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Ann Arbor, MI48106 PARTIAL MELTING ON THE ACAPULCOITE-LODRANITE METEORITE PARENT BODY A DISSERTATION SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAII IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOLOGY AND GEOPHYSICS MAY 1994 By Timothy J. McCoy Dissertation Committee: Klaus Keil, Chairperson G. Jeffrey Taylor Edward R.D. Scott Jeffrey F. Bell David W. Muenow ACKNOWLEDGMENTS lowe great debts of gratitude to so many people. First, I thank my wife Darlene who has cheerfully tolerated graduate school, including the constant moving associated with a life in academia. Without her support, this would never have been possible. I would also like to thank my parents - Dr. Harold E. McCoy and Joyce E. McCoy. They have been a constant source of support. In my academic life, Klaus Keil, G. Jeffrey Taylor and Edward R.D. Scott have guided me both professionally and personally. They have literally taught me everything I know about meteorites. In the process, I also learned that being a good scientist doesn't equate with being unbearable. As pointed out by Jeff, this is a lesson that some of our more successful colleagues at other universities have yet to learn. No dissertation on meteorites could possibly be complete without thanking the people who supplied the meteorites. lowe much to the late Glenn Huss, Elbert King, David New, Robert Haag, Adrian Brearley, Kurt Marti, Art Ehlmann, Carleton Moore, Lise Vistisen, Ivan Wilson, Monica Grady and the British Museum, Roy S. Clarke, Jr. and the Smithsonian Institution, the Meteorite Working Group, the National Institute of Polar Research and EUROMET. Roy S. Clarke, Jr. (Smithsonian) was particularly helpful to me during a two week visit (invasion?). I am particularly grateful to Glenn Huss, who first brought Monument Draw to our attention. This single meteorite has probably done more to spark my interest in acapulcoites and lodranites and has taught me more about the early evolution of the solar system than any other I have studied. I deeply regret that Glenn Huss didn't live long enough to understand the importance of this rock. I am grateful to my many co-authors and collaborators. Within the University of Hawaii, Klaus Keil, Jeff Taylor, Ed Scott, Henning Haack, Rachel Friedman, Gretchen Benedix, Lisa Kinsey, Pete Mouginis-Mark, Dave Mueonw and Lionel Wilson have been (or will be) the best co-authors anyone could ever want. The bulk of my co-authors have, iii however, been outside of the University of Hawaii. These people willingly signed on to multi-author, multi-year projects with the only assurance being our word that papers would be published. I hope they aren't disappointed. These include Robert N. Clayton, Toshiko Mayeda, Mini Wadhwa, Ghislaine Crozaz, Don Bogard, Dan Garrison, Art Ehlmann, Ignacio Casanova, Marilyn Lindstrom, Ian Steele, Magnus Endreji, B.F. Leonard, Richard Ash, A.D. Morse, Colin Pillinger, Rainer Wieler, Carleton Moore, Derek Sears, Paul Benoit, Ian Hutcheon, Adrian Brearley, Chuck Hohenberg, Karl Kehm and Bob Nichols. Bob Clayton deserves a special tip of the hat. I think it is fair to say that the acapulcoite­ lodranite project could not have been completed with out his enormous effort. It is easy to forget the technicians who toil day after day with little recognition. Tom Servilla, Tom Hulsebosch, Mike Garcia, Tom Tatnall and Don McGee all deserve special thanks for their expert technical assistance. You don't really appreciate how easy they make your life. I also would like to thank Karen Ogino, Myrna Miyashiro, Fred Waldman, Lorna Ramiscal, Gary Kabazawa and all the others in PGD who kept the paperwork at bay and made sure I had a paycheck every two weeks (although it could have been a bit bigger). I am one of the lucky graduate students who never had to think twice about the source of my next paycheck. I can thank NASA grants NAG 9-30 and NAGW-3281 for most of this support, but the person to really thank is the Principal Investigator, Klaus Keil. I should also thank a few organizations who saw fit to award me scholarships, namely the Nininger Meteorite Award, the Watamull Foundation and the ARCS Foundation. Finally, I would like to thank the other graduate students and post-docs who I have been fortunate enough to know for the past few years. Aurora Pun has been my e-mail buddy and I probably talked more to her bye-mail than I talked to anyone I worked with in real life. Gretchen Benedix and Rachel Friedman moved into our office just in time to save iv me from being buried under Mark Robinson's stuff. Beth Clark and James Granahan were a constant source of amusement. So many questions about meteorites!!! Henning Haack and Marc Norman were good friends and better post-docs. Mark Robinson and Keith Horton were always good for a laugh in our office. Puanani Akaka will always be the data center dudette. Dave Blewett and Chris Peterson were good for a conversation over the wall and Dave even survived microprobe training with me!!! I'm absolutely convinced Scott Rowland has personally been everywhere in Hawaii. Michelle Tatsumura, Rick Holasek, Barb Bruno, Charles Budney, Karl Bornhoeft, and Cynthia Wilburn always had an open door (although Cynthia should carefully check that rock on her desk every morning). Finally, thanks to all the students ofHIG, particularly Sarah Sherman and Sara Finnemore. v ABSTRACT Many asteroids experienced partial melting and incomplete differentiation. Our knowledge of the detailed of these processes are incomplete, owing to the paucity of partially melted meteorites. I studied two groups of meteorites which originated on a common parent body and are residues of a wide range of partial melting - acapulcoites and lodranites. These meteorites formed from a chemically and isotopically heterogeneous precursor chondrite. Heating and cooling occurred early in the history of the solar system, as evidenced by the -4.51 Ga 39ArAOAr age of acapulcoites and the -4.48 Ga 39ArAOAr age of the lodranite Gibson. The heating was probably caused by non-collisional heat sources. Acapulcoites (Acapulco, Monument Draw, Yamato 74063, ALH A77081, ALH A81261, ALH A81315, ALH 78230, ALH A81187 and ALH 84190) formed by low degrees of partial melting (e.g., Fe,Ni-FeS eutectic melting, but not silicate partial melting). Fe,Ni-FeS partial melts concentrated into micron- to centimeter-sized veins, but migration distances were short. In contrast, lodranites (Lodran, Gibson, Yamato 791491, Yamato 791493, Yamato 74357, Yarnato 8002, Yamato 75274, MAC 88177, LEW 88280, EET 84302 and FRO 90011) experienced higher degrees of partial melting, including silicate partial melting. The higher degree of partial melting allowed efficient melt migration, depleting the residues in plagioclase and troilite. Volatiles played a major role in melt migration, driving partial melts to the surface where they were erupted at greater than the escape velocity and lost into space. Thus, basaltic partial melts are not sampled as discrete meteorites. In one meteorite (LEW 86220), these basaltic, Fe,Ni, FeS-rich partial melts from a lodranite source region were injected into a cooler, acapulcoite region. The acapulcoite-lodranite parent body experienced a range of partial melting and melt migration. Cooling of this body may have been complex, with slow cooling at high temperatures, rapid cooling at intermediate temperatures, and slow cooling at low temperatures, indicating Vi that the body may have broken up and gravitationally reassembled. One to three impact events liberated the acapulcoites and lodranites from their parent body. These meteorites represent our best opportunity to understand partial melting and incomplete differentiation of asteroids. vii TABLE OF CONTENTS ACKNOWLEDGMENTS iii ABSTRACT vi LIST OF TABLES , xi LIST OF FIGURES , xii CHAPTER 1 INTRODUCTION 1 CHAPTER 2 MONUMENT