Shock-darkening in ordinary chondrites: determination of the pressure-temperature conditions by shock physics mesoscale modeling

TL;DR

This study uses mesoscale shock physics modeling to determine the pressure range causing shock-darkening in ordinary chondrites, revealing it occurs between 40 and 50 GPa and highlighting the roles of porosity and material properties.

Contribution

The paper introduces a mesoscale modeling approach with iSALE to accurately estimate shock-darkening conditions in chondrites, considering heterogeneity and material properties.

Findings

Shock-darkening occurs between 40 and 50 GPa.

All troilite reaches melting at 52 GPa.

Porosity significantly influences shock heating effects.

Abstract

We determined the shock-darkening pressure range in ordinary chondrites using the iSALE shock physics code. We simulated planar shock waves on a mesoscale in a sample layer at different nominal pressures. Iron and troilite grains were resolved in a porous olivine matrix in the sample layer. We used equations of state (Tillotson EoS and ANEOS) and basic strength and thermal properties to describe the material phases. We used Lagrangian tracers to record peak shock pressures in each material unit. The post-shock temperatures (and the fractions of tracers experiencing temperatures above the melting point) for each material were estimated after the passage of the shock wave and after reflections of the shock at grain boundaries in the heterogeneous materials. The results showed that shock-darkening, associated with troilite melt and the onset of olivine melt, happened between 40 and 50 GPa - with 52 GPa being the pressure at which all tracers in the troilite material reach the melting point. We demonstrate the difficulties of shock heating in iron and also the importance of porosity. Material impedances, grain shapes and the porosity models available in the iSALE code are discussed. We also discussed possible not-shock-related triggers for iron melt.