Dehydration of chlorite explains anomalously high electrical conductivity in the mantle wedges

Abstract

Development of interconnected magnetite during chlorite dehydration explains anomalous high conductivity at shallow mantle wedges.

Influence of dehydration on the electrical conductivity of epidote and implications for high‐conductivity anomalies in subduction zones

“…At high temperatures during the dehydration process, the impedance arcs in the low‐frequency regime indicate the positive Z ″ of the presence of the inductive loop, which is related to electrode‐fluid reaction at the sample electrode interface, as reported previously [ Bai and Conway , ; Macdonald , ]. Therefore, the inductive loop that appears at low frequencies reflects the occurrence of dehydration reaction, as are also observed for other hydrous minerals such as talc [ Wang and Karato , ] and chlorite [ Manthilake et al , ]. After dehydration, the impedance spectra in the lower frequency range are remarkably developed, which is usually attributed to the contribution of a grain boundary component to the sample resistance [ Roberts and Tyburczy , ; Dai et al , ].…”

“…Extensive laboratory work has sought to measure the electrical conductivity of the major hydrous phases in subduction zones such as serpentinites and talc [ Guo et al , ; Reynard et al , ; Wang and Karato , ], amphibole [ Wang et al , ], lawsonite [ Manthilake et al , ], phlogopite [ Li et al , ], and chlorite [ Manthilake et al , ], but large differences are evident in the results of these experiments, and in some cases, the laboratory measurement results are inconsistent with field MT observations. Additionally, the mechanism of enhanced electrical conductivity of hydrous minerals during dehydration temperature regime is still controversial.…”

“…The electrical conductivity results of phlogopite also showed that the conductivity is not caused by water, but probably F and K [ Li et al , ]. Recent experimental study on electrical conductivity of chlorite demonstrated that aqueous fluid alone cannot explain the anomalously high conductivity in the mantle wedge, but an interconnected network of chemically impure magnetite produced during the dehydration of chlorite does [ Manthilake et al , ]. In addition, molecular dynamic simulation results reveal that the presence of low‐salinity (0.5 wt %) NaCl‐H 2 O fluid can account for the anomalous high‐conductivity zones at a relative shallow depths above the subducting oceanic crust [ Sakuma and Ichiki , ].…”

“…In these regions, electrical conductivity is characterized by the high value of~0.1-1 S/m [Soyer and Unsworth, 2006;Chen and Clayton, 2009;Pozgay et al, 2009;Worzewski et al, 2011;Evans et al, 2014;Pommier, 2014]. By combining petrological studies [Liu et al, 1996;Ono, 1998;Schmidt and Poli, 1998] with experimentally conductivity measurements [Guo et al, 2011;Ni et al, 2011;Wang et al, 2012;Manthilake et al, 2015Manthilake et al, , 2016, the high conductivity anomalies in these regions are commonly explained by the presence of partial melt or free fluids released from dehydration of hydrous minerals (e.g., amphibole, chlorite, lawsonite, zoisite/epidote, chloritoid, and talc) in the subducting slab. In the setting of young and hot subduction zones, partial melting in the mantle wedge, caused by ascending fluids released from the subducting oceanic lithosphere or escaped along fracture zones to the upper mantle, is often at depths shallower than 70 km [Liu et al, 1996].…”

Effect of chemical composition on the electrical conductivity of gneiss at high temperatures and pressures

“…Aside from the chemical composition, other available alternative causes for high conductivity anomalies can be considered, such as water in nominally anhydrous minerals (Wang et al, 2006;Yang, 2011;Karato, 2009, 2014a), interconnected saline (or aqueous) fluids (Hashim et al, 2013;Shimojuku et al, 2014;Sinmyo and Keppler, 2017;Guo et al, 2015;Li et al, 2018), partial melting (Wei et al, 2001;Maumus et al, 2005;Gaillard et al, 2008;Ferri et al, 2013;Laumonier et al, 2015Laumonier et al, , 2017Ghosh and Karki, 2017), interconnected secondary high conductivity phases (e.g., FeS, Fe 3 O 4 ; Jones et al, 2005;Bagdassarov et al, 2009;Padilha et al, 2015), dehydration of hydrous minerals (Wang et al, 2012(Wang et al, , 2017Manthilake et al, 2015Manthilake et al, , 2016Hu et al, 2017;Sun et al, 2017a, b;Chen et al, 2018) and graphite films on mineral grain boundaries (Freund, 2003;Pous et al, 2004;Chen et al, 2017). In consideration of the similar formation conduction and geotectonic environments, the Himalaya-Tibetan orogenic system was compared with the Dabie-Sulu UHPM belt and explained high electrical conductivity anomalies.…”