The Second Conference on the Lunar Highlands Crust and New Directions. The petrogenesis of impact basin melt rocks in lunar meteorite Shişr 161
The Second Conference on the Lunar Highlands Crust and New Directions. The petrogenesis of impact basin melt rocks in lunar meteorite Shişr 161
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DOI：
10.2138/am.2014.4837
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发表时间：
2014-08
影响因子：
3.1
通讯作者：
A. Wittmann;R. Korotev;B. Jolliff;T. Lapen;A. Irving
中科院分区：
文献类型：
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作者：
A. Wittmann;R. Korotev;B. Jolliff;T. Lapen;A. Irving
本文探讨了未成熟的月球风化角砾陨石Shihşr161的岩石成因，该陨石具有低的不相容元素丰度、长石亲和性和重要的镁组分。我们的方法是在薄片中识别所有大小为0.5毫米的碎屑，表征它们的矿物和熔体成分，并重建它们的主要和次要元素组成。不同结构和成分类型的代表性碎屑中的微量元素含量表明，Shihşr161的碎屑清单以撞击熔体为主，其中包括具有镁铁质矿物组合的缓慢冷却的堆积熔体岩石。次要的外来成分是不相容的富元素熔体球体和玻璃碎片，以及与气体伴生的球状沉淀物。我们对Shiişr161岩石学背景的假设是，结晶的熔融碎屑起源于月球长石高地直径300至500公里的月球撞击盆地熔体板块上部~1公里处。这一假设是基于累积撞击熔体的大小要求，以及我们解释为地幔来源的镁成分的加入。玻璃状熔体很可能是在挖掘熔片组合的过程中形成的，撞击产生了一个直径15公里的陨石坑。Shiişr161的组装发生在这次发掘事件的近端喷射物沉积中。后来撞击到这个喷出的沉积物中，然后从月球发射了shişr161。我们对遥感数据进行的地球化学模拟，结合Shihşr161的岩石学和化学特征，揭示了月球表面靠近死亡前黎曼-法布里盆地的优选物源。
Abstract This study explores the petrogenesis of Shişr 161, an immature lunar regolith breccia meteorite with low abundances of incompatible elements, a feldspathic affinity, and a significant magnesian component. Our approach was to identify all clasts >0.5 mm in size in a thin section, characterize their mineral and melt components, and reconstruct their bulk major and minor element compositions. Trace element concentrations in representative clasts of different textural and compositional types indicate that the clast inventory of Shişr 161 is dominated by impact melts that include slowly cooled cumulate melt rocks with mafic magnesian mineral assemblages. Minor exotic components are incompatible-element-rich melt spherules and glass fragments, and a gas-associated spheroidal precipitate. Our hypothesis for the petrologic setting of Shişr 161 is that the crystallized melt clasts originate from the upper ~1 km of the melt sheet of a 300 to 500 km diameter lunar impact basin in the Moon’s feldspathic highlands. This hypothesis is based on size requirements for cumulate impact melts and the incorporation of magnesian components that we interpret to be mantle-derived. The glassy melts likely formed during the excavation of the melt sheet assemblage, by an impact that produced a >15 km diameter crater. The assembly of Shişr 161 occurred in a proximal ejecta deposit of this excavation event. A later impact into this ejecta deposit then launched Shişr 161 from the Moon. Our geochemical modeling of remote sensing data combined with the petrographic and chemical characterization of Shişr 161 reveals a preferred provenance on the Moon’s surface that is close to pre-Nectarian Riemann-Fabry basin.