Volume measurements of zoisite at simultaneously elevated pressure and temperature

Unit-cell parameters of zoisite, Ca2Al3Si3O12(OH), measured at simultaneously high P (≤ 6.1 GPa) and T (≤ 800°C) vary smoothly as P and T are increased; individual expansivities and compressibilities vary in the order c > b > a. A linear fit of isothermal bulk moduli calculated from unit-cell volumes measured at 30, 100, 400, 600 and 800°C yields a bulk modulus of 125 (3) GPa at 298 K and decreases to approximately 103 (3) GPa at 1073 K. These data imply that in a typical subduction zone (geotherm < 8°C/cm) zoisite becomes more dense as subduction proceeds and is therefore capable of transporting H2O into the upper mantle.