Dynamic Properties of Earth Materials

9903806阿伦斯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--镁SiO_3(钙钛矿)和镁镁(方镁石)的高压熔点。下地幔深度为670~2900 km，对应的压力为24~126 Gpa。模型计算的最低地幔屈服温度为3500~4000K，然而，目前实验室(钻石晶胞熔融)的结果可能对镁硅酸盐的下地幔峰值温度施加严格的界限，相差近2000K。方镁石的单一实验数据集与根据公认的理论模型预测的熔化曲线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。拟议的熔融测定是基于之前对冲击熔化矿物的研究，例如冲击到方镁石+镁硅03(钙钛矿)组合稳定性的压力制度下的矿物，预计将使用研究人员开发的技术来完成，在撞击前将样品预热到1300摄氏度。1995年在地幔底部发现了1-40公里厚的明显部分熔融的区域，这促使他们计划测量熔融硅酸盐如钙长石(CaAl2Si2O8)、透辉石(MgCaSi2O6)、铁辉石(Fe2SiO4)和顽辉石(MgSiO3)在~150 Gpa压力下的状态方程、声速和冲击温度。这些数据将允许将先前关于熔融硅酸盐热力学性质的知识扩展到压力区域，在那里这些数据可以用来理解在地幔底部产生这一部分熔融层的过程。

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.