Fate of MgSiO3 melts at core-mantle boundary conditions

Abstract

One key for understanding the stratification in the deep mantle in the determination of the density and structure of matter at pressures, as well as the density contrast between solid and silicate phases. Indeed, the density contrast is the main control the entrainment or settlement of matter and is of fundamental for understanding the past and present dynamic behavior the deepest part of the Earth's mantle. Here, we adapted the X-ray method to the small dimensions of the diamond anvil cell, density measurements of amorphous materials to unprecedented conditions of pressure. Our density data for MgSiO3 glass up 127 GPa are considerably higher than those previously derived Brillouin spectroscopy but validate recent ab initio molecular simulations. A fourth-order Birch-Murnaghan equation state reproduces our experimental data over the entire pressure of the mantle. At the core-mantle boundary (CMB) pressure, the density of MgSiO3 glass is 5.48 ± 0.18 g/cm3 , which is 1.6% lower than that of MgSiO3 bridgmanite at 5.57 g/cm3 , they are the same within the uncertainty. Taking into account partitioning of iron into the melt, we conclude that melts are than the surrounding solid phases in the lowermost mantle that melts will be trapped above the CMB.