High electrical conductivity in the shallow mantle has long been recognized by electromagnetic depth soundings, but the origin remains debated. Various candidates, of which the two most popular are water enrichment in olivine (the dominant mineral in the upper mantle) and partial melt, have been proposed to explain the electrical anomalies. These models nearly exclusively assume a very low conductivity for dry or water-poor olivine. Here, we show by experimental work that, under well-controlled conditions of pressure, temperature, oxygen fugacity (fO₂), and water inventory, the conductivity of olivine is in fact insensitive to water content at mantle temperature (e.g., >1,000°C), although the enhancement is substantial at relatively low temperature. In particular, the conductivity of olivine at temperature beyond ∼1,000°C is strikingly high, about 0.01–0.1 S/m, at the oxidizing conditions of the shallow mantle. The high conductivity is comparable to the geophysically measured high conductivity in many conductive regions of the shallow mantle. The results provide a new framework for understanding the electrical anomalies and electrical structure of the shallow mantle.

中文翻译：

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浅层地幔氧化条件下橄榄石的高电导率和地球物理意义

电磁测深早已认识到浅地幔的高导电性，但其起源仍有争议。已经提出了各种候选物来解释电异常，其中最流行的两种是橄榄石（上地幔中的主要矿物）中的水富集和部分熔融。这些模型几乎完全假设干燥或缺水橄榄石的电导率非常低。在这里，我们通过实验工作表明，在压力、温度、氧逸度 ( f O ₂) 和水存量，橄榄石的电导率实际上在地幔温度（例如，> 1,000°C）下对水含量不敏感，尽管在相对较低的温度下增强是显着的。特别是，在浅地幔的氧化条件下，橄榄石在超过 1000°C 的温度下的电导率非常高，约为 0.01-0.1 S/m。高电导率与地球物理测量的浅地幔许多导电区域的高电导率相当。研究结果为理解浅层地幔的电异常和电结构提供了新的框架。