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

CSEDI 合作研究：变形部分熔融岩石的电导率：对上地幔结构和动力学的影响

• 批准号: 1265428
• 负责人: David Kohlstedt
• 金额: $ 21.46万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-04-15 至 2017-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1265428&HistoricalAwards=false
• 关键词: CSEDI; Collaborative; Research; Electrical; conductivity

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.

这个项目是对变形的部分熔融岩石的导电性进行的实验室研究，以帮助理解板块构造的运作机制。构成地球岩石圈的刚性板块相对于下面的对流地幔的运动被认为促进了岩石圈下剪切岩石和/或部分熔融带的形成。这种变形被认为可以解释在岩石圈深处探测到的地球物理异常，如高电导率和低地震速度带。已知部分熔体在剪切作用下重新分布成一种结构，在这种结构中，熔体集中成沿剪切方向具有强烈择优取向的条带。拟议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变化的方式。这些结果将有助于理解岩石圈板块与下伏地幔的耦合机制以及支配板块构造的过程。这项工作将涉及多学科研究部分熔融地幔岩石变形为高剪切应变的电导率特征，包括大小和相对于剪切方向的各向异性，并与野外电性测量相关联。当上地幔部分熔融物质变形为高剪切应变时，熔体的空间排列会导致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，促进了富熔体带的形成，预计将对块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，并在亚固相线和超固相线条件下，对这些样品的制备截面进行电导率测量，测量方向与最大应用剪应力有关。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对材料性能的影响。样品将通过光学和电子显微镜进行二维表征，并通过同步加速器X射线层析成像进行三维表征。电学测量将与样品的纹理表征相结合，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野外电性数据。这些结果将有助于限制软流圈的性质和过程。