Phase Relations and Melting in the Systems of Peridotite-H_2O-CO_2 and Eclogite-H_2O-CO_2 at Pressures up to 27 GPa

摘要

Experimental study of phase equilibria with volatile components is the most important task for solution of the problems related to the processes of melting and distribution of matter in the Earth's mantle [1]. The main volatile components in the mantle may be described in the C—O—H system. Oxidized compounds, namely H_2O and CO_2 dominate in the upper mantle at depths up to 100—200 km. CH_4, as well as possibly other hydrocarbons, and H_2 become more important on deeper levels at a gradual decrease of f_(O_2) values [2, 3]. However oxidized species may be preserved at a depth up to at least 600—700 km [4], as well as participate in "redox-melting" [5]. Because of this, it is important to study their influence on phase relations in mantle rocks at high pressures. Solidus and phase equilibria of H_2O-bearing peridotite and eclog-ite systems have been studied in detail up to a pressure of 25 GPa [6, 7]. The same systems with CO_2 are studied up to pressures of 20—32 GPa [8—11]. However, the systems containing both H_2O and CO_2 are studied only at low pressures up to 6 GPa [5, 12—14]. In this paper we report the main results of the experimental study of the systems peridotite—H_2O—CO_2 and eclog-ite—H_2O—CO_2 up to a pressure of 27 GPa.