Density and lithospheric thickness of the Marius Hills shield volcano on the Moon

Marius Hills is a large volcanic complex on the Oceans Procellarum of the lunar nearside. Numerous volcanic features, including domes, cones, and rilles occur in this region. Due to limitations in lunar remote sensing data, most previous studies on this region focused on its morphological and geochemical properties but little was known about the subsurface and interior structures of this volcanic complex. Knowledge of the local crustal density is meaningful to both determine the composition for this volcanic complex and understand the crustal evolutionary history for this region. Constraining the lithospheric thickness in this region is helpful to estimate the heat flux at the time of volcanic loading, which is a crucial parameter to study the thermal evolutionary history of the nearside mantle. Here, we applied a localized gravity and topography admittance analysis for the Marius Hills region to constraint its crustal density and lithospheric thickness. The gravity filed is modeled using a thin elastic lithspheric model that considers both surface and subsurface loads. Localized admittance and correlations spectra are used to constrain these modeled parameters. The best-fit crustal density in our model is ~3040 kg m - 3 , which is much higher than the average lunar crustal density as 2550 kg m - 3 , indicating that magma chambers or sills has intruded to the shallow crust and/or that intrusive magma has filled up the porous subsurface crust. The total volume of basalts emplaced in the Marius Hills region is ~2.9×10 4 km 3 , suggesting that Marius Hills is a major volcanic center in the Oceanus Procellarum. The best-fit lithospheric thickness of this region is constrained to be as small as ~4 km, indicating that a significant amount of heat production elements have concentrated in this region during the formation of the volcanic complex. This result is consistent with the previous spectral studies that heat production elements (such as thorium) are more abundant in the Oceanus Procellarum.