The thermal equation of state of (Fe0.86Mg0.07Mn0.07)3Al2Si3O12 almandine

Abstract

In situ X-raydiffraction measurements on almandine, (Fe0.86Mg0.07Mn0.07)3Al2Si3O12, were performed using a heating diamond-anvil cell instrument with synchrotron radiation at Beijing Synchrotron Radiation Facilityup to 27.7 GPa and 533 K. The pressure-volume-temperature data were fitted to a third-order Birch-Murnaghan equation of state. The isothermal bulk modulus of K0 = 177±2 GPa, a temperature derivative of the bulk modulus of (∂K/∂T)P= –0.032±0.016 GPaK–1 and a thermal expansion coefficient (α0) of (3.1±0.7)×10–5 K–1 were obtained. This is the first time that the temperature derivative of the bulk modulus of almandine has been determined at high pressure and high temperature. Combining these results with previous results, the compositional dependence of the bulk modulus, thermal expansion, and temperature derivative of the bulk modulus are discussed.