Nelson William S, Hammer Julia E, Shea Thomas, Hellebrand Eric, Jeffrey Taylor G
Department of Earth Sciences, School of Ocean and Earth Science and Technology (SOEST), University of Hawaii at Mānoa, Honolulu, HI, USA.
Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands.
Nat Commun. 2021 Dec 14;12(1):7054. doi: 10.1038/s41467-021-26841-4.
The evolution of the lunar interior is constrained by samples of the magnesian suite of rocks returned by the Apollo missions. Reconciling the paradoxical geochemical features of this suite constitutes a feasibility test of lunar differentiation models. Here we present the results of a microanalytical examination of the archetypal specimen, troctolite 76535, previously thought to have cooled slowly from a large magma body. We report a degree of intra-crystalline compositional heterogeneity (phosphorus in olivine and sodium in plagioclase) fundamentally inconsistent with prolonged residence at high temperature. Diffusion chronometry shows these heterogeneities could not have survived magmatic temperatures for >~20 My, i.e., far less than the previous estimated cooling duration of >100 My. Quantitative modeling provides a constraint on the thermal history of the lower lunar crust, and the textural evidence of dissolution and reprecipitation in olivine grains supports reactive melt infiltration as the mechanism by which the magnesian suite formed.
月球内部的演化受到阿波罗任务带回的镁质岩套样本的限制。调和该岩套矛盾的地球化学特征构成了月球分异模型的可行性测试。在此，我们展示了对典型样本——橄长岩76535进行微观分析的结果，该样本此前被认为是从一个大型岩浆体缓慢冷却形成的。我们报告了晶内成分的不均匀程度（橄榄石中的磷和斜长石中的钠），这与在高温下长时间停留根本不一致。扩散年代测定表明，这些不均匀性在岩浆温度下不可能存在超过约2000万年，即远低于先前估计的超过1亿年的冷却持续时间。定量建模对月球下地壳的热历史提供了限制，橄榄石颗粒中溶解和再沉淀的结构证据支持反应性熔体渗透是镁质岩套形成的机制。
