Ab-initiosimulations of low-Zfluids under pressure

Abstract

High-pressure phase equilibria studies provide important constraints on the mineralogy and composition of the earth's interior. However, most of these high-pressure experimental studies have concentrated upon the magnesiumrich simple system. It is generally acknowledged that the phase change of the basaltic crust and surrounding mantle plays significant role in mantle dynamics. In the present study, the cell parameters of minerals in the basaltic (morb) and peridotitic (klb-1) compositions have been determined by a laserheated diamond anvil cell technique and in situ X-ray method at the synchrotron beam line bl10xu, Spring-8, Japan. The morb and peridotite composition crystallized into assemblages of Mg-perovskite + Ca-perovskite + stishovite + aluminous phase and of Mg-perovskite + Ca-perovskite + magnesiowustite phase, respectively. The results of phase relation are generally consistent with previous studies by multi-anvil press and diamond-anvil cell experiments. The estimated densities of morb were denser than those of the seismic observations (e.g. Prem). Therefore, the oceanic crust may subduct into the base of the lower mantle. This result does not consist with the previous studies (Kesson et al, 1998; Ono et al., 2001). In previous studies, the thermoelastic parameters of minerals of simple compositions were used to estimate the mineral volumes. In this study, however, the mineral volumes were directly determined by in situ X-ray methods. Therefore, the compositional effect of the thermoelastic parameters should be considered to investigate the densities of high-pressure minerals in the multicomponent systems.