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Computer Simulation of the Physical and Chemical Properties of the Seismic Discontinuities in the Mantle

地幔地震间断面物理和化学性质的计算机模拟

基本信息

批准号：
10640469
负责人：
MATSUI Masanori
金额：
$ 2.05万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10640469/
关键词：
Earth's mantle high presssure and high temperature computer simulation seismic discontinuity mantle minerals interatomic interactions

项目摘要

Molecular dynamics (MD) simulation is used to predict the structure and elasticity of the olivine(α), modified-spinel(β), and spinel(γ) forms of Mg_2SiO_4, MgO, and MgSiO_3 perovskite at high temperatures and high pressures. The interionic potentials are taken to be the sum of pairwise additive Coulomb, van der Waals attraction, and repulsive interactions. In order to take account of non-central forces in crystals, the breathing shell model (BSM) is used for simulation, in which the repulsive radii of O ions are allowed to deform isotropically under the effects of other ions in the crystal. The MD simulation with BSM is found to be very successful in reproducing accurately the observed values for these five phases, including the structural parameters and individual elastic constants at ambient conditions, the temperature and pressure derivatives of bulk and shear moduli, and the volume thermal expansivity and volume compression over wide temperature and pressure ranges. We apply MD sim … More ulation to predict the density and bulk sound velocity jumps in the phase transformation from Mg_2SiO_4 spinel to MgSiO_3 perovskite plus MgO periclase at high-temperature and high-pressure conditions corresponding to the 660 km seismic discontinuity in the mantle. The simulated density and bulk sound velocity jumps are then compared with seismological models reported for the 660 km discontinuity. The MD simulation for a pyrolite composition (60 vol% spinel) is found to be compatible with a recent model SF99 [Shearer and Flanagan, Science 285 (1999) 1545-1548] within the 1σ limit for both density and bulk sound velocity jumps. The MD simulated bulk sound velocity jump for a piclogite composition (40 vol% spinel) is also consistent with SF99 within 1σ, while the MD density jump for the piclogite lies outside the SF99 data. Our MD computed density and bulk sound velocity jumps, either for the pyrolite or the piclogite composition, differ substantially from the values by the PREM or the ak135 model. Less

采用分子动力学（MD）模拟方法预测了Mg_2SiO_4、MgO和MgSiO_3钙钛矿中橄榄石（α）、改性尖晶石（β）和尖晶石（γ）形态在高温高压下的结构和弹性。离子间势取成对加性库仑、范德华引力和排斥相互作用的和。为了考虑晶体中的非中心力，采用呼吸壳模型（BSM）进行模拟，该模型允许O离子的排斥力半径在晶体中其他离子的作用下各向同性变形。用BSM进行的MD模拟非常成功地准确地再现了这五个阶段的观测值，包括结构参数和环境条件下的单个弹性常数，体积和剪切模量的温度和压力导数，以及在宽温度和压力范围内的体积热膨胀率和体积压缩率。本文应用MD模拟方法，预测了高温高压条件下由mg2sio_4尖晶石向MgSiO_3钙钛矿+ MgO方长石相变过程中的密度和体声速跳变。然后将模拟的密度和体声速跳变与660 km不连续的地震模型进行了比较。在密度和体声速跳变的1σ范围内，发现软软岩成分（60 vol%尖晶石）的MD模拟与最近的SF99模型兼容[Shearer和Flanagan， Science 285(1999) 1545-1548]。MD模拟的尖晶石成分（40 vol%尖晶石）的体声速跳也与SF99在1σ范围内一致，而MD密度跳则在SF99数据之外。我们的MD计算出的软锰矿或榴辉石成分的密度和体声速跳变与PREM或ak135模型的值有很大不同。少