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Mg2SiO4和（Mg, Fe）2SiO4在与模式地幔地热和大洋俯冲岩石圈相关的更大范围PT条件下的高压地幔相变机制。这项研究将继续我们的努力，以描绘不同的转变机制可能在地幔中运作的压力-温度状态，并确定哪些因素可能导致转变机制的变化（P，T，超越程度等）。特别地，我们将集中于涉及Mg2SiO4和（Mg,Fe）2SiO4的多晶型的转化机制。我们将研究水在涉及-相的转变中可能发挥的作用，并详细研究-相中有序-无序转变的性质以及它们如何影响-相在地幔中的稳定性。研究结果对上地幔动力学，特别是俯冲洋板块的流变行为和深震源地震机理具有重要的地质意义。该项目将包括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来阐明转化机制。

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.