title: Fate of MgSiO3 melts at core-mantle boundary conditions.
abstract: One key for understanding the stratification in the deep mantle lies in the determination of the density and structure of matter at high pressures, as well as the density contrast between solid and liquid silicate phases. Indeed, the density contrast is the main control on the entrainment or settlement of matter and is of fundamental importance for understanding the past and present dynamic behavior of the deepest part of the Earth's mantle. Here, we adapted the X-ray absorption method to the small dimensions of the diamond anvil cell, enabling density measurements of amorphous materials to unprecedented conditions of pressure. Our density data for MgSiO3 glass up to 127 GPa are considerably higher than those previously derived from Brillouin spectroscopy but validate recent ab initio molecular dynamics simulations. A fourth-order Birch-Murnaghan equation of state reproduces our experimental data over the entire pressure regime of the mantle. At the core-mantle boundary (CMB) pressure, the density of MgSiO3 glass is 5.48 ± 0.18 g/cm(3), which is only 1.6% lower than that of MgSiO3 bridgmanite at 5.57 g/cm(3), i.e., they are the same within the uncertainty. Taking into account the partitioning of iron into the melt, we conclude that melts are denser than the surrounding solid phases in the lowermost mantle and that melts will be trapped above the CMB.
authors.affiliation: Bayerisches Geoinstitut, University of Bayreuth, Bayreuth D-95490, Germany; sylvain.petitgirard@uni-bayreuth.de.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Petitgirard
authors.affiliation: Laboratory for Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland;
authors.forename: Wim J
authors.initials: WJ
authors.lastname: Malfait
authors.affiliation: Bayerisches Geoinstitut, University of Bayreuth, Bayreuth D-95490, Germany;
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Sinmyo
authors.affiliation: Bayerisches Geoinstitut, University of Bayreuth, Bayreuth D-95490, Germany; European Synchrotron Radiation Facility, BP 220, Grenoble F-38043, France;
authors.forename: Ilya
authors.initials: I
authors.lastname: Kupenko
authors.affiliation: Conditions Extrêmes et Matériaux: Haute Température et Irradiation, CNRS UPR 3079, Université d'Orléans, 45071 Orléans Cedex 2, France;
authors.forename: Louis
authors.initials: L
authors.lastname: Hennet
authors.affiliation: Analytical Mineralogy of Micro- and Nanostructures, Institute of Geoscience, Friedrich Schiller University Jena, Jena 07745, Germany;
authors.forename: Dennis
authors.initials: D
authors.lastname: Harries
authors.affiliation: European Synchrotron Radiation Facility, BP 220, Grenoble F-38043, France;
authors.forename: Thomas
authors.initials: T
authors.lastname: Dane
authors.affiliation: European Synchrotron Radiation Facility, BP 220, Grenoble F-38043, France; Department of Analytical Chemistry, Ghent University, B-9000 Ghent, Belgium.
authors.forename: Manfred
authors.initials: M
authors.lastname: Burghammer
authors.affiliation: Bayerisches Geoinstitut, University of Bayreuth, Bayreuth D-95490, Germany;
authors.forename: Dave C
authors.initials: DC
authors.lastname: Rubie
keywords: X-ray absorption; basal magma ocean; silicate glass density