The Apollo 15 mission returned various samples of regolith breccias, typical lunar rocks lithified by impact events on the Moon’s surface. Here we report our observations on shock features recorded in a section of the Apollo Sample 15299. We observe the presence of ferropericlase crystals confined in a shock-melt pocket and conclude that their formation is related to a shock-induced incongruent melting of olivine. While predicted by experiments, this phenomenon has never been observed in a natural sample. The incongruent melting of olivine provides an important signature of melting under high-pressure conditions and allows for estimating the pressure-temperature (P-T) experienced by the studied sample during the impact event. We infer that the fracture porosity that likely characterized the studied sample prior to the shock event critically affected the P-T path during the shock compression and allowed the studied sample to be subjected to elevated temperature during relatively low shock pressures.

中文翻译：

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阿波罗 15 号风化层角砾岩为橄榄石不一致熔融提供了第一个自然证据

阿波罗 15 号任务返回了各种风化层角砾岩样本，这是典型的月球岩石，因月球表面的撞击事件而石化。在这里，我们报告了我们对 Apollo 样品 15299 的一部分中记录的冲击特征的观察。我们观察到限制在冲击熔化袋中的铁方镁石晶体的存在，并得出结论，它们的形成与冲击引起的橄榄石不一致熔化有关。虽然通过实验预测，但从未在自然样本中观察到这种现象。橄榄石的不一致熔融提供了高压条件下熔融的重要特征，并允许估计所研究样品在撞击事件期间所经历的压力-温度 (PT)。