Mass transfer in the oceanic lithosphere: Serpentinization is not isochemical

Malvoisin, Benjamin

doi:10.1016/j.epsl.2015.07.043

Cited by 126 publications

(77 citation statements)

References 43 publications

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“…The samples are characterized by a wide array of fractures, cracks and serpentine or chlorite filled veins. Serpentine is sometimes associated to brucite and magnesite suggesting incomplete reaction between these phases 14 . The veins, with thickness reaching 300 μm, generally occur at the boundary of the main primary minerals, mainly Cr-rich spinel and, in a less amount, olivine and pyroxene (details are in Supplementary Information).…”

Section: Resultsmentioning

confidence: 99%

Widespread abiotic methane in chromitites

Etiope

Ifandi

Nazzari

et al. 2018

Sci Rep

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Recurring discoveries of abiotic methane in gas seeps and springs in ophiolites and peridotite massifs worldwide raised the question of where, in which rocks, methane was generated. Answers will impact the theories on life origin related to serpentinization of ultramafic rocks, and the origin of methane on rocky planets. Here we document, through molecular and isotopic analyses of gas liberated by rock crushing, that among the several mafic and ultramafic rocks composing classic ophiolites in Greece, i.e., serpentinite, peridotite, chromitite, gabbro, rodingite and basalt, only chromitites, characterized by high concentrations of chromium and ruthenium, host considerable amounts of 13C-enriched methane, hydrogen and heavier hydrocarbons with inverse isotopic trend, which is typical of abiotic gas origin. Raman analyses are consistent with methane being occluded in widespread microfractures and porous serpentine- or chlorite-filled veins. Chromium and ruthenium may be key metal catalysts for methane production via Sabatier reaction. Chromitites may represent source rocks of abiotic methane on Earth and, potentially, on Mars.

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Section: Resultsmentioning

confidence: 99%

Widespread abiotic methane in chromitites

Etiope

Ifandi

Nazzari

et al. 2018

Sci Rep

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“…Tutolo et al (2016) proposed that fluid access into these rocks occurs through nano-scale micropores and defects inside serpentine minerals, which represent a significant fraction of the rock porosity. Permeability changes during deformation, metamorphism and fluid-controlled mineral dissolution play a key control on fluid stagnation versus fluid channelling and on development of reaction fronts and element transport into serpentinite and mantle domains being serpentinized (Kelemen & Matter, 2008;Malvoisin, 2015;Leclère et al, 2018). The above studies steer current research towards an understanding of fluid circulation patterns and reaction kinetics and stimulate scientists to refine textural observations from micro-to nanoscales, so to identify the mechanisms driving to largescale fluid flow in serpentinite.…”

Section: Rock Structures and Fluid Flowmentioning

confidence: 98%

“…Defining the above features can improve our understanding of the physical mechanism controlling open-system fluid influx in the oceanic lithosphere and in the mantle wedge (e.g. Malvoisin, 2015;Malvoisin et al, 2015), whether punctuated and temporally associated to dehydration pulses, or continuous and due to migration of fluids from far dehydration fronts.…”

Section: Rock Structures and Fluid Flowmentioning

confidence: 99%

“…Development of reaction (3) is suggested by the silica enrichment shown by many antigorite serpentinites with respect to chrysotile/lizardite ones, that likely results from exchange with sediment-derived subduction fluids Schwartz et al, 2013;Malvoisin, 2015). Overall, transition from chrysotile/lizardite to antigorite is also accompanied by water and fluid-mobile element loss from serpentinite (Kodolányi & Pettke, 2011).…”

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confidence: 99%

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The water and fluid-mobile element cycles during serpentinite subduction. A review

Scambelluri

Cannaò

Gilio

2019

ejm

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The key role of serpentinites in the global cycles of volatiles, halogens and fluid-mobile elements in oceans and in subduction zones is now ascertained by many studies quantifying their element budgets and the composition of fluids they release during subduction. Geochemical tracers (e.g. B, As, Sb; stable B and radiogenic Sr and Pb isotopes) have also been employed to trace the provenance of serpentinites (slab or forearc mantle?) accreted to the plate interface of fossil subduction zones. In turn, this helps defining the tectonic processes, seismicity and mass transfer attending rock burial and exhumation within subduction zones. The results suggest that the sole use of geochemical data is insufficient to track the origin of subduction-zone serpentinites and the timing of serpentinization, whether oceanic or subduction-related. Integrated multidisciplinary studies of ophiolitic serpentinites show that pristine, oceanic, geochemical imprints (e.g. high 11 B, marine Sr isotopes, low As + Sb) become reset towards more radiogenic Sr, lower 11 B, and higher As + Sb via metasomatic exchange with crust-derived fluids during subduction accretion to the plate interface.The dehydration fluids released by serpentinite dehydration at various subduction stages and still preserved in these rocks as inclusions, carry significant amounts of halogens and fluid-mobile elements. The key compositional similarities of antigorite-breakdown fluids from different localities (Betic Cordillera, Spain; Central Alps, Switzerland) indicate that rocks record comparable subduction processes. We individuate the fluid-mediated exchange with sedimentary and/or crustal reservoirs during subduction as the key mechanism for geochemical hybridization of serpentinite. The antigorite dehydration fluids produced by hybrid serpentinites have high Cs, Rb, Ba, B, Pb, As, Sb and Li overlapping those of the arc lavas and representing the mixed serpentinite-sediment (crustal) component released to arcs. This helps discriminating the mass transfer processes responsible for supra-subduction mantle metasomatism and arc magmatism. The studied plate-interface hybrid serpentinites are also proxies of forearc mantle metasomatized by slab fluids. Based on the above observations, we propose that the mass transfer from slabs to plate interface and/or forearc mantle and the subsequent down-drag of this altered mantle to subarc depths potentially is a major process operating in subduction zones.The nominally anhydrous olivine, orhopyroxene, clinopyroxene and garnet produced by serpentinite dehydration host appreciable amounts of halogens and fluid-mobile elements that can be recycled in the deep mantle beyond arcs. Involvement of de-serpentinized residues in lower mantle metasomatism begins to be increasingly recognized by studies of ocean island basalts (OIB) and of B-bearing blue diamonds and by the isotopic serpentinite compositions presented here.

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“…[8,9] and references therein), though in detail there could be small changes in major element concentrations (e.g. [10]). Reaction pathways for serpentinization vary, depending on temperature, pressure, fluid composition, fluid/rock ratios and the primary mineralogy of the protolith.…”

Section: Introductionmentioning

confidence: 99%