Elastic anisotropy of lizardite at subduction zone conditions

TL;DR

This study uses ab initio calculations to determine the high-temperature elastic properties and anisotropy of lizardite, a serpentine mineral in subduction zones, revealing its significant anisotropy and implications for seismic observations.

Contribution

It provides the first ab initio estimates of lizardite's elasticity at subduction zone conditions, improving understanding of mantle hydration and seismic anisotropy.

Findings

Lizardite's high-temperature velocities are higher than previous estimates.

Its elastic anisotropy is significantly larger than that of antigorite.

Results help explain observed shear-wave splitting in cold subduction slabs.

Abstract

Subduction zones transport water into Earth's deep interior through slab subduction. Serpentine minerals, the primary hydration product of ultramafic peridotite, are abundant in most subduction zones. Characterization of their high-temperature elasticity, particularly their anisotropy, will help us better estimate the extent of mantle serpentinization and the Earth's deep water cycle. Lizardite, the low-temperature polymorph of serpentine, is stable under the P-T conditions of cold subduction slabs (< 260{\deg}C at 2 GPa), and its high-temperature elasticity remains unknown. Here we report ab initio elasticity and acoustic wave velocities of lizardite at P-T conditions of subduction zones. Our static results agree with previous studies. Its high-temperature velocities are much higher than previous experimental-based lizardite estimates with chrysotile but closer to antigorite velocities. The elastic anisotropy of lizardite is much larger than that of antigorite and could better account for the observed large shear-wave splitting in some cold slabs such as Tonga.