Sub‐Volcanic Structure Beneath Marius Hills, Moon, Inferred From Vent Distribution

Abstract

Marius Hills is a volcanic region located slightly north of the equator on the west side of the nearside of the Moon (Figure 1). It comprises more than 200 small-to-mid-sized volcanic domes and cones (diameter commonly <15 km, occasionally reaching 25 km) and 20 sinuous rilles, covering an area of ca. 35,000 km 2 near the center of Oceanus Procellarum (Deutsch et al., 2019;Lawrence et al., 2013;Whitford-Stark & Head, 1977). This region has been interpreted as either a shield volcano (Spudis et al., 2013) or a volcanic complex lacking a central zone of magma accumulation at depth . Both, low-resolution Lunar Prospector gravity data and high-resolution data from the Gravity Recovery and Interior Laboratory (GRAIL) mission yield two positive anomalies (>150 mGal contrast) in the Marius Hills region (Deutsch et al., 2019;Evans et al., 2016;Huang et al., 2014;Kiefer, 2013). The two main zones of high-density material were interpreted by Kiefer (2013) as the magma chambers that fed the overlying volcanism. This interpretation was advocated by Zhang et al. (2018). As pointed out by Deutsch et al. (2019), however, the presence of a unique magma chamber beneath each of the prominent gravimetric anomalies is weakened because it requires a cumulative thickness of 10 km, which is unlikely to exist given the lack of a corresponding topographic uplift, especially on the south. Thus, instead of the presumed magma chambers, the positive Bouguer anomaly was interpreted by Deutsch et al. (2019) as the result of the presence of a dyke swarm that could extend from the crust-mantle boundary to either the present-day surface of the Moon or to a previous surface marked by the bottom of a pre-existing impact structure.