Phase equilibria on the join MgSiO₃–MnSiO₃ at high pressure and temperature

Abstract

The phase equilibria on the join MgSiO₃–MnSiO₃ were determined experimentally in the pressure – temperature range 1–25 kb and 600–1150°C. The following phase assemblages were encountered from MgSiO₃ side to MnSiO₃ component, the single phase of orthopyroxene_SS, orthopyroxene + clinopyroxene, clinopyroxene_SS (kanoite), clinopyroxene + pyroxmangite, pyroxmangite_SS, pyroxmangite + rhodonite, and rhodonite_SS. Below 700°C, olivine is present and the following two fields are encountered; olivine + clinopyroxene + quartz and olivine + quartz + pyroxmangite.
Rhodonite has a limited field (95 mol% MnSiO₃) for all pressures and temperatures. Solubility of MgSiO₃ in pyroxmangite increases linearly with increasing temperature, at least below 10 kb, and that of MnSiO₃ in orthopyroxene increases with increasing pressure. Unit cell constants of the pyroxenes increase linearly with increasing MnSiO₃ content. The clinopyroxene is indexed in the space group P2₁/c, analogous to the natural kanoite. The miscibility gaps observed in our study are consistent with those in natural samples from Tatehira mine, Hokkaido, Japan.