Thermal expansivity of mantle relevant magnesium silicates derived from vibrational spectroscopy at high pressure

摘要: Thermal expansivities for the MgSiO 3 phases of orthoenstatite, high clinoenstatite, ilmenite, and majorite; stishovite were estimated using thermodynamic Maxwell relation (∂ S /∂ P ) T = −(∂V/∂ where entropies at pressures derived a statistical method spectroscopic data. The spectroscopically determined thermal all minerals are in excellent agreement with previously volumetric data, available. A value 3.25(10) × 10 −5 K −1 orthoenstatite room temperature was obtained; this is situated middle large spread reported values two latest determinations. For α as 2.56(9) . This provides good estimates high-pressure polymorphs, data scanty or unavailable. Included report previous Mg 2 SiO 4 MgO completeness. following equations may be used to extrapolate higher temperatures 1 atm : α(majorite) 2.95 + 0.000521 x ; α(γ-Mg 2.70 0.000648 α(ilmenite) 2.64+ 0.000537 α(perovskite) 2.51 0.000805 α(stishovite) 2.19 0.000485 , ( / -750).