Kinetics and Mechanism of Olivine Phase Transformations: Implications for Subduction

了解俯冲带条件下橄榄石向其高压多晶型华德士来石和灵伍德石转变的动力学和机制，对于理解俯冲动力学、深源地震机制和俯冲岩石圈的力学性质具有重要意义。本研究的目的是研究橄榄石在俯冲板片的压力和温度域（即，高压和相对较低的温度）。研究人员将利用同步加速器X辐射源和多砧高压系统，在高达20 Gpa的压力范围和广泛的温度范围内进行实验研究。转变动力学和机制将作为晶粒尺寸、偏应力、水含量和缺陷浓度（即，氧逸度;热压对冷压）。通过对回收的部分转化样品进行TEM分析，研究转化机制。研究人员将确定偏应力对转变机制的影响，并通过使用单色X射线的结构细化来量化高压相随时间的结构特性。

Weidner 0001217 A knowledge of the kinetics and mechanisms of the transformation of olivine to its high-pressure polymorphs wadsleyite and ringwoodite under subduction zone conditions is important for understanding the dynamics of subduction, the mechanism of deep earthquakes, and the mechanical properties of subducting lithosphere. The goal of this research is to study the transformational characteristics of olivine to its high-pressure polymorphs in the pressure and temperature domain of a subducting slab (i.e., high pressures and relatively low temperatures). The investigaotors will utilize a synchrotron x-radiation source coupled with a multi-anvil high-pressure system to conduct experimental studies in the pressure range up to 20 Gpa and a wide range of temperature. The transformation kinetics and mechanisms will be examined as a function of grain size, deviatoric stress, water content, and defect concentration (i.e., oxygen fugacity; hot-pressing vs. cold-pressing). Transformation mechanisms will be investigated through TEM analysis of recovered partially-transformed samples. The investigators will determine the effect of deviatoric stress on the transformation mechanisms and will also quantify the structural properties of high-pressure phases with time through structural refinements using monochromatic x-rays.