PETROLOGIC, ISOTOPIC AND ELEMENTAL CHARACTERIZATION OF SHOCK-MELTED INTERMEDIATE OLIVINE GABBROIC SHERGOTTITE NORTHWEST AFRICA 11509
A fresh 500 gram stone found in Mali is a relatively coarse grained gabbroic shergottite containing shock-melted intercumulus zones. Among the 108 unpaired Martian meteorites now recognized, only NWA 6342 exhibits some similar shock features.
NWA 11509 is a unique permafic non-poikilitic olivine gabbroic shergottite (possibly a magmatic cumulate) with intermediate ITE affinities but an aberrant Hf isotopic composition. Polycrystalline olivine, which was also recognized in intermediate shergottite NWA 6342, implies high temperature thermal annealing of shock-deformed grains. Rapid crystallization of interstitial, shock-produced vesicular melts resulted in regions of intergrown plagioclase+low-Ca pyroxene, as well as possibly immiscible “blobs” of residual evolved liquid, which in turn quenched rapidly to aggregates of skeletal grains.