Compton–Belkovich Volcanic Complex (CBVC): An ash flow caldera on the Moon

Abstract

Volcanic calderas are found on Earth, Mars, Venus and Io, and are rare, but unique volcanic structures in the Solar System. Compton–Belkovich Volcanic Complex (CBVC) (60.5°N–99.5°E) on the far side of the Moon is a unique non-mare feature due to its evolved lithology, regional tectonic setting, its location being near the north pole, far from the Procellarum KREEP Terrane (PKT) and its recent association with endogenic water. High-resolution remote sensing observations of several structural features at CBVC such as ring faults, radial faults, fractures manifested by various morphological features such as domes of varied sizes and shapes and pyroclastic ash flows characterize it to be a volcanic caldera. The loading of Humboldtianum basin with basalts and subsequent development of extensional structures outside it along with high-thorium anomaly and resulting silicic volcanism at CBVC producing central collapsed caldera could be considered as an analogy to silicic calderas on Earth formed in extensional tectonic regime even though the tectonic processes involved in these two cases are entirely different, the former being impact-related, whereas the latter involves rifting or hotspot-related activities associated with extensional plate tectonics. Presence of high-reflectance feature and its extension to the east–southeast of the topographic expression and its relation with pyroclastic dispersal have been supported by radar-based Mini-RF observations and high-resolution LROC-NAC imagery. It suggests the presence of a late-stage fine pyroclastic layer within the CBVC region. The diverse volcanic features that exist at the studied site indicate a series of deformation and eruption events associated with silicic magmatism and thus, CBVC could be considered as an ash flow caldera on the Moon. Here, we present a detailed appraisal of various volcanic and structural features detected at CBVC through high-resolution optical as well as radar observations. Based on the previous and present studies, an evolutionary model of the area has been proposed and the petrological implications of silicic magmatic activity, its manifestation, evolution and association with endogenic water have been discussed.