High-pressure serpentinites, a trap-and-release system controlled by metamorphic conditions: Example from the Piedmont zone of the western Alps

Lafay, Romain; Deschamps, F.; Schwartz, Stéphane; Guillot, Stéphane; Godard, Marguerite; Debret, Baptiste; Nicollet, Christian

doi:10.1016/j.chemgeo.2013.02.008

Cited by 92 publications

(85 citation statements)

References 63 publications

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“…The highest conductivities requires fluids with salinities of the order of or above that of seawater, which can be provided by fluid release from the slab and salt enrichment by serpentinization or other partial hydration reactions (Reynard, et al 2011). Current reports show a large range of Cl concentration in serpentinites from subduction context, suggesting interactions with highsalinity fluids at various levels Deschamps, et al 2010;Lafay, et al 2013;Scambelluri, et al 2004;Scambelluri, et al 1997). Cl concentrations in serpentinites that equilibrated with up to 12 m NaCl fluids should vary in the range 20-5000 ppm (Fig.…”

Section: Discussionmentioning

confidence: 99%

Mantle hydration and Cl-rich fluids in the subduction forearc

Reynard

2016

Prog. in Earth and Planet. Sci.

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In the forearc region, aqueous fluids are released from the subducting slab at a rate depending on its thermal state. Escaping fluids tend to rise vertically unless they meet permeability barriers such as the deformed plate interface or the Moho of the overriding plate. Channeling of fluids along the plate interface and Moho may result in fluid overpressure in the oceanic crust, precipitation of quartz from fluids, and low Poisson ratio areas associated with tremors. Above the subducting plate, the forearc mantle wedge is the place of intense reactions between dehydration fluids from the subducting slab and ultramafic rocks leading to extensive serpentinization. The plate interface is mechanically decoupled, most likely in relation to serpentinization, thereby isolating the forearc mantle wedge from convection as a cold, potentially serpentinized and buoyant, body. Geophysical studies are unique probes to the interactions between fluids and rocks in the forearc mantle, and experimental constrains on rock properties allow inferring fluid migration and fluid-rock reactions from geophysical data. Seismic velocities reveal a high degree of serpentinization of the forearc mantle in hot subduction zones, and little serpentinization in the coldest subduction zones because the warmer the subduction zone, the higher the amount of water released by dehydration of hydrothermally altered oceanic lithosphere. Interpretation of seismic data from petrophysical constrain is limited by complex effects due to anisotropy that needs to be assessed both in the analysis and interpretation of seismic data. Electrical conductivity increases with increasing fluid content and temperature of the subduction. However, the forearc mantle of Northern Cascadia, the hottest subduction zone where extensive serpentinization was first demonstrated, shows only modest electrical conductivity. Electrical conductivity may vary not only with the thermal state of the subduction zone, but also with time for a given thermal state through variations of fluid salinity. High-Cl fluids produced by serpentinization can mix with the source rocks of the volcanic arc and explain geochemical signatures of primitive magma inclusions. Signature of deep high-Cl fluids was also identified in forearc hot springs. These observations suggest the existence of fluid circulations between the forearc mantle and the hot spring hydrothermal system or the volcanic arc. Such circulations are also evidenced by recent magnetotelluric profiles.

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Section: Discussionmentioning

confidence: 99%

Mantle hydration and Cl-rich fluids in the subduction forearc

Reynard

2016

Prog. in Earth and Planet. Sci.

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“…Most of serpentinites are composed of lizardite and chrysotile assemblages displaying mesh and bastite textures (Liz-serpentinites) crystallized in an oceanic setting Lafay et al, 2013). The local crystallization of antigorite, high-pressure and high-temperature serpentine variety (HP/HT) (Wunder et al, 2001), at the expense of lizardite (Atg/Liz-serpentinites) can be interpreted in terms of an increase in P -T conditions during subduction.…”

Section: The Montgenèvre Ophiolitementioning

confidence: 98%

“…Indeed, these ophiolites are considered to have been highly hydrated and serpentinized during an oceanic stage (distal continental margin or mid-ocean ridge environment) prior to partial dehydration during prograde metamorphism (Debret et al, 2013a(Debret et al, , 2013bHattori and Guillot, 2007;Lafay et al, 2013;Li et al, 2004;Schwartz et al, 2013;Vils et al, 2011). Here we propose to use the redox state of iron in serpentinites, an abundant element in this type of rock, in order to assess the possible nature of the released fluids during serpentine phase changes in subduction zones.…”

Section: Introductionmentioning

confidence: 97%

Evolution of Fe redox state in serpentine during subduction

Debret

Andréani

Muñoz

et al. 2014

Earth and Planetary Science Letters

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“…Exchange with surrounding sedimentary rocks can cause serpentinite enrichment in specific tracers like As, Be, Sb, B, radiogenic Sr, Pb and isotopically light B (Hattori and Guillot, 2003;Marchesi et al, 2013;Harvey et al, 2014;Scambelluri et al, 2014;Angiboust et al, 2014;Lafay et al, 2013;Cannaò et al, 2015). Element addition to serpentinite may occur during prograde burial (Deschamps et al, 2011;Scambelluri et al, 2014), or during fluid channeling along shear zones in subducting slabs (Angiboust et al, 2014).…”

Section: Introductionmentioning

confidence: 98%

Fluid-related inclusions in Alpine high-pressure peridotite reveal trace element recycling during subduction-zone dehydration of serpentinized mantle (Cima di Gagnone, Swiss Alps)

Scambelluri

Pettke

Cannaò

2015

Earth and Planetary Science Letters

104

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Available online xxxx Editor: T.A. Mather Keywords: serpentinized mantle garnet peridotite chlorite harzburgite polyphase inclusions subduction fluids fluid-mobile elementsSerpentinites release at sub-arc depths volatiles and several fluid-mobile trace elements found in arc magmas. Constraining element uptake in these rocks and defining the trace element composition of fluids released upon serpentinite dehydration can improve our understanding of mass transfer across subduction zones and to volcanic arcs. The eclogite-facies garnet metaperidotite and chlorite harzburgite bodies embedded in paragneiss of the subduction melange from Cima di Gagnone derive from serpentinized peridotite protoliths and are unique examples of ultramafic rocks that experienced subduction metasomatism and devolatilization. In these rocks, metamorphic olivine and garnet trap polyphase inclusions representing the fluid released during high-pressure breakdown of antigorite and chlorite. Combining major element mapping and laser-ablation ICP-MS bulk inclusion analysis, we characterize the mineral content of polyphase inclusions and quantify the fluid composition. Silicates, Cl-bearing phases, sulphides, carbonates, and oxides document post-entrapment mineral growth in the inclusions starting immediately after fluid entrapment. Compositional data reveal the presence of two different fluid types. The first (type A) records a fluid prominently enriched in fluid-mobile elements, with Cl, Cs, Pb, As, Sb concentrations up to 10 3 PM (primitive mantle), ∼10 2 PM Tl, Ba, while Rb, B, Sr, Li, U concentrations are of the order of 10 1 PM, and alkalis are ∼2 PM. The second fluid (type B) has considerably lower fluid-mobile element enrichments, but its enrichment patterns are comparable to type A fluid. Our data reveal multistage fluid uptake in these peridotite bodies, including selective element enrichment during seafloor alteration, followed by fluid-rock interaction along with subduction metamorphism in the plate interface melange. Here, infiltration of sediment-equilibrated fluid produced significant enrichment of the serpentinites in As, Sb, B, Pb, an enriched trace element pattern that was then transferred to the fluid released at greater depth upon serpentine dehydration (type A fluid). The type B fluid hosted by garnet may record the composition of the chlorite breakdown fluid released at even greater depth. The Gagnone study-case demonstrates that serpentinized peridotites acquire water and fluid-mobile elements during ocean floor hydration and through exchange with sediment-equilibrated fluids in the early subduction stages. Subsequent antigorite devolatilization at subarc depths delivers aqueous fluids to the mantle wedge that can be prominently enriched in sediment-derived components, potentially triggering arc magmatism without the need of concomitant dehydration/melting of metasediments or altered oceanic crust.

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High-pressure serpentinites, a trap-and-release system controlled by metamorphic conditions: Example from the Piedmont zone of the western Alps

Cited by 92 publications

References 63 publications

Mantle hydration and Cl-rich fluids in the subduction forearc

Mantle hydration and Cl-rich fluids in the subduction forearc

Evolution of Fe redox state in serpentine during subduction

Fluid-related inclusions in Alpine high-pressure peridotite reveal trace element recycling during subduction-zone dehydration of serpentinized mantle (Cima di Gagnone, Swiss Alps)

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