The Cauchy 5 small shield volcano, located in Mare Tranquillitatis (7.169°N, 37.592°E), is a circular mound about 5-6 km in base diameter and ~40 m high at its summit. At the same time, the lunar shield volcano Cauchy-5 is the only known example containing two different types of Irregular Mare Patches (IMPs) in very close association: a large "mound-type" irregularity is distributed inside the top crater. Lunar sea patches (Figure 1C), and hundreds of smaller " pit-type" irregular lunar sea patches are distributed along the northern flanks and south-eastern crater crater (Figure 1D, E).

Associate researcher Le Qiao from the planetary science group used high-resolution images of the lunar surface and topographic data to analyze the geological background information and geological features of Cauchy 5, combined with the latest theoretical analysis of lunar magmatism, A four‐phase lunar magma ascent/eruption model is proposed. The model shows that in the most advanced stage of the eruption, high-porosity magma overflowed to the outside of the crater and covered the flanks of the shield volcano with a thin lava flow. Subsequent impact collapse formed a "sag" irregularity. The lunar sea patches, and the thick, highly porous lava flow filled inside the crater formed "hill-shaped" IMPs. The statistical age of the unusually young impact craters inside and on the flanks of the Cauchy 5 may be caused by the impact of the high-porosity target on the impact crater.

The research results were published in Journal of Geophysical Research: Planets.

Qiao, L., Head, J. W., Wilson, L., Ling, Z., 2020. The Cauchy 5 small, low-volume lunar shield volcano: Evidence for volatile exsolution-eruption patterns and type 1/type 2 hybrid irregular mare patch formation. Journal of Geophysical Research: Planets, 125, e2019JE006171, doi: 10.1029/2019JE006171.

Link: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JE006171

This work is partly supported by the National Natural Science Foundation of China (Nos. 41703063, 11941001, and 41972322), a Pre‐research Project on Civil Aerospace Technologies No. D020205 funded by CNSA and Qilu (Tang) Young Scholars Program of Shandong University, Weihai (2015WHWLJH14).

Figure 1. The lunar shield volcano Cauchy 5: (A) LROC NAC image (frame M119815703), (B) LROC NAC DTM topography, (C) "hill-shaped" IMPs shield volcano summit pit crater, (D) Detailed image of the northern shield flank pit‐type IMP occurrences and (E) the southeast crater rim pit‐type IMP occurrences. The white dashed box in Figure A delineates the scope of Figure C-D.