Elastic Moduli of Wadsleyite (β-Mg 2 SiO 4 ) to 7 Gigapascals and 873 Kelvin

Abstract

Simultaneous sound velocity measurements and x-ray diffraction studies were made on wadsleyite (β-Mg ₂ SiO ₄ ) to 7 gigapascals and 873 kelvin. The calculated adiabatic bulk ( K ) and shear ( G ) moduli yield K (at room conditions) = 172(2) gigapascals, dK / dP = 4.2(1), and dK / dT = −0.012(1) gigapascals per kelvin, and G (at room conditions) = 113(1) gigapascals, dG / dP = 1.5(1), and dG / dT = −0.017(1) gigapascals per kelvin, respectively. The data imply that the P and S wave velocity contrasts between olivine and wadsleyite require an olivine amount of 38 to 39 percent in the upper mantle to satisfy the observed 410-kilometer discontinuity, but 55 to 60 percent to account for the velocity increase through the transition zone.