An Overview of the Experimental Studies on the Electrical Conductivity of Major Minerals in the Upper Mantle and Transition Zone

Abstract

In this paper, we present the recent progress in the experimental studies of the electrical conductivity of dominant nominally anhydrous minerals in the upper mantle and mantle transition zone of Earth, namely, olivine, pyroxene, garnet, wadsleyite and ringwoodite. The main influence factors, such as temperature, pressure, water content, oxygen fugacity, and anisotropy are discussed in detail. The dominant conduction mechanisms of Fe-bearing silicate minerals involve the iron-related small polaron with a relatively large activation enthalpy and the hydrogen-related defect with lower activation enthalpy. Specifically, we mainly focus on the variation of oxygen fugacity on the electrical conductivity of anhydrous and hydrous mantle minerals, which exhibit clearly different charge transport processes. In representative temperature and pressure environments, the hydrogen of nominally anhydrous minerals can tremendously enhance the electrical conductivity of the upper mantle and transition zone, and the influence of trace structural water (or hydrogen) is substantial. In combination with the geophysical data of magnetotelluric surveys, the laboratory-based electrical conductivity measurements can provide significant constraints to the water distribution in Earth’s interior.

Electrical Conductivity of Ti‐Bearing Hydrous Olivine Aggregates at High Temperature and High Pressure

“…The role of hydrogen to enhance many defect‐related properties such as high‐pressure experiments from the electrical conductivity and plastic deformation in olivine is well established (e.g., Dai et al, 2020; Karato, 2019; Karato & Jung, 2003; Karato & Wang, 2013; Mei & Kohlstedt, 2000a, 2000b). A large number of previous investigations are mainly focused on the effects of hydrogen on high‐pressure physical properties of olivine, and the influence of impurities other than hydrogen has not been studied in any detail.…”

Complex Electrical Conductivity of Biotite and Muscovite Micas at Elevated Temperatures: A Comparative Study

“…In the first case, the mechanism is better known as "small polaron" conduction, where the hopping of electron with low mobility causes the local distortion of the lattice, and the corresponding E a varies in the range 0.7 eV-1.5 eV [35,[64][65][66]. Lower values of E a such as~0.8 eV for olivine and 0.6 eV for wadsleyite are consistent with proton conduction due to the high mobility of hydrogen species [35,67].…”

“…Generally, in the case of Fe-bearing hydrous minerals, the electron charge transfer between ferrous and ferric states of structural iron, as well as the diffusion of H (proton) or H-related defects, are the main mechanisms of conduction at moderate temperatures, while the predominant contribution of ionic conduction occurs at high temperatures, i.e., above~1100 K [35,62,63]. In the first case, the mechanism is better known as "small polaron" conduction, where the hopping of electron with low mobility causes the local distortion of the lattice, and the corresponding E a varies in the range 0.7 eV-1.5 eV [35,[64][65][66]. Lower values of E a such as~0.8 eV for olivine and 0.6 eV for wadsleyite are consistent with proton conduction due to the high mobility of hydrogen species [35,67].…”

“…The necessity of performing electrical measurements in minerals over a broad frequency and temperature range has been consolidated in recent decades, in order to properly identify the electrical conduction mechanisms [ 34 , 35 ]. The frequency dependence of the dielectric properties of different micas has been studied in the past by Chaundry and his coworkers [ 14 , 15 , 16 , 17 , 20 , 21 ].…”

Some Remarks on the Electrical Conductivity of Hydrous Silicate Minerals in the Earth Crust, Upper Mantle and Subduction Zone at High Temperatures and High Pressures

“…Whereas, the electrical conductivity of hydrous silicate minerals and rocks are highly sensitive to temperature, pressure, oxygen fugacity, crystallographic anisotropy, water-bearing content, dehydration effect, iron content, trace element of titanium-bearing content, oxidation-dehydrogenation effect, structural phase transition, etc. As pointed out by Karato (1990) [2], Huang et al (2005a, b; [21][22][23], Wang et al (2006) [24], Dai and Karato (2009a, b, c;2014a, b, c, d; [25][26][27][28][29][30][31], Karato and Dai (2009) [32], Hu et al ( , 2018 [33,34], [35], and He et al (2021) [36], water content is one of most important influential factor on the electrical properties of minerals and rocks at high-temperature and high-pressure conditions. Water can enhance several orders of magnitude in the electrical conductivity of hydrous minerals and rocks, and its effect is substantial.…”