Carbon isotope composition of CO2-rich inclusions in cumulate-forming mantle minerals from Stromboli volcano (Italy)

We report on measurements of concentration and carbon isotope composition (delta C-13(co2)) of CO2 trapped in fluid inclusions of olivine and clinopyroxene crystals separated from San Bartolo ultramafic cumulate Xenoliths (SBX) formed at mantle depth (i.e., beneath a shallow Moho supposed to be at 14.8 km). These cumulates, erupted about 2 ka ago at Stromboli volcano (Italy), have been already investigated by Martelli et al. (2014) mainly for Sr-Nd isotopes and for their noble gases geochemistry. The concentration of CO2 varies of one order of magnitude from 3.8-10-8 mol g(-1) to 4.8.10(-7) mol g(-1), with delta C-13 values between -2.8%. and -1.5%. vs V-PDB. These values overlap the range of measurements performed in the crater gases emitted at Stromboli (-2.5%0 < delta C-13(co2) < 1.0%.). Since SBX formed from relatively primitive mantle-derived basic magmas, we argue that the isotope composition displayed by fluid inclusions and surface gases can be considered representative of the magma volatile imprinting released by partial melting of the mantle source beneath Stromboli (-2.8%. < delta C-13 < 1.0 parts per thousand). In addition, the delta C-13 signature of CO2 is not significantly modified by fractionation due to magmatic degassing or intracrustal contamination processes owing to magma ascent and residence within the volcano plumbing system. Such delta C-13 values are higher than those commonly reported for MORB-like upper mantle (-8 divided by -4%.) and likely reflect the source contamination of the local mantle wedge by CO2 coming from the de carbonation of the sediments carried by the subducting Ionian slab with a contribution of organic carbon up to 7%. (C) 2017 Elsevier B.V. All rights reserved.