Abstract We investigate lunar troctolite petrogenesis with a series of forward models. We simulate the cumulate mantle overturn hypothesis by modeling the adiabatic ascent and decompression melting of primary mantle cumulates produced during differentiation of a lunar magma ocean (LMO). Combined equilibrium and fractional crystallization of candidate liquids generated by the melting model can reproduce the predominant constituents of the lunar magnesian-suite (Mg-suite: troctolites and norites), contrary to previous hypotheses. Model results are consistent with previous studies challenging the proposed and long-standing genetic relationship between Mg-suite and gabbronorites. Our Mg-suite petrogenetic model validates a direct temporal and chemical link between Mg-suite melt production and pressure-release melting of primary LMO cumulates. If so, Mg-suite crystallization ages (4345 ± 15 Ma) can be used to constrain the onset and duration of melting associated with mantle overturn. Based on our model results, we propose an alternative mantle overturn hypothesis whereby upwelling olivine-dominated cumulates experience decompression melting to produce the Mg-suite primary melt (∼1.9% melt at ∼2.1 GPa), but that this melt was extracted from depth akin to lunar picritic glass magmas (low-degree partial melts at depths corresponding to ∼1.3–2.5 GPa). Thus, our revised mantle overturn hypothesis reconciles Mg-suite petrogenesis without the expanse of an olivine-dominated upper mantle (as suggested by the current paradigms, but contradicted by orbital data). This hypothesis supports the presence of a low-Ca pyroxene dominated upper mantle, consistent with mantle stratigraphy constrained by experimental and numerical simulations of LMO differentiation and proposed mantle exposures within impact basins.

中文翻译：

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关于月球圆滑石的岩石成因：对撞击盆地中累积地幔翻转和地幔暴露的新见解

摘要 我们用一系列正演模型研究了月球 troctolite 岩石成因。我们通过模拟月球岩浆海洋 (LMO) 分化过程中产生的初级地幔堆积的绝热上升和减压熔化来模拟堆积地幔翻转假设。由熔化模型生成的候选液体的组合平衡和分步结晶可以再现月球镁套件（镁套件： troctolites 和 norites）的主要成分，这与之前的假设相反。模型结果与先前的研究一致，这些研究挑战了镁组和辉长岩之间提出的和长期存在的遗传关系。我们的 Mg-suite 成岩模型验证了 Mg-suite 熔体生产与主要 LMO 累积的压力释放熔化之间的直接时间和化学联系。如果是这样的话，Mg-suite 结晶年龄 (4345 ± 15 Ma) 可用于限制与地幔翻转相关的熔化的开始和持续时间。根据我们的模型结果，我们提出了另一种地幔翻转假说，即上涌橄榄石为主的堆积物经历减压熔融以产生镁组原生熔体（~2.1 GPa 时~1.9% 熔体），但这种熔体是从类似深度提取的到月球苦味玻璃岩浆（在对应于~1.3-2.5 GPa 深度处的低度部分熔化）。因此，我们修正的地幔翻转假说在没有橄榄石占主导地位的上地幔的情况下协调镁组成岩作用（如当前范式所建议的那样，但与轨道数据相矛盾）。这个假设支持了低钙辉石主导的上地幔的存在，