Torsion of a cylinder of partially molten rock with a spherical inclusion: theory and simulation

TL;DR

This study uses 3D simulations to explore how partially molten rocks deform under torsion with inclusions, revealing conditions for melt-rich band formation and effects of strain-rate-dependent viscosity, aiding understanding of mantle melt migration.

Contribution

It introduces a 3D numerical model of torsional deformation in partially molten rocks with inclusions, highlighting differences from 2D models and the impact of strain-rate dependence.

Findings

Melt-rich bands form in simulations at low bulk-to-shear-viscosity ratios.

3D models show easier formation of melt-rich bands compared to 2D.

Strain-rate dependence alters the shape of pressure shadows around inclusions.

Abstract

The processes that are involved in migration and extraction of melt from the mantle are not yet fully understood. Gaining a better understanding of material properties of partially molten rock could help shed light on the behavior of melt on larger scales in the mantle. In this study, we simulate three-dimensional torsional deformation of a partially molten rock that contains a rigid, spherical inclusion. We compare the computed porosity patterns to those found in recent laboratory experiments. The laboratory experiments show emergence of melt-rich bands throughout the rock sample, and pressure shadows around the inclusion. The numerical model displays similar melt-rich bands only for a small bulk-to-shear-viscosity ratio (five or less). The results are consistent with earlier two-dimensional numerical simulations; however, we show that it is easier to form melt-rich bands in three dimensions compared to two. The addition of strain-rate dependence of the viscosity causes a distinct change in the shape of pressure shadows around the inclusion. This change in shape presents an opportunity for experimentalists to identify the strain-rate dependence and therefore the dominant deformation mechanism in torsion experiments with inclusions.