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The Strucutures and physical properties of ultrahigh-pressure silicate phases at high temperatures and high pressures in the lower mantle

下地幔高温高压超高压硅酸盐相的结构和物理性质

基本信息

批准号：
06452100
负责人：
MATSUI Masanori
金额：
$ 4.48万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06452100/
关键词：
lower mantle silicates ultrahigh pressure high temperature computer simulation X-ray analysis lower mantle silicates ultra-high pressure high temperature physical properties computer simulation X-ray analysis high tempcrature s

项目摘要

Cryatals and liquids in the system Na_2O-CaO-MgO-Al_2O_3-SiO_2 (NCMAS) are important constituents of the Earth's mantle. A transferable interatomic potential model has been developed for use in computer simulation of both crystals and liquids in this geophysically important system. The potential energy of the system is taken as the sum of pairwise additive Coulomb, van der Waals, and repulsive interactions. The net charges on the Na, Ca, Mg, Al, Si, and O ions are constrained to be 2q(Na)=q(Ca)=q(Mg)=2/3q(Al)=1/2q(Si)=-q(O) in order to preserve the requirement of transferability between phases with different composition in the NCMAS system. The reliability and applicability of the potential model has been tested using the molecular dynamics (MD) simulation, with the results that the simulation has succeeded in reproducing accurately (1) the observed structures and measured bulk moduli of a wide variety of 29 crystals in the NCMAS system, and (2) the observed temperature-pressure-volume equation-of-state parameters of the five silicate liquids with the composition, enstatite (MgSiO_3), wollastonite (CaSiO_3), diopside (CaMgSi_2O_6), anorthite (CaAl_2Si_2O_8) and albite (NaAlSi_3O_8). The MD technique is then successfully used to investigate (1) the equation-of state parameters of forsterite (Mg_2SiO_4) liquid at high temperatures, (2) the possible occurrence of the density inversion between diopside crystal and liquid at high temperatures and high pressures, and (3) the melting temperature of MgSiO_3 perovskite at ultrahigh pressures and high temoperatures prevailing in the lower mantle.

Na_2 O-CaO-MgO-Al_2 O_3-SiO_2（NCMAS）系统中的晶体和液体是地幔的重要组成部分。本文发展了一个可转移的原子间相互作用势模型，用于晶体和液体这一重要物理体系的计算机模拟。系统的势能取为两两相加的库仑相互作用、货车德瓦尔斯相互作用和排斥相互作用的和。Na、Ca、Mg、Al、Si和O离子上的净电荷被限制为2 q（Na）=q（Ca）=q（Mg）=2/3q（Al）=1/2 q（Si）=-q（O），以保持NCMAS系统中具有不同组成的相之间的可转移性的要求。用分子动力学（MD）模拟方法验证了势模型的可靠性和适用性，结果表明，该模拟方法成功地再现了NCMAS系统中29种晶体的结构和体积模量，以及5种硅酸盐液体的温度-压力-体积状态方程参数，顽火辉石（MgSiO_3）、硅灰石（CaSiO_3）、透辉石（CaMgSi_2O_6）、钙长石（CaAl_2Si_2O_8）和钠长石（NaAlSi_3O_8）。利用分子动力学方法成功地研究了镁橄榄石（Mg_2SiO_4）在高温下的状态方程参数、高温高压下透辉石晶体与液体之间密度反转的可能性以及下地幔MgSiO_3钙钛矿在超高压高温下的熔融温度。