Fluid composition and evolution in coesite-bearing rocks (Dora-Maira massif, Western Alps): implications for element recycling during subduction

Article Abstract:

The fluid inclusions and concentrations of F, Cl of the hydrous minerals in the coesite-pyrope quartzite, the interlayered jadeite quartzite and their country-rock gneiss from the Dora-Maira massif are scrutinized. The partitioning of H2O, Na, Ca, Fe and heavy metals in melt during enhanced metamorphism in a residual aqueous fluid lead to decomposition of Na, Ca and Fe of the pyrope quartzite. Melt extraction occurs in subduction zones. The implications of these findings for the transport of elements between downward slabs and overlying mantle are discussed.

Natural history, Subduction zones (Geology), Subduction zones, Quartzite, Western Alps

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High pressure breakdown of antigorite to spinifex-textured olivine and orthopyroxene, SE Spain

Article Abstract:

A study was undertaken to determine the breakdown reaction of antigorite serpentinite to enstatite-olivine observed on the ultramafic rocks of Cerro del Almirez at southeastern Spain. Serpentinites are composed of schitose assemblage of antigorite, diopside and olivine whereas enstatite-olivine rocks have two varieties characterized by their spinifex-like and granular textures. Results indicated that antigorite breakdown resulted to orthopyrene and olivine and there was parallel elongation of olivine.

Spain, Natural resources, Olivine, Rocks, Ultrabasic, Ultrabasic rocks, Serpentinite

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Highly reducing conditions during Alpine metamorphism of the Malenco peridotite (Sondrio, northern Italy) indicated by mineral paragenesis and H(2) in fluid inclusions

Article Abstract:

The prograde metamorphic fluids at the site of dehydration reactions of serpentinite are analyzed. The regional metamorphism of the Malenco serpentinized peridotite gives rise to the formation of the mineral assemblage diopside-antigorite-olivine-brucite and the opaque assemblage magnetite-native copper-chalcocite-pentlandite-heazlewoodite-awaruite. Moreover, primary fluid inclusions are trapped in diopside overgrowth, concurrent with the opaque assemblage.

Analysis, Mineralogical research, Peridotite, Metamorphism (Geology)

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