Talc is expected to be an important water carrier in Earth's upper mantle, and understanding its electrical and seismic properties under high pressure and temperature conditions is required to detect possible talc-rich regions in subduction zones imaged using geophysical observations. We conducted acoustic and electrical experiments on natural talc aggregates at relevant pressure-temperature conditions. Compressional wave velocity (Vp) was measured using ultrasonic interferometry in a Paris-Edinburgh press at pressures up to 3.4 GPa and temperatures up to 873 K. Similar Vp values are obtained regardless of the initial crystallographic preferred orientation of the samples, which can be explained by talc grain reorientation during the experiment, with the (001) plane becoming perpendicular to the uniaxial compression axis. Electrical conductivity of the same starting material was determined using impedance spectroscopy in a multi-anvil press up to 6 GPa and 1263 K. Two conductivity jumps are observed, at ∼860–1025 K and ∼940–1080 K, depending on pressure, and interpreted as talc dehydroxylation and decomposition, respectively. Electrical anisotropy is observed at low temperature and decreases with increasing pressure (∼10 at 1.5 GPa and ∼2 at 3.5 GPa). Comparison of acoustic and electrical results with geophysical observations in central Mexico supports the presence of a talc-bearing layer atop the subducted Cocos plate.

中文翻译：

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高压高温条件下滑石粉的电导率和声速及其在俯冲 Cocos 板中的应用


预计滑石粉将成为地球上地幔中的重要水载体，需要了解其在高压和高温条件下的电学和地震特性，以检测使用地球物理观测成像的俯冲带中可能富含滑石粉的区域。我们在相关压力-温度条件下对天然滑石粉骨料进行了声学和电学实验。在巴黎-爱丁堡压力机中，在高达 3.4 GPa 的压力和高达 873 K 的温度下使用超声波干涉法测量压缩波速度 （Vp）。无论样品的初始晶体学择优取向如何，都可以获得相似的 Vp 值，这可以通过实验过程中滑石粉晶粒的重新取向来解释，（001） 平面变得垂直于单轴压缩轴。在高达 6 GPa 和 1263 K 的多砧压力机中使用阻抗谱法测定相同起始材料的电导率。根据压力，在 ∼860–1025 K 和 ∼940–1080 K 处观察到两个电导率跃迁，分别解释为滑石粉脱羟基化和分解。在低温下观察到电各向异性，并随着压力的增加而减小（1.5 GPa 时为 ∼10,3.5 GPa 时为 ∼2）。声学和电气结果与墨西哥中部的地球物理观测结果的比较支持在俯冲的 Cocos 板块顶部存在含滑石层。