硅酸钙钙钛矿弹性及熔融相关系的第一性原理计算

硅酸钙钙钛矿(CaSiO3 perovskite, CaPv)是下地幔的主要矿物之一。准确的高温高压弹性数据是利用地震波观测确定其在地幔分布状态的前提。 此外，CaPv与其它地幔矿物如硅酸镁钙钛矿(MgSiO3 perovskite, MgPv)的熔融相关系是确定钙镁偏硅酸盐矿物在下地幔赋存形式的基础。本项目将利用最近发展的基于第一性原理准确计算固、液相自由能的新方法，系统地研究CaPv在下地幔温压条件下的弹性及熔融相关系。 通过本项目研究，有望获得可靠的CaPv弹性数据，弥合现有理论计算与实验测量间的分歧；建立自洽的MgPv-CaPv二元体系热力学模型并给出两者在下地幔条件下的互溶度，近而确定钙镁偏硅酸盐在下地幔的赋存形式、密度及弹性波速。这些结果对研究地幔的矿物构成及俯冲洋壳的循环演化机制具有重要的基础性意义。

CaSiO3 perovskite (CaPv) is a major mineral in the Earth’s lower mantle. Accurate elastic data at high pressure and temperature is a prerequisite for seismic determination of its distribution. Moreover, melting phase relations of CaPv with other mantle minerals such as MgSiO3 perovskite (MgPv) are essential for determining the composition of Ca-Mg metasilicates in the lower mantle. Here we propose a systematic study on the elasticity and melting phase relations of CaPv at conditions of the Earth’s lower mantle using recently developed, highly accurate, ab initio free energy methods. From this study we will (i) get reliable elasticity data for CaPv and reconcile the large discrepancy between theory and experiment; (ii) build a self-consistent thermodynamic model for the MgPv-CaPv binary system, determine their mutual solubility, so as to infer the composition, density, and seismic features of metasilicates in the lower mantle. These results are crucial for understanding the mineralogical composition of the Earth's mantle as well as the cycling and evolution of subducting oceanic plates.