Equation of state and strength of natural majorite

Abstract

The bulk modulus of a natural sample of cubic majorite, one of the primary components of the Earth's transition zone, has been determined by two independent methods: quasi-hydrostatic compression in the diamond anvil cell and Brillouin spectroscopy at room pressure. The two measurements agree well, and together yield a zero-pressure isothermal bulk modulus K0T=162.7 (± 3.3) GPa, and a pressure derivative K0T′=6.6 (± 0.8). Additional compression experiments under nonhydrostatic conditions show that majorite supports shear stresses of at least 2 to 3 GPa at pressures of 7-11 GPa, among the highest values yet documented in silicates or oxides at comparable pressures. These results imply a high strength for majorite, suggesting that the transition zone could be strong to a degree that may influence deformation and heat transfer within the Earth. Copyright 2000 by the American Geophysical Union.