Tracking slab surface temperatures with electrical conductivity of glaucophane

Geeth Manthilake,Mainak Mookherjee,Kenneth T. Koga,Ye Peng

doi:10.1038/s41598-021-97317-0

Abstract

Slab surface temperature is one of the key parameters that incur first-order changes in subduction dynamics. However, the current thermal models are based on empirical thermal parameters and do not accurately capture the complex pressure–temperature paths of the subducting slab, prompting significant uncertainties on slab temperature estimations. In this study, we investigate whether the dehydration-melting of glaucophane can be used to benchmark the temperature in the slab. We observe that dehydration and melting of glaucophane occur at relatively low temperatures compared to the principal hydrous phases in the slab and produce highly conductive Na-rich melt. The electrical properties of glaucophane and its dehydration products are notably different from the hydrous minerals and silicate melts. Hence, we conclude that the thermodynamic instability of glaucophane in the slab provides a unique petrological criterion for tracking temperature in the present-day subduction systems through magnetotelluric profiles.

Highlights

Glaucophane (Na2(Mg3Al2)Si8O22(OH)2) and lawsonite (CaAl2Si2O7(OH)[2].H2O) are the principal hydrous mineral phases associated with the blueschist facies lithology[1,22,23]
Because glaucophane is one of the principal hosts of Na in subducting slabs, we focus on understanding whether the dehydration-melting of glaucophane can generate distinct geophysically detectable electrical anomalies, standing out from the hydrous minerals, fluid, and melts in subduction zones
We investigate the electrical conductivity of glaucophane in situ under high pressure and high temperature up to 6 GPa and 1258 K

Summary

Introduction

Glaucophane (Na2(Mg3Al2)Si8O22(OH)2) and lawsonite (CaAl2Si2O7(OH)[2].H2O) are the principal hydrous mineral phases associated with the blueschist facies lithology[1,22,23]. The presence of glaucophane and lawsonite is often associated with anomalous geophysical observations including a relatively low-velocity layer[24,25] and enhanced electrical conductivity[26,27] at the top of subducting slabs. (> 9 GPa) and high temperature up to 1300 K means that the lawsonite potentially remains stable to depths of more than 200 km[22,23]. Because glaucophane is one of the principal hosts of Na in subducting slabs, we focus on understanding whether the dehydration-melting of glaucophane can generate distinct geophysically detectable electrical anomalies, standing out from the hydrous minerals, fluid, and melts in subduction zones. We show that the dehydration melting of glaucophane produces highly conductive Na-rich fluids and melt that can serve as geophysical indicators for accurately benchmarking the slab temperatures

Methods

Results

Conclusion