Elasticity of Selected Deep Earth Phases Under Simultaneous High P-T Conditions Using Nuclear Resonant Inelastic X-ray Scattering

最近观测到的地震复杂性需要对候选下地幔物质进行新的、更精确的测量。努力了解这些地震复杂性的起源是现代跨学科研究的一个活跃领域。通常，地球深部的模型是通过将矿物特性外推到相关的压力-温度（P-T）条件下，并将其与地震学确定的纵波和横波速度和密度进行比较来建立的。然而，深部地幔物质的剪切特性的行为却鲜为人知。因此，许多外推使用低P-T数据、类似材料和/或推断化学复杂矿物的行为与其端元组成相同。尽管铁方长石（Mg,Fe）O和铝（Mg,Fe）SiO3钙钛矿合计占地球下地幔体积的75%以上，但它们大多是光学不透明的，因此很难或不可能使用光学散射方法对它们进行研究。为了克服这些挑战，利用已建立的同步加速器微x射线衍射（Xrd）和核共振非弹性x射线散射（Nrixs）方法，结合金刚石顶石细胞和激光加热技术，在适当的高p - t条件下获得化学复杂的深层地球材料的状态方程。通过Xrd测定这些材料的密度，可以通过Nrixs测定的部分声子密度来确定总的纵波和横波速度，以及绝热体积和剪切模量。这些数据允许评估铁和铝对以前未开发的P-T扇区深部地球材料的声速和弹性的影响。这些结果有望为地震横向变化与化学成分之间的相关性提供约束。

Recently observed seismic complexities require new and more accurate measurements of candidate lower mantle materials. The effort to understand the origin of these seismic complexities is an active area of modern cross-disciplinary research. Typically, models of the deep Earth have been made by extrapolating mineral properties to relevant pressure-temperature (P-T) conditions and comparing them with seismological determined compressional- and shear-wave velocities and density. However, the behavior of the shear properties of deep mantle materials is widely unknown. As a result, many extrapolations use either low P-T data, analogue materials, and/or infer that the chemically complex minerals behave the same as their end-member compositions. Even though ferropericlase (Mg,Fe)O and aluminous (Mg,Fe)SiO3 perovskite together make up more than 75% by volume of Earth's lower mantle, they are mostly optically opaque, making them difficult or impossible to study using optical scattering methods. In an effort to overcome these challenges, the use of established synchrotron methods of micro x-ray diffraction (Xrd) and nuclear resonant inelastic x-ray scattering (Nrixs) is engaged with diamond anvil cell and laser heating technology to obtain equations of state for chemically complex deep Earth materials under appropriate, yet uncharted, high-P-T conditions. With knowledge of the density determined from Xrd for these materials, the aggregate compressional and shear wave velocities, as well as the adiabatic bulk and shear moduli, is determined from the measured partial phonon density of states determined from Nrixs. These data permit the evaluation of the effects of iron and aluminum on the sound velocities and elasticity of deep Earth materials in a previously unexplored P-T sector. The results are expected to provide constraints on the correlation between seismological lateral variations and chemical composition.