PHASE TRANSFORMATIONS OF PURE Mg2SiO4 INTO A SPINEL STRUCTURE UNDER HIGH PRESSURES AND TEMPERATURES

Abstract

A double-stage split-sphere apparatus has been developed for a series of phase-transformation studies at high pressures up to about 300kb and at high tempepatures of around 1000°C. First, the coesite-stishovite transition curve has been determined to calibrate the pressures at high temperatures. Then the olivine-distorted spinel transition in pure Mg₂SiO₄ has been investigated in the temperature range from 700 to 1200°C and at pressures above 100kb. The spinel phase of pure Mg₂SiO₄ has been finally synthesized at 1000°C at pressures higher than 220kb. Mg-rich spinels in the system Fe₂SiO₄-Mg₂SiO₄ have also been synthesized in order to complete the phase diagram at 1000°C.