Shock-recovered maskelynite indicates low-pressure ejection of shergottites from Mars.

Abstract

Diaplectic feldspathic glass, commonly known as maskelynite, is a widely used impact indicator, notably for shergottites, whose shock conditions are keys to their geochemistry and launch mechanism. However, classic reverberating shock recovery experiments show maskelynitization at higher shock pressures (>30 gigapascals) than the stability field of the high-pressure minerals found in many shergottites (15 to 25 gigapascals). Most likely, differences between experimental loading paths and those appropriate for martian impacts have created this ambiguity in shergottite shock histories. Shock reverberation yields lower temperature and deviatoric stress than single-shock planetary impacts at equivalent pressure. We report the Hugoniot equation of state of a martian analog basalt and single-shock recovery experiments, indicating partial-to-complete maskelynitization at 17 to 22 gigapascals, consistent with the high-pressure minerals in maskelynitized shergottites. This pressure explains the presence of intact magmatic accessory minerals, used for geochronology in shergottites, and offers a new pressure-time profile for modeling shergottite launch, likely requiring greater origin depth.