CSEDI Collaborative Research: Electrical conductivity of deformed partially molten rocks: Implications for upper mantle structure and dynamics

这个项目是对变形的部分熔融岩石的电导率的实验室研究，以帮助理解板块构造运作的机制。构成地球岩石圈的刚性板块相对于底层对流地幔的运动被认为促进了岩石圈下方剪切岩石和/或部分熔融带的形成。这种变形被认为可以解释在岩石圈以下深度探测到的地球物理异常，例如高导电性和低地震速度的区域。已知部分熔体在剪切作用下会重新分布，形成一种织构，其中熔体在剪切方向上集中成具有强优先取向的条带。所提出的实验旨在确定变形的部分熔融地幔岩石的电导率随剪切和取向的变化方式。这些结果将提供有助于理解岩石圈板块与下地幔耦合的机制以及控制板块构造的过程的信息。这项工作将涉及对部分熔融地幔岩石在高剪切应变下变形的电导率特征的多学科研究，包括相对于剪切方向的大小和各向异性，并结合与现场电测量的相关性。上地幔部分熔融物质在高剪切应变下变形时，其熔体空间分布具有高度各向异性的地球物理特征。剪切实验中熔体结构的演变，促进了熔体富带的形成，预计会对体电导率和电各向异性产生重大影响，但这种影响尚未得到充分的实验研究。将合成橄榄石-熔体系统中变形的部分熔融样品，并在这些样品的制备部分上进行电导率测量，在亚固体和超固体条件下，相对于最大施加剪切应力进行定向。熔体成分包括无水熔体、含水熔体和含碳酸盐熔体。研究了温度、压实长度和总剪切应变的影响。样品将用光学和电子显微镜进行二维表征，用同步加速器x射线断层扫描进行三维表征。电测量将与样品的纹理特征相结合，以开发基于几何的电导率模型，作为物理和化学参数的函数。我们将应用我们的电导率模型来解释电场数据。这些结果将有助于约束软流层的性质和过程。

This project is a laboratory investigation of the electrical conductivity of deformed partially molten rocks to help understand the mechanisms by which plate tectonics operates. The motion of rigid plates that comprise Earth's lithosphere relative to the underlying convecting mantle is thought to promote the formation of sheared rock and/or partially molten zones beneath the lithosphere. This deformation has been suggested to explain geophysical anomalies detected at depths below the lithosphere, such as zones of high electrical conductivity and low seismic velocity. Partial melt is known to redistribute under shear into a texture in which melt is focused into bands with a strong preferred orientation in the direction of the shearing. The proposed experiments are designed to determine the manner in which the electrical conductivity of deformed partially molten mantle rocks varies with shear and orientation. The results will provide information that helps to understand the mechanisms of coupling of lithospheric plates with the underlying mantle and the processes that govern plate tectonics. This work will involve multidisciplinary investigation of the electrical conductivity signature, in terms of both magnitude and anisotropy relative to the shear direction, of partially molten mantle rocks deformed to high shear strain combined with correlation to field electrical measurements. Melt spatial arrangement in partially molten materials in the upper mantle can result in highly anisotropic geophysical signatures when the materials are deformed to high shear strains. The evolution of melt structure in shear experiments, promoting formation of melt-rich bands, is expected to have significant effects on both bulk conductivity and electrical anisotropy, but such effects have not been fully experimentally investigated. Deformed partially molten samples in the olivine-melt system will be synthesized and electrical conductivity measurements will be performed on prepared sections of these samples, oriented with respect to the maximum applied shear stress, under sub- and super-solidus conditions. Melt compositions will include anhydrous, hydrous and carbonate-bearing melts. The effects of temperature, compaction length and total shear strain will be investigated. Samples will be characterized in 2-D with optical and electron microscopy and in 3-D by synchrotron x-ray tomography. Electrical measurements will be combined with the textural characterization of the samples to develop geometry-based conductivity models as a function of physical and chemical parameters. We will apply our conductivity models to interpret field electrical data. These results will help constrain the nature of and processes in the asthenosphere.