The Shergottite age paradox and the relative probabilities for Martian meteorites of differing ages

Abstract

The apparent paradox that the majority of impacts yielding Martian meteorites appear to have taken place on only a few percent of the Martian surface can be resolved if all the shergottites were ejected in a single event rather than in multiple events. The apparent degree by which shergottites are overrepresented among Martian meteorites is thereby reduced to about fourfold relative to other types of Martian meteorites for nominal cratering rate models, and further reduced for higher cratering rate models. If the shergottite‐ejection event is assigned to one of three craters in the vicinity of Olympus Mons that were previously identified as candidate source craters for the SNC (shergottites, nakhlites, Chassigny) meteorites, and the nakhlite/chassignite event is assigned to a candidate crater in the vicinity of Ceraunius Tholus, the implied ages of the surrounding terrains agree well with crater density ages. Because of their young crystallization ages, the likely origin of the shergottites is in the Tharsis region even for cratering rates up to twice the nominal value (minimum terrain ages). For these higher cratering rates, the nakhlite source need not be in the Tharsis region. Since the source of the ancient orthopyroxenite, ALH84001, was probably in the ancient southern uplands, meteorite‐yielding impacts may have been widely dispersed on the Martian surface.