X-ray Raman scattering study of MgSiO3 glass at high pressure:: Implication for triclustered MgSiO3 melt in Earth's mantle
X-ray Raman scattering study of MgSiO3 glass at high pressure:: Implication for triclustered MgSiO3 melt in Earth's mantle
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DOI：
10.1073/pnas.0802667105
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发表时间：
2008-06-10
影响因子：
11.1
通讯作者：
Yoo, Choong-Shik
中科院分区：
文献类型：
--
作者：
Lee, Sung Keun;Lin, Jung-Fu;Yoo, Choong-Shik
过渡带顶部和核幔边界的硅酸盐熔体对地球内部的动力学和性质有重要影响。富mgsio3硅酸盐熔体是岩浆海的主要成分之一，在早期地球的化学分异中起着重要作用。地球内部硅酸盐熔体的各种宏观特性，如密度、粘度和晶体-熔体分配，取决于它们在高压和高温下的电子和短程局部结构。尽管硅酸盐熔体在许多地球物理和地球动力学问题中起着重要作用，但人们对其在地球内部条件下的性质知之甚少，包括致密化机制和高压下宏观性质的原子起源。在这里，我们利用高达39 GPa的高压x射线拉曼光谱探测了MgSiO3玻璃（mg -硅酸盐熔体的前驱体）的局部电子结构，其中高压氧k边特征表明在12至20 GPa之间形成了三簇氧（氧与三个Si框架配合；1310）。我们的研究结果表明，MgSiO3熔体中的致密化因此可能伴随着三角结构的形成，以及非桥接氧的减少。压力引起的氧三团簇分数的增加将导致密度、粘度和晶体-熔体分配的增强，以及MgSiO3熔体中元素向下地幔更深部分扩散的降低。
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. MgSiO3-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 MgSiO3 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; 1310) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 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 MgSiO3 melt toward deeper part of the Earth's lower mantle.