Electrical Transport in Mantle and Crustal Materials

美国国家科学基金会EAR 0073987 PI：James A.Tyburczy，亚利桑那州立大学大地电磁和地磁深度测深揭示了在各种地壳和地幔环境中存在异常高电导率的区域。在大陆碰撞带、大洋中脊和洋底、大陆屏蔽区等之下观察到地壳和浅地幔高导带，在300-400公里深处普遍观察到地幔过渡带高导带。对于这些高导电性特征，人们提出了各种解释，包括部分熔体的存在，矿物、水相流体中氢的存在，以及相互关联或取向的金属或其他高导电性矿物的存在(对不同区域有不同的解释)。为了正确地反演和解释大地电磁响应函数，必须确定地球材料在低频范围内的电响应。该提案概述了在0.0001至100,000赫兹的温度和压力范围内确定相关地质材料在高温和压力下的电导率和复阻抗的实验工作。特别是，1)低熔体分数时熔体组成和织构对部分熔体体系电学性质的影响；2)含水矿物(角闪石、蛇纹石)和名义上无水矿物(橄榄石和辉石)中氢对电学性质的影响。结构平衡的部分熔融橄榄石-玄武岩系统的电学性质将在一巴总压力和高温和压力(高达2000摄氏度和20 GPA)下在多个砧座设备中进行研究。在适当的水逸度条件下，在内部加热装置中，将在1200摄氏度和0.8-1 Gpa的温度下检查含水矿物和名义上含氢的无水矿物的电学性质。这些结果将被解释为与离子过程模型相关的等效电路。这项研究的结果将对大地电磁数据的解释和建模具有重要意义，并将为各种地质环境中的物理传输过程提供新的线索。最终的好处将是更详细地了解地球内部深处的温度分布和物质的物理状态。

NSF EAR 0073987 PI: James A. Tyburczy, Arizona State University Magnetotellurics and geomagnetic depth sounding have revealed zones of anomalously high electrical conductivity in a variety of crustal and mantle environments. Crustal and shallow mantle high conductivity zones are observed beneath continental collision zones, mid ocean ridges and the ocean floor, and continental shields, among other areas, and mantle transition zone high-conductivity zones are generally observed at depths of 300-400 km. A variety of explanations for these high conductivity features have been invoked including the presence of partial melt, hydrogen in minerals, aqueous fluids, and the presence of interconnected or oriented metals or other highly conducting minerals (with different explanations for different areas). In order to properly invert and interpret magnetotelluric response functions, the electrical response of Earth materials in the low frequency range must be determined. This proposal outlines an experimental effort to determine the electrical conductivity and the complex electrical impedance of relevant geological materials at elevated temperatures and pressures over the frequency range 0.0001 to 100,000 Hz. In particular, 1) the influence of melt composition and texture at low melt fraction on the bulk electrical properties of partially molten systems and 2) the influence of hydrogen in hydrous minerals (amphibole, serpentine) and nominally anhydrous minerals (olivine and pyroxene) on electrical properties will be examined. The electrical properties of texturally equilibrated partially molten olivine-basalt systems will be studied at one bar total pressure and at elevated temperatures and pressures (up to 2000 degrees C and 20 GPa) in a multiple anvil device. The electrical properties of hydrous minerals and hydrogen-containing nominally anhydrous minerals will be examined at temperatures up to 1200 degrees C and .8 - 1 GPa in an internally heated device under appropriate water fugacity conditions. The results will be interpreted in terms of equivalent electrical circuits that can be related to models of ionic processes. The results of this study will be important for the interpretation and modeling of magnetotelluric data and will also shed new light on physical transport processes in a variety of geological environments. The ultimate benefits will be more detailed understanding of the temperature profile and physical state of matter at depth in the Earth's interior.