Abstract Rare-element granitic pegmatites enriched in lithium are economically important hosts for the lithium aluminosilicates, spodumene and petalite. Most spodumene and petalite crystallize from the pegmatite melt, depending on pressure and temperature. This paper reports the rare occurrence of petalite postdating the subsolidus stage in spodumene pegmatites within the ~2.02 Ga Vredefort impact structure, the largest, oldest and most deeply eroded meteorite impact structure currently known on Earth. The studied spodumene-bearing pegmatites postdate the deformation fabric in the surrounding amphibolites of the granitoid-greenstone terrane. Impact-related veins of fragment-rich pseudotachylites cut across the pegmatites. Spodumene, albite and quartz constitute the primary mineral assemblage of the pegmatites. Muscovite is late magmatic and contains inclusions of spodumene and albite. During the subsolidus stage, K-feldspar replaced spodumene and albite during pervasive metasomatic alteration. Samples collected closer to the pseudotachylites show reaction textures between spodumene and quartz without the involvement of muscovite. Raman spectroscopy and microprobe analyses show that the reaction textures consist of quartz and petalite. Unlike spodumene, petalite does not show a replacement by K-feldspar. The 40Ar/39Ar muscovite age of 2027 ± 8 Ma coincides with the timing of the meteorite impact and documents its effect on the spodumene pegmatites. We suggest that the formation of petalite after spodumene was related to heating, which was generated in the target rocks by the post-shock thermal event. Thus, the unique conditions associated with the meteorite impact can not only result in the formation of rare minerals in the target rocks, but can also account for rare scenarios resulting in phases that would not otherwise form in nature.

中文翻译：

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由于约 2.02 Ga 陨石撞击南部非洲 Vredefort 结构，伟晶岩中的辉长岩年代后期锂辉石

摘要 富含锂的稀有元素花岗岩伟晶岩是铝硅酸锂、锂辉石和透锂长石的重要经济主体。大多数锂辉石和透辉石从伟晶岩熔体中结晶，这取决于压力和温度。本文报告了在~2.02 Ga Vredefort 撞击结构内锂辉石伟晶岩中亚固相线阶段后罕见的花瓣岩，这是目前地球上已知的最大、最古老和侵蚀最深的陨石撞击结构。所研究的锂辉石伟晶岩晚于花岗岩-绿岩地体周围角闪岩中的变形构造。与撞击相关的富含碎片的伪速晶岩脉穿过伟晶岩。锂辉石、钠长石和石英构成伟晶岩的主要矿物组合。白云母是晚岩浆岩，含有锂辉石和钠长石包裹体。在亚固相阶段，钾长石在广泛的交代蚀变过程中取代了锂辉石和钠长石。收集的更接近伪速晶石的样品显示锂辉石和石英之间的反应结构，而没有白云母的参与。拉曼光谱和微探针分析表明反应结构由石英和透长石组成。与锂辉石不同的是，透锂长石没有被钾长石替代。2027 ± 8 Ma 的 40Ar/39Ar 白云母年龄与陨石撞击的时间相吻合，并记录了其对锂辉石伟晶岩的影响。我们认为锂辉石后透辉石的形成与加热有关，加热是由震后热事件在目标岩石中产生的。因此，