Constraints from the dehydration of antigorite on high-conductivity anomalies in subduction zones

Duojun Wang,Tao Liu,David O Welch,Xiaowei Liu,Baosheng Li,Kewei Shen

doi:10.1038/s41598-017-16883-4

Abstract

Regions with high electrical conductivities in subduction zones have attracted a great deal of attention. Determining the exact origin of these anomalies could provide critical information about the water storage and cycling processes during subduction. Antigorite is the most important hydrous mineral within deep subduction zones. The dehydration of antigorite is believed to cause high-conductivity anomalies. To date, the effects of dehydration on the electrical conductivity of antigorite remain poorly understood. Here, we report new measurements of the electrical conductivity of both natural and hot-pressed antigorite at pressures of 4 and 3 GPa, respectively, and at temperatures reaching 1073 K. We observed significantly enhanced conductivities when the antigorite was heated to temperatures beyond its thermodynamic stability field. Sharp increases in the electrical conductivity occurred at approximately 848 and 898 K following the decomposition of antigorite to forsterite, enstatite and aqueous fluids. High electrical conductivities reaching 1 S/m can be explained by the presence of an interconnected network of conductive aqueous fluids. Based on these results for the electrical conductivity of antigorite, we conclude that high-conductivity regions associated with subduction zones can be attributed to dehydration-induced fluids and the formation of interconnected networks of aqueous fluids during the dehydration of antigorite.

Highlights

The water liberated from the breakdown of hydrous minerals within a subduction zone may be transported to the overlying mantle wedge and subsequently trigger magmatism[1,2], thereby inducing seismic[3,4] and magnetotelluric (MT) anomalies[5,6,7,8,9,10,11,12,13,14,15] above the subduction zone
The results indicate that the electrical conductivity of antigorite has a weak or non-existent pressure dependence but varies significantly with temperature
Sharp increases in the electrical conductivity of the hot-pressed sample occurred at temperatures exceeding 923 K, resulting in an increase of three orders of magnitude to a value of 1 S/m at 973 K

Summary

Introduction

The water liberated from the breakdown of hydrous minerals within a subduction zone may be transported to the overlying mantle wedge and subsequently trigger magmatism[1,2], thereby inducing seismic[3,4] and magnetotelluric (MT) anomalies[5,6,7,8,9,10,11,12,13,14,15] above the subduction zone. The dehydration of certain hydrous minerals, including talc, amphibole, lawsonite and chlorite, can significantly enhance the electrical conductivity anomaly[29,30,31,32]. It constitutes the only stable hydrous phase down to a depth of 200 km, the electrical conductivity of dehydrated antigorite has not yet been investigated. Results to an explanation of the high electrical conductivity anomalies observed during geophysical surveys in subduction settings

Methods

Results

Conclusion