Electrical Conductivity of Clinopyroxene‐NaCl‐H₂O System at High Temperatures and Pressures: Implications for High‐Conductivity Anomalies in the Deep Crust and Subduction Zone

Abstract

Electrical conductivities of the clinopyroxene (Cpx)-NaCl-H 2 O system with various salinities (5, 10, 15, 20, 25 wt%) and fluid fractions (5, 10, 15, 20, 25 vol%) were measured at 1 GPa and 673-973 K. For comparison with electrical properties of the Cpx-NaCl-H 2 O system, the conductivities of dry Cpx, hydrous Cpx, and a Cpx-H 2 O system were researched at the same temperature and pressure. The experimental results included (1) the electrical conductivities of all samples that were associated with Cpx and the temperatures conform to the Arrhenius relationship that is used to fit the activation enthalpy, which decreased with increasing salinity (mass fraction of NaCl in saline fluids) and fluid fraction (volume fraction of saline fluids in the Cpx-NaCl-H 2 O system); (2) at a fixed fluid fraction of 10 vol%, the conductivities of the Cpx-NaCl-H 2 O system increased slightly with an increase in salinity, and the gap between the conductivities of the systems with 5 and 25 wt% saline fluids was approximately 1 order of magnitude;(3) at a fixed salinity of 5 wt%, the conductivity of the Cpx-NaCl-H 2 O system with 25 vol% saline fluids was approximately 1.5 orders of magnitude higher than that of the system with 5 vol% saline fluids. Furthermore, it was proposed that the unusually high conductivities of southern Tibetan Plateau, Dabie Orogen, Grenville province and central New Zealand can be caused by clinopyroxene with interconnected saline fluids with corresponding salinities and fluid fractions.

Electrical Conductivity of Talc Dehydration at High Pressures and Temperatures: Implications for High‐Conductivity Anomalies in Subduction Zones

“…In addition to geometry, the composition of the aqueous fluid is important for electrical conductivity (Reynard, 2016; Reynard et al, 2011). NaCl is thought to be the critical solute for aqueous liquids originated from a variety of geological environments, which was widely studied by both experiments and calculations (H. Guo & Keppler, 2019; X. Guo et al, 2015; Sakuma & Ichiki, 2016; Shimojuku et al, 2014, 2012; Sinmyo & Keppler, 2017; Sun et al, 2020). In addition, the NaCl‐bearing aqueous fluids was also thought to control the electrical conductivity for albite‐NaCL‐H 2 O, albite‐(quartz)‐H 2 O (X. Guo et al, 2015), plagioclase‐NaCl‐H 2 O (Li et al, 2018), and clinopyroxene‐NaCl‐H 2 O system (Sun et al, 2020).…”

Insights on the deep carbon cycle from the electrical conductivity of carbon-bearing aqueous fluids

“…The laboratory-based constraints on the electrical conductivity of fluids have provided valuable insight into the fluid-driven processes in the subduction zone and overlying mantle wedge 23 , 24 . The experimental constraints on the electrical conductivity of aqueous fluid include pure water 25 , 26 , aqueous fluids released by dehydration 23 , 24 , 27 , 28 and saline aqueous fluids with varying salinities 29 – 34 . However, the effect of both carbon and hydrogen bearing (C–H–O) aqueous fluids on electrical conductivity remain unknown.…”

Influence of Saline Fluids on the Electrical Conductivity of Olivine Aggregates at High Temperature and High Pressure and Its Geological Implications

“…Saline ions (Na + and Cl − ) in aqueous fluids are released from subduction slabs during dehydration and metasomatism (Reynard, 2016;Förster et al, 2019;Manthilake et al, 2021b). Numerous studies have attributed the origin of the high-conductivity anomalies in the mid-lower crust and some subduction zones to the distribution of NaClbearing aqueous fluids along the grain boundaries of silicate minerals (Shimojuku et al, 2012(Shimojuku et al, , 2014Guo et al, 2015;Sinmyo and Keppler, 2017;Li et al, 2018;Sun et al, 2020). However, the effect of saline fluids on the electrical conductivity of silicate minerals in mantle wedge regions remains poorly constrained.…”

“…Huang et al (2019) recently demonstrated that NaCl-bearing aqueous fluids might be interconnected in mantle wedges. The electrical conductivities of clinopyroxene (Cpx)-NaCl-H 2 O, plagioclase (Pl)-NaCl-H 2 O, albite (Ab)-NaCl-H 2 O and pure NaCl-bearing saline fluid systems have been previously investigated (Guo et al, 2015;Li et al, 2018;Guo and Keppler, 2019;Sun et al, 2020), but the electrical conductivity of saline fluid-bearing olivine aggregates has not been reported. Although saline fluids exert a dominant control over the conductivities of saline fluid-bearing mineral aggregates, the mineral species still play a significant role in the system conductivity as a whole (Guo et al, 2015;Li et al, 2018;Sun et al, 2020).…”

“…The electrical conductivities of clinopyroxene (Cpx)-NaCl-H 2 O, plagioclase (Pl)-NaCl-H 2 O, albite (Ab)-NaCl-H 2 O and pure NaCl-bearing saline fluid systems have been previously investigated (Guo et al, 2015;Li et al, 2018;Guo and Keppler, 2019;Sun et al, 2020), but the electrical conductivity of saline fluid-bearing olivine aggregates has not been reported. Although saline fluids exert a dominant control over the conductivities of saline fluid-bearing mineral aggregates, the mineral species still play a significant role in the system conductivity as a whole (Guo et al, 2015;Li et al, 2018;Sun et al, 2020). The conductivities of saline fluids in mineral-NaCl-H 2 O systems calculated using theoretical models (e.g., Hashin-Shtrikman upper model (HS + ) and cube model) were reported to be substantially lower than those of pure NaCl-bearing aqueous fluids (Sinmyo and Keppler, 2017;Li et al, 2018;Guo and Keppler, 2019;Sun et al, 2020).…”