Hydrous Melting in Mantle Wedge and Magmatism in Subduction Zones

Factors controlling magmatism in subduction zones and location of volcanic arcs are explored through variable H2O and pressure-experiments on peridotite, primitive magnesian andesite, and basaltic andesite under the supervision of T.L. Grove at the MIT Experimental Petrology Laboratory. Our studies indicate that an H2O-rich fluid, formed by dehydration of hydrous minerals in the subducted oceanic lithosphere, rises into the overlying mantle wedge and causes flux melting that continues to shallow mantle depths (< 30 km). The resulting melts segregate at the top of the wedge and pass through the crust where they differentiate and follow distinctive SiO2 enrichment paths at low FeO/MgO.