Crystallization Age and Source Signature of Chassigny

Abstract

Chassigny is the Martian dunite composed of cumulate olivine (92%), chromite (1.4%), pyroxene (5%) and interstitial feldspar (1.7%). Although nakhlites (clinopyroxenite) are less intensely affected by shock metamorphism, Chassigny has been subjected to a peak shock pressure of about 35 GPa. The cosmic-ray exposure age of Chassigny (11.3 +/- 0.6 Ma) is comparable to those of nakhlites, suggesting launch pairing of these meteorites. Prior chemical and isotopic studies of Chassigny suggest that the meteorite crystallized approx. 1.3 Ga ago and is closely related to nakhlites. Nevertheless, compared to other Martian meteorites there are limited isotopic data for Chassigny. To examine the relationship of Chassigny to nakhlites, we have undertaken new Rb-Sr and Sm-Nd isotopic studies. Here we present the new Sm-Nd isotopic data for Chassigny and discuss the nature of its source materials.