The Chronology of the Nakhlite, Lafayette: Rb-Sr and Sm-Nd Isotopic Ages

Abstract

The Sm-Nd isotopic data of whole rock and mineral separate samples from the nakhlite, Lafayette, define a good isochron age of 1.32+0.05 Ga. However, the Rb-Sr data for the samples show minor disturbances and define a slightly younger age of 1.26+0.07 Ga. Both ages are in agreement with the Ar-Ar age of 1.33+0.03 Ga obtained previously for this meteorite [1]. In addition, the Rb-Sr data for HCl leachates from two iddingsite-rich samples yield a secondary tie-line age of 679+66 Ma. This age is in good agreement with the oldest K-Ar age of 655+75 Ma recently reported for iddingsite fragments [2] and may represent the formation age of iddingsite. Our isotopic data suggest that Lafayette was crystallized ~1.32 Ga ago and underwent aqueous alterations which led to the formation of iddingsite probably ~700 Ma ago on Mars.