Chronological study of martian meteorites, shergottites

对玄武岩-斜锆石混合物进行了冲击恢复和退火实验，以评价冲击对斜锆石U-Pb系统学的影响。在这里研究的斜锆石中没有观察到由于冲击变质作用和随后的退火而导致的完全放射成因铅损失。为了解决火星地质活动的时间尺度，我们进行了U-Pb的研究在罗伯茨地块04261 shergottite的斜锆石。斜锆石的原位U-Th-Pb同位素分析获得了~200 Ma的年轻238 U-206 Pb年龄。目前的结果意味着火星岩浆在200 Ma前仍在形成，火星的地质活动一直持续到最近。目前的结果证实了以前的Rb-Sr，Sm-Nd和Lu-Hf系统学，但与里昂群shergottites的4.1 Ga的Pb-Pb年龄相冲突，可能是由于火星地壳成分（S）可能已被纳入shergottites在冲击变质的组成相。

Shock-recovery and annealing experiments on basalt-baddeleyite mixtures were undertaken to evaluate shock effects on U-Pb systematics of baddeleyite. Complete radiogenic lead loss due to shock metamorphism and subsequent annealing was not observed in the baddeleyites studied here. In order to address the timescale over which Mars was geologically active, we have undertaken U-Pb studies on baddeleyite in the Roberts Massif 04261 shergottite. In situ U-Th-Pb isotopic analyses of baddeleyite yield a young 238U-206Pb age of ~200 Ma. The present results imply that Martian magma was still forming only 200 Ma ago, and that Mars had been geologically active until the recent past. The present results confirm the previous Rb-Sr, Sm-Nd and Lu-Hf systematics but conflict with the Pb-Pb ages of 4.1 Ga for shergottites by the Lyon group, possibly due to Martian crustal component(s) which might have been incorporated into constituent phases of shergottites during shock metamorphism.