P-V-T relations of gamma -Ca (sub 3) (PO (sub 4) ) (sub 2) tuite determined by in situ X-ray diffraction in a large-volume high-pressure apparatus

Tuite, gamma -Ca (sub 3) (PO (sub 4) ) (sub 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 (sub 3) (PO (sub 4) ) (sub 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 (sub 3) (PO (sub 4) ) (sub 2) were fitted by the high-temperature Birch-Murnaghan equation of state to yield V (sub 0) =447.4(4) Aa (super 3) , K (sub 10) =100.8(18) GPa, K' (sub T0) =5.74(13), (theta K (sub T) /theta T) (sub P) =-0.020(1) GPa/K, and alpha (sub T) =3.26(18)X10 (super -5) +1.76(24)X10 (super -8) T. In addition, fitting the present data to the Mie-Gruneisen-Debye equation of state gives gamma (sub 0) =1.35(6), Theta (sub 0) =944(136) K, and q=0.37(29). Based on the thermoelastic properties obtained in our study, the density profiles of gamma -Ca (sub 3) (PO (sub 4) ) (sub 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.