Insights Into Lunar Basaltic Volcanism From Mare Domes Superposed by Ring-Moat Dome Structures (RMDSs) in Mare Tranquillitatis

Abstract

Mare domes (interpreted to be a type of shield volcano) represent one important endmember of a variety of volcanic edifices occurring across the volcanic plains on the Moon, whereas Ring-Moat Dome Structures (RMDSs) are interpreted to reflect the thermodynamic behavior of plain-forming mare flows during their emplacement and cooling. A comprehensive study of the direct association between mare domes and RMDSs can not only provide deep insights into their formation mechanisms but also yield key information on the nature of mantle sources. We characterized a total of 200 mare domes and more than 6,400 RMDSs within Mare Tranquillitatis using multiple sets of imagery and topography data. RMDS-bearing domes (80 out of 200) are on average larger than those hosting no RMDSs (average diameter 10.2 vs. 5.5 km) and have lower height/diameter (H/D) ratios (0.01 vs. 0.02) and flank slopes (1.2° vs. 2°). We attribute the presence of RMDSs on some domes to be due to relatively higher effusion rates forming longer thinner flows, producing favorable conditions for the formation of RMDSs. The average diameter of the RMDSs on mare domes (226 m, n = 1,027) appears to be slightly smaller than those located in mare plains (256 m, n = 527). This may be due to slope effects and that the relatively thicker off-dome part of flows undergoes a relatively higher degree inflation process, producing slightly larger RMDSs. We adapt the RMDS-formation theoretical model to shallow subcrustal magma reservoir model to account for the Tranquillitatis dome-RMDS associations.