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<title lang=en>Serpentinization and Fluid Pathways in Tectonically Exhumed Peridotites from the Southwest Indian Ridge (62-65 degrees E)</title>
<creator>Roumejon, Stephane</creator>
<creator>Cannat, Mathilde</creator>
<creator>Agrinier, Pierre</creator>
<creator>Godard, Marguerite</creator>
<creator>Andreani, Muriel</creator>
<contributor>Institut de Physique du Globe de Paris (IPGP) ; Institut national des sciences de l'Univers (INSU - CNRS) - IPG PARIS - Université Paris Diderot - Paris 7 (UPD7) - Université de la Réunion (UR) - Centre National de la Recherche Scientifique (CNRS)</contributor>
<contributor>Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS)</contributor>
<contributor>Manteau et Interfaces ; Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) - Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS)</contributor>
<contributor>Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement [Lyon] (LGL-TPE) ; École normale supérieure - Lyon (ENS Lyon) - Université Claude Bernard Lyon 1 (UCBL) - Institut national des sciences de l'Univers (INSU - CNRS) - Centre National de la Recherche Scientifique (CNRS)</contributor>
<description>International audience</description>
<source>ISSN: 0022-3530</source>
<source>EISSN: 1460-2415</source>
<source>Journal of Petrology</source>
<publisher>Oxford University Press (OUP): Policy B - Oxford Open Option A</publisher>
<publisher>Oxford University Press (OUP)</publisher>
<identifier>hal-01174047</identifier>
<identifier>https://hal.archives-ouvertes.fr/hal-01174047</identifier>
<source>https://hal.archives-ouvertes.fr/hal-01174047</source>
<source>Journal of Petrology, Oxford University Press (OUP), 2015, 56 (4), pp.703-734. 〈10.1093/petrology/egv014〉</source>
<identifier>DOI : 10.1093/petrology/egv014</identifier>
<relation>info:eu-repo/semantics/altIdentifier/doi/10.1093/petrology/egv014</relation>
<language>en</language>
<subject lang=en>serpentinization</subject>
<subject lang=en>slow-spreading ridges</subject>
<subject lang=en>fluid-rock interactions</subject>
<subject lang=en>fluid pathways</subject>
<subject>[SDU.STU.PE] Sciences of the Universe [physics]/Earth Sciences/Petrography</subject>
<type>info:eu-repo/semantics/article</type>
<type>Journal articles</type>
<description lang=en>Peridotites exhumed in the footwall of axial detachment faults at slow-spreading ridges are highly serpentinized. Most mid-ocean ridge detachment settings are magmatically active and hydrous fluid circulation in and near the fault has been shown to be influenced by the presence of melt or magmatic lithologies. Our working area along the Southwest Indian Ridge (62–65°E) is nearly amagmatic and represents an end-member to study the hydrous alteration of exhumed peridotites without these magmatic influences. We use an integrated petrological approach combining microstructural, mineralogical and chemical observations to unravel the sequence of serpentinization in 272 dredged samples of variably serpentinized peridotites and to document the circulation of serpentinizing fluids in and near the exhumation faults. We find that serpentine recrystallization and veins overprint the initial serpentinite mesh texture in ∼25% of the samples. Oxygen isotope data suggest that this sequence developed at relatively high temperatures (271–336°C) and under increasing fluid–rock ratios, from near stoichiometry for mesh texture formation to >10 during recrystallization. Increasing fluid supersaturation relative to serpentine favors the replacement of mesh texture lizardite by chrysotile and polygonal or polyhedral serpentine. We attribute local recrystallization into antigorite to moderate Si-metasomatism, possibly following pyroxene serpentinization. We do not observe the more pronounced Si-metasomatism leading to talc replacing serpentine that is reported for the more magmatically active Mid-Atlantic Ridge detachment settings and is attributed to prior leaching of magmatic rocks. Scales of preferential fluid pathways in our samples evolved from pervasive and close-spaced (<500 µm) microfractures during the formation of the initial serpentine mesh texture, to centimeter-thick planar domains of enhanced fluid flux, spaced at ∼10 cm intervals and probably grouped in corridors that may be up to ∼100 m across. Serpentine minerals are enriched in some fluid-mobile elements (Cl, B, U) relative to the peridotite protolith, and several elements (Al, Fe, Si, Cu, As, Sb, REE) are redistributed at the millimeter to decimeter scale. Serpentinizing fluids were seawater-derived, probably mildly alkaline (small to no europium anomalies), reducing and H2-enriched (formation of magnetite). These fluids may have been similar to, though warmer than, those venting at the ultramafic-hosted Lost City hydrothermal fluid (30°N, Mid-Atlantic Ridge).</description>
<date>2015-04</date>
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