Reaction kinetics and plastic deformation in mantle rocks

我们建议在动态条件下实验研究三种形成石榴石的反应，即在偏应力下和在积累大量塑性应变的情况下。通过这种方法，我们想要研究变质反应和同时变形之间的相互作用。特别是，我们感兴趣的是变形微观结构如何影响变质反应的进展，进而相变如何影响流变行为和变形机制。我们选择石榴石作为主要感兴趣的矿物，因为它的流变性对了解俯冲板块和地幔过渡带的流变性起着至关重要的作用。我们想要密切研究的三个反应是：1)尖晶石橄榄岩形成石榴石橄榄岩；2)辉长岩形成榴辉岩；3)辉石岩在高达15 Gpa的高压下形成主要石榴石。该项目的研究结果将有助于更好地认识石榴石的塑性变形机制，建立反应进程与塑性应变之间的定量关系，并有助于理解变质反应在地幔流动中的作用。在这个项目中，我们还将应用一种新的方法来测量用压电晶体进行的多顶锤变形实验中的偏应力，这是在高压下进行定量流变实验的关键步骤。

We propose to study three garnet-forming reactions experimentally under dynamic conditions, i.e. under deviatoric stresses and while accumulating significant amounts of plastic strain. With this approach we want to investigate the interaction between metamorphic reactions and concurrent deformation. In particular, we are interested how deformation microstructures influence the progress of metamorphic reactions and in turn, how the phase change affects the rheological behaviour and deformation mechanisms. We chose garnet as the main mineral of interest since its rheological behaviour plays a crucial role for the understanding of the rheology of subducting slabs and the mantle transition zone. The three reactions we would like to investigate closely are 1) the formation of garnet peridotite from spinel peridotite, 2) the formation of eclogite from gabbro and 3) the formation of majoritic garnet from pyroxenes under high pressure up to 15 GPa. The results of this project will give an improved insight into the plastic deformation mechanisms of garnet, yield a quantitative relationship between reaction progress and plastic strain and contribute to the understanding ofthe role of metamorphic reactions during mantle flow. Within this project we will also apply a new method of measuring deviatoric stresses in multianvil deformation experiments with piezoelectric crystals, which is a critical step for performing quantitative rheological experiments at high pressure.