Compositional Variability of 2.0‐Ga Lunar Basalts at the Chang'e‐5 Landing Site

Abstract

AbstractChina's Chang'e‐5 (CE‐5) mission successfully returned a total of 1.731 kg of lunar material from the north‐eastern Oceanus Procellarum region. Young (∼2.0 Ga) ages were reported from the CE‐5 basalts. However, there are controversies on whether they are low‐Ti or high‐Ti mare basalt type. Here, we report the results of a comprehensive petrographic, elemental, and Pb isotopic investigation on a 17.6 mg CE‐5 basalt clast (CE5C0000YJYX048). By combining high‐resolution X‐ray tomography of the clast and microbeam (scanning electron microscope SEM, electron probe microanalyzer EPMA) analyses of mineral grains peeled off the clast surface, we derived the bulk clast chemical composition with a very small sample consumption (i.e., <3 mg). The poikilitic clast has a bulk TiO2 content of 3.78 ± 1.01 wt%, which is representative of a low‐Ti basalt end‐member in the lunar mare basalts samples. Furthermore, the pyroxene in the studied clast is dominantly pigeonite, in contrast to other reported CE‐5 samples where augite is the dominant pyroxene mineralogy. Despite these compositional peculiarities, in situ secondary ion mass spectrometer dating yielded a Pb‐Pb age of 2,040 ± 22 Ma for the fragment, which is consistent with ages reported from other CE‐5. Based on the chemical and age data analyzed in this study, it can be concluded that the lunar basalts obtained from the CE‐5 mission originated from a low‐Ti mare basalt‐type source. The mineral composition of the mare basalt clast studied, which is dominated by pigeonite, fayalite, and anorthite, likely resulted from late‐stage magmatic crystallization when the magma was enriched in Fe.