DOCSLIB.ORG

Global Rates of Free Hydrogen (H2) Production by Serpentinization and Other Abiogenic Processes Wi

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Global Rates of Free Hydrogen (H2) Production by Serpentinization and Other Abiogenic Processes Wi Global Rates of Free Hydrogen (H2) Production by Serpentinization and other Abiogenic Processes within Young Ocean Crust by Stacey Lynn Worman Department of Earth and Ocean Sciences Duke University Date: ___________________________ Approved: ___________________________ Lincoln F. Pratson, Supervisor ___________________________ A. Brad Murray ___________________________ Emily M. Klein ___________________________ William H. Schlesinger Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Earth and Ocean Sciences in the Graduate School of Duke University 2015 ABSTRACT Global Rates of Free Hydrogen (H2) Production by Serpentinization and other Abiogenic Processes within Young Ocean Crust by Stacey Lynn Worman Department of Earth and Ocean Sciences Duke University Date: ___________________________ Approved: ___________________________ Lincoln F. Pratson, Supervisor ___________________________ A. Brad Murray ___________________________ Emily M. Klein ___________________________ William H. Schlesinger An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Earth and Ocean Sciences in the Graduate School of Duke University 2015 Copyright by Stacey Lynn Worman 2015 Abstract The main conclusion of this dissertation is that global H2 production within young ocean crust (<10 Mya) is higher than currently recognized, in part because current estimates of H2 production accompanying the serpentinization of peridotite may be too low (Chapter 2) and in part because a number of abiogenic H2-producing processes have heretofore gone unquantified (Chapter 3). The importance of free H2 to a range of geochemical processes makes the quantitative understanding of H2 production advanced in this dissertation pertinent to an array of open research questions across the geosciences (e.g. the origin and evolution of life and the oxidation of the Earth’s atmosphere and oceans). The first component of this dissertation (Chapter 2) examines H2 produced within young ocean crust [e.g. near the mid-ocean ridge (MOR)] by serpentinization. In the presence of water, olivine-rich rocks (peridotites) undergo serpentinization (hydration) at temperatures of up to ~500°C but only produce H2 at temperatures up to ~350°C. A simple analytical model is presented that mechanistically ties the process to seafloor spreading and explicitly accounts for the importance of temperature in H2 formation. The model suggests that H2 production increases with the rate of seafloor spreading and the net thickness of serpentinized peridotite (S-P) in a column of lithosphere. The model is applied globally to the MOR using conservative estimates for the net thickness of lithospheric S-P, our least certain model input. Despite the large uncertainties surrounding the amount of serpentinized peridotite within oceanic crust, 12 conservative model parameters suggest a magnitude of H2 production (~10 moles 11 H2/y) that is larger than the most widely cited previous estimates (~10 although iv 10 12 previous estimates range from 10 -10 moles H2/y). Certain model relationships are also consistent with what has been established through field studies, for example that the highest H2 fluxes (moles H2/km2 seafloor) are produced near slower-spreading ridges (<20 mm/y). Other modeled relationships are new and represent testable predictions. Principal among these is that about half of the H2 produced globally is produced off-axis beneath faster-spreading seafloor (>20 mm/y), a region where only one measurement of H2 has been made thus far and is ripe for future investigation. In the second part of this dissertation (Chapter 3), I construct the first budget for free H2 in young ocean crust that quantifies and compares all currently recognized H2 sources and H2 sinks. First global estimates of budget components are proposed in instances where previous estimate(s) could not be located provided that the literature on that specific budget component was not too sparse to do so. Results suggest that the nine known H2 sources, listed in order of quantitative importance, are: Crystallization 12 12 (6x10 moles H2/y or 61% of total H2 production), serpentinization (2x10 moles H2/y 11 or 21%), magmatic degassing (7x10 moles H2/y or 7%), lava-seawater interaction 11 11 (5x10 moles H2/y or 5%), low-temperature alteration of basalt (5x10 moles H2/y or 10 8 5%), high-temperature alteration of basalt (3x10 moles H2/y or <1%), catalysis (3x10 8 moles H2/y or <<1%), radiolysis (2x10 moles H2/y or <<1%), and pyrite formation 6 (3x10 moles H2/y or <<1%). Next we consider two well-known H2 sinks, H2 lost to the ocean and H2 occluded within rock minerals, and our analysis suggests that both are of 11 similar size (both are 6x10 moles H2/y). Budgeting results suggest a large difference 13 between H2 sources (total production = 1x10 moles H2/y) and H2 sinks (total losses = v 11 1x10 moles H2/y). Assuming this large difference represents H2 consumed by 11 microbes (total consumption = 9x10 moles H2/y), we explore rates of primary production by the chemosynthetic, sub-seafloor biosphere. Although the numbers presented require further examination and future modifications, the analysis suggests that the sub-seafloor H2 budget is similar to the sub-seafloor CH4 budget in the sense that globally significant quantities of both of these reduced gases are produced beneath the seafloor but never escape the seafloor due to microbial consumption. The third and final component of this dissertation (Chapter 4) explores the self- organization of barchan sand dune fields. In nature, barchan dunes typically exist as members of larger dune fields that display striking, enigmatic structures that cannot be readily explained by examining the dynamics at the scale of single dunes, or by appealing to patterns in external forcing. To explore the possibility that observed structures emerge spontaneously as a collective result of many dunes interacting with each other, we built a numerical model that treats barchans as discrete entities that interact with one another according to simplified rules derived from theoretical and numerical work, and from field observations: Dunes exchange sand through the fluxes that leak from the downwind side of each dune and are captured on their upstream sides; when dunes become sufficiently large, small dunes are born on their downwind sides (“calving”); and when dunes collide directly enough, they merge. Results show that these relatively simple interactions provide potential explanations for a range of field-scale phenomena including isolated patches of dunes and heterogeneous arrangements of similarly sized dunes in denser fields. The results also suggest that (1) dune field characteristics depend on the sand flux fed into the upwind boundary, although (2) moving downwind, the system approaches a common attracting state in vi which the memory of the upwind conditions vanishes. This work supports the hypothesis that calving exerts a first order control on field-scale phenomena; it prevents individual dunes from growing without bound, as single-dune analyses suggest, and allows the formation of roughly realistic, persistent dune field patterns. vii To throwing your heart out in front of you, and then running to catch up to it! viii Contents Abstract ......................................................................................................................................................... iv List of Tables .............................................................................................................................................. xii List of Figures .......................................................................................................................................... xiii Acknowledgements ................................................................................................................................ xvi 1. Introduction ............................................................................................................................................ 1 2. Faster-spreading ridges may rival slower-spreading ridges in free H2 gas production by serpentinization ........................................................................................................... 6 2.1 Introduction ..................................................................................................................................... 6 2.2 Analytical Model .......................................................................................................................... 10 2.3 Model Behavior and Results ................................................................................................... 14 2.3.1 H2 Production Rates .......................................................................................................... 14 2.3.2 Global Estimate of H2 Production ................................................................................ 17 2.3.3 Off-axis variations in H2 Production .......................................................................... 18 2.4 Discussion ...................................................................................................................................... 20 3. The H2 budget of young ocean crust .......................................................................................... 28 3.1 Introduction .................................................................................................................................
Load more

Recommended publications
  • Late Precambrian Balkan-Carpathian Ophiolite
    University of South Florida Masthead Logo Scholar Commons Geology Faculty Publications Geology 10-2001 Late Precambrian Balkan-Carpathian Ophiolite - A Slice of the Pan-African Ocean Crust?: Geochemical and Tectonic Insights from the Tcherni Vrah and Deli Jovan Massifs, Bulgaria and Serbia Ivan P. Savov University of South Florida, [email protected] Jeffrey G. Ryan University of South Florida, [email protected] Ivan Haydoutov Bulgarian Academy of Sciences, Geological Institute Johan Schijf University of South Florida Follow this and additional works at: https://scholarcommons.usf.edu/gly_facpub Part of the Geology Commons Scholar Commons Citation Savov, Ivan P.; Ryan, Jeffrey G.; Haydoutov, Ivan; and Schijf, Johan, "Late Precambrian Balkan-Carpathian Ophiolite - A Slice of the Pan-African Ocean Crust?: Geochemical and Tectonic Insights from the Tcherni Vrah and Deli Jovan Massifs, Bulgaria and Serbia" (2001). Geology Faculty Publications. 139. https://scholarcommons.usf.edu/gly_facpub/139 This Article is brought to you for free and open access by the Geology at Scholar Commons. It has been accepted for inclusion in Geology Faculty Publications by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Journal of Volcanology and Geothermal Research 110 *2001) 299±318 www.elsevier.com/locate/jvolgeores Late Precambrian Balkan-Carpathian ophiolite Ð a slice of the Pan-African ocean crust?: geochemical and tectonic insights from the Tcherni Vrah and Deli Jovan massifs, Bulgaria and Serbia Ivan Savova,*, Jeff Ryana, Ivan Haydoutovb, Johan Schijfc aDepartment of Geology, University of South Florida, 4202 E. Fowler Ave., SCA 520, Tampa, FL 33620-5201, USA bBulgarian Academy of Sciences, Geological Institute, So®a 1113, Bulgaria cDepartment of Marine Science, University of South Florida, 140 7th Ave S, St.
    [Show full text]
  • Lithospheric Modification During Crustal Extension in the Main Ethiopian Rift
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B10201, doi:10.1029/2006JB004916, 2007 Click Here for Full Article Lithospheric modification during crustal extension in the Main Ethiopian Rift Tyrone Rooney,1,2 Tanya Furman,1 Ian Bastow,3,4 Dereje Ayalew,5,6 and Gezahegn Yirgu5 Received 22 December 2006; revised 11 May 2007; accepted 27 June 2007; published 5 October 2007. [1] Quaternary lavas erupted in zones of tectonomagmatic extension within the Main Ethiopian Rift (MER) preserve details of lithospheric structure in the East African Rift System. Despite observed source heterogeneity, basalts, trachybasalts, and basaltic trachyandesites erupted in the Wonjii Fault Belt (WFB) and the Silti-Debre Zeyit Fault Zone (SDFZ) form coherent fractionation paths dominated by variable removal of observed phenocryst phases. Crustal assimilation is not widespread, though it is observed at the southern end of the WFB where both fault belts merge; farther north, assimilation of cumulate phases related to fractional crystallization of previous magmas is identified. Shallow fractionation conditions ( 1 kbar) within the WFB do not change from north to south. In contrast, lavas erupted within the contemporaneous SDFZ fractionate at various crustal depths. These results indicate a better developed magmatic system beneath the WFB where magmas rose quickly before undergoing more significant fractionation at near surface levels and a less developed system beneath the SDFZ. The distribution of magmatism and extant geophysical data indicate thinned crust and a single rift-centered zone of magmatic activity northeast of 8°300N, consistent with a transitional lithosphere between continental and oceanic settings. Southwest of 8°300N, thicker crust and rift- marginal axes of extension suggest lithosphere with continental affinities.
    [Show full text]
  • Author's Personal Copy
    Author's personal copy Chemical Geology 271 (2010) 70–85 Contents lists available at ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo Chemical variations and regional diversity observed in MORB Ricardo Arevalo Jr. ⁎, William F. McDonough Department of Geology, University of Maryland, College Park, MD, 20742, USA article info abstract Article history: An assemblage of MORB analyses (n =792 samples), including a suite of new, high-precision LA-ICP-MS Received 14 April 2009 measurements (n =79), has been critically compiled in order to provide a window into the chemical Received in revised form 4 December 2009 composition of these mantle-derived materials and their respective source region(s), commonly referred to Accepted 17 December 2009 as the depleted MORB mantle (DMM). This comprehensive MORB data set, which includes both “normal- ” fi b “ ” ≥ Editor: D.B. Dingwell type (N-MORB, de ned by (La/Sm)N 1.00) and enriched-type samples (E-MORB, (La/Sm)N 1.00), defines a global MORB composition that is more enriched in incompatible elements than previous models. A Keywords: statistical evaluation of the true constancy of “canonical” trace element ratios using this data set reveals that MORB during MORB genesis Ti/Eu, Y/Ho and Ce/Pb remain constant at the 95% confidence-level; thus, the ratios DMM recorded in MORB (Ti/Eu=7060±1270, 2σ; Y/Ho=28.4±3.6, 2σ; Ce/Pb=22.2±9.7, 2σ)mayreflect the Basalt composition of the DMM, presuming the degree of source heterogeneity, component mixing and conditions Trace element of melting/crystallization of the DMM are adequately recorded by global MORB.
    [Show full text]
  • The Depths of Magma Chambers Under the Galapagos Ridge Presented in Partial Fulfillment of the Requirements for Graduation With
    The Depths of Magma Chambers under the Galapagos Ridge Presented in Partial Fulfillment of the Requirements for Graduation with a Bachelor of Science in Geological Sciences in the undergraduate colleges of The Ohio State University by Emily V. England The Ohio State University August 2008 Dr. Michael Barton Advisor Table of Contents Acknowledgements……………………………………………………………………..p.1 Abstract…………………………………………………………………………………p.2 Introduction…………………………………………………………………………….p.4 Background……………………………………………………………………………..p.6 Methods………………………………………………………………………………..p.9 Samples……………………………………………………………………………..…p.11 Results…………………………………………………………………………………p.13 Discussion……………………………………………………………………………..p.15 Conclusions……………………………………………………………………………p. 18 References…………………………………………………………………………….p.19 Appendix (Summary of P and T)……………………………………………………..p. 21 ACKNOWLEDGEMENTS I would like to give thanks to the following people for helping me with my research on the Galapagos ridge while at The Ohio State University: my research advisor Dr. Michael Barton who suggested this project and mentored me along the way, Dr. Wendy Panero for her time and conversation, graduate student Daniel Kelley, and classmate Jameson “Dino” Scott. I would also like to acknowledge the entire Geological Sciences Department at OSU. I have been thoroughly pleased with my education and believe that I have found a field that I will enjoy and pursue for the rest of my life. And of course I thank my parents and family for more than words can say. 1 ABSTRACT The Galapagos Ridge System is one of the
    [Show full text]
  • University of Florida Thesis Or Dissertation
    GEOLOGY AND PETROGENESIS OF LAVAS FROM AN OVERLAPPING SPREADING CENTER: 9°N EAST PACIFIC RISE By V. DORSEY WANLESS A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2010 1 © 2010 V. Dorsey Wanless 2 To my family and friends 3 ACKNOWLEDGMENTS I would like to thank my advisor (Michael Perfit), collaborators (W. Ian Ridley, Emily Klein, Scott White, Paul Wallace, John Valley, and Craig Grimes) and supervisory committee (Paul Mueller, Ray Russo, George Kamenov, and David Richardson) for their mentoring and encouragement throughout this study. Additionally, I would like to thank the Captain, officers and crew of the R/V Atlantis for all their help during cruise AT15-17, the MEDUSA2007 Science party (including S. White, K. Von Damm, D. Fornari, A. Soule, S. Carmichael, K. Sims, A. Fundis, A. Zaino, J. Mason, J. O’Brien, C. Waters, F. Mansfield, K. Neely, J. Laliberte, E. Goehring, and L. Preston) for their diligence in collecting data and samples for this study. I thank the ROV Jason II shipboard and shore-based operations group for their assistance in collecting these data and HMRG for processing all DSL-120 side scan and bathymetry data collected during this cruise. Discussions with S. White and A. Goss are gratefully acknowledged. Thanks to G. Kamenov and the UF Center for Isotope Geosciences for laboratory assistance and to the Department of Geological Sciences staff for all of their help. Finally, I thank my friends and family for all their support over the years.
    [Show full text]
  • Possible New Fish Species Found in Pacific 17 April 2007
    Possible new fish species found in Pacific 17 April 2007 A new undersea mineral chimney emitting hot, iron- darkened water that attracts unusual marine life has been discovered in the Pacific Ocean off Costa Rica. The vent, located about 8,500 feet beneath the surface, was found by a U.S.-led expedition exploring a section of volcanic ridge. Expedition members from Duke University; the Universities of New Hampshire, South Carolina and Florida; and the Woods Hole Oceanographic Institution named their discovery the Medusa hydrothermal vent field. That name was selected because numerous spiky tubeworm casings that festoon the vent chimney bring to mind "the serpent-haired Medusa of Greek myth," said expedition leader Emily Klein, a Duke University geology professor. Bell-shaped pink jellyfish sighted near the vent "are really unusual, and the ones we found may be of a different species because nobody has seen types of this color before," said Karen Von Damm, a University of New Hampshire earth sciences professor. The researchers are working aboard WHOI's research vessel Atlantis, and the expedition is funded by the National Science Foundation. Copyright 2007 by United Press International APA citation: Possible new fish species found in Pacific (2007, April 17) retrieved 28 September 2021 from https://phys.org/news/2007-04-fish-species-pacific.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. 1 / 1 Powered by TCPDF (www.tcpdf.org).
    [Show full text]
  • Abiotic Hydrogen (H2) Sources and Sinks Near the Mid-Ocean Ridge (MOR) with Implications for the Subseafloor Biosphere
    Abiotic hydrogen (H2) sources and sinks near the Mid-Ocean Ridge (MOR) with implications for the subseafloor biosphere Stacey L. Wormana,1, Lincoln F. Pratsona, Jeffrey A. Karsonb, and William H. Schlesingera,c,1 aDivision of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC 27708; bDepartment of Earth Sciences, Syracuse University, Syracuse, NY 13244; and cCary Institute of Ecosystem Studies, Millbrook, NY 12545 Contributed by William H. Schlesinger, April 1, 2020 (sent for review February 18, 2020; reviewed by Marvin Lilley and Kenneth H. Nealson) Free hydrogen (H2) is a basal energy source underlying chemosyn- Juan de Fuca Ridge (JdFR), where subsurface microbes con- thetic activity within igneous ocean crust. In an attempt to system- sume ∼50 to 80% of H2 production (25), and on the Mid- atically account for all H2 within young oceanic lithosphere (<10 Atlantic Ridge (MAR), where consumption is ∼90% (26). Ma) near the Mid-Ocean Ridge (MOR), we construct a box model Our MOR-scale estimate is the result of a bottom-up analysis of this environment. Within this control volume, we assess abiotic that includes 19 different processes, more than half of which we 12 12 H2 sources (∼6 × 10 mol H2/y) and sinks (∼4 × 10 mol H2/y) and could not locate previous estimates for (Fig. 2). The type, ∼ × 12 then attribute the net difference ( 2 10 mol H2/y) to microbial quantity, and quality of published information available for these consumption in order to balance the H2 budget. Despite poorly processes vary dramatically; so, each estimate in our model is constrained details and large uncertainties, our analytical frame- surrounded by its own and often considerable uncertainties.
    [Show full text]
  • Petrology and Geochemistry of the GalÁ
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 98, NO. Bll, PAGES 19,533-19,563, NOVEMBER 10, 1993 Petrologyand Geochemistryof the GaMpagosIslands' Portrait of a PathologicalMantle Plume WILLIAM M. WmT• Departmentof GeologicalSciences, Cornell University, Ithaca, New York ALEXANDER R. McBIRNEY Centerfor Volcanology,University of Oregon,Eugene ROBERT A. DUNCAN Collegeof Oceanography,Oregon State University,Corvallis We reportnew major element,trace element,isotope ratio, and geochronologicaldata on the Galfipagos Archipelago.Magmas erupted from the largewestern volcanos are generallymoderately fractionated tholeiites of uniformcomposition; those erupted on otherislands are compositionallydiverse, ranging from tholeiites to picritic basanitoids.While thesevolcanos do notform a strictlylinear age progressive chain, the agesof the oldestdated flows on anygiven volcano do form a reasonableprogression from youngest in thewest to oldestin theeast, consistent with motionof theNazca plate with respect to thefixed hotspot reference frame. lsotoperatios in theGalfipagos display a considerablerange, from values typical of mid-oceanridge basalt on Genovesa(87Sr/86Sr: 0.70259, end: +9.4, 206pb/204pb:! 8.44), to typical oceanic island values on Floreana (87Sr/86Sr: 0.70366, œNd: +5.2, 206pb/204pb: 20.0). La/SmN rangesfrom 0.45 to 6.7; otherincompatible element abundances and ratios show comparable ranges. Isotope andincompatible element ratios define a horseshoepattern with the mostdepleted signatures in the centerof the GalfipagosArchipelago and the moreenriched
    [Show full text]
  • The Petrography and Chemistry of Basaltic Magmas
    From Layered Intrusions to Mid-Ocean Rides: The Petrography and Chemistry of Basaltic Magmas by Benjamin W. Wernette Earth and Ocean Sciences Duke University Date: _______________________ Approved: ___________________________ Emily Klein, Advisor ___________________________ Alan Boudreau ___________________________ Drew Coleman ___________________________ Avner Vengosh Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Earth and Ocean Sciences in the Graduate School of Duke University 2020 i v ABSTRACT From Layered Intrusions to Mid-Ocean Rides: The Petrography and Chemistry of Basaltic Magmas by Benjamin W. Wernette Earth and Ocean Sciences Duke University Date: _______________________ Approved: ___________________________ Emily Klein, Advisor ___________________________ Alan Boudreau ___________________________ Drew Coleman ___________________________ Avner Vengosh An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Earth and Ocean Sciences in the Graduate School of Duke University 2020 i v Copyright by Benjamin W. Wernette 2020 Abstract The geochemical evolution of basaltic magmas, in a variety of settings, has been the subject of countless studies. In some instances, basaltic magmas evolve to form economic transition and precious metal ore bodies. The metals extracted from these ore bodies are of critical importance to a wide variety of industries, such as automotive manufacturing. On a larger scale, basaltic magmas evolve to form the oceanic crust, the interface between the Earth’s mantle and the oceans. These are just two examples of how basaltic magmas are entwined with life on Earth and together represent the focus of this dissertation. The second chapter of this dissertation uses detailed petrography to characterize the late-stage evolution of the Eocene Skaergaard Intrusion, Greenland.
    [Show full text]
  • UNH Scientists, Students, Part of Team Exploring New "Black Smoker" Undersea Chimney
    University of New Hampshire University of New Hampshire Scholars' Repository Media Relations UNH Publications and Documents 4-17-2007 UNH Scientists, Students, Part Of Team Exploring New "Black Smoker" Undersea Chimney David Sims UNH Institute for the Study of Earth, Oceans and Space Follow this and additional works at: https://scholars.unh.edu/news Recommended Citation Sims, David, "UNH Scientists, Students, Part Of Team Exploring New "Black Smoker" Undersea Chimney" (2007). UNH Today. 717. https://scholars.unh.edu/news/717 This News Article is brought to you for free and open access by the UNH Publications and Documents at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Media Relations by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. 9/17/2016 UNH Scientists, Students, Part Of Team Exploring New "Black Smoker" Undersea Chimney UNH Media Relations UNH Scientists, Students, Part Of Team Exploring New "Black Smoker" Undersea Chimney Contact: David Sims 603­862­5369 Science Writer Institute for the Study of Earth, Oceans, and Space April 17, 2007 DURHAM, N.H. ­­ A new "black smoker" – a deep­sea mineral chimney associated with extraordinary ecosystems that thrive without sunlight – has been discovered at a depth of about 8,500 feet by a multi­institutional expedition currently exploring an unusual section of a volcanic ridge along the Pacific Ocean floor off Costa Rica. Professor Karen Von Damm of the University of New Hampshire’s Institute for the Study or Earth, Oceans, and Space (EOS) and Department of Earth Sciences is the hydrothermal vent expert on board the Research Vessel Atlantis currently plying the waters above the East Pacific Rise spreading center at 9 degrees north latitude.
    [Show full text]
  • Continental Rifting in Central Ethiopia
    The Pennsylvania State University The Graduate School College of Earth and Mineral Sciences CONTINENTAL RIFTING IN CENTRAL ETHIOPIA: GEOCHEMICAL AND ISOTOPIC CONSTRAINTS FROM LAVAS AND XENOLITHS A Thesis in Geosciences by Tyrone O. Rooney © 2006 Tyrone O. Rooney Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2006 The thesis of Tyrone O. Rooney was reviewed and approved* by the following: Tanya Furman Professor of Geosciences Thesis Adviser Chair of Committee Richard R. Parizek Professor of Geology and Geo-Enviormental Engineering Andrew A. Nyblade Associate Professor of Geosciences David H. Eggler Emeritus Professor of Petrology Derek Elsworth Professor of Energy & Geo-Enviornmental Engineering Barry B. Hanan Professor of Geosciences, Dept. of Geological Sciences, San Diego State University. Special Member Katherine H. Freeman Professor of Geosciences Associate Head of Graduate Programs and Research *Signatures are on file in the Graduate School. ii ABSTRACT This dissertation will integrate geochemical and geophysical constraints from central-northern Ethiopia, moving closer to an integrated tectonic, structural and magmatic model of rifting process, from its initiation through the final transition to seafloor spreading. I focus on Quaternary magmatism within the Main Ethiopian Rift (MER), which is concentrated in extensional faults belts on the rift floor, specifically - the Wonjii Fault Belt and the Silti-Debre Zeyit Fault Zone. The location of these Quaternary eruptives within presently active extensional fault belts of the MER, presents the opportunity to deduce the primitive source(s) of rift magmatism, probe crustal structure and assess the role of magmatism in continental rifting. Mass balance of bulk rock & phenocryst composition and thermodynamic modeling of mafic lavas from both zones of extension indicates heterogeneity between the two extensional fault belts in the MER.
    [Show full text]
  • Volcanic Eruptions on Mid-Ocean Ridges
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. B6, 10.1029/2000JB000090, 2002 Volcanic eruptions on mid-ocean ridges: New evidence from the superfast spreading East Pacific Rise, 17°–19°S John Sinton,1 Eric Bergmanis,1 Ken Rubin,1 Rodey Batiza,1,2 Tracy K. P. Gregg,3 Karl Gro¨nvold,4 Ken C. Macdonald,5 and Scott M. White6 Received 6 December 2000; revised 25 November 2001; accepted 30 November 2001; published 14 June 2002. [1] Side-scan sonar, submersible observations and sampling of lava flows from the East Pacific Rise, 17°–19°S constrain the character and variability of submarine volcanic eruptions along mid-ocean ridges. Nine separate lava sequences were mapped using relative age and lithological contrasts among recovered samples. Axial lengths activated during eruptive episodes range from 1 to >18 km; individual flow field areas vary from <1 to >19 km2. Estimated erupted volumes range from <1 to >200 Â 106 m3. The largest unit is the chemically uniform Animal Farm lava near 18°370S. The youngest lava is the Aldo-Kihi flow field, 17°240–340S, probably erupted in the early 1990s from a fissure system extending >18 km along axis. Near 18°330S two distinct lava compositions with uniform sediment cover were recovered from lava that buries older faulted terrain. The boundary in lava composition coincides with a change in depth to the top of an axial magma lens seismic reflector, consistent with magmas from two separate reservoirs being erupted in the same event. Chemical compositions from throughout the area indicate that lavas with identical compositions can be emplaced in separate volcanic eruptions within individual segments.
    [Show full text]