Molybdenum isotope as tracers for subduction components: the case of Roman Magmatic Province magmas

Understanding the fate of recycled material into the convecting mantle is important to provide new constraints on the chemical budget of subduction zones. Molybdenum isotopes have been shown to fractionate during the incorporation into oceanic sediments (Freymuth et al., 2015), being perceptive to ocean redox condition. Indeed, the Mo isotope variability offers the opportunity to use these isotopes as tracers of recycled material into the mantle. The occurrence in the Middle Latin Valley volcanic region of extremely variable products in terms of geochemical and isotopic compositions, makes this area a perfect case study to tackle the role of different subduction-related metasomatic agents. In this magmatic region, the compositional variability of the recycled sedimentary component into the mantle wedge during subduction, has been proposed to explain the distinct geochemical signature of volcanic products (Avanzinelli et al., 2009). Here we present the first results of high precision Mo isotopic compositions for Italian magmatic rocks, demonstrating that the isotopically heavy 98Mo is anomalous with respect to other subduction-related magmas. In order to reproduce such heavy isotopic composition, organic carbon-rich material, in addition to the sedimentary component, is required, revealing the potential of Mo isotopes as tracers of the fate of organic carbon in subduction zones.