRACT A stratigraphic section developed for the Bremerton rocks in the Kitsap Peninsula suggests formation by rifting in a marine environment. Basal gabbro, dated by 40Ar/39Ar at 49.8 Ma plus or minus 0.8 Ma, and associated mafic to felsic plutonics, appear to be the source of a mafic dike complex that composes 100% of the stratigraphic level above the plutonics. These dikes are the apparent feeders to overlying submarine and subaerial volcanics. The previously unrecognized submarine sequence consists of interbedded basaltic breccia, tuffs, basalt flows, and basaltic sandstone, siltstone, and conglomerate. Approximately 1 km of columnar basalt flows cap the sequence. Structures in the Bremerton rocks suggest that as many as four deformations may have affected these rocks. In the middle Eocene, extension to the north or northwest caused rifting and emplacement of the mafic dikes and lavas; several faults show that this extension was joined or followed by northeast-directed compression. Small faults and shears may have formed later by compression to the northwest. Reactivation of one of these faults and emplacementof northwest-striking Cascade arc(?) dikes suggestthe latest deformation was extension to the northeast. The gabbro and basalts have chemistry transitional between N-type MORB and enriched ocean island basalt. Large-ion-lithophile to high-field-strength trace element ratios are similar to those of back-arc basin basalt. Felsic plutonics are enriched in elements (especially Zr) indicative of an arc influence. Several dikes intruding the gabbro are chemically indistinguishable from P-type (plume) ocean island basalt. Stratigr aphic sections were developed in the basalts of the Crescent Formation and for basalts near Port Townsend in the Olympic Peninsula. Comparison to the subaerial basalts near Bremerton shows that the latter are quite similar to the upper subaerial Crescent Formation basalts and Port Townsend basalts. New chemical data for 16 flows of the Olympic Peninsula basalts are also similar to that of the Bremerton rocks. Stratigr aphic and chemical similarities imply that rocks of all three areas are coeval. Deposition of the Crescent Formation basalts on a continentally-derived fan, stratigraphic and structural characteristics of the Bremerton rocks, and geochemical data on rocks of ail three areas suggestthat these rocks formed by rifting of the western margin of the North America continent. Following rifting and basalt generation, the rocks may have moved north IV due to oblique convergence of the oceanic and continental plates, where they were thrust under Vancouver Island along the Leech River Fault. Thrusting moved outboard of the basalts and underlying fan; continued convergence thrust marine sediments that make up the Olympic core rocks beneath the basalts and underlying fan. V ACWNOWLEDGEMENTS First I would like to thank my thesis committee. Scott Babcock's help interpreting the geochemical data was invaluable, as were our many discussions over beer and campfires. Speaking of beer, I'll always owe Dave Engebretson a keg for his help (that is, he will never collect); he always tooktime outto talk about my newest difficulty. Both Dave and Scott were excellent at cutting away the extraneous and getting to the core of a problem. Thanks are also due to Ross Ellis for his help interpreting my structural data. I would like to thank Devon Edrington, who taught me how to think, and Dr. James Hinthorne and Dr. Robert Bentley, who taught me how to use my head. They are not responsible for the deficiencies in either. Many thanks to Patty Combs; she made my work half as difficult and twice as much fun. Now if I could only get her to do field work too .... Vicki Critchlow can juggle nine tasks and still take time to help with a tenth. I would like to thank Pat Goldstrand, Joe Dragovich, Ben Adams, Jennie De Chant, Alice Shilhanek, and Galan Mclnelly for many lively debates concerning the Crescent Formation. Special thanks go to Jon Einarsen for shared insights; he also taught me to look up from the rock once in a while. When I was cold and tired, Jacquie Mclnelly took me in and gave me a place to get clean, rested, and fed. Julie Shuitz offered many pertinent observations on the geologyof western Washington; she fed me when I was hungry and gave me a new coffee percolatorl Joel Purdy and Tim Roberts worked with me on related problems throughout this study, and their help cannot be overestimated. We plan to come out with a small paper in the near future; hopefully, authors will be listed alphabetically. Bill McKinney, Forestry Supervisor for the Bremerton Water Department, was always ready to help. Without his cheerful assistance I could not have mapped the southern half of the Bremerton rocks. I look forward to working with him in the near future. I would like to thank the Washington State Division of Geology and Earth Resources for funding my date work and geochemical analysis. Tim Walsh and Josh Logan of the Department of Natural Resources in Olympia helped me in the field and with many tactical problems. Tim also gently stiff armed me into giving a talk, from which I learned a great deal. VI Finally I would like to thank my family. My folks, Galen and Marceille, were always there when I needed financial and moral support, and I love them dearly. Gary and Pat always had a place to sleep, good food, and good conversation: Jeff bought me a pair of boots when his own resembled sandals; I love you guys too. VII TABLE OF CONTENTS Page Number LIST OF FIGURES xi LIST OF TABLES xlii INTRODUCTION 1 Regional Geology 1 Previous Work 3 Bremerton area 3 Port Townsend area 4 The Crescent Formation on the Olympic Peninsula 4 STRATIGRAPHY 5 Introduction 5 Volcanic Stratigraphy 5 The lower Crescent Formation 9 The upper Crescent Formation 10 The Port Townsend basalts 10 The Bremerton volcanics 11 Comparison of the Volcanic Stratigraphies 11 Bremerton Stratigraphy 12 Regional and Geological Implications 14 Regional Correlations and the Bremerton Rocks as an 14 EruptiveSource The Bremerton Rocks compared with Oohiolites 15 The Eruptive Environment of the Bremerton Rocks 18 AGE-DATE SECTION 19 STRUCTURE 2i