Experimental Investigation of the Rheology of Eclogite and Its Constituent Minerals at High Pressure

榴辉岩是暴露在地球表面的密度最大的正常岩石，通常由大约等量的石榴石和辉长石，+/-少量的石英、蓝晶石、黝帘石和/或角闪洞组成。榴辉岩形成于高压、高温变质的玄武岩组成的岩石。这种转变可能导致海洋地壳俯冲到很大的深度，可能影响中震源地震的分布，并被认为产生一个可能从岩石圈其余部分剥离的强大层。研究人员建议对榴辉岩及其组成矿物的流变学进行详细的实验研究。他们展示了用他们独特的5 GPa变形装置获得的初步结果，表明现在在技术上可以在此类研究所需的压力下获得高质量的数据（2-4 GPa）。这些初步结果表明，榴辉岩的强度可与辉石相媲美，辉石是一种位于海洋地壳下方的岩石类型；这种平衡是由于多晶硅酸盐石榴石的强大强度被辉石的弱点所补偿。多晶硅酸盐石榴石的非凡强度支持了先前的建议，即地幔过渡带的下部（~500-700 km）可能是一个增强粘度层。为了更好地了解深层俯冲过程，研究人员计划在初步结果的基础上，对2-4 GPa压力下榴辉岩及其组成矿物的流变学进行为期三年的扩展研究，以详细绘制其流动规律、变形机制和微观结构特征。他们将：(a)详细阐述50-50榴辉岩在3 GPa温度和应变率较大范围内的流变学，并选择P = 2.0-4.0 GPa的实验；(b)对单矿物辉石端部和石榴石端部进行类似实验，确定其流动参数；(c)对添加H2O的试样进行对比实验和等效分析；(d)如果时间允许，他们将在我们的多砧装置中合成多数榴石，并在多数榴石稳定性场内使用多数榴石和热辉榴石的短圆柱形样品进行定性变形实验，一个放在另一个上面，这将确定这两相的相对强度。

Green, Harry W.EAR-0003631 Eclogite is the densest normal rock exposed at the surface of Earth, typically consisting of approximately equal amounts of garnet and omphacite, +/- small amounts of quartz, kyanite, zoisite, and/or amphibole. Eclogite forms from high-pressure, high-temperature metamorphism of rocks of basaltic composition. This transformation may contribute to the subduction of oceanic crust to great depth, may affect the distribution of intermediate-focus earthquakes, and has been suggested to produce a strong layer that may delaminate from the rest of the lithosphere. The investigators propose a detailed experimental study of the rheology of eclogite and its constituent minerals. They presented preliminary results acquired with their unique, 5 GPa, deformation apparatus showing that it is now technically possible to acquire high-quality data at the pressures required for such studies (2-4 GPa). These preliminary results show that eclogite has a strength comparable to harzburgite, the rock type located immediately below the oceanic crust; this equality is achieved because the great strength of polycrystalline silicate garnet is compensated by the weakness of omphacite. The extraordinary strength of polycrystalline silicate garnet supports previous suggestions that the lower portion of the mantle transition zone (~500-700 km) may be a layer of enhanced viscosity. Toward a better understanding of deep subduction processes, the investigators plan to build on their preliminary results with a three-year expanded study of the rheology of eclogite and its constituent minerals at pressures of 2-4 GPa to map out in detail their flow laws, deformation mechanisms and microstructural characteristics. They will: (a) Elaborate the rheology of 50-50 eclogite over a larger domain of temperature and strain rate at 3 GPa and selected experiments at P = 2.0-4.0 GPa; (b) perform analogous experiments on the monomineralic omphacite and garnet end members to determine their flow parameters;(c) conduct comparable experiments and equivalent analysis of specimens with H2O added; and (d) if time permits, they will synthesize majoritic garnet in our multianvil apparatus and conduct qualitative deformation experiments within the majorite stability field using short cylindrical specimens of majoritic and pyropic garnets, one on top of the other, which will determine the relative strengths of these two phases.