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Finite-element modeling of large impact craters: Implications for the size of the Vredefort structure and the formation of multiple ring craters Item Type text; Dissertation-Reproduction (electronic) Authors Turtle, Elizabeth Pope, 1967- 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 10/10/2021 19:25:07 Link to Item http://hdl.handle.net/10150/282720 INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly fi-om 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. 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Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI A Bell & Howell Information Company 300 North Zeeb Road, Ann Aibor MI 48106-1346 USA 313/761-4700 800/521-0600 FINITE-ELEMENT MODELING OF LARGE IMPACT CRATERS: IMPLICATIONS FOR THE SIZE OF THE VREDEFORT STRUCTURE AND THE FORMATION OF MULTIPLE RING CRATERS by Elizabeth Pope Turtle A Dissertation Submitted to the Faculty of the DEPARTMENT OF PLANETARY SCIENCES In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 1998 UMI Nximber: 9901692 UMI Microform 9901692 Copyright 1998, 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 we have read the dissertation prepared by Elizabeth Pope Turtle entitled Finite-element modeling of large impact craters: Implications for the size of the Vredefort structure and the formation of multiple ring craters and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of Doctor of Philosophy fig., fkJW Date / , '•2.2 /^'s Richard J. Greenberg Date 2- Wi 1 1 iam B. Hubbard Date Randall M. Richardson Date 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. Disse^atipn^2^-1 Director /1A^ Date 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 from 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 4 ACKNOWLEDGEMENTS One of the advantages of my rather long stay in graduate school is the wide variety of projects in which I have the opportunity to become involved. As a result there are countless people with whom I have worked and to whom I am indebted for helping to make the research I have done and this dissertation possible; the acknowledgements given here are necessarily brief and regrettably incomplete. I wish to thank my advisor, Jay Melosh, for his suppon and guidance in the variety of research projects we have worked on together, as well as for his encouragement to become involved with other, sometimes unrelated, projects. I also wish to thank Elisabetta Pierazzo and Cynthia Phillips whose collaboration made a significant portion of the research presented in this dissertation possible. I am grateful to David lOnng for more reasons than can be listed here, to Andrew Freed who has helped me immensely with Tekton and finite-element modeling in general, to Uwe Reimold who showed me Vredefort, and to Alfired McEwen who not only got Cynthia and me out of some political hot water, but also made it possible for us to continue the research that got us there in the first place. I would especially like to thank Betty Pierazzo and Ralph Lorenz for reading early drafts of this dissertation from which it benefited greatly. I also want to take this opportunity to thank Carolyn Palmer for all her support, both administrative and otherwise. Joe Gotobed and Scottie Cantrell for maintaining the computers on which most of my research has been carried out, and Chris Schaller, Cynthia Phillips, Mike Nolan. Joe, and Scottie for answering my endless questions about and solving numerous problems with said computers. I am grateful to all of the professors from whom I have leamed so much both in and out of the classroom, especially Jay Melosh, Bill Boynton, Randy Richardson, Clem Chase, Bill Hubbard, Carolyn Porco, and Jim Elliott. I would also like to thank the many former LPL students who were here when I first arrived for their friendship and all their help and advice, especially Ellen Howell, Mike Nolan, Bill Bottke, Eric Asphaug, Will Grundy, John Stansberry, Steffi Engel, Ginny Gulick, Valerie Hillgren, Paul Geissler, Bashar Rizk, Doyle Hall, Ann Sprague, Lisa McFarlane, Alan Hildebrand, Kevin Garlow. and Anna Spitz. I wish to express my gratitude to all the friends and colleagues with whom 1 have both worked and played and who have made the work part much more fun: Barbara Cohen, Kimberly Cyr, Andrew Rivkin, Jennifer Grier, Betty Pierazzo, Cynthia Phillips, Rachel Mastrapa, Nancy Chabot, David Trilling, Seran Gibbard, Beth Clark, Mark Lemmon, Joe Spitale, Greg Hoppa, Josh Emery, Peter Lanagan, Dan Durda, Aileen Yingst, Michelle Minitti, the DIVA and AMBASSADOR design teams, Noreen Conarro, Seth Hansell, the members of all the various incarnations of LFP, Doug Dawson, Ron Vervack, Chris Schaller, Bob Reid, Rob Coker, FGC, and many others. Special thanks are due to Kimberly Cyr and Mark Lemmon with whom I shared two of the most difficult experiences of my graduate education (writing up and the written preliminary exam). I also wish to thank Gaelyn Davidson, Betz Quinan, Kim Golden, Andrew Schwarz, Susan Mol, David Hatch, and Carl Andersen for their continuing friendship. Finally, I wish to express my gratitude to my entire family for all their support and encouragement, especially: my husband, Ralph Lorenz, whose inspiration and love of science and engineering are contagious; my father, John Turtle, and grandmother, Lydia Turtle, who kindled my interest in the planets; my mother and father, Letitia and John Turtle, grandparents, Lydia and William Turtle and Letitia and Peter Williams, my aunts and uncles, especially. Bill Williams, Isabel and Kenneth Conant, and Sally and Peter Farrow for sharing with me their love of learning; Schrodinger for reminding me what the really important things in life are; and my sister, Sally Turtle, for everything. 5 TABLE OF CONTENTS STATEMENT BY AUTHOR 3 ACKNOWLEDGEMENTS 4 TABLE OF CONTENTS 5 LIST OF FIGURES 7 LIST OF TABLES 9 ABSTRACT 10 CHAPTER I: INTRODUCTION 12 CHAPTER 2: IMPACT CRATERING AND CRATER MORPHOLOGIES 19 2.1 Dynamics of hyper-velocity meteorite impacts 19 2.2 Impact crater morphology 24 2.3 Multiple ring craters 28 2.4 Formation mechanisms for multiple ring craters 33 2.4.1 Volcanic Modification (Hartmann and Yale, 1968, 1969) 33 2.4.2 Tsunamis or Gravity Waves (Van Dom, 1968; Baldwin, 1972) 35 2.4.3 Megaterraces (Head, 1974, 1977) 36 2.4.4 Nested Craters (Hodges and Wilhelms, 1978) 37 2.4.5 Ring-tectonics (Melosh and McKinnon, 1978) 39 2.5 Research Objectives 41 CHAPTER 3; MODELING 43 3.1 Overview 43 3.2 The Z-model of the crater excavation flow field 44 3.3 Finite-element modeling 49 3.3.1 Overview 49 3.3.2 The finite-element program Tekton 52 3.3.3 Rheology 55 3.3.4 Mesh Generation 58 CHAPTER 4: THE SIZE OF THE VREDEFORT STRUCTURE 69 4.1 Introduction 69 4.2 Present Structure and Age of Vredefort 70 4.3 History of study and evidence for impact origin 73 4.4 Previous estimates of the diameter of the Vredefort crater