Abstract Ages determined for magnesian and ferroan anorthosite crustal rock suites overlap, suggesting they formed contemporaneously about 4.3 to 4.5 Ga. A notable exception is the Sm-Nd age previously determined on Mg-suite gabbronorite 67667 which is at least 100 Ma younger than the youngest ferroan anorthosite. New chronologic measurements of 67667 presented here yield concordant Sm-Nd and Rb-Sr mineral isochron ages of 4349 ± 31 Ma and 4368 ± 67 Ma, suggesting the samples is older than previous estimates. Furthermore, a whole rock Sm-Nd isochron of Mg-suite rocks from the Apollo 14, 15, 16, and 17 landing sites yields an age of 4348 ± 25 Ma, indicating that Mg-suite magmatism was widespread and roughly contemporaneous on the lunar nearside. Analysis of Sm-Nd internal isochron ages confirms that Mg-suite magmatism was restricted to a period between about 4.33 and 4.35 Ga at the Apollo 14, 15, 16, and 17 landing sites and was synchronous with magmatism at the Apollo 16 site associated with the ferroan anorthosite suite between 4.35 and 4.37 Ga. Magnesian- and ferroan anorthosite suite rocks with ages younger than ∼4.33 Ga appear to have experienced slow cooling in the deep lunar interior, so that the ages record when the samples cooled below the closure temperature of the Sm-Nd isotopic system and not the time they crystallized. The ages determined for Mg-suite and ferroan anorthosite suite rocks are concordant with the age determined for the formation of urKREEP of 4350 ± 34 Ma using the Sm-Nd isotopic systematics of 67667 and measurements completed on norite 78238, troctolite 76535, KREEP basalt 15386, and gabbronorite NWA 773. Crystallization ages of Mg-suite and FAS are also concordant with the average of 146Sm-142Nd ages previously determined for the formation of the mare basalt source region of 4333 ± 30 Ma. The similarity of ages for Mg-suite magmatism, ferroan anorthosite suite magmatism, urKREEP formation, and formation of the mare basalt source regions implies the processes that produced these rocks were petrogenetically linked. It also implies that both early-stage and late-stage lunar magma ocean cumulates formed over a relatively short duration of

中文翻译：

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从高原岩石的Sm-Nd同位素系统推断月球地壳的形成和演化

摘要 镁质和铁质斜长岩地壳岩石组确定的年龄重叠，表明它们同时形成约 4.3 至 4.5 Ga。一个值得注意的例外是先前在镁组辉长岩 67667 上确定的 Sm-Nd 年龄，它比最年轻的至少年轻 100 Ma铁质斜长岩。此处介绍的 67667 的新年代学测量结果得出一致的 Sm-Nd 和 Rb-Sr 矿物等时线年龄为 4349 ± 31 Ma 和 4368 ± 67 Ma，表明这些样品比以前的估计更古老。此外，来自阿波罗 14、15、16 和 17 号着陆点的镁套岩的全岩 Sm-Nd 等时线产生的年龄为 4348±25 Ma，表明镁套岩浆活动在月球上广泛存在且大致同时期近侧。对 Sm-Nd 内部等时线年龄的分析证实，阿波罗 14、15、16 和 17 号着陆点的 Mg 组岩浆活动仅限于约 4.33 至 4.35 Ga 的时期，并且与阿波罗 16 号站点的岩浆活动同步。 4.35 至 4.37 Ga 之间的铁质斜长岩套件。年龄小于 ~4.33 Ga 的镁质和铁质斜长岩套件在月球深处似乎经历了缓慢冷却，因此当样品冷却至闭合温度以下时，年龄记录Sm-Nd 同位素系统而不是它们结晶的时间。确定的镁套房和铁质斜长岩套房岩石的年龄与使用 67667 的 Sm-Nd 同位素系统学和对紫长石 78238、滑石 76535 完成的测量确定的 urKREEP 形成年龄为 4350 ± 34 Ma 一致。KREEP 玄武岩 15386 和辉长岩 NWA 773。 Mg-suite 和 FAS 的结晶年龄也与先前确定的 4333 ± 30 Ma 玄武岩源区形成的 146Sm-142Nd 年龄的平均值一致。镁套岩浆作用、铁质斜长岩套岩浆作用、urKREEP 形成和母海玄武岩源区形成年龄的相似性意味着产生这些岩石的过程与岩石成因有关。这也意味着早期和晚期月球岩浆海洋在相对较短的时间内形成 镁套岩浆作用、铁质斜长岩套岩浆作用、urKREEP 形成和母海玄武岩源区形成年龄的相似性意味着产生这些岩石的过程与岩石成因有关。这也意味着早期和晚期月球岩浆海洋在相对较短的时间内形成 镁套岩浆作用、铁质斜长岩套岩浆作用、urKREEP 形成和母海玄武岩源区形成年龄的相似性意味着产生这些岩石的过程与岩石成因有关。这也意味着早期和晚期月球岩浆海洋在相对较短的时间内形成