Uranium-lead Isotopic Systematics of the Martian Meteorite Zagami
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چکیده
Introduction: The crystallization age of Zagami has been well established by the Rb-Sr and Sm-Nd isochron techniques. Isotopic analysis on purified mineral fractions yield Rb-Sr ages of 178±3, 174±14, and 163±19 Ma [1-2], and a Sm-Nd age of 163±7 Ma [2]. Whole rock and leachate pairs have also been analyzed for U-Th-Pb isotopes and yield a Th-Pb age of 230±5 Ma and a U-Pb age of 229±8 Ma [3]. Chen & Wasserburg [3] interpreted the ~230 Ma UTh-Pb ages as the time of U-Th-Pb fractionation of an ancient reservoir. They hypothesized that this fractionation event was associated with shock metamorphism of a ~4.5 Ga rock. The goal of this study is to investigate the U-Pb isotopic systematics of Zagami in the context of the well defined Rb-Sr and Sm-Nd crystallization ages. Below preliminary results on Zagami maskelynite, pyroxene, and whole rock fractions are presented. These results demonstrate that the U-Pb isotopic system records both the age of formation of the Zagami source region and the age at which this source region was disturbed.
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