Understanding the electrical conductivity of high pressure metamorphic rocks is essential to constrain the compositions in the subduction zone and continental crust. In this study, we calculated the electrical conductivity for such rocks sampled from the central Qiangtang metamorphic belt in the northern Tibetan Plateau. The results reveal that, when aqueous fluids are absent, the conductivity of meta-mafic rocks (e.g., eclogite and amphibolite) is strikingly higher than that of meta-felsic rocks (e.g., garnet-quartz-mica schist). The conductivity of eclogite decreases due to the enrichment of amphibole, but this effect is diminished when a critical degree of amphibolization is reached. Our calculated conductivity of eclogite and amphibolite differs greatly from the experimentally derived results for the eclogites from other localities, partly owing to the strong effects of different mineral assemblages and chemical compositions on the conduction mechanisms and efficiencies. However, the disparity of conductivity between our calculated and the previously measured results for a similar amphibole-rich eclogite sampled from the same locality suggests that trails of highly conductive rutile-ilmenite aggregates may contribute to the higher bulk-rock conductivity in the laboratory measurements. Moreover, since the calculated conductivity of eclogite and amphibolite is not high enough at the temperatures relevant to their metamorphic thermal condition, partial melts or aqueous fluids originated from the upwelling asthenosphere are more likely to explain the anomalously high electrical conductivity zones in magnetotelluric images in the Qiangtang terrane in the northern Tibetan Plateau.

中文翻译：

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青藏高原北部the塘地块榴辉岩，闪石和石榴石-石英-云母片岩的电导率

了解高压变质岩的电导率对于限制俯冲带和大陆壳中的成分至关重要。在这项研究中，我们计算了从青藏高原北部Qian塘中央变质带取样的岩石的电导率。结果表明，当缺少含水流体时，变质镁铁质岩石（如榴辉岩和角闪石）的电导率显着高于变质镁质岩（如石榴石-石英-云母片岩）的电导率。由于闪石的富集，榴辉岩的电导率降低，但是当达到临界程度的闪石化时，这种作用就会减弱。我们计算出的榴辉岩和角闪石的电导率与其他地方的榴辉岩的实验得出的结果大不相同，部分是由于不同的矿物组合和化学组成对传导机理和效率的强烈影响。但是，从相同位置取样的相似的富含闪石的榴辉岩的计算值与先前测量的结果之间的电导率差异表明，高导电性金红石-钛铁矿聚集体的痕迹可能有助于实验室测量中更高的块岩电导率。此外，由于榴辉岩和角闪石的电导率在与它们变质的热条件相关的温度下不够高，因此来自上升流软流层的部分熔体或含水流体更有可能解释了大地电磁图像中异常高的电导率区域。青藏高原北部的tang塘地层。