As a dominant water carrier, hydrous silicate minerals and rocks are widespread throughout the representative regions of the mid-lower crust, upper mantle, and subduction zone of the deep Earth interior. Owing to the high sensitivity of electrical conductivity on the variation of water content, high-pressure laboratory-based electrical characterizations for hydrous silicate minerals and rocks have been paid more attention to by many researchers. With the improvement and development of experimental technique and measurement method for electrical conductivity, there are many related results to be reported on the electrical conductivity of hydrous silicate minerals and rocks at high-temperature and high-pressure conditions in the last several years. In this review paper, we concentrated on some recently reported electrical conductivity results for four typical hydrous silicate minerals (e.g., hydrous Ti-bearing olivine, epidote, amphibole, and kaolinite) investigated by the multi-anvil press and diamond anvil cell under conditions of high temperatures and pressures. Particularly, four potential influence factors including titanium-bearing content, dehydration effect, oxidation−dehydrogenation effect, and structural phase transition on the high-pressure electrical conductivity of these hydrous silicate minerals are deeply explored. Finally, some comprehensive remarks on the possible future research aspects are discussed in detail.

The elevated pressure and temperature conditions encountered by a subducted slab entering the deep Earth can substantially alter the chemical composition and physical properties of recycled carbonates. Carbonate-silicate reactions are believed to have a pivotal role in this process. Here we conduct high temperature and high pressure experiments on carbonated eclogite and measure the electrical conductivity in order to constrain the evolution of geophysical properties and chemical composition in the carbonate-bearing eclogitic slab. We find that the carbonate-silicate reaction elevates the conductivity of carbonated eclogite by cations (e.g., Ca, Mg, Fe) exchange between carbonates and silicate. We propose that carbonate-silicate cations exchange can alter the chemical composition of recycled carbonates, potentially impacting their stability and reducing the solidus temperature of carbonate-bearing systems. Combining thermodynamic calculations with the elevated conductivity in our experiments, we re-evaluate the contribution of recycled carbonates to the Earth mantle geophysical anomalies and obtain the potential carbonate capacity in the subducting slab.

Electrical conductivities of the dry hot-pressed sintering gabbro with various mineralogical proportions (Cpx_XPl_100−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 multi-anvil 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. For the fixed mineralogical composition of Cpx₅₀Pl₅₀, the electrical conductivities of the samples significantly increased with the rise of temperature, but slightly decreased with increasing pressure. Furthermore, the activation energy and activation volume were determined as 1.06 ± 0.12 eV and 6.00 ± 2.00 cm³/mole, respectively. As for the various mineralogical compositions of dry gabbro, the electrical conductivities of the samples increased with the rise of volume percentage of clinopyroxene (Cpx) at 1.0 GPa. It is proposed that the main conduction mechanism is the small polaron, owing to the positive relation between the electrical conductivity and the iron content in samples. On the basis of these obtained conductivity results, laboratory-based electrical conductivity–depth profiles for the hot-pressed sintering gabbro with various mineralogical proportions and temperature gradients were successfully established. In conclusion, 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.

The electrical conductivity of gabbroic melt with four different water contents (i.e., 0 %, 2.59 wt %, 5.92 wt %, and 8.32 wt %) was measured at temperatures of 873–1373 K and pressures of 1.0–3.0 GPa using a YJ-3000t multi-anvil high-pressure apparatus and Solartron-1260 impedance spectroscopy analyzer. At a fixed water content of 2.59 wt %, the electrical conductivity of the sample slightly decreased with increasing pressure in the temperature range of 873–1373 K, and its corresponding activation energy and activation volume were determined as 0.87 ± 0.04 eV and −1.98 ± 0.02 cm³ molec.⁻¹, respectively. Under the certain conditions of 873–1373 K and 1.0 GPa, the electrical conductivity of the gabbroic melts tends to gradually increase with a rise in water content from 0 wt % to 8.32 wt %, and the activation enthalpy decreases from 0.93 to 0.63 eV accordingly. Furthermore, functional relation models for the electrical conductivity of gabbroic melts with variations of temperature, pressure, and water content were constructed at high-temperature and high-pressure conditions. In addition, the dependence relation of the electrical conductivity of melts with the degree of depolymerization was explored under conditions of four different water contents at 1373 K and 1.0 GPa, and three previously available reported results on those of representative calc-alkaline igneous rock melts (i.e., dacitic melt, basaltic melt, and andesitic melt) were compared in detail. In combination with our presently acquired electrical conductivity data on gabbroic melt with four different water contents and the available data on polycrystalline olivine, the electrical conductivity of a gabbroic melt–olivine system with variation of the volume percentage of anhydrous and hydrous melts was successfully constructed by using the typical Hashin–Shtrikman upper-bound model. In light of the electrical conductivity of the gabbroic melt–olivine system with previous magnetotelluric (MT) results, we find that anhydrous and hydrous gabbroic melts can be employed to reasonably interpret the high-conductivity anomalies in the Mohns Ridge of the Arctic Ocean.

The electrical conductivity of gabbroic melt with four different water contents (i.e. 0, 2.59 wt%, 5.92 wt% and 8.32 wt%) was measured at temperatures of 873–1373 K and pressures of 1.0–3.0 GPa using YJ–3000t multi‒anvil high−pressure apparatus and Solartron‒1260 impedance spectroscopy analyzer. At a fixed water content of 2.59 wt%, the electrical conductivity of the sample slightly decreased with increasing pressure at the temperature range of 873‒1373 K, and its corresponding activation energy and activation volume were determined as 0.87 ± 0.04 eV and ‒1.98 ± 0.02 cm³ mole^–1, respectively. Under the certain conditions of 873‒1373 K and 1.0 GPa, the electrical conductivity of the gabbroic melts tends to gradually increase as the rise of water content from 0 to 8.32 wt%, and the activation enthalpy decreases from 0.93 eV to 0.63 eV, accordingly. Furthermore, the functional relation models for the electrical conductivity of gabbroic melts with the variations of temperature, pressure and water content were constructed at high‒temperature and high‒pressure conditions, respectively. In addition, the dependence relation of the electrical conductivity of melts with the degree of depolymerization was explored under conditions of four different water contents, 1373 K and 1.0 GPa, and three previously available reported results on those of representative calc‒alkaline igneous rock melts (i.e. dacitic melt, basaltic melt and andesitic melt) were detailedly compared. In comprehensive combination with our presently acquired electrical conductivity data of gabbroic melt with four different water contents and the available data of polycrystalline olivine, the electrical conductivity of gabbroic melt‒olivine system on the variation of volume percentage of anhydrous and hydrous melts was successfully constructed by virtue of the typical Hashin–Shtrikman upper bound model. In light of the electrical conductivity of gabbroic melt‒olivine system with the previous MT results, we find that the anhydrous and hydrous gabbroic melts can be employed to reasonably interpret the high conductivity anomalies in the Mohns ridge of the Arctic Ocean.

Shallow marine carbonates are recognized as key agents in deep carbon cycling. However, the formation and burial of carbonates below the carbonate compensation depth still remain poorly understood. Here, we investigate carbonates from the > 7000 m water-depth Japan Trench hadal zone and find widespread authigenic calcium carbonate buried in these ultra-deep sediments. Stable and radiocarbon isotope depletions in the authigenic carbonates indicate an organic carbon (OC) source, likely primarily delivered by deep-sea landslides. Isotopic modeling suggests that subduction of these OC-derived carbonates can impart negative δ¹³C signatures to fluids released in the NE Japan subduction zone. The OC-derived carbonate flux in the Japan Trench is estimated to reach ~ 28.6 Tg C Myr^–1. We propose that earthquake-driven organic matter influx into the hadal zone may have facilitated sustained carbonate production. Thus, OC-derived authigenic carbonates in hadal trenches represent an underappreciated carbon sink and a potential mechanism for transferring OC into the deep Earth.