Iron partitioning and hydrogen generation during serpentinization of abyssal peridotites from 15°N on the Mid-Atlantic Ridge

Klein, Frieder; Bach, Wolfgang; Jöns, Niels; McCollom, T. M.; Moskowitz, Bruce M.; Berquó, Thelma S.

doi:10.1016/j.gca.2009.08.021

Cited by 282 publications

(254 citation statements)

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“…Partial or total re-equilibration of C-H bonds in CH 4 during extraction by seawater heated to >300°C during active hydrothermal circulation would pull the δD values of CH 4 towards an equilibrium value of −130 to −110‰ (depending on the calibration), consistent with the narrow range of data from high-temperature endmember fluids (Fig. 3.5).It is worth noting that while serpentinization of olivine and orthopyroxene in oceanic peridotites generates large quantities of H 2 (Klein et al, 2009;McCollom and Bach, 2009;Klein et al, 2013), methane synthesis does not necessarily require serpentinization of peridotite. At temperatures of~400°C, oxygen fugacities at or below FMQ are sufficiently reducing for CH 4 to be stable relative to CO 2 (Figs.…”

supporting

confidence: 70%

“…It is worth noting that while serpentinization of olivine and orthopyroxene in oceanic peridotites generates large quantities of H 2 (Klein et al, 2009;McCollom and Bach, 2009;Klein et al, 2013), methane synthesis does not necessarily require serpentinization of peridotite. At temperatures of~400°C, oxygen fugacities at or below FMQ are sufficiently reducing for CH 4 to be stable relative to CO 2 (Figs.…”

Section: Hydrogen Exchange and The Origin Of Hydrogen In Chmentioning

confidence: 99%

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The geochemistry of methane isotopologues

Wang¹

2017

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This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of 12 CH 4 , 13 CH 4 , 12 CH 3 D, and 13 CH 3 D record the formation, transport, and breakdown of methane in selected settings.Chapter 2 reports precise determinations of 13 CH 3 D, a "clumped" isotopologue of methane, in samples collected from various settings representing many of the major sources and reservoirs of methane on Earth. The results show that the information encoded by the abundance of 13 CH 3 D enables differentiation of methane generated by microbial, thermogenic, and abiogenic processes. A strong correlation between clumped-and hydrogen-isotope signatures in microbial methane is identified and quantitatively linked to the availability of H 2 and the reversibility of microbially-mediated methanogenesis in the environment. Determination of 13 CH 3 D in combination with hydrogen-isotope ratios of methane and water provides a sensitive indicator of the extent of C-H bond equilibration, enables fingerprinting of methane-generating mechanisms, and in some cases, supplies direct constraints for locating the waters from which migrated gases were sourced. Chapter 3 applies this concept to constrain the origin of methane in hydrothermal fluids from sediment-poor vent fields hosted in mafic and ultramafic rocks on slow-and ultraslow-spreading mid-ocean ridges. The data support a hypogene model whereby methane forms abiotically within plutonic rocks of the oceanic crust at temperatures above ca. 300• C during respeciation of magmatic volatiles, and is subsequently extracted during active, convective hydrothermal circulation. Chapter 4 presents the results of culture experiments in which methane is oxidized in the presence of O 2 by the bacterium Methylococcus capsulatus strain Bath. The results show that the clumped isotopologue abundances of partially-oxidized methane can be predicted from knowledge of 13 C/ 12 C and D/H isotope fractionation factors alone.: Shuhei Ono, Ph.D. Acknowledgments I fear that this section will not do justice to the people I have not the space to thank individually. Alas, here goes. To those whose names are not specifically listed here, thank you too. I wish first to thank Shuhei Ono. The work this thesis represents could not have happened without his bold vision and the license to explore and question that working in his lab afforded. His unbridled optimism, breadth of scientific curiosity, personal integrity, and accessibility to his personnel are traits I one day hope to emulate. I thank him for his nonjudgmental yet appropriately measured support of many of my ideas-even those that led nowhere-, for believing in me even when I found it difficult to do so myself, and for teaching me to change pump oil, build vacuum lines, and drink Icelandic vodka.I also wish to thank my thesis committee members Jeff Seewald, Roger Summons, and John Pohlman, for their in...

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confidence: 70%

Section: Hydrogen Exchange and The Origin Of Hydrogen In Chmentioning

confidence: 99%

The geochemistry of methane isotopologues

Wang¹

2017

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“…Nevertheless, as the magnetite magnetization does not depend on 224 the serpentinization degree, the origin of the weak magnetic signature can only result from its 225 concentration within the host rock. Studies of Allen and Seyfried (2003), Klein et al (2009Klein et al ( , 226 2014, Malvoisin et al (2012) reveal that low-temperature 227 serpentinization favors brucite formation rather than magnetite below 150°C, resulting in a 228 magnetite-poor (i.e., less magnetic) rock, while high-temperature serpentinization is associated 229 with magnetite formation and thus a more magnetic rock. However, no brucite has been found 230 within the serpentinized basement rocks of the Atlantis Massif.…”

mentioning

confidence: 99%

Magnetic exploration of a low-temperature ultramafic-hosted hydrothermal site (Lost City, 30°N, MAR)

Szitkar

Tivey

Kelley

et al. 2017

Earth and Planetary Science Letters

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25A 2003 high-resolution magnetic survey conducted by the Autonomous Underwater Vehicle ABE 26 over the low-temperature, ultramafic-hosted hydrothermal field Lost City reveals a weak positive 27 magnetic anomaly. This observation is in direct contrast to recent observations of strong positive 28 magnetic anomalies documented over the high-temperature ultramafic-hosted hydrothermal vents 29 fields Rainbow and Ashadze, which indicates that temperature may control the production of 30 magnetization at these sites. The Lost City survey provides a unique opportunity to study a field 31 that is, to date, one of a kind, and is an end member of ultramafic-hosted hydrothermal systems. 32Our results highlight the key contribution of temperature on magnetite production resulting from 33 serpentinization reactions. Whereas high temperature promotes significant production and 34 partitioning of iron into magnetite, low temperature favors iron partitioning into various alteration 35 phases, resulting in a magnetite-poor rock. Moreover, the distribution of magnetic anomalies 36 confirms results of a previous geological survey indicating the progressive migration of 37 hydrothermal activity upslope. These discoveries contribute to the results of 25 years of magnetic 38 exploration of a wide range of hydrothermal sites, from low-to high-temperature and from 39 basalt-to ultramafic-hosted, and thereby validate using high-resolution magnetics as a crucial 40 parameter for locating and characterizing hydrothermal sites hosting unique chemosynthetic-41 based ecosystems and potentially mineral-rich deposits. 42 43 1) Introduction 44The discovery of hydrothermal activity along the Galapagos Rift (Corliss et al., 1979) paved the 45 way for large-scale, deep-sea exploration of oceanic ridges, revealing a myriad of hydrothermal 46 vent fields primarily hosted on basaltic crust, with lesser gabbroic and ultramafic material (Kelley 47 and Shank, 2010). In contrast to intermediate-and fast-spreading systems where basaltic rocks 48 dominate, along slow-to ultraslow-spreading centers, the tectonically-dominated geology 49 (Karson and Elthon, 1987; Tucholke et al., 1998; Escartin et al., 2008) gives rise to a higher 50 abundance of hydrothermal systems hosted by variable amounts of ultramafic and gabbroic 51 material, such as the well-known Rainbow and Ashadze hydrothermal fields (Charlou et al., 52 2002; Charlou et al., 2010; Fouquet et al., 2008). These high-temperature venting systems 53 (>350°C) are characterized by sulfide chimneys emitting low pH fluids rich in carbon dioxide, 54 methane and hydrogen; chemical signatures that are hallmarks of fluid interaction with mafic and 55 ultramafic material in the subsurface (Charlou et al., 2002; Fouquet et al., 2010; Kelley and 56 Shank, 2010;Ohara et al., 2012). 57Although the magnetic signature of basalt-hosted hydrothermal sites is well constrained (Tivey et 58 al., 1993; Tivey and Johnson, 2002; Tivey and Dyment, 2010;Szitkar et al., 2014a; Szitkar et al., 59 2015),...

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“…The high X Mg (0.95) of lizardite in mesh texture and the presence magnetite suggests that serpentinization occurred at relatively high temperatures (>200°C) [Klein et al, 2009] in the near axis region of the MAR.…”

Section: Discussionmentioning

confidence: 99%

“…Seawater reacts with olivine (+-pyroxene) creating serpentine, magnetite, and brucite (+-talc, chlorite, Ni-Fe sulfides). Reaction pathways are dependent on temperature, fluid chemistry (silica activity, pH), and waterrock ratio [Klein et al, 2009]. Examining the resulting mineral assemblages, pseudomorphic textures, and elemental partitioning in serpentinized peridotites can thus provide constraints on the conditions under which the rock formed.…”

Section: Introductionmentioning

confidence: 99%

Geophysical and geochemical constraints on the evolution of oceanic lithosphere from formation to subduction

Horning¹

2017

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This thesis investigates the evolution of the oceanic lithosphere in a broad sense from formation to subduction, in a focused case at the ridge, and in a focused case proximal to subduction. In general, alteration of the oceanic lithosphere begins at the ridge through focused and diffuse hydrothermal flow, continues off axis through low temperature circulation, and may occur approaching subduction zones as bending related faulting provides fluid pathways. In Chapter 2 I use a dataset of thousands of microearthquakes recorded at the Rainbow massif on the Mid-Atlantic Ridge to characterize the processes which are responsible for the long-term, high-temperature, hydrothermal discharge found hosted in this oceanic core complex. I find that the detachment fault responsible for the uplift of the massif is inactive and that the axial valleys show no evidence for faulting or active magma intrusion. I conclude that the continuous, low-magnitude seismicity located in diffuse pattern in a region with seismic velocities indicating ultramafic host rock suggests that serpentinization may play a role in microearthquake generation but the seismic network was not capable of providing robust focal mechanism solutions to constrain the source characteristics. In Chapter 3 I find that the Juan de Fuca plate, which represents the young/hot end-member of oceanic plates, is lightly hydrated at upper crustal levels except in regions affected by propagator wakes where hydration of lower crust and upper mantle is evident. I conclude that at the subduction zone the plate is nearly dry at upper mantle levels with the majority of water contained in the crust. Finally, in Chapter 4 I examine samples of cretaceous age serpentinite sampled just before subduction at the Puerto Rico Trench. I show that these upper mantle rocks were completely serpentinized under static conditions at the Mid-Atlantic Ridge. Further, they subsequently underwent 100 Ma of seafloor weathering wherein the alteration products of serpentinization themselves continue to be altered. I conclude that complete hydration of the upper mantle is not the end point in the evolution of oceanic lithosphere as it spreads from the axis to subduction. Chapter 1: IntroductionThe total water content of the oceanic lithosphere is the sum of the free water in pore spaces in the sedimentary cover and highly porous upper crust, chemically bound water in sediment clay minerals, chemically bound water in the upper and lower crust resulting from the precipitation of secondary hydrous alteration products, free water in fault zones, and bound water of hydrous minerals in the uppermost mantle resulting from serpentinization of peridotite. This thesis is focused on characterizing the location, extent, and timing of the processes that result in this alteration of the lithosphere.In Chapter 2 I focus on the alteration that occurs in the near axis region at an oceanic core complex located on the slow spreading Mid-Atlantic Ridge. At the Rainbow massif long-lived high-T hydrothermal venting h...

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Iron partitioning and hydrogen generation during serpentinization of abyssal peridotites from 15°N on the Mid-Atlantic Ridge

Cited by 282 publications

References 59 publications

The geochemistry of methane isotopologues

The geochemistry of methane isotopologues

Magnetic exploration of a low-temperature ultramafic-hosted hydrothermal site (Lost City, 30°N, MAR)

Geophysical and geochemical constraints on the evolution of oceanic lithosphere from formation to subduction

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