Subsurface geophysical investigation of the lunar Aristarchus Plateau volcanism system through high resolution GRAIL gravity data inversion

The Aristarchus plateau is an elevated crustal block located at the midset of the Oceanus Procellarum Mare at the northwest near side of the Moon. It has always fascinated lunar observers, because of its strong bright reflectance and its particular structure when observed through a telescope. The plateau exhibits the Vallis Schröteri, the largest sinuous rill on the Moon, the 40km diameter Aristarchus crater as well as the 35km diameter Herodotus crater. The plateau is surrounded by lava flows, and almost completely covered by one of the largest regional pyroclastic deposits. Many scientists associate the structure with an extensive volcanic activity and its formation process remains a subject of debate. The bulk of the studies aiming to understand the Aristarchus plateau volcanism are based on topographic imagery and surface remote sensing mineral analysis. These surface studies can be complemented by subsurface selenophysical models, providing additional interpretative elements to understand the volcanism system of the Aristarchus plateau. In fact, subsurface geological structure densities leave specific signature at the gravity values measured at the surface and it is possible to retrieve an approximative subsurface density models and map the high- and low-densities features through geophysical inversion of the gravity data alone. In this study, we attempt to provide a three-dimensional subsurface density distribution model beneath the Aristarchus plateau through high resolution gravity bouguer anomaly inversion of the Gravity Recovery and Interior Laboratory (GRAIL) data. We used a gravity inversion algorithm based on the frequency-wavenumber domain to estimate the 3D density distribution at the subsurface without the need of an initial density model, then filtered out the lowest densities beneath the Aristarchus plateau to map potential volcanic chambers and other geological anomalies in depth. Inversion results shows a subsurface network of a very low-density material that correlates well with the surface topographic rills, and the Bouguer gravity gradient estimated at the surface. Density cross sections also show a different subsurface structure between the Aristarchus crater and the Herodotus crater, suggesting different formation mechanisms.