Chemical and isotopic analyses of hydrocarbon-bearing fluid inclusions in olivine-rich rocks

Grozeva, Niya G.; Klein, Frieder; Seewald, Jeffrey S.; Sylva, Sean P.

doi:10.1098/rsta.2018.0431

Cited by 49 publications

(66 citation statements)

References 117 publications

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“…Brucite was not identified in any of the studied inclusions, similar to other locations (e.g., Sachan et al, 2007). However, brucite is a widespread product in olivine-hosted fluid inclusions in ophiolitic samples (e.g., Klein et al, 2019;Grozeva et al, 2020).…”

Section: Resultsmentioning

confidence: 54%

Diamond forms during low pressure serpentinisation of oceanic lithosphere

Pujol-Solà¹,

Garcia‐Casco²,

Proenza³

et al. 2020

Geochem. Persp. Let.

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Diamond is commonly regarded as an indicator of ultra-high pressure conditions in Earth System Science. This canonical view is challenged by recent data and interpretations that suggest metastable growth of diamond in low pressure environments. One such environment is serpentinisation of oceanic lithosphere, which produces highly reduced CH 4-bearing fluids after olivine alteration by reaction with infiltrating fluids. Here we report the first ever observed in situ diamond within olivine-hosted, CH 4-rich fluid inclusions from low pressure oceanic gabbro and chromitite samples from the Moa-Baracoa ophiolitic massif, eastern Cuba. Diamond is encapsulated in voids below the polished mineral surface forming a typical serpentinisation array, with methane, serpentine and magnetite, providing definitive evidence for its metastable growth upon low temperature and low pressure alteration of oceanic lithosphere and super-reduction of infiltrated fluids. Thermodynamic modelling of the observed solid and fluid assemblage at a reference P-T point appropriate for serpentinisation (350°C and 100 MPa) is consistent with extreme reduction of the fluid to logfO 2 (MPa) = −45.3 (ΔlogfO 2 [Iron-Magnetite] = −6.5). These findings imply that the formation of metastable diamond at low pressure in serpentinised olivine is a widespread process in modern and ancient oceanic lithosphere, questioning a generalised ultra-high pressure origin for ophiolitic diamond.

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Section: Resultsmentioning

confidence: 54%

Diamond forms during low pressure serpentinisation of oceanic lithosphere

Pujol-Solà¹,

Garcia‐Casco²,

Proenza³

et al. 2020

Geochem. Persp. Let.

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“…The lower limit of methane flux suggested from this ratio is slightly higher than that of Emmanuel and Ague (2007) (hereafter, EA07) (~2.7 Mt/a or 1.6 • 10 11 mol/a) and than that estimated by Cannat et al (2010) of 0.4 Mt/a (2.4 • 10 10 mol/a). EA07 assumed that methane was generated as a result of hydrogen production through the stoichiometric Sabatier equation; however, recent work has suggested more strongly that abiotic methane sampled at mid‐ocean ridges has a deeper, mantle origin, rather than produced in the crustal column using hydrogen generated from serpentinization (e.g., Grozeva et al, 2020; Klein et al, 2019; McDermott et al, 2015; Wang et al, 2018).…”

Section: Discussionmentioning

confidence: 99%

“…Proposed sources include Fischer‐Tropsch‐type or Sabatier reactions (see review by McCollom, 2013) or degassing of deep fluid inclusions (e.g. Grozeva et al, 2020; Klein et al, 2019; McDermott et al, 2015; Wang et al, 2018). In the Phanerozoic, the most common and regular exposure of the mantle minerals to water, which lead to these reactions, occurs at mid‐ocean ridges (MORs).…”

Section: Introductionmentioning

confidence: 99%

Pulsated Global Hydrogen and Methane Flux at Mid‐Ocean Ridges Driven by Pangea Breakup

Merdith

Real

Daniel

et al. 2020

Geochem Geophys Geosyst

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Molecular hydrogen production occurs through the serpentinization of mantle peridotite exhumed at mid-ocean ridges. Hydrogen is considered essential to sustain microbial life in the subsurface; however, estimates of hydrogen flux through geological time are unknown. Here we present a model of the primary, abiotic production of molecular hydrogen from the serpentinization of oceanic lithosphere using full-plate tectonic reconstructions for the last 200 Ma. We find significant variability in hydrogen fluxes (1-70 • 10 16 mol/Ma or 0.2-14.1 • 10 5 Mt/a), which are a function of the sensitivity of evolving ocean basins to spreading rates and can be correlated with the opening of key ocean basins during the breakup of Pangea. We suggest that the primary driver of this hydrogen flux is the continental reconfiguration during Pangea breakup, as this produces ocean basins more conducive to exhuming and exposing mantle peridotite at slow and ultraslow spreading ridges. Consequently, present-day flux estimates are~7 • 10 17 mol/Ma (1.4 • 10 6 Mt/a), driven primarily by the slow and ultraslow spreading ridges in the Atlantic, Indian, and Arctic oceans. As methane has also been sampled alongside hydrogen at hydrothermal vents, we estimate the methane flux using methane-to-hydrogen ratios from present-day hydrothermal vent fluids. These ratios suggest that methane flux ranges between 10 and 100% of the total hydrogen flux, although as the release of methane from these systems is still poorly understood, we suggest a lower estimate, equivalent to around 7-12 • 10 16 mol/Ma (1.1-1.9 • 10 7 Mt/Ma) of methane.Plain Language Summary Hydrogen gas is produced when mantle rocks are exposed and react with ocean water at slow spreading mid-ocean ridges. Only these ridges tend to expose vast expanses of mantle rocks because the temperature is too cool to generate sufficient melt to produce basaltic oceanic crust. Hydrogen produced in this way is consumed by microbial life; however, there is no record of hydrogen through geological time. To overcome this we built a model approximating the volume of serpentinized mantle rocks produced at slow spreading ridges and used geochemical data to constrain the amount of hydrogen that can be produced, as the Fe (II)/[Fe (II) + Fe (III)] of serpentinite is a proxy of hydrogen production from serpentinization. In order to estimate the flux through time, we use global plate models which trace mid-ocean ridges and the spreading rate. We find that the volume of hydrogen produced is greatest when slow ridges are most abundant and that hydrogen production is concentrated from ridges in the Atlantic, Arctic, and Indian oceans. This is because when a supercontinent breaks up, it produces internal ocean basins that evolve slowly, relative to an ocean basin encompassing the supercontinent (i.e., the Pacific Ocean).

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“…As CO 2 escaped from the mantle, it would be reduced to CH 4 along the fracture walls at temperatures below ~400 °C, before the methane was entrained in the aforementioned hydrothermal cells [ 37 , 54 , 55 , 136 ]. This methane is another potential fuel, one that could have introduced abiotically reduced carbon to a putative metabolism [ 39 , 55 , 130 , 139 , 140 , 141 , 142 ] ( Figure 1 and Figure 2 ).…”

Section: Four Minerals To Set the Stage For Life’s Emergencementioning

confidence: 99%

Six ‘Must-Have’ Minerals for Life’s Emergence: Olivine, Pyrrhotite, Bridgmanite, Serpentine, Fougerite and Mackinawite

Russell

Ponce

2020

Life

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Life cannot emerge on a planet or moon without the appropriate electrochemical disequilibria and the minerals that mediate energy-dissipative processes. Here, it is argued that four minerals, olivine ([Mg>Fe]2SiO4), bridgmanite ([Mg,Fe]SiO3), serpentine ([Mg,Fe,]2-3Si2O5[OH)]4), and pyrrhotite (Fe(1−x)S), are an essential requirement in planetary bodies to produce such disequilibria and, thereby, life. Yet only two minerals, fougerite ([Fe2+6xFe3+6(x−1)O12H2(7−3x)]2+·[(CO2−)·3H2O]2−) and mackinawite (Fe[Ni]S), are vital—comprising precipitate membranes—as initial “free energy” conductors and converters of such disequilibria, i.e., as the initiators of a CO2-reducing metabolism. The fact that wet and rocky bodies in the solar system much smaller than Earth or Venus do not reach the internal pressure (≥23 GPa) requirements in their mantles sufficient for producing bridgmanite and, therefore, are too reduced to stabilize and emit CO2—the staple of life—may explain the apparent absence or negligible concentrations of that gas on these bodies, and thereby serves as a constraint in the search for extraterrestrial life. The astrobiological challenge then is to search for worlds that (i) are large enough to generate internal pressures such as to produce bridgmanite or (ii) boast electron acceptors, including imported CO2, from extraterrestrial sources in their hydrospheres.

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Chemical and isotopic analyses of hydrocarbon-bearing fluid inclusions in olivine-rich rocks

Cited by 49 publications

References 117 publications

Diamond forms during low pressure serpentinisation of oceanic lithosphere

Diamond forms during low pressure serpentinisation of oceanic lithosphere

Pulsated Global Hydrogen and Methane Flux at Mid‐Ocean Ridges Driven by Pangea Breakup

Six ‘Must-Have’ Minerals for Life’s Emergence: Olivine, Pyrrhotite, Bridgmanite, Serpentine, Fougerite and Mackinawite

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