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Redox Status of Fe in Serpentinites of the Coast Range and Zambales Ophiolites

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Redox Status of Fe in Serpentinites of the Coast Range and Zambales Ophiolites University of Rhode Island DigitalCommons@URI Open Access Master's Theses 2014 REDOX STATUS OF FE IN SERPENTINITES OF THE COAST RANGE AND ZAMBALES OPHIOLITES Amy Stander University of Rhode Island, [email protected] Follow this and additional works at: https://digitalcommons.uri.edu/theses Recommended Citation Stander, Amy, "REDOX STATUS OF FE IN SERPENTINITES OF THE COAST RANGE AND ZAMBALES OPHIOLITES" (2014). Open Access Master's Theses. Paper 460. https://digitalcommons.uri.edu/theses/460 This Thesis is brought to you for free and open access by DigitalCommons@URI. It has been accepted for inclusion in Open Access Master's Theses by an authorized administrator of DigitalCommons@URI. For more information, please contact [email protected]. REDOX STATUS OF FE IN SERPENTINITES OF THE COAST RANGE AND ZAMBALES OPHIOLITES BY AMY STANDER A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIRMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN BIOLOGICAL AND ENVIRONMENTAL SCIENCES WITH A SPECIALIZATION IN ENVIRONMENTAL AND EARTH SCIENCES UNIVERSITY OF RHODE ISLAND 2014 MASTER OF BIOLOGICAL AND ENVIRONMENTAL SCIENCES WITH A SPECIALIZATION IN ENVIRONMENTAL AND EARTH SCIENCES THESIS OF AMY STANDER APPROVED: Thesis Committee: Major Professor Dawn Cardace Katherine Kelley Mark Stolt Nasser H. Zawia DEAN OF THE GRADUATE SCHOOL UNIVERSITY OF RHODE ISLAND 2014 ABSTRACT Although, the reduced status of the Earth’s upper mantle is a possible controller of the deep, rock-hosted biosphere, knowledge of the redox state of the mantle is incomplete. Peridotites (mantle rocks) are composed of ultramafic (Fe, Mg- rich) minerals such as olivine and pyroxene. During serpentinization, water and ultramafic minerals react, generating a package of secondary minerals dominated by serpentine. This releases hydrogen gas in amounts dependent on system geochemistry and largely controlled by the Fe(II) budget in the protolith, as well as other products. Microbial life can be fueled by the hydrogen produced by serpentinization in environments that are generally not regarded as hospitable to life—cool, dark, low energy, subseafloor settings. Peridotite-hosted vents in the seabed and springs in continental ophiolites reveal active microbial communities at work in these distinctive serpentinization-associated waters. In this study, 16 variably serpentinized peridotite samples from the Coast Range Ophiolite (CRO) (11 core samples and one hand sample) and Zambales Ophiolite (ZO) (four hand samples) were selected for study based on mineralogy. The objective of this study was to understand better the redox status of Fe in these rocks and produce possible H2 generation values for the CRO and ZO. Each sample was analyzed using X-ray diffraction and thin sections (when available) to identify possible Fe bearing minerals (olivine, spinel, serpentine, pyroxene, magnetite, other Fe-oxides). X-ray fluorescence was used to obtain the bulk concentration of Fe in each sample (~28,000 to 51,000 ppm (~3.7 to 6.5 wt% FeO)). Mössbauer spectroscopy was used to determine the percentage of total Fe that is Fe2+ (~23 to 70%), Fe3+ (~14 to 65%), and magnetite (~0 to 63%), which is a combination of Fe2+ and Fe3+. The data sets were integrated into a hydrogen generation model. I assumed that each sample was representative of the peridotite units of the corresponding ophiolite. This permitted computation of a range of total hydrogen production possible by the peridotite considered, until serpentinization is complete (~900 to 4800 Tmol H2 or ~2000 to 12,735 Tmol H2 if density is factored into the calculation). The CRO can produce less H2 per rock volume than the ZO because the CRO samples generally have a lower Fe concentration, but the CRO has a greater volume and can produce a larger total amount of H2. Variability in bulk rock Fe concentration and Fe valence states in samples taken in close proximity indicate diverse serpentinization reaction paths even in a single ultramafic unit. Tectonics, emplacement history, age, climate, composition, and hydrology of the ophiolite all influence the redox status in the modern, ophiolite- hosted ultramafics. ACKNOWLEDGEMENTS I would like to thank my adviser, Dr. Dawn Cardace, for all the support and help that she has given me over the last 2 years. She has led and guided me with patience, respect, and care throughout the process from applying to URI to completing this thesis. I most certainly couldn’t have done it without her. Thanks, Dawn. You rock! Thank you to my other committee members Dr. Katherine Kelley and Dr. Mark Stolt, and to my committee chair Dr. Louis J. Kirschenbaum for their willingness to support me in this endeavor. Thank you also, Mark Stolt, for the use of the XRF. Thanks go to my fellow graduate student and officemate, Ken Wilkinson, for his willingness to help with XRD sample prep. I think pounding rocks into powder did us both some good. Thank you, T. Julie Scott for being my partner in ophiolite crime and wading through the water and microbes while I hammered out the rocks. Thank you for all the talks, collaborations, and for all the fun we’ve had and adventures we’ve shared. Big thanks go to Dr. M. Darby Dyer for being an advisor on Mössbauer spectroscopy and allowing me use her instrument and run my samples. Thanks also goes to her lab, especially Melissa Nelms, for running my samples, training me on how to fit the resulting data, and fitting many of the samples for me. Further thanks go to CROMO investigators T. Hoehler, T. McCollom, and M. Schrenk; to C. Arcilla and colleagues at NIGS, University of the Philippines at iv Diliman; to A. Bowman and D. Carnevale for using GIS and geologic maps to constrain the area of the CRO; to Homestake Mining Co. and UC Davis McLaughlin Natural Reserve for core samples and advice especially from Scott Moore, Peggy King, Catherine Koehler, and Paul Aigner. Thank you for all the monetary support as well: Drilling and CROMO well installation was funded by the NASA Astrobiology Institute Director's Discretionary Fund under Carl Pilcher; subsequent research was funded jointly by the NSF Geobiology and Low Temperature Geochemistry Program, Award 1146910, and the Sloan Foundation, Deep Carbon Observatory via Deep Life I: Microbial Carbon Transformations in Rock-Hosted Deep Subsurface Habitats. I thank the University of Rhode Island, College of the Environment and Life Sciences and Department of Geosciences for helping provide support for attending Fall 2013 Geological Society of America (GSA) and American Geophysical Union (AGU) meetings where I was able to gain valuable experience and meet more amazing people. And last, but not least, thank you to my wonderful family and other friends for believing in me, praying for me, and knowing that I could get it all done. I couldn’t have done it without y’all. Thanks a million! v PREFACE This thesis is written in manuscript format for the American Geophysical Union’s (AGU) peer-reviewed journal Geochemistry, Geophysics, Geosystems (G3). vi TABLE OF CONTENTS ABSTRACT .................................................................................................................. ii ACKNOWLEDGMENTS .......................................................................................... iv PREFACE .................................................................................................................... vi TABLE OF CONTENTS ........................................................................................... vii LIST OF TABLES ...................................................................................................... ix LIST OF FIGURES ..................................................................................................... x LIST OF ACRONYMS ............................................................................................ xiii Manuscript introductory page ........................................................................................ 1 1. Introduction ................................................................................................................ 2 1.1 Deep life can be fueled by serpentinization ....................................................... 2 1.2 Serpentinization as a geologic process ............................................................... 4 1.3 Means of inferring serpentinite redox status and relevance to H2 yield ............ 6 1.4 Importance of Al-rich phases, spinels, in H2 production ................................... 7 1.5 Geologic Setting ................................................................................................. 9 1.5.1 Coast Range Ophiolite (CRO) .................................................................. 9 1.5.2 Zambales Ophiolite (ZO) ........................................................................ 10 2. Methods ................................................................................................................... 12 2.1 Sample descriptions ......................................................................................... 12 2.1.1 Coast Range Ophiolite Samples .............................................................. 12 2.1.2 Zambales Ophiolite Samples .................................................................. 13 2.2 XRD ................................................................................................................ 13 2.3Thin section microscopy ................................................................................... 15 vii 2.4 XRF ................................................................................................................
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