Computer simulation of the densities and the seismic velocities of the mantle transition zone

从本项目中获得以下结果：1.在密度和声音的16个极限范围内，对热解石组合物(60vol%尖晶石)的MD模拟与最近的模型SF99(Sheeller和Flanagan，1999)兼容。速度跳跃。40%尖晶石组分的体积声速跃变的MD模拟结果与SF99的模拟结果在16以内也是一致的，而苦橄岩的MD密度跃迁在SF99数据之外。我们的MD计算的密度和声速跳跃，无论是对于地榴石还是对于苦橄岩成分，都与Prem或ak135模型的值有很大的不同。2.我们将MD模拟应用于镁铝榴石、镁铝榴石和粗晶石，发现MD模拟的晶体对称性和弹性常数非常准确地再现了这三个石榴石的观测值。3.基于带有量子修正的呼吸壳模型MD模拟，我们计算了γ-Mg_2SiO_4的温度-压力-体积(T-P-V)状态方程，在温度高达2000K、压力高达25~30 GPa时可作为可靠的压力校准标准。我们发现松井等人[2000年]给出的γ-Mg_2SiO_4状态方程与之前给出的状态方程吻合得很好，在1500K和2000K温度下两种状态方程的压力估计值之间的平均差小于0.3 Gpa，而P在19~23 Gpa之间的压力估计值之间的平均值相差不到0.3 Gpa。

The following results are obtained from the present project.1.The MD simulation for a pyrolite composition(60 vol% spinel) is compatible with a recent model SF99 (Shearer and Flanagan, 1999) within the 16 limit for both density and sound. velocity jumps. The MD simulated bulk sound velocity jump for a piclogite composition(40 vol% spinel) is also consistent with SF99 within 16, while the MD density jump for the piclogite lies outside the SF99 data. Our MD computed density and sound velocity jumps, either for the pyrolite or the piclogite composition, differ substantially from the values by the PREM or the ak135 model.2.We applied the MD simulation to pyrope, majorite, and grossular, and found that the MD simulated crystal symmetry and elastic constants for each of the three garnets reproduce the observed values very accurately.3.Based on breathing-shell-model MD simulations with quantum correction, we calculated the temperature-pressure-volume (T-P-V) equation of state(EOS) of γ-Mg_2SiO_4 to be used as a reliable pressure calibration standard at temperatures up to 2000 K and pressures up to 25 〜 30 GPa. We found that the MgO EOS previously given by Matsui et al.[2000] and the present γ-Mg_2SiO_4 EOS agreed very well, with the average differences in the estimated pressures between the two EOS's being less than 0.3 GPa at T between 1500 and 2000 K and P between 19 and 23 GPa.