Thermal equation of state of Mg3Al2Si3O12 pyrope garnet up to 19 GPa and 1,700 K

Thermoelastic properties of synthetic Mg3Al2Si3O12 pyrope garnet have been measured at high pressure and high temperature by using in situ energy-dispersive X-ray diffraction, using a Kawai-type multi-anvil apparatus. Measurements have been conducted up to 19 GPa and 1,700 K, equivalent to the P-T conditions of the middle part of mantle transition zone. Analyses of the room-temperature P-V data to a third-order Birch-Murnaghan (BM) equation of state (EoS) yields: V (0) = 1,500 +/- A 1 (3), K (0) = 167 +/- A 6 GPa and = 4.6 +/- A 0.3. When fitting the entire P-V-T data using a high-temperature Birch-Murnaghan (HTBM) EoS at a fixed = 4.6, we obtain V (0) = 1,500 +/- A 2 (3), K (T0) = 167 +/- A 3 GPa, (a,K/a,T) (P) = -0.021 +/- A 0.009 GPa K-1 and alpha (300) = (2.89 +/- A 0.33) x 10(-5) K-1. Fitting the present data to the Mie-Gruneisen-Debye (MGD) EoS with Debye temperature I similar to(0) = 806 K gives gamma(0) = 1.19 and 1.15 at fixed q = 1.0 and 1.5, respectively. Comparison of these fittings with two different approaches, we propose to constrain the bulk modulus and its pressure derivative to K (0) = 167 GPa and = 4.4-4.6, as well as the Gruneisen parameter to gamma (0) = 1.15-1.19.