Effect of water on subduction of oceanic crust into lower mantle

This paper reports results of experimental studies in the system MORB-water at 18-26 GPa and 10001800 °C. It has been found that the pressure of garnet-to-perovskite transition in a hydrous system is about 1 GPa lower than that in a "dry" system. This means that at a mean temperature of the subduction slab, the basalt layer remains denser than peridotite at the 660 km discontinuity, i.e., there is no density crossover between basalt and peridotite, as it is established for "dry" MORE. Thus, hydrous basalt can gravitationally sink into the lower mantle without separation from peridotite of the slab. The basalt crust may be detached from peridotite at the 660 km discontinuity under relatively "dry" conditions of subduction or at a higher temperature of the slab.