ISOTHERMAL COMPRESSION CURVE OF MGSIO3 TETRAGONAL GARNET

The bulk modulus of MgSiO3 tetragonal garnet was measured using a diamond anvil-type high-pressure apparatus combined with synchrotron radiation. An imaging plate X-ray detector was used to get high resolution diffraction data and the whole-powder-pattern decomposition method was employed to analyze the tetragonal unit cell which was only slightly distorted from cubic symmetry. The isothermal bulk modulus (K0) of the garnet-structured MgSiO3 was determined to be 161 GPa when (dK/dP)0 was assumed to be 4. Combining this result with previous results. the compositional dependence of the bulk modulus of majorite in a pyrope-enstatite join is expressed as K0(GPa) = (171.8 +/- 3.5) - (0.11 +/- 0.5)X(En) where X(En) is the mole fraction of the enstatite composition in majorite.