HR: 1050h
AN: MR32A-03    [Abstracts]
TI: Structure of Ca and Mg aluminosilicate melts under pressure
AU: * Urakawa, S
EM: urakawa@cc.okayama-u.ac.jp
AF: Okayama Univesity, 3-1-1 Tsushimanaka, Okayama, 700-8530, Japan
AU: Kikegawa, T
EM: kikegawa@post.kek.jp
AF: Photon Factory, 1-1 Oho, Tsukuba, 305-0801, Japan
AB: Viscosity and density are important physical properties to control the transportation of magma in the Earth's interior, which are affected by microscopic structure of magma. Magmas have been considered to be densified by structural change with increasing pressure. Recently, Allwardt et al. (2005) found the structure change in auminosilicate glasses quenched under pressure using the NMR spectroscopy, in which an average coordination number of aluminium increases from four to five up to about 10 GPa. We carried out direct observation of structural change in aluminsilicate melts by using in-situ X-ray diffraction method. High-pressure and high-temperature experiments were conducted using MAX80 installed at AR-NE5C of Photon Factory, Tsukuba, Japan. Energy dispersive X-ray diffraction method is applied to acquire diffraction patterns from molten samples. X-ray diffraction spectra were acquired for Ca3Al2Si6O18 and Mg3Al2Si6O18 composition melts up to 5 GPa and 2000 K. Signs of pressure-induced structural change are observed in radial distribution functions as well as in diffraction patterns. The first sharp diffraction peaks (FSDP) shift to higher-Q side with increasing pressure, indicating reduction of the size of the intermediate rage structure, such as rings or chains composed of SiO4 and AlO4 tetrahedra. Radial distribution function also changes with pressure. The nearest neighbour T-O peak (composed of Si-O and Al-O interactions) becomes asymmetric, indicating the coordination increase of the nearest neighbour ions. These observations are consistent with the densification of high-pressure quenched aluminosilicate glasses.
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