Aqueous alteration age ofMartian nakhlites

1.对火星陨石沙斯米进行了同位素分析，获得了1406±14 Ma的Rb-Sage年龄和0.702251±0.000034的锶/锶比值，Sm-ND年龄为1386±28 Ma，初始ε为+16.9±0.3，年龄为1360±40-20 Ma。NWA2737的WR样品的Sm-ND数据在Chassigny等时线上绘制，表明它们可能具有几乎相同的结晶年龄~138Ga。这些年龄与Rb-Sr和Sm-Nd初始同位素特征的一致性表明，大约1390 Ma前，雀斑玄武岩的结晶来自低Rb/Sr、轻稀土元素亏损的源岩。硅质岩和纳赫利特岩的年龄和ε-143Nd值重叠，表明它们可能来自非常相似的地幔来源。Nakhla、西北非洲998和大和000593似乎来自相似但不同的来源。到目前为止，所研究的方晶石和所有钠长石都经历了相似的演化史。也就是说，Chassi…更多的麻粒岩/钠长石来自火山活动持续至少50 Ma的地区，并从不同的熔岩流或地下岩床结晶而来。它们可能是由一次撞击事件从火星发射的。2.YAMATO-793605获得的Sm-ND内等时线年龄为185±16 Ma，初始ε^&lt；143&Gt；Nd值为+9.7±02。获得的Sm-ND年龄在分析误差范围内与该陨石的Rb-Sr年龄以及Allan Hills-77005和Lewis Cliff88516以前的Rb-Sr和Sm-ND年龄相同，尽管ε^&lt；143&Gt；Nd值彼此不相同。亲石微量元素的元素丰度几乎不受火星表面水蚀变的影响。因此，二辉橄榄岩的同位素体系被认为是本土的，尽管明显地观察到了冲击变质作用的干扰。从这次和以前的Rb-Sr、Sm-ND和U-Pb同位素研究中，一直获得了约180 Ma的年轻年龄，似乎代表了结晶事件。较少

1.Isotopic analysis of the Martian meteorite Chassigny yields a Rb-Srage of 1406±14Ma with an initial ^<87>Sr/^<86>Sr ratio of 0.702251±0.000034, a Sm-Nd age of 1386±28 Ma with an initial ε^<143>Nd-value of+16.9±0.3 and an ^<39>Ar-^<40>Ar age of 1360+40-20 Ma. The Sm-Nd data for WR samples ofNWA 2737 plots on the Chassigny isochron, suggesting that the chassignites may have almost identical crystallization age of〜138Ga. The concordance of these ages and the Rb-Sr and Sm-Nd initial isotopic signatures suggest that chassignites crystallized from low Rb/Sr, light rare earth element depleted source materials〜1390 Ma ago. The ages and ε143Nd-values of chassignites and the nakhlites Govemador Valadares and Lafayette overlap, suggesting that they could have come ＆urn very similar mantle sources. Nakhla, Northwest Africa 998 and Yamato 000593 appear to be from similar but distinct sources. Chassignites and all nakhlites so far studied have undergone similar evolution histories. That is, chassi … More gnites/nakhlites were derived from a region where volcanism lasted at least 50 Ma and crystallized from different lava flows or subsurface sills. They probably were launched from Mars by a single impact event.2.The Sm-Nd internal isochron obtained for Yamato-793605 yields an age of 185±16 Ma with an initial ε^<143>Nd value of+9.7±02. The obtained Sm-Nd age is, within analytical errors, identical to the Rb-Sr age ofthis meteorite as well as to the previous Rb-Sr and Sm-Nd ages of Allan Hills-77005 and Lewis Cliff88516, although the ε^<143>Nd values are not identical to each other. Elemental abundances of lithophile trace elements remain nearly unaffected by aqueous alteration on the Martian surface. The isotopic systems of lherzolitic shergottites, thus, are considered to be indigenous, although disturbances by shock metamorphism are clearly observed. "Young ages of〜180 Ma" have been consistently obtained from this and previous Rb-Sr, Sm-Nd and U-Pb isotopic studies and appear to represent crystallization events. Less