Carbon mobility and exchange in a plate-interface subduction mélange: A case study of meta-ophiolitic rocks in Champorcher Valley, Italian Alps

Ultramafic and carbonate-rich rocks juxtaposed in an oceanic sedimentary mélange that experienced Alpine subduction (Champorcher, Aosta Valley, Italy) show evidence of metasomatic alteration at their contacts. The reactions occurred these contacts afford assessment the sources compositions fluids associated with alteration, degree scale which mobilized carbon. At contacts, display calcite replacement by diopside tremolite along foliations pressure-dissolution planes as result decarbonation and/or carbonate dissolution. ultramafic bodies record serpentine carbonates formation metamorphic veins hosting + chlorite. These two sets observations point to coeval, coupled carbonation resulting C mobility interface (at about 60 km depth) but conceivably without considerable net loss large-scale transport. δ18OV-SMOW values all samples analyzed this study are lower than expected for protoliths (for marine limestone, +28 +30‰; seafloor ophicarbonate somewhat lower), suggesting pervasive interaction externally derived fluids, has been observed throughout region calcschists such Schistes Lustrés, lowering +20 ± 2‰). calcschist unit Champorcher δ18O (+21.9 +23.6‰) falling into regionally developed range; however, other locality (carbonate mélange/broken formation, rinds, veins) tend have (to low +13.5‰). appear require a fluid affecting on regional more consistent derivation from mafic/ultramafic (ophiolitic) source. Some showing 1 2‰ hosts occurrence horizons anomalously high 87Sr/86Sr circulation isotopically distinct external enriched radiogenic Sr within suite, perhaps involving source devolatilizing terrigenous rocks. Juxtaposition scales units could enhance mobilization via if deformation is accompanied infiltration H2O-rich capable driving reaction process. Information regarding metasomatism hybrid carbonate-ultramafic bears question interfaces whether magnitude any or gain investigated significantly influence whole-margin cycling.