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Geophysical applications in compressional orogens Item Type text; Dissertation-Reproduction (electronic) Authors Libarkin, Julie Carol Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 04/10/2021 15:26:40 Link to Item http://hdl.handle.net/10150/289021 INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. 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Contact UMI directly to order. Bell & Howell Information and Learning 300 North Zeeb Road, Ann Artx>r, Ml 48106-1346 USA 800-521-0600 GEOPHYSICAL APPLICATIONS IN COMPRESSIONAL OROGENS by Julie Carol Libarkin A Dissertation Submitted to the Faculty of the DEPARTMENT OF GEOSCDENCES In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 1 999 UMI Number: 9946823 UMI Microform 9946823 Copyright 1999, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 2 THE UNIVERSITY OF ARIZONA ® GRADUATE COLLEGE As members of the Final Examination Committee, we certify that ve have read the dissertation prepared by jniio r. riharkln entitled Geophysical Applications in Compressional Orogens and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of Doctor of Philosophy n H.,, Robert Butl Date I Date Date susan Beck . Date 1, J999 Michelle Hall-Wallace Date ^ Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copy of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement. P __ _ _iH w • 191 Dissertation Director pobert Butler I 3 STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations firom this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED bu 4 ACKNOWLEDGMENTS This dissertation has taken many unforeseen turns and changed many times over the past five years. First and foremost, I would like to thank my advisor, Robert Butler for giving me the freedom to indulge my scientific interests in a variety of different arenas. His willingness to introduce me to the world of paleomagnetism and teach me the tricks of the trade was invaluable for my successful paleomagnetic study of Bolivia. As well, Clement Chase and Jay Quade deserve thanks for including me in their innovative cosmogenic isotope studies and encouraging my own theoretical meanderings. Comments made by these and the other members of my dissertation committee, Peter Coney, Susan Beck, and Michelle Wallace, vastly improved this manuscript. The paleomagnetic study of Bolivia would not have been possible without the field assistance of David Richards, Thierry Sempere, and Robert Butler. Thierry Sempere also provided valuable insight into the geology of Bolivia. Laboratory work completed by Brigette Martini, Scott Balay, and Rob Feyerharm helped speed this project along. Finally, conversations with Rob Van der Voo were very useful to our final data interpretation. The 2lNe cosmogenic work would not have been possible without the assistance of Jane Poths and Bill Phillips of Los Alamos National Laboratory and Nat Lifton of the University of Arizona. Both Bill and Nat were invaluable in the early sample preparation stages. Bill and Jane spent many hours training me on the noble gas mass spectrometer and in processing and interpreting my data. All three were willing participants in many enthusiastic discussions about cosmogenic isotopes in general and my project in particular. Dr. Laurie Brown and Dr. Peter Lipman participated in several insightful discussions of the San Juan Volcanic Field and Fish Canyon Tuff of Colorado. Finally, William Hart provided field assistance without which I would not have been able to collect all of my samples. I would like to thank my family and friends for their wholehearted encouragement and support. I would not have been able to complete this dissertation without their motivation. Finally, I thank Michael G. Moore for his unwavering encouragement and for acting as an enthusiastic sounding board for all of my ideas. 5 TABLE OF CONTENTS Page ABSTRACT 6 1. INTRODUCTION 7 1.1. Cosmogenic Isotopes and Their Uses 8 1.2. Cosmic Radiation 9 1.2.a. Galactic cosmic rays 11 1.2.b. Solar cosmic rays 14 1.3. History of Cosmogenic Isotope Studies 15 2. PRESENT STUDY 19 2.1. General Conclusions: Appendix A 19 2.2. General Conclusions: Appendix B 20 2.3. General Conclusions: Appendix C 21 APPENDIX A. COSMOGENIC 2lNE IN QUARTZ AS A POTENTIAL PALEOALTIMETER: CASE STUDY FROM THE 28 MA FISH CANYON TUFF, COLORADO 23 APPENDIX B. TWO-ISOTOPE METHOD FOR ESTIMATING PALEOELEVATION 52 APPENDIX C. TERTIARY REMAGNETIZATION OF PALEOZOIC ROCKS FROM THE EASTERN CORDILLERA AND SUB-ANDEAN BELT OF BOLIVIA 76 REFERENCES 115 6 ABSTRACT Geologic endeavor is a continual search for windows into the past. Our ability to characterize ancient geological processes is only as good as the techniques we have at our disposal; often the desire to uncover new information drives the development of new geologic methods or the modification of old techniques. This dissertation is composed of a series of projects focused on gaining new insights into the history of orogenic systems through the application of existing techniques or the development of new methods. Three primary projects were undertaken, the first a paleoelevation study aimed at determining the elevation of the Colorado Rockies 28 million years ago (Ma). This study was an attempt to both constrain the paleoelevational geometry of North America and test a new paleoaltimetry technique. This "one-isotope" technique relies on the relationship between cosmogenic isotope production rates and elevation; while a paleoelevation for the Colorado Rockies was not derived, the technique should prove useful in other geologic situations. From this initial technique, a two-isotope technique was derived which bypasses some of the difficulties inherent to the one-isotope method. A complete theoretical development of this two-isotope technique is included. Finally, a project documenting the wide-spread remagnetization of a suite of pre-Cenozoic Bolivian red sedimentary rocks reflects the impact orogenesis can have on an entire region. Taken as a whole, these projects focus on both the effects of mountain-building events and the techniques we can use to better understand them. 7 CHAPTER 1. INTRODUCTION Hutton's Principle of Uniformitarianism states that the geological processes we see operating today occurred in the same way throughout the Earth's history. Geologic research is based upon this idea; we infer the evolution of the Earth by making comparisons between the rock record and present-day geological processes. Making these connections requires many assumptions, primary of which are assumptions about the morphology and timing of deformation of the earth's landmasses. To truly be able to interpret the rock record, geologists need to know, at the very least, the paleotopography of the major continents. In this work, cosmogenic isotopes and magnetization preserved in rocks are used as a means for determining paieoelevation and understanding the processes associated with mountain-building, respectively. Two techniques are developed which rely upon the relationship between cosmic ray flux and elevation. The one-isotope technique yields a cosmogenic isotope production rate calculated from measured cosmogenic isotope concentrations and a known paleosurface exposure time. Comparing this production rate to a known sea level rate and using the production rate-elevation relationship will give a paieoelevation for the studied surface. This technique was tested on the 28 Ma Fish Canyon Tuff in Colorado (see Appendix A for full details). Alternatively, two cosmogenic isotopes with different production mechanisms (such as muon capture and neutron spallation) can be used to estimate a paieoelevation.

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