Aqueous alteration age ofMartian nakhlites

1.对火星陨石Chassigny的同位素分析结果表明，Rb-Sr年龄为1406± 14 Ma，初始ε <87>Sr/ε <86>Sr比值为0.702251±0.000034，Sm-Nd年龄为1386±28 Ma，初始ε <143>Nd值为+16.9 ±0.3，ε <39>Ar-ε <40>Ar年龄为1360 ± 40-20 Ma。NWA 2737的WR样品的Sm-Nd数据在Chassigny等时线上作图，表明这些Chassigny岩可能具有几乎相同的结晶年龄，为138 Ga。这些年龄和Rb-Sr和Sm-Nd初始同位素特征的一致性表明，从低Rb/Sr，轻稀土元素贫化源物质结晶的硅质岩约1390 Ma前。Chassignite和Nakhlites Govemador Valadares和Lafayette的年龄和ε 143 Nd值重叠，表明它们可能来自非常相似的地幔来源。Nakhla，Northwest Africa 998和Yamato 000593似乎来自相似但不同的来源。Chassignites和迄今为止研究的所有nakhlites都经历了类似的演化历史。也就是说， ...更多信息 片麻岩/nakhlites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。Yamato-793605的Sm-Nd等时线年龄为185±16 Ma，ε^ Nd<143>初始值为+9.7± 0.2。在分析误差范围内，所获得的Sm-Nd年龄与该陨石的Rb-Sr年龄以及Allan Hills-77005和刘易斯Cliff 88516的Rb-Sr和Sm-Nd年龄一致，但ε^<143>Nd值不一致。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，尽管清楚地观察到冲击变质作用的干扰，但二辉橄榄质shergottites的同位素系统被认为是本土的。从这一研究和以前的Rb-Sr、Sm-Nd和U-Pb同位素研究中一致地获得了“180 Ma的年轻年龄”，似乎代表了结晶事件。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