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