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之前被认为是简单和单调的，它构成了地球上最大的部分(体积的55%)。一种具有钙钛矿结构的铁镁硅酸盐被认为是一种稳定的矿物，在地球表面以下约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。在之前NSF的资助下，Pi的团队有了一个令人惊讶的发现：在下地幔深处的条件下，铁镁硅酸盐分解成一种纯的硅酸镁和一种以前未知的具有全新性质的富铁硅酸盐矿物。因此，目前赠款的下一个挑战是调查新矿物如何对地震波做出反应，以及它们如何在压缩下变形。该团队将使用一组新颖的探头，在实验室产生的高压和温度下原位表征这些特性。这些结果将为破译地震信息和了解地球深部提供关键信息。提出了下地幔深部前缘的重点研究方向。最近，在相当于海底1000公里的压力-温度(P-T)条件下，(Mg，Fe)SiO_3的钙钛矿相被发现不成比例地转变为无Fe的MgSiO_3 PV和新的富铁六方硅酸盐(H相)，这是一个重要的、令人惊讶的发现。在本方案中，将进一步探索歧化和H相的观察，并将研究它们的确切P-T边界和物理性质。新开发的多晶结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的P-V-T-x研究。同步辐射穆斯堡尔谱、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。径向X射线衍射和新近发展起来的Bragg相干衍射成像方法将被用来研究D“层地震各向异性的可能来源--晶格择优取向和形状择优取向。这一研究结果将有助于从根本上理解下地幔深部的地震复杂性。

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.