Electrical Conductivity of Clinochlore Dehydration and Implications for High‐Conductivity Anomalies and the Melting in the Mantle Wedge

Abstract

The dehydration of clinochlore may supply water for the creation of high‐conductivity anomalies and melting beneath volcanic arc. However, this process has not yet been constrained even though it is critical to understanding water cycling processes during subduction. The electrical conductivity of clinochlore was measured at pressures of 1.0–4.0 GPa and temperatures of up to 1273 K. The pressure weakly affected the electrical conductivity of clinochlore. In contrast, the electrical conductivity was significantly enhanced when the clinochlore was heated to temperatures beyond 1048 K, which was accompanied by decomposition into spinel, forsterite, enstatite and aqueous fluids. The elevated conductivity associated with the high activation energy may reflect the migration of Mg2+ and Al3+ during dehydration. We suggested that the aqueous fluids were released from both talc‐like and brucite‐like layer in the clinochlore, and the volumes of fluids released by samples post mortem determined using X‐ray computed tomography were 7.9‐11.5 vol.%. Our results indicate that the dehydration of clinochlore results in a significant increase in conductivity of up to ∼1 S/m due to the interconnected network formed by the fluids. Combined with the geothermal gradient, the experimental data were used to interpret the high‐conductivity anomalies observed at depths of 75‐ 120 km in hot subduction zones and 150–200 km in cold subduction zones. The updip migration of aqueous liquids liberated by clinochlore may act as a major water source for the melting at depths of 110±20 km above the descending slab beneath a volcanic arc.