Kinetics of the post-gamet transformation and dynamics of the subducting oceanic plates

我们开发了高压世代技术，使用烧结金刚石多砧系统结合同步辐射，可以获得每10-30秒的时间分辨x射线衍射数据，最高可达35gpa和2000K。我们还测试了Ringwood公司生产的新型烧结金刚石砧，用于多砧仪的x射线窗口。在此基础上，我们定量研究了天然石榴石的后石榴石转化动力学、辉石（顽辉石和透辉石）的高压转化动力学以及水对橄榄石-尖晶石转化动力学的影响。利用透射电镜（TEM）和傅里叶红外光谱（FTIR）分析了样品的相变组织和含水量。除此之外，我们还研究了亚稳立方钙钛矿的形成，高压含水矿物的脱水反应，以及冲击陨石中高压转化的机制和动力学，这些对俯冲过程具有重要意义。实验研究了沃兹利岩中的阳离子扩散动力学，并讨论了俯冲板块和地幔过渡带的流变学。我们将获得的定量动力学数据外推到俯冲带条件，并构建了俯冲板块的亚稳矿物学。考虑到转化动力学，我们计算了俯冲板块的密度，这表明俯冲板块在下地幔顶部由于亚稳低压相的存在而浮力。非平衡转变引起的晶粒尺寸减小会降低俯冲板块的强度。这些对下地幔顶部停滞板块的形成很重要。

We have developed techniques on high-pressure generations using sintered diamond multi-anvil systems combined with synchrotron radiation, which enables to obtain time-resolved X-ray diffraction data every 10-30 seconds up to 35 GPa and 2000K. We also tested new sintered diamond anvils manufactured by Ringwood Superabrasives for the X-ray window of multi-anvil apparatus.Based on these techniques, we have quantitatively studied on kinetics of post garnet transformations in natural garnet, high-pressure transformations in pyroxenes (enstatite and diopside), and effects of water on the olivine-spinel transformation kinetics. Transformation microstructures and water contents of samples recovered were examined using TEM and FTIR. In addition to these studies, we have also examined about formation of metastable cubic perovskite, dehydration reaction of high-pressure hydrous minerals, and mechanisms and kinetics of high-pressure transformations in shocked meteorites, those have important implications for subduction processes. Cation diffusion kinetics in wadsleyite have been experimentally examined and rheology of subducting plates and mantle transition zone was discussed.We have extrapolated quantitative kinetic data obtained to subduction zone conditions and construct metastable mineralogy in subducting plates. We have calculated the density of subducting slabs taking transformation kinetics into accounts, which suggests that the subducting slabs are buoyant at the top of the lower mantle due to the presence of metastable low-pressure phases. Grain-size reductions caused by non-equilibrium transformations can reduce strength of subducting plates. These are important for the formation of stagnant slabs at the top of the lower mantle.