Ion microprobe U-Pb dating of individual phosphate minerals in Martian meteorite ALH 84001.

Abstract

Allan Hills 84001, a unique Martian meteorite, shows extremely old crystallization age and complicated shock metamorphic history. While igneous phosphate minerals are volumetrically minor, they concentrate trace elements in the magma and give various information. Phosphates contain U and Th, and has been used for U-Th-Pb dating. In this study, we determine U-Pb age of phosphates in ALH 84001 from measurements of single-grain with size of 50-100 micron, using NanoSIMS. From obtained distributions of U and Pb within a grain, the thermal history of the meteorite can be estimated.