HR: 10:35h
AN: MR32A-02    [Abstracts]
TI: Pressure-Induced Changes in Crystal-Melt Partitiong Coefficient between Silicate Melts and Crystals: A View from Solid-State NMR
AU: Cody, G
EM: gcody@ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, United States
AU: * Lee, S
EM: sungklee@snu.ac.kr
AF: Seoul National University, School of Earth and Environ. Sci., Seoul, 151-742, Korea, Republic of
AU: Mysen, B
EM: mysen@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, United States
AU: Fei, Y
EM: fei@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, United States
AB: Silicate melts in the Earth's interior played essential roles in physicochemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in the Earth's interior including crystal-melt partitioning depend on their atomic structures at high pressures. Despite their essential implications to many geophysical and geodynamic problems, little is known about the nature of silicate glasses at high pressure, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressure, mostly due to the lack of suitable high-pressure experimental probes. Recent advances in high-resolution multi-dimensional solid-state NMR and synchrotron x-ray raman scattering yielded improved insights into the structure of oxide glasses with varying pressure (e.g. Lee SK. Geochim. Cosmochim. Acta 2005, 69, p3695; Lee SK et al. Nature Materials 2005, 4, p851; Lee SK et al. Phys. Rev. Lett. 2007, 98, 105502)). The structural information from the above advanced spectroscopic tools has been useful to calculate thermodynamic properties including crystal-melt partitioning coefficient (Lee SK. Geochim. Cosmochim. Acta 2005). Here, we report the spectroscopic evidence of differential pressure dependence controlling the abundances of several types oxygen configuration in complex silicate glasses at high pressure. While all of the glasses studied exhibit a general trend of decreasing non-bridging oxygen concentration with pressure, the details of their pressure dependence is strongly dependent on the composition of melts. Several types of non- bridging oxygen in the divers glass also have varying pressure dependence. Fraction of ^[4,5]Al-O-^[4,5]Al in aluminosilicate glasses, a measure of configurational entropy in aluminosilicate glasses decreases with pressure, suggesting a decrease in configurational disorder caused by the mixing among high energy framework units. We then calculated the crystal-melt partition coefficient from the structural information from solid-state NMR and inelastic x-ray scattering. Our results indicate that the detailed structural information around oxygen in silicate melts at high pressures should be taken into the modeling of their thermodynamic properties.
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
DE: 3939 Physical thermodynamics
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting