Dynamic Properties of Earth Materials

9903806 Ahrens研究人员建议继续测量冲击温度，以确定地球下地幔的主要地幔矿物MgSiO 3（钙钛矿）和MgO（方镁石）的高压熔点。 下地幔延伸深度为670 ~ 2900 km，对应的压力为24 ~ 126 GPa。 模型计算的最低地幔温度为3500至4000 K。 然而，目前的实验室（金刚石细胞熔化）的结果，可以把严格的界限上的下地幔的MgSiO 3的峰值温度是非常不一致的近2000 K。 方镁石的一个单一的实验数据集和熔融曲线预测的基础上，一个公认的理论模型之间存在类似的差异。 将这些矿物在高压和高温下的地震速度与地球深处的地震速度进行直接比较，可以限制驱动地球对流的下地幔温度变化。 所提出的熔化的确定是基于先前对矿物（例如Mg 2SiO 4）的冲击熔化的研究，所述矿物冲击到方镁石加MgSiO 3（钙钛矿）组合的稳定性的压力状态，并且预期使用研究者已经开发的用于在冲击之前将样品预热到1300 ℃的技术来完成。 1995年在地幔底部发现了1-40 km厚的明显部分熔融区域，这促使他们计划测量熔融硅酸盐的状态方程、声速和冲击温度，如钙长石（CaAl 2Si 2 O 8）、透辉石（MgCaSi 2 O 6）、铁橄榄石（Fe 2SiO 4）和顽火辉石（MgSiO 3），压力约为150 GPa。 这些数据将允许扩展到压力制度的熔融硅酸盐的热力学性质的以前的知识，这些数据可以应用于理解的过程中，引起这个部分熔融层在地幔的底部。

9903806 Ahrens The investigators propose to continue measurements of shock temperatures in order to determine the high-pressure melting point of the major mantle minerals, MgSiO3 (perovskite) and MgO (periclase) of the lower mantle of the Earth. The lower mantle extends from a depth of 670 to 2900 km and the corresponding pressures are 24 to 126 GPa. Model calculations of the lower-most mantle yield temperatures of 3500 to 4000 K. However, present laboratory (diamond cell melting) results that could place firm bounds on the peak temperatures of the lower mantle for MgSiO3 are very discrepant by nearly 2000 K. A similar discrepancy exists between a single experimental data set for periclase and a melting curve predicted on the basis of a well-accepted theoretical model. Direct comparison between seismic velocities in these minerals at high pressure and high temperature with the seismic velocities at depths of the Earth would allow constraints on the temperature variations in the lower mantle which drive convection in the Earth. The proposed determination of melting is based on previous research on shock melting of minerals such as Mg2SiO4 shocked to the pressure regime of the stability of the assemblage periclase plus MgSi03 (perovskite), and is expected to be accomplished using techniques the investigators have developed for preheating samples to temperatures of 1300 C prior to impact. The 1995 discovery of a 1-40 km thick apparently partially-molten region at the base of the mantle has motivated their plan to measure equations of state, sound velocities, and shock temperatures in molten silicates such as anorthite (CaAl2Si2O8) diopside (MgCaSi2O6), fayalite (Fe2SiO4), and enstatite (MgSiO3) to pressures of ~150 GPa. These data will permit extending previous knowledge of the thermodynamic properties of molten silicates into a pressure regime where these data can be applied to understand the processes which give rise to this partially molten layer at the base of the mantle.