Some New Progress in the Experimental Measurements on Electrical Property of Main Minerals in the Upper Mantle at High Temperatures and High Pressures

Abstract

In this chapter, we present the recent progress in the experimental studies of the electrical conductivity of dominant nominally anhydrous minerals in the upper mantle of the deep Earth interior, namely, olivine, pyroxene, and garnet. The influences from pressure, oxygen partial pressure, and anisotropic orientation on hydrous and anhydrous electrical conductivities of minerals and rocks have been already explored detailedly. There are two main electric conduction mechanisms in Fe-bearing mantle minerals, for example, small proton and proton hopping conditions, which are well distinguished by the magnitude of activation enthalpy at high temperature and high pressure. Likewise, the conduction mechanisms are efficiently characterized by these obtained positive and negative effects from the oxygen fugacity on electrical conductivities of corresponding dry and wet Fe-bearing silicate minerals at the regions of the upper mantle under conditions of different oxygen partial pressures. On the base of high-pressure laboratory-based conductivity measurements for these nominally anhydrous minerals (e.g., olivine, pyroxene, and garnet), the water content will be estimated within the depth range of the upper mantle. In comprehensive considerations of filed geophysical magnetotelluric results, the electrical conductivity measurements of dominant upper-mantle minerals can thoroughly disclose the distribution, storage state, and migration conduction in the deep Earth interior.

Effect of Different Mineralogical Proportions on the Electrical Conductivity of Dry Hot-Pressed Sintering Gabbro at High Temperatures and Pressures

“…In conclusion, our obtained experimental results on the electrical conductivities of the dry hot-pressed sintering gabbro with various mineralogical proportions (CpxXPl100-X, X = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 vol%) at high temperature and high pressure are abnormally lower than those of field magnetotelluric data of the gabbro-rich regions, which cannot explain the high conductivity anomalies for the oceanic crust and West African craton. Some potential causes need to be considered conscientiously, such as the structural water in nominally anhydrous minerals [9,28,30,50,51], dehydration (oxidation-dehydrogenation) of hydrous minerals [23,52,53], partial melting [54][55][56][57], the interconnected high conductive phases [24,28,58,59], and the salinity-bearing (or water-bearing) fluids [15,31,[60][61][62], in the future. Although the present acquired electrical conductivity results on the dry hot-pressed sintering gabbro with various mineralogical proportions cannot explain the high conductivity anomaly in the oceanic crust and West African craton, it can provide one reasonable constraint on the mineralogical composition in these representative gabbro-rich regions.…”

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Electrical conductivities of the dry hot-pressed sintering gabbro with various mineralogical proportions (CpxXPl100-X, X = 0, 10,20,30,40,50,60, 70, 80, 90, and 100 vol% (the signals of Cpx and Pl denote clinopyroxene and plagioclase, respectively) were measured in the YJ-3000t multianvil pressure and Solartron-1260 impedance spectroscopy analyzer at temperatures of 773-1073 K and pressures of 1.0-3.0 GPa. At the given pressure conditions, the electrical conductivity and temperature conformed to an Arrhenius relation.

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