Mantle plumes and flood basalts: Enhanced melting from plume ascent and an eclogite component

Abstract

New numerical models of starting plumes reproduce the observed volumes and rates of flood basalt eruptions, even for a plume of moderate temperature arriving under thick lithosphere. These models follow the growth of a new plume from a thermal boundary layer and its subsequent rise through the mantle viscosity structure. They show that as a plume head rises into the lower-viscosity upper mantle it narrows, and it is thus able to penetrate rapidly right to the base of lithosphere, where it spreads as a thin layer. This behavior also brings the hottest plume material to the shallowest depths. Both factors enhance melt production compared with previous plume models. The model plumes are also assumed to contain eclogite bodies, inferred from geochemistry to be recycled oceanic crust. Previous numerical models have shown that the presence of nonreacting eclogite bodies may greatly enhance melt production. It has been argued that the eclogite-derived melt would react with surrounding peridotite and refreeze; however, recent experimental studies indicate that eclogite-derived melts may have reached the Earth's surface with only moderate or even minor modification. Combined with an assumed 15 vol % component of eclogite, our models yield a sharp peak in melting of about 1-3 Myr duration and volumes of melt that encompass those observed in flood basalt provinces.