The scale of late-stage basalts in Mare Imbrium

Abstract

The basaltic volcanism is one of the most important geologic processes of the Moon, which reveals its interior evolution. As lunar basalts are formed from the partial melting of mantle materials, the volume of basalts reflects the size and the degree of partial melting of the source region. The Eratosthenian volcanism deposited large scale of high/medium-Ti basalts in Mare Imbrium, which could provide key information for studying the late-stage lunar volcanism in Mare Imbrium. Using a variety of remote sensing data and techniques (topographic profile and crater excavation method), we studied the scale of the Upper and Lower Eratosthenian (UEm and LEm) basalts in Mare Imbrium. The results show that the UEm is 13–33 m thick with several layers of individual lava (7–15 m) inside, and the thickness of LEm is 14.49–43.61 m. Adding the volume of exposed UEm basalts (~539.3 km3), the volume of exposed LEm basalts (~5198 km3) and the volume of young basalts underlying UEm (~55 6.2 km3) together, the total volume of the late-stage basalts in Mare Imbrium is ~6479 km3. It’s far lower than that of the Schaber’s estimation (~4×104 km3). The volume of the exposed UEm basalts accounts for only about 1/8 of the volume of the exposed LEm basalts, which means that basaltic eruption decreases with time during the Eratosthenian Period in Mare Imbrium. Besides, we estimated the decrease of the areal flux of Em5–Em7: Em5 (249.56 km2/Ma), Em6 (39.49 km2/Ma) and Em7 (46.89 km2/Ma). These results indicate that the basaltic volcanism receded with time during the Eratosthenian Period.