The cause of chemical depletion and isotopic fractionation of moderately volatile elements (MVEs) in the Moon is a long-standing problem. Here we examine MVE isotopic fractionation during Moon formation using potassium as a primary example. We show that the degree of isotopic fractionation due to evaporation of the lunar magma ocean (LMO) depended critically on the vapor pressure above the LMO. Based on our analysis of evaporation and escape of the resulting rock-vapor atmosphere, LMO evaporation alone could not have caused the observed MVE isotopic compositions. The combination of exposure of the liquid of the LMO to the surface for on the order of 10 2 –10 3 yr, near-equilibrium evaporation at the melt surface, and hydrodynamic escape facilitated by proximity of the Earth leads to no resolvable isotope or elemental fractionation. This study provides a basis for the simplifying assumption that rock vapor immediately above a magma ocean will be in thermodynami...

中文翻译：

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月球岩浆海洋的蒸发不是月球中度挥发性元素分馏的机制

月球中的中等挥发性元素（MVE）的化学消耗和同位素分馏的原因是一个长期存在的问题。在这里，我们以钾为主要实例，研究月球形成过程中的MVE同位素分馏。我们显示，由于登月岩浆海洋（LMO）的蒸发，同位素分级的程度主要取决于LMO上方的蒸气压。根据我们对所产生的岩石-蒸气气氛的蒸发和逸出的分析，仅靠LMO蒸发不可能导致观察到的MVE同位素组成。LMO液体暴露于表面的时间约为10 2 –10 3 yr，熔体表面接近平衡的蒸发，以及由于地球附近而促进的流体动力逸出，这些都不会导致可分辨的同位素或元素分馏。