Graphite impacts crustal rheology and electric conductivity in the lower crust. In a combined geophysical and geological study from the Proterozoic Lofoten-Vesterålen Complex, Norway, we show the enrichment of graphite resulted in zones with strong schistosity and a sharp strain gradient towards host massive granulite gneiss. Increased graphite content resulted in high-conductivity zones with true resistivity values <10 Ωm compared with a resistivity of >3,000 Ωm in the low-conductive crust. The regionally distributed graphite zones contain up to 39% graphite with variable amounts of quartz, feldspars, biotite and pyroxenes and where graphite is present in stable assemblage to orthopyroxene. High-ordered graphite and biotite with a strong-preferred orientation define the well-developed foliation. Our results demonstrate that graphite accounts for the high electric conductivity of this former Proterozoic lower-crustal segment. The presence of graphite causes strain localisation in the granulite facies crust, reducing crustal strength and may thereby influence continental architecture and evolution of collision zones.

中文翻译：

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麻粒岩中石墨对剪切带发展和电导率的控制：以挪威北部元古界 Lofoten-Vesterålen 杂岩为例

石墨影响下地壳的地壳流变学和电导率。在来自挪威元古代罗弗敦-韦斯特洛伦杂岩体的地球物理和地质综合研究中，我们表明石墨的富集导致了具有强烈片理性和朝向宿主块状麻粒岩片麻岩的尖锐应变梯度的区域。与低导电地壳中的电阻率 >3,000 Ωm 相比，增加的石墨含量导致高导电率区域的真实电阻率值 <10 Ωm。区域分布的石墨区包含高达 39% 的石墨，以及不同数量的石英、长石、黑云母和辉石，并且石墨以稳定的组合形式存在于斜方辉石中。具有强烈优先取向的高有序石墨和黑云母定义了发育良好的叶理。我们的结果表明，石墨解释了这个前元古代下地壳部分的高电导率。石墨的存在导致麻粒岩相地壳中的应变局部化，降低地壳强度，从而可能影响大陆结构和碰撞带的演化。