Abstract

Magnetotelluric soundings have detected high-conductivity zones in some regions of the deep lithosphere, and these conductive areas were usually interpreted to reflect the presence of hydrous phases, silicate/carbonatite melts, or water incorporated in olivine. Augite megacrysts are the most abundant single-crystal mantle samples entrained by volcanic basalts/kimberlites in a wide variety of tectonic environments, and are usually characterized by higher Fe (∼5%–12% in total FeO), Fe3+ (∼25%–45% in Fe3+/Fetotal), and H2O (∼200–1800 ppm) contents. Based on experimental work, we show that Fe3+- and H2O-rich augites have electrical conductivities that are several orders of magnitude higher than those of dry olivine. High conductivities in at least some regions of the lithospheric mantle can be explained by the presence of small amounts of augite (and other pyroxenite analogues, e.g., ∼10% to even less depending on composition, temperature, and models used for the estimation), which may ultimately indicate the infiltration of silicate melts and their subsequent crystallization and interaction with wall rocks in the deep lithosphere.

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