Melt- and Fluid-Rock Interaction in Supra-Subduction Lithospheric Mantle: Evidence from Andesite-hosted Veined Peridotite Xenoliths

• Published in: Journal of Petrology
• Main Authors: Bénard, Antoine, IONOV, Dmitri
• Other Authors: Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet Saint-Étienne (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2013
• Subjects: Avacha; vein; mantle xenolith; fluid-rock interaction; subduction zone; melt-rock interaction; geo; archi; Wall Rocks; Kamchatka
• Online Access: https://doi.org/10.1093/petrology/egt050; https://hal.archives-ouvertes.fr/hal-01066862

International audience We report petrographic, major and trace element data for xenoliths from the andesitic Avacha volcano (Kamchatka), which host orthopyroxene (opx)-rich veins of mantle origin formed either by rapid crystallization of intruded melts or by their interaction with the host harzburgite. Studies of such veins may give better insights into sub-arc mantle processes (in particular on a millimetre to centimetre scale) than those of (1) arc xenoliths that do not preserve solidified initial metasomatizing agents, (2) massif peridotites, probably modified during their emplacement, or (3) arc magmatic rocks, which provide indirect information. We seek to trace the evolution of these agents as they react with the host peridotite and to assess their impact on the wall-rocks. The veins cross-cut spinel harzburgite and consist mainly of opx with minor olivine, clinopyroxene (cpx) and/or amphibole. We identify 'rapidly crystallized' veins that cut wall-rock olivine without petrographic evidence of reaction, and 'reactive' veins subdivided into 'thick' (0*5-1 mm) and 'thin' (<€0*5 mm). Minerals in the rapidly crystallized veins are depleted in rare earth elements (REE) and high field strength elements (HFSE) and enriched in fluid-mobile elements relative to REE. Minerals in the reactive veins have higher Ti, Al, Cr and alkalis than minerals in the rapidly crystallized veins, as well as highly variable trace element abundances, especially in reaction zones, thin veins and related metasomatic pockets in the host peridotite. They commonly show U-shaped REE patterns and positive Zr and Hf spikes in normalized trace element patterns. Our data, supported by recent reports, show that the rapidly crystallized veins formed between 1200°C and 900°C from a liquid derived by fluid-fluxed melting of a refractory (harzburgitic) mantle source depleted in heavy REE. The reactive veins formed via 'fractionation-reactive percolation' from fractionated hydrous derivatives of the melts that precipitated the rapidly crystallized ...