Thermal equation of state of CaFe2O4-type MgAl2O4

Abstract: In situ X-ray diffraction measurements of CaFe2O4-type MgAl2O4 have been conducted at pressures up to 42GPa and temperatures to 2400K using Kawai-type multianvil apparatus with sintered diamond anvils. Additional measurements have also been conducted at pressures to 12GPa using diamond anvil cell with helium as a pressure medium at room temperature, and at temperatures to 836K at the ambient pressure using a high-temperature X-ray diffractometer. The analysis of room-temperature data yielded V 0 =240.1(2)Å3, K 0 =205(6)GPa, and . A fit of the present data to high-temperature Birch–Murnaghan equation of state (EOS) yielded (∂K 0/∂T) P =−0.030(2)GPa/K and α 0 = a 0 + b 0 T with values of a 0 =1.96(13)×10−5 K−1 and b 0 =1.64(24)×10−8 K−2. The present data set was also fitted to Mie–Grüneisen–Debye (MGD) EOS and we obtained γ 0 =1.73(7), q =2.03(37), and θ 0 =1546(104)K. Density changes of MORB have been estimated using the newly obtained thermoelastic parameters, assuming that the Al-rich phase in this composition possesses the CaFe2O4-type structure under the lower mantle P, T conditions. The calculated densities along geotherms for the normal mantle and subducting cold slabs are both significantly higher than those of typical seismological models, confirming the conclusion of some recent results on MORB by laser-heated diamond anvil cell experiments. [Copyright &y& Elsevier]