Tectonically driven carbonation of serpentinite by mantle CO2: Genesis of the Castiglioncello magnesite deposit in the Ligurian ophiolite of central Tuscany (Italy)

•Serpentinite carbonation driven by tectonic activity during the Apennine orogenesis.•CO2 mineralisation at epithermal conditions in the Ligurian ophiolite.•Magnesite and dolomite C-O isotopes indicate a mantle origin for CO2.•Transfer zones provide crustal-scale permeable pathways for CO2.