The Anomalous Seismic Behavior of Aqueous Fluids Released during Dehydration of Chlorite in Subduction Zones

Abstract

Dehydration and fluid circulation are integral parts of subduction tectonics that govern the dynamics of the wedge mantle. The knowledge of the elastic behavior of aqueous fluid is crucial to understand the fluid–rock interactions in the mantle through velocity profiles. In this study, we investigated the elastic wave velocities of chlorite at high pressure beyond its dehydrating temperature, simulating the progressive dehydration of hydrous minerals in subduction zones. The dehydration resulted in an 8% increase in compressional (Vp) and a 5% decrease in shear wave (Vs) velocities at 950 K. The increase in Vp can be attributed to the stiffening of the sample due to the formation of secondary mineral phases followed by the dehydration of chlorite. The fluid-bearing samples exhibited Vp/Vs of 2.45 at 950 K. These seismic parameters are notably different from the major mantle minerals or hydrous silicate melts and provide unique seismic criteria for detecting mantle fluids through seismic tomography.

Halogen Bearing Amphiboles, Aqueous Fluids, and Melts in Subduction Zones: Insights on Halogen Cycle From Electrical Conductivity

“…This interconnected network of highly conductive fluid/melt could dominate the bulk conductivity of rock and mask the relatively resistive matrix made up of remaining mineral phases. Similarly, an interconnected network of fluids/melt also affects the shear modulus of the rock, reducing both compressional and shear wave velocities (Chantel et al, 2016;Freitas et al, 2017Manthilake et al, 2021a;Soustelle et al, 2014;Weidner et al, 2018). The concomitant reduction of seismic wave velocities and the seismic attenuation are considered as strong indications of the presence of a liquid phase.…”

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

“…Previous field magnetotelluric results confirmed that high-conductivity layers (HCLs), as the special weak zones, are widely distributed in the Earth's interior (McGary et al, 2014;Selway, 2015;Hata et al, 2017). Typically, the HCLs have a characteristic of abnormally low velocity on the basis of seismic sounding data (Selway and O'Donnell, 2019;Manthilake et al, 2021a). The electrical conductivities of geological samples at high temperatures and high pressures are required to invert the MT profiles.…”