P-V-T relations of γ-Ca3(PO4)2 tuite determined by in situ X-ray diffraction in a large-volume high-pressure apparatus

Tuite, gamma-Ca-3(PO4)(2), is regarded as an important phosphate mineral in the deep mantle playing a crucial role as a host for rare earth elements, large ion lithophile elements, and phosphorus. In this study we report the thermoelastic properties of synthetic gamma-Ca-3(PO4)2 at simultaneously high pressures and temperatures of up to 35.4 GPa and 1300 K, respectively, as determined by means of in situ energy-dispersive X-ray diffraction in a large-volume multi-anvil apparatus. The pressure-volume-temperature data obtained for gamma-Ca-3(PO4)(2) were fitted by the high-temperature Birch-Murnaghan equation of state to yield V-0 = 447.4(4) angstrom(3), K-T0 = 100.8(18) GPa, K-T0' = 5.74(13), (partial derivative K-T/partial derivative T)(p) = -0.020(1) GPa/K, and alpha(T) = 3.26(18) x 10(-5) + 1.76(24) x 10(-8) T. In addition, fitting the present data to the Mie-Gruneisen-Debye equation of state gives gamma(0) = 1.35(6), Theta(0) = 944(136) K, and q = 0.37(29). Based on the thermoelastic properties obtained in our study, the density profiles of gamma-Ca-3(PO4)(2) tuite along typical cold and hot slab geotherms were calculated and are compared with those of the coexisting silicate minerals in subducting mid-ocean ridge basalt.