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-- -- U11111" EXPERIMENTAL INVESTIGATIONS OF DIFFERENTIATION PROCESSES IN THE TERRESTRIAL PLANETS by GLENN ALLAN GAETANI B.S. Geology University of Massachusetts at Amherst, 1985 M.S. Geology State University of New York at Albany, 1990 Submitted to the Department of Earth, Atmospheric, and Planetary Sciences in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY in GEOLOGY at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 1996 @ Massachusetts Institute of Technology Signature of Author Department of Eari, Atmospheric, and Planetary Sciences May 17, 1996 Certified by Timothy L. Grove Thesis Supervisor S- -> Accepted b' y i ' Thomas H. Jordan MASSACHUSETTS INSTi ' OF TECHNOLOGY AIN Department Head YIYI ,Ul0llMYili'im , III IIillllli m u mooul i 3 EXPERIMENTAL INVESTIGATIONS OF DIFFERENTIATION PROCESSES IN THE TERRESTRIAL PLANETS by GLENN ALLAN GAETANI Submitted to the Department of Earth, Atmospheric, and Planetary Sciences in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Geology ABSTRACT Experimental phase equilibria studies are used to place geochemical and petrologic constraints on the processes by which terrestrial planets differentiate into crust, mantle, and core. Chapter 1 presents melting experiments performed at 1.2 to 2.0 GPa to determine the influence of H20 on partial melting of mantle peridotite. The experimental results indicate that the solidus-lowering effect of 1H20 on peridotite has a strong influence on the phase equilibria of hydrous mantle melting. This study places experimental constraints on the conditions of melt generation in subduction zones, and the composition of material added to the crust by convergent margin magmatism. Chapter 2 presents experiments that determine the influence of f 2/fs2 conditions on olivine/sulfide melt dihedral angles. The results demonstrate that increasing the concentration of oxygen dissolved in an FeS melt lowers the olivine/sulfide interfacial energy enough to produce dihedral angles less than 600 at upper mantle conditions. These experimental results indicate that during the later stages of accretion of the Earth, sulfide may have efficiently segregated from the upper mantle into the core via porous flow. Chapter 3 presents experiments performed over a range of fo2/fs2 conditions, at constant pressure and temperature, that investigate the partitioning of first series transition metals and W among coexisting silicate melt, sulfide melt, and olivine. The experimental results quantify the effects of variable fo2/f 2 ratio on partitioning. Trace element modeling performed using the experimentally-determined partition coefficients place constraints on the conditions at which core formation took place in the Earth and Mars. Chapter 4 presents experiments performed in the system CaO-MgO-Al20 3-SiO2 at 1 atm pressure, over a small temperature range, that differentiate crystal-chemical controls on mineral/melt partitioning of rare earth elements from the effects of pressure and temperature. The experimental results demonstrate that the Ca-Tschermakite content of high-Ca clinopyroxene exercises an important control on rare earth element partitioning for pyroxene co-existing with basaltic melt. These results provide a clearer understanding of the geochemical behavior of the rare earth elements during mantle melting and crystallization differentiation of the basaltic magmas that form the oceanic crust. Thesis Supervisor: Timothy L. Grove Title: Professor of Geology Ili 11,1, W11111~l 1 , 01,1U6 10 i lil" 5 To Renee I couldn't have done it without you. - "'IIIY~~~~I ,,i NYIIIIHEM II1Yii ACKNOWLEDGMENTS When I was young my grandmother liked to tell the story of my graduation from kindergarten. All of the graduates were standing in a church parking lot wearing our little red robes while the teacher went around and spoke with each of the families. When she came to us the teacher asked me what I wanted to be when I grew up, to which I replied without hesitation "A scientist". The teacher turned to my family and said "And he will be one too!" For better or worse, I guess that's what I am now. The six years that it took to earn my scientist's union card (also known as a Ph.D.) have enabled me to grow in ways that I never could have anticipated when I first came to MIT. During that time it has been my privilege to learn from an amazing group of people. Tim Grove has been both an advisor and a friend. The breadth of his knowledge and his scientific interests has provided me with the opportunity to work on a wider array of problems than I ever could have imagined 6 years ago. I will be forever grateful that he taught me the value of a good experiment. There is no way to properly acknowledge all of the hours that he spent helping me decide which experiment to do, listening to practice talks, bleeding red ink all over yet another version of some manuscript, looking at thin sections, or just drinking beer. Trekking across Oregon with the Grove family is an experience that I will never forget. Fred Frey's door was always open (well, it was actually slightly ajar), and he was never too busy to talk about some scientific problem, or the rigors of graduate school. His seminars taught me to think objectively and critically about science. Sam Bowring was always there to remind the lab rats about the geology. I also appreciated the fact that his office was messier than mine. Greg Hirth brought an unbridled enthusiasm to bear on every scientific problem and, perhaps more importantly, was always willing to talk baseball. I consider myself lucky to have him as a colleague and a friend. Paul Hess provided a refreshing point of view during my thesis defense. I am grateful to him for letting me know that it was supposed to be "a celebration, not a test". I was nervous anyway. I probably never would have done any of this if it were not for Tony Morse, who sparked my interest in experimental petrology more than 10 years ago. I owe a debt of thanks to friends and fellow graduate students. Eiichi Takazawa, Huai-Jen Yang, and I arrived at MIT together and finished graduate school together. In the interim, I got to know them as dedicated scientists and great people. I had the unusual privilege of sharing an office with Tom Wagner for more than 5 years. I enjoyed the times we spent talking about science, smoking cigars at Fenway Park, or just being WG's. I don't know if I would have kept my sanity without the friendship of Alberto Saal (a.k.a. the Barbecue King). I will always carry a mental picture of him as a young boy (with a beard) wearing a Batman costume while jumping up and down on the furniture and yelling "It's okay". He is surely Argentina's most valuable export. Ro Kinzler has been a constant source of advice and support. I value her friendship more than she knows. Deb Hassler made every trip to WHOI fun (usually by getting me drunk). Ken Koga gave our office that special smell of stir-fried fish, even though he swore that he was having chicken for lunch. The friendship and support of Ben Hanson has been invaluable. I respect him as much as anyone I know (although I do question his sanity). I thoroughly enjoyed his late night, long distance telephone calls complaining about Mike Hargrove. Barry Croke provided a welcome relief from graduate school as a drinking buddy and fellow baseball addict. The Friday night beer hours and trips to the Cambridge Brewery with Mike Jercinovic were great. Having Steve Parman and Jim Van Orman in the lab has made the past 2 years fun and interesting. Steve also provided me with a lifetime supply of bubble gum. Neel Chatterjee has been a wonderful addition to the microprobe lab. Living with all of the people in McCormick Hall has really made me feel like a part of MIT society. The friendship of Monica Gupta, Gargi Patel, and Umber Ahmad was especially important. My family, both immediate and extended, contributed many things in many ways. The love and support of my parents, Nick and Joan Gaetani, through 6 more years of school has been greatly appreciated. I will always be indebted to my father for teaching me, through the way he lives his life, the value of hard work and family. I am also grateful to my in-laws, Bob and Carol Mandarano, for their support and for always being there with a rally when one was needed. I did not earn this Ph.D. alone. My wife, Renee, made many sacrifices over the past 6 years. She worked at jobs she didn't like, lived in an apartment that was too small, and put up with having a husband who was never home. Her strength and courage during the most difficult times have served as an inspiration to others. This dissertation is dedicated to her. The arrival of Hope Claire has made the past year very special. I will always treasure the mornings I spent trying to feed her rice crispies while Sesame Street was so much more interesting than eating. May she always smile and enjoy life just the way that she does now. She sets an example for us all. -MM 11,100,1114101i.0 i0-m1Mi,, 0h1h .0 Ingl 9 TABLE OF CONTENTS ABSTRACT ................................................. ............................................................. 3 DEDICATION .............................................................................................................. 5 ACKNOWLEDGMENTs ............................................................. ........................... 7 TABLE OF CONTENTS ................................................................................................. 9 INTRODUCTION
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