Abstract

Tuite, γ-Ca3(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 γ-Ca3(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 γ-Ca3(PO4)2 were fitted by the high-temperature Birch-Murnaghan equation of state to yield V0 = 447.4(4) Å3, KT0 = 100.8(18) GPa, KT0 = 5.74(13), (∂KT/∂T)P = −0.020(1) GPa/K, and αT = 3.26(18) × 10−5 + 1.76(24) × 10−8T. In addition, fitting the present data to the Mie-Grüneisen-Debye equation of state gives γ0 = 1.35(6), Θ0 = 944(136) K, and q = 0.37(29). Based on the thermoelastic properties obtained in our study, the density profiles of γ-Ca3(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.

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