Bowing
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Planets
The geological history of the Moon speaks of a time older than most of the Earth’s surface. The relatively small size of our satellite led to an accelerated geological demise dominated by progressive cooling over the last 3 billion years or so. However, the earlier history of the Moon likely featured global expansion driven by large heat production and reorganization of the Moon’s interior. Randomly oriented gravity lineaments present evidence of that period of expansion when the Moon’s lithosphere may have cracked and magma would have been intruded as tabular bodies in its crust. However, finding the age of these gravity features is challenging.
Remarkably, one of these lineaments appears truncated by the 171-km-diameter Rowland crater, which is typically seen as evidence that the lineament is older than the crater. However, Nishiyama et al. [2024] show that a crater of that size cannot erase the signature of a preexisting tabular intrusion. This finding implies that the intrusion is actually younger than the crater and that its emplacement was influenced by the presence of the crater. In contrast, a separate gravity lineament crosses the similar-sized Roche crater with only a small decrease in amplitude, consistent with the predicted effect of the crater on a preexisting gravity anomaly.
The authors also document exposures of high-calcium pyroxene around Roche crater but not Rowland crater, consistent with the idea that the gravity lineament corresponds to an intrusion rich in this mineral and partially excavated by the impact process. As the two craters have similar ages, this study demonstrates that the emplacement of linear gravity anomalies, and thus expansion of the Moon, lasted into the Imbrian Epoch, later than deduced from earlier studies. It also implies that the material in the intrusions is similar to that in the later volcanic deposits that form lunar maria.
Citation: Nishiyama, G., Morota, T., Namiki, N., Inoue, K., & Sugita, S. (2024). Lunar low-titanium magmatism during ancient expansion inferred from ejecta originating from linear gravity anomalies. Journal of Geophysical Research: Planets, 129, e2023JE008034. https://doi.org/10.1029/2023JE008034
—Laurent G. J. Montési, Former Editor-in-Chief, JGR: Planets
