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，构成了我们星球的最大一部分（55%的体积），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稳定的矿物，在地球表面以下400至1800英里（660至2900公里）的巨大压力和深度范围内保持不变。在NSF的资助下，PI的团队有了一个惊人的发现：在深下地幔的条件下，铁镁硅酸盐分解成一种纯镁硅酸盐和一种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对地震波的反应以及它们在压缩下如何变形。该团队将在实验室产生的高压和高温下使用一组新型探针来原位表征这些特性。这些结果将为破译地震信息和获得对地球深部内部的基本认识提供关键。提出了深部下地幔前沿的重点研究方向。最近，（Mg,Fe）SiO3的钙钛矿相在对应于底部~1000 km的压力-温度（P-T）条件下被发现与不含铁的MgSiO3 pv和新的富铁六方硅酸盐（h相）不成比例，这是一个重要的，令人惊讶的发现。在本研究中，将进一步探讨歧化和H相的观察，并对其确切的P-T边界和物理性质进行研究。新开发的多晶学技术将应用于钙钛矿、h相和/或后钙钛矿共存的多相区域的P-V-T-x研究。利用同步加速器Mössbauer光谱、x射线发射光谱和核共振非弹性x射线散射分别探测高P-T条件下原位h相的Fe2+/Fe3+比、自旋态和态声子密度。射线x射线衍射和新开发的Bragg相干衍射成像方法将研究晶格优先取向和形状优先取向作为D”层地震各向异性的可能来源。本研究的结果将有助于从根本上理解深部下地幔的地震复杂性。

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.