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

绿色，哈里W.EAR-0003631榴辉岩是地球表面暴露的最致密的正常岩石，通常由大致相同数量的石榴石和绿辉石，+/-少量的石英，蓝晶石，橄榄石和/或角闪石组成。榴辉岩形成于玄武岩成分岩石的高压高温变质作用。这种转换可能有助于洋壳向深部俯冲，可能影响中源地震的分布，并被认为产生了可能与岩石圈其余部分剥离的强层。研究人员提议对榴辉岩及其组成矿物的流变学进行详细的实验研究。他们介绍了用他们独特的5 Gpa形变仪器获得的初步结果，表明现在在这种研究所需的压力(2-4 Gpa)下获取高质量数据在技术上是可能的。这些初步结果表明，榴辉岩的强度与方辉橄榄岩相当，方辉橄榄岩是一种紧邻洋壳下方的岩石类型；之所以能达到同样的强度，是因为多晶硅酸盐石榴石的巨大强度被绿辉石的弱点所补偿。多晶硅酸盐石榴石的超常强度支持了先前的观点，即地幔过渡带的下部(约500-700公里)可能是粘性增强的一层。为了更好地了解深俯冲过程，研究人员计划在初步结果的基础上，对榴辉岩及其组成矿物在2-4 Gpa压力下的流变学进行为期三年的扩展研究，以详细绘制出它们的流动规律、变形机制和微结构特征。他们将：(A)在3 Gpa的温度和应变速率的较大范围内阐述50-50榴辉岩的流变学，并在P=2.0-4.0 GPa时进行选定的实验；(B)对单矿物绿辉石和石榴石端元进行类似的实验，以确定其流动参数；(C)对添加H2O的试件进行对比实验和等效分析；以及(D)如果时间允许，他们将在我们的多砧装置中合成主晶石榴石，并使用主晶石榴石和火成石石榴石的短圆柱形试件在马约石稳定场内进行定性变形实验，其中一个在另一个之上，这将确定这两个相的相对强度。

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.