Mechanisms of High Pressure Phase Transformations Between the a, B and T Polymorphs of Mg2SiO4 and (Mg,Fe)2SiO4

本项目的主要目的是详细研究在与模式地幔地热和俯冲洋壳岩石圈有关的更广泛的PT条件下，Mg_2SiO_4和（Mg，Fe）_2SiO_4的高压地幔相变机制。 这项研究将继续我们的努力，以描绘压力-温度制度，不同的转换机制可能在地球的地幔中运作，并确定哪些因素可能导致变化的转换机制（P，T，程度的超越等）。 特别是，我们将集中在涉及的转换机制， Mg 2SiO 4和（Mg，Fe）2SiO 4的多晶型物。 我们将研究水可能在涉及以下方面的转变中发挥的作用： - 阶段和详细检查的性质，有序无序的转变， - 相位以及它们如何影响 - 地幔中的相位。 研究结果对上地幔动力学，特别是俯冲洋板的流变学行为和深源地震机制具有重要的地质意义。 该项目将涉及使用多砧高压装置进行高压动力学实验，并使用光学和电子显微镜进行详细的微观结构研究。 特别强调将放在使用透射电子显微镜技术，特别是电子衍射和高分辨率电子显微镜，以阐明转化机制。

9305184 Brearley The principal objective of this project is to study in detail the mechanisms of the high pressure mantle phase transformations of Mg2SiO4 and (Mg, Fe)2SiO4 under a wider range of PT conditions relevant to the model mantle geotherm and subducting oceanic lithosphere. The study will continue our efforts to delineate the pressure-temperature regimes over which different transformation mechanisms may operate in the Earth's mantle and identify what factors may cause changes in the transformation mechanism (P,T, degree of overstepping etc.). In particular we will concentrate on the mechanisms of transformations involving the polymorph of Mg2SiO4 and (Mg,Fe)2SiO4. We will examine the role that water may play in transformations involving -phase and examine in detail the nature of order-disorder transformations in -phase and how they may influence the stability of -phase in the mantle. The results have important geological implications for upper mantle dynamics, especially the rheological behavior of subducting oceanic slabs and the mechanisms of deep focus earthquakes. The project will involve high pressure kinetic experiments using a multi anvil high pressure apparatus coupled with detailed microstructural studies using optical and electron microscopy. Special emphasis will be placed on the use of transmission electron microscope techniques, particularly electron diffraction and high resolution electron microscopy to elucidate the transformation mechanisms.