HR: 0800h
AN: MR31A-0145    [Abstracts]
TI: Structure and Properties of Amorphous MgSiO₃ in Earth's Mantle: A View from Synchrotron Inelastic X-ray Scattering
AU: * Lee, S
EM: sungklee@snu.ac.kr
AF: Seoul National University, School of Earth. & Environ. Sci., Seoul, 151-742, Korea, Republic of
AU: Lin, J
EM: lin24@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94588, United States
AU: Mao, H
EM: mao@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, United States
AU: Eng, P
EM: eng@cars.uchicago.edu
AF: University of Chicago, Consortium for Advanced Radiation Sources, Chicago, IL 60637, United States
AU: Cai, Y
EM: cai@spring8.or.jp
AF: National Synchrotron Radiation Research Center, Spring-8, Hsinchu, 30076, Taiwan
AB: The structure of amorphous MgSiO₃ at high pressure is essential for understanding magmatic processes in the Earth's interior and chemical differentiation of the Earth in the Hadean magma ocean. The pressure- induced structural changes in the Mg-silicate melts play an important role in the macroscopic thermodynamic and transport properties at high pressure. In spite of the importance and implications for global geophysical processes in the Earth's interior, the high-pressure structure of MgSiO₃ glasses and melts has not been well-understood, contrary to its crystalline analogues, due to the inherent structural disorder and the lack of suitable experimental probes at high pressures. We have recently shown that synchrotron in-situ inelastic x-ray scattering at high pressure provides detailed pressure-induced electronic bonding changes in amorphous oxides (Lee SK et al. Nature Materials 2005 69, p3695; Lin et al. Phys. Review B. 2007 75, 012201; Lee SK et al. Phys. Rev. Lett. 2007, 98, 105502), providing improved understanding of atomistic origins of melt properties at high pressure (Lee SK, Geochim. Cosmochim. Acta. 2005, 69, p3695). Here, we report the inelastic x-ray scattering spectra for diverse binary and ternary oxide glasses including MgiSiO₃ at pressure up to 40 GPa and revealed the previously unknown structural details of their pressure-induced electronic bonding changes. Direct in-situ measurements provide evidence for a gradual coordination transformation of framework cations as well as anions with multiple densification mechanisms and show that the onset of an electronic bonding transition in MgiSiO₃ glass occurs between 12 to 20 GPa. While it is well established that the lattice structure of mantle minerals exhibits control on element partitioning behavior, our modeling based a strucutral input from x-ray Raman scattering indicates that the oxygen-specific bonding changes in MgiSiO₃ melt with pressures also exhibits a profound control on elemental partition coefficients between silicate melts and crystal in Earth's mantle.
DE: 3621 Mantle processes (1038)
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting