Determination of the second critical endpoint in peridotite-H2O system

Abstract

Judging from existing data, we could speculate that silicate melt and aqueous fluid in the Earth's interior became indistinguishable from each other beyond the second critical endpoint with pressure. Here we report the determination of the second critical endpoint in peridotite-H2O system using high-pressure X-ray radiography technique. We found the second critical endpoint occurs at around 3.8 GPa and 1050 C (corresponding to depth of c.a. 110 km) in the Earth's hydrous upper mantle. This position of the second critical endpoint could play an important role in magmatism and chemical evolution of the Earth's interior. Our new technique can be applied to the direct observations of various kinds of 2-fluid coexisting under deep mantle conditions.