Mineral Physics Studies of Elasticity, Phonon, and Rheology at Pressure-Temperature Conditions of the Earth's Deep Interior

地球下地幔的矿物学，包括我们星球的最大部分（55%体积），以前被认为是简单和单调的。具有钙钛矿结构的铁镁硅酸盐被认为是在地球表面以下约400至1，800英里（660至2，900公里）的巨大压力和深度范围内不变的稳定矿物。在先前的NSF资助下，PI的团队取得了一个令人惊讶的发现：在下地幔深处的条件下，铁镁硅酸盐分解成纯镁硅酸盐和以前未知的富铁硅酸盐矿物，具有全新的性质。因此，本基金的下一个挑战是研究新矿物如何对地震波作出反应，以及它们在压缩下如何变形。该团队将使用一组新型探针，在实验室产生的高压和高温下原位表征这些特性。研究结果将为进一步破译地震学信息和对地球深部的认识提供关键，并提出了深部下地幔前沿的研究方向。最近，发现（Mg，Fe）SiO 3的钙钛矿相在对应于底部~1000 km的压力-温度（P-T）条件下与不含Fe的MgSiO 3 pv和新的富Fe六方硅酸盐（H-相）不成比例，这代表了一个重要的、令人惊讶的发现。在本建议中，将进一步探索双折射和H相的观测，并研究它们的精确P-T边界和物理性质。新发展的多晶粒晶体学技术将应用于钙钛矿、H相和/或后钙钛矿共存的多相区的P-V-T-x研究。同步穆斯堡尔谱、X射线发射谱和核共振非弹性X射线散射将分别用于探测高P-T下H相的Fe 2 +/Fe 3+比、自旋态和声子态密度。将发展径向X射线衍射和新开发的布拉格相干衍射成像方法来研究D”层中作为地震各向异性的可能来源的晶格优选取向和形状优选取向。本研究的结果将有助于从根本上认识下地幔深部地震的复杂性。

The mineralogy of the Earth's lower mantle, which comprises the largest fraction of our planet (55% by volume), was previously regarded as simple and monotonous. An iron-magnesium silicate with the perovskite structure was thought to be the stable mineral unchanging over the enormous pressure and depth range some 400 to 1,800 miles (660 to 2,900 kilometers) below the Earth's surface. With prior NSF grant support, the PI's team made a surprising discovery: at the conditions of the deep lower mantle, the iron-magnesium silicate decomposes into a pure magnesium silicate and a previously unknown Fe-rich silicate mineral with entirely new properties. The next challenge in the present grant is, therefore, to investigate how the new minerals respond to seismic waves and how they deform under compression. The team will use a battery of novel probes for characterization of these properties in-situ under the high pressures and temperatures generated in their laboratory. The results will provide the key for deciphering the seismological information and gain fundamental understanding of the deep Earth interior.Focused research on the frontier of the deep lower mantle is proposed. Very recently, the perovskite phase of (Mg,Fe)SiO3 was found to disproportionate to an Fe-free MgSiO3 pv and a new Fe-rich hexagonal silicate (H-phase) at the pressure-temperature (P-T) conditions corresponding to the bottom ~1000 km, representing an important, surprising discovery. In the present proposal, the observation of disproportionation and H phase will be further explored and their exact P-T boundaries and physical properties will be investigated. The newly developed multigrain crystallography technique will be applied to P-V-T-x studies in the multiphase region that perovskite, H-phase, and/or post-perovskite coexist. Synchrotron Mössbauer spectroscopy, x-ray emission spectroscopy, and nuclear resonant inelastic x-ray scattering will be used to probe the Fe2+/Fe3+ ratio, spin state, and phonon density of state, respectively, for the H-phase in-situ under high P-T. Radial x-ray diffraction and the newly developed Bragg coherent diffraction imaging method will be developed to study lattice preferred orientation and shape-preferred orientation as possible sources of seismic anisotropy in the D" layer. Results from the present study will contribute to fundamental understanding the seismic complexities of the deep lower mantle.