X-ray Raman scattering study of MgSiO 3 glass at high pressure: Implication for triclustered MgSiO 3 melt in Earth's mantle

• DOI: 10.1073/pnas.0802667105
• Publication Date: 2008-06-06T01:06:31Z
• Authors: Sung Keun Lee; Jung-Fu Lin; Yong Q. Cai; Nozomu Hiraoka; Peter J. Eng; Takuo Okuchi; Ho-kwang Mao; Yue Meng; Michael Y. Hu; Paul Chow; Jinfu Shu; Baosheng Li; Hiroshi Fukui; Bum Han Lee; Hyun Na Kim; Choong-Shik Yoo
• Keywords: 13. Climate action; 01 natural sciences; 0105 earth and related environmental sciences

Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO 3 -rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO 3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; [3] O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO 3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO 3 melt toward deeper part of the Earth's lower mantle.