Wang Ying, Hsu Weibiao, Guan Yunbin
Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210034, China.
The State Key Laboratory of Lunar and Planetary Science/Space Science Institute, Macau University of Science and Technology, Taipa, Macau, China.
Sci Rep. 2019 Apr 5;9(1):5727. doi: 10.1038/s41598-019-42224-8.
Chlorine, an extremely hydrophilic volatile element, provides important information regarding the origin of intrinsic volatiles in the Moon. Lunar apatite was found to have a wider spread of δCl (from -1 to +40‰ versus standard mean ocean chloride) than most terrestrial and chondritic ones (0 ± 0.5‰). However, the provenance of the elevated lunar δCl is still enigmatic. Here we report new isotopic data for H and Cl in apatite from three lunar meteorites and discuss possible mechanisms for Cl isotopic fractionation of the Moon. The apatite grain in Dhofar 458 has an average δCl value of +76‰, indicative of an extremely heavy Cl reservoir in the Moon. Volatile loss associated with the Moon-forming Giant Impact and the formation of lunar magma ocean could account for the large Cl isotopic fractionation of the Moon. The observed HO contents (220-5200 ppm), δD (-100 to +550‰) and δCl values (+3.8 - +81.1‰) in lunar apatite could be understood if late accretion of hydrous components were added to the Moon after the fractionation of Cl isotopes. The heterogeneous distribution of lunar Cl isotopes is probably resulted from complex lunar formation and differentiation processes.
氯是一种极易溶于水的挥发性元素，它为月球内部挥发性物质的起源提供了重要信息。人们发现月球磷灰石的δCl值（相对于标准平均海洋氯化物，范围为-1‰至+40‰）比大多数地球和球粒陨石的δCl值（0±0.5‰）分布范围更广。然而，月球δCl值升高的来源仍然是个谜。在此，我们报告了来自三块月球陨石的磷灰石中氢和氯的新同位素数据，并讨论了月球氯同位素分馏的可能机制。佐法尔458中的磷灰石颗粒平均δCl值为+76‰，这表明月球中存在一个氯含量极高的储库。与月球形成的巨碰撞以及月球岩浆海洋的形成相关的挥发性物质损失，可能是月球氯同位素分馏程度大的原因。如果在氯同位素分馏之后，含水组分后期添加到月球中，则可以解释在月球磷灰石中观测到的氢氧含量（220 - 5200 ppm）、δD值（-100‰至+550‰）和δCl值（+3.8‰至+81.1‰）。月球氯同位素的不均匀分布可能是由复杂的月球形成和分化过程导致 的。
