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A Serial Cross-Section Analysis of the Lewiston Structure

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A Serial Cross-Section Analysis of the Lewiston Structure A SERIAL CROSS-SECTION ANALYSIS OF THE LEWISTON STRUCTURE, CLARKSTON, WASHINGTON By MICHAEL ROBERT ALLOWAY A Thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN GEOLOGY WASHINGTON STATE UNIVERSITY School of Earth and Environmental Sciences December 2010 To the Faculty of Washington State University The members of the Committee appointed to examine the thesis of MICHAEL ROBERT ALLOWAY find it satisfactory and recommend that it be accepted. ______________________________ A. John Watkinson, Ph.D., Chair ______________________________ Simon A. Kattenhorn, Ph.D. ______________________________ John A. Wolff, Ph.D. ii ACKNOWLEDGMENTS First and foremost I would like to thank Dr. A. John Watkinson not only for serving as chair on my committee, but for his patience, guidance, friendship, and mentorship throughout my graduate career. I am grateful to Dr. Watkinson for thorough edits and constructive criticism during the development of the final manuscript. I also thank committee members Dr. Simon A. Kattenhorn and Dr. John A. Wolff for reviewing the initial manuscript and providing helpful suggestions. Special thanks to Dr. Kattenhorn for teaching me the most valuable lesson I have learned during my graduate education: to trust and have confidence in my intuition. Thanks to Dr. Wolff for his help with the chemical analysis. I would like to express extreme gratitude to Dr. Stephen P. Reidel for help in the field, help with chemical data, allowing me to borrow his personal fluxgate magnetometer, constant email correspondence, sponsoring my abstract for AGU, providing helpful references, and editing figures and tables. Thank you Dr. Victor E. Camp, Dr. Peter R. Hooper, and Dean Garwood for helpful conversations, either through email or through the United States Postal Service. Also, thanks Dr. Camp and Dr. Hooper for allowing the reanalysis of samples from your past projects in the area. Thank you very much to the WSU Geoanalytical Laboratory staff for help preparing XRF samples. Special thanks to Rick Conrey for patience and kindness during the chemical analysis phase of the project in addition to teaching me how to use the fluxgate magnetometer. Also, thanks to Matt Engle for training me to prepare samples for XRF analysis. Thanks to Dr. Jure Žalohar for giving me access to and helping me with the software T-TECTO 3.0. iii A number of assistants helped in the field through helpful discussions and carrying samples. Thank you very much Rachel Brewer, Kevin Tarbert, and Brian Spall. Also, thanks to Jenice Jim for allowing me to borrow her dog Kona to help carry samples down the hill. Thanks to all of the landowners in the field area for allowing me access to their property, especially Pat McCann, and Gary and Cara Snyder. Very special thanks to Pat and Ryan McCann for helping me during a case of heat exhaustion. Also, thanks to Jenice Jim and Rachel Brewer for being there for me when I needed help as well. I thank my parents for financial support during my graduate career, but most of all for emotional guidance. Also, this project would not have been possible without the financial support from the School of Earth and Environmental Sciences, Geology departmental grants which include the Apatite to Zircon, Inc. (A-Z) Award and the H. Walter and Jeanette Praetorius / Exxon Graduate Fellowship in Geology. iv A SERIAL CROSS-SECTION ANALYSIS OF THE LEWISTON STRUCTURE, CLARKSTON, WASHINGTON Abstract By Michael Robert Alloway, M.S. Washington State University December 2010 Chair: A. John Watkinson The Lewiston Structure is located in southeastern Washington / west-central Idaho and is a generally E-W trending, asymmetric, non-cylindrical anticline in the Columbia River Basalt Group (CRBG) that transfers displacement into the Limekiln fault system to the southeast and the Silcott fault system to the southwest. A serial cross-section analysis and 3-D construction of this structure shows how the fold varies along its trend and sheds light on the deformational history of the Lewiston Basin. Construction of the fold’s 3-D form shows that the fold’s wavelength increases and amplitude decreases near its eastern and western boundaries. Balanced cross-sections show approximately 5 shortening across the structure which is consistent with the Yakima Fold Belt (YFB). Although the structure is similar to the YFB, it does not form part of a belt and its local nature has been suggested to mark the North American continental margin of the Cretaceous Discovery of an angular unconformity below the Grande Ronde Basalt – normal polarity unit 1 (GRB-N1) in addition to a variation of N1 unit thickness across the structure suggests that the fold was deforming before emplacement of N1. Analysis of structural data using the Gauss method for heterogeneous fault-slip data indicate N-S shortening prior to and after N1 v emplacement. Analysis of slip data for strain-inversion and specification of spatial-distribution patterns help identify the existence of a transpressional tectonic environment. The nature of faulting associated with the Lewiston Structure is a topic of some debate, namely the presence of a reverse fault on the southern limb of the fold. The reverse fault under debate outcrops to the east of the field area and is GRB-R2 (reverse polarity unit 2) juxtapose with Pliocene (?) gravels. Better control on unit thicknesses and map contacts rule out the surface exposure of a reverse fault on the southern limb of the fold in the field area. This major fault dies out or becomes blind before reaching the ID-WA border and the change in flow attitude from the north side of the river to the south is interpreted to be accommodated by an abrupt fold hinge beneath the Snake River. vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ........................................................................................................... iii ABSTRACT .....................................................................................................................................v LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES .........................................................................................................................x DEDICATION .............................................................................................................................. xii CHAPTER 1. INTRODUCTION ..................................................................................................................1 Geologic Setting ..............................................................................................................1 Structural-Tectonic Setting ..............................................................................................4 Stratigraphy .....................................................................................................................7 Location of Field Area ....................................................................................................8 2. PREVIOUS INVESTIGATIONS ........................................................................................10 3. ANALYSIS OF THE LEWISTON STRUCTURE .............................................................16 Introduction ...................................................................................................................16 Methods of Investigation ...............................................................................................19 Field Observations .........................................................................................................20 Chemical Analysis .........................................................................................................23 Results ...........................................................................................................................29 vii Discussion .....................................................................................................................40 Conclusion .....................................................................................................................53 REFERENCES ..............................................................................................................................55 APPENDICES 1. CHEMICAL ANALYSIS AND SAMPLE LOCATION ....................................................59 2. STRUCTURAL DATA ........................................................................................................70 3. PARAMETERS AND EXPLANATION OF PARAMETER VALUES USED FOR PALEOSTRESS INVERSION IN T-TECTO 3.0 ...............................................................72 4. REGIONAL STRATIGRAPHIC NOMENCLATURE AND ISOTOPIC AGES ...............78 5. TECHNIQUES USED WITH FIELD FLUXGATE MAGNETOMETER .........................80 GEOLOGIC MAP ..................................................................................................................Plate 1 viii LIST OF TABLES Table Page 1.1 Stratigraphic section for CRBG units in field area ..............................................................8 A-1.1. Normalized major element chemistry ................................................................................60 A-1.2. Unnormalized trace element chemistry .............................................................................63 A-1.3. Normalized major element chemistry for samples within field area but not collected by this
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