Serpentinization, Carbonation, and Metasomatism of Ultramafic Sequences in the Northern Apennine Ophiolite (NW Italy)

Fluid-rock interaction in ultramafic rocks considerably affects the chemical and isotopic composition of oceanic lithosphere. We present a geochemical petrological study serpentinites ophicalcites Northern Apennine ophiolite, Italy. This ophiolite sequence represents fragments Jurassic lithosphere that have been denuded by low angle detachment faults, exposing peridotites on ocean floor triggering hydrothermal alteration. Seawater circulation is documented (Jurassic) seawater-like 87Sr/86Sr values ?13C 1.1–3.0‰ carbonate veins ophicalcites. Bulk rock 0.70489–0.70599, elevated SiO2 contents, talc druses filling calcite record Si-metasomatism. In contrast, underlying above seawater values. ?D ?18O suggest with an evolved seawater-derived and/or magmatic fluid. These signatures result from complex history serpentinization, carbonation, metasomatism. Multiphase water-rock includes infiltration basement-derived fluids during initial mantle upwelling within opening basin, followed localized high-temperature fluid infiltration, extensive resulting oxidation near seawater-exposed surface, finally, fluid-rock overlying mafic lithologies leading to The studied excellent example evolution serpentinite ophicalcite continuous uplift exposure seafloor documents associated this process. transformation likely has impact cycles subduction zone processes.