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Hydrothermal Alteration of Oceanic HYDROTHERMAL ALTERATION OF OCEANIC LITHOSPHERE: A GEOCHEMICAL STUDY OF THE OMAN OPHIOLITE ! ! ! ! ! ! ! ! ! A Thesis Presented to the Faculty of the Graduate School of Cornell University in Partial Fulfillment of the Requirements for the Degree of Master of Science By Chen Chen January 2012 ! ! © 2012 Chen Chen ! ! HYDROTHERMAL ALTERATION OF OCEANIC LITHOSPHERE: A GEOCHEMICAL STUDY OF THE OMAN OPHIOLITE Chen Chen Cornell University 2012 The Oman ophiolite, one of the best preserved and best exposed ophiolites, is part of the Tethyan Ophiolite series in the Mediterranean, formed during the spreading of Tethys Ocean and obducted during the closure of this ocean. Isotopic, major and trace element analyses were conducted on samples collected from Nahkl, Sumail and Wadi-Tayin nappes in this study. 87Sr/86Sr and !18O values indicate the circulation system is not a decoupled two-layer alteration system. Instead, high temperature alteration and low temperature alteration are alternately swiping down to the lower gabbro section, as suggested by Nicolas et al 2003. Fixation of CO2 into ultramafic rocks after the obduction has changed the isotopic compositions, increasing the 87Sr/86Sr and !18O values, which should be considered when interpreting isotope ratios of ophiolites. ! ! BIOGRAPHIC SKETCH Chen Chen was born in Xinyang, Henan Province, China, but grew up in Qingdao, Shandong Province. She had a wonderful childhood in the coastal city and her memories were full of delicious seafood and happy times at the beach. In high school, she studied very hard in order to be admitted to a good university, as all Chinese students do. She originally chose Civil Engineering as first undergraduate major and English as second, however was assigned to the field of Geochemistry. At China University of Geosciences (Wuhan), she found out that Earth Science is actually very different from simply coal mining, and studying the Earth is a very fascinating subject. After four years of classroom lectures and summer field schools, she decided to continue her interest in exploring the Earth in the United States. Since summer 2008, she has been studying with Professor William White at Cornell University. Life at graduate school, though challenging, has been an exciting and rewarding experience. She has learned how to cope with difficulties that life throws up, and is now ready to turn over a new page in her life. !!!" " BIOGRAPHIC SKETCH Chen Chen was born in Xinyang, Henan Province, China, but grew up in Qingdao, Shandong Province. She had a wonderful childhood in the coastal city and her memories were full of delicious seafood and happy times at the beach. In high school, she studied very hard in order to be admitted to a good university, as all Chinese students do. She originally chose Civil Engineering as first undergraduate major and English as second, however was assigned to the field of Geochemistry. At China University of Geosciences (Wuhan), she found out that Earth Science is actually very different from simply coal mining, and studying the Earth is a very fascinating subject. After four years of classroom lectures and summer field schools, she decided to continue her interest in exploring the Earth in the United States. Since summer 2008, she has been studying with Professor William White at Cornell University. Life at graduate school, though challenging, has been an exciting and rewarding experience. She has learned how to cope with difficulties that life throws up, and is now ready to turn over a new page in her life. !!!" " ACKNOWLEDGMENTS I would like to firstly thank my advisors Professor William White and Professor Christopher Andronicos for their generous support and guidance that I am truly thankful for. It has been a great pleasure to work with them, critically discuss results and get helpful guidance on research from them. They not only taught me a serious attitude towards research is very important, but also gave me advice on life choices. Professor Louis Derry helped me a lot with laboratory work and data processing. Both his intelligence and humor really made problems much easier to solve. Professor Lawrence Cathles has supported the field trips and the chemistry analyses in this study. Without his help, the study would not have been able to happen. I would also like to thank my fellow students Naomi Kirk-Lawlor, Kyle Trostle, Sander Hunter, Herdis Schopka, Ceren Karaca, Phoebe Judge, Gregg McElwee, Felipe Aron, Ashley Tibbetts, Caitlin Cox, Scott Henderson and many more who have helped me through difficulties in my studies and in my personal life. Having all of you as friends have made my graduate student life so enjoyable. I am greatly indebted to George Hade for his help with laboratory equipments. Without his help, I would not be able to get 87Sr/86Sr data, which is very important for this thesis. With the help of John Hunt, I have learned how to do microprobe work and conducted major element analysis. Finally, I would like to thank my parents Yiyuan Chen and Ying Wang and my good friends Sally Tang, Ben Hasseldine, Shanshan Zhang for their unwavering support. !#" " TABLE OF CONTENTS BIOGRAPHIC SKETCH............................................................................................... iii" ACKNOWLEDGMENTS ...............................................................................................iv" INTRODUCTION ...........................................................................................................1" Development of the Concept of Ophiolite ...........................................................2" Magmatic Process at Ocean Ridges.....................................................................7" Geological Setting of the Oman Ophiolite ..........................................................8" Mid-Ocean Ridge vs. Supra-Subduction Zone ..................................................10" Alteration Mechanism .......................................................................................20" METHODS ....................................................................................................................23" Sampling.............................................................................................................23" Major Elements ..................................................................................................23" Trace Elements...................................................................................................26" Isotope Ratios .....................................................................................................28" RESULTS ......................................................................................................................31" Major Elements ..................................................................................................31" Trace Elements...................................................................................................39" Isotope Analysis .................................................................................................39" METASOMATIC ANALYSIS.......................................................................................48" Principle..............................................................................................................48" Mathematics.......................................................................................................49" Analysis Results.................................................................................................52" DISCUSSIONS .............................................................................................................66" Hydrothermal Alteration of the Oman ophiolite..............................................66" Carbonation of the Oman Ophiolite..................................................................70" CONCLUSIONS............................................................................................................79" APPENDIX....................................................................................................................80" REFERENCES..............................................................................................................82" !" " LIST OF FIGURES Figure 1. Structure of the oceanic crust and representative outcrops in ophiolite complexes.........................................................................................................................6" Figure 2. Geologic map of the Oman ophiolite with sampling locations......................9" Figure 3. Tectonostratigraphy of the Oman ophiolite ................................................11" Figure 4. Schematic diagrams depicting detachment and initial emplacement of the Semail ophiolite.............................................................................................................14" Figure 5. Model of hydrothermal circulation system at a fast spreading ridge ........22" Figure 6. Google map locations of sampled lower gabbros from Wadi Samarh in Sumail nappe ................................................................................................................36" Figure 7. Bivariate diagrams of major elements/MgO ...............................................37" Figure 8. MORB normalized spider diagram of trace elements.................................41" Figure 9. MORB normalized spider diagram of rare earth elements ........................42" Figure 10. Variation of 87Sr/86Sr composition as a function of the depth.
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