[M-IS16] Planetary Volcanology

[MIS16-P02] Basaltic intrusions in the lunar lower crust

*Tomokatsu Morota¹ (1.Department of Earth and Planetary Science, The University of Tokyo)

Keywords:Moon, mare volcanism, intrusion, crust

According to models of magma ascent on the Moon (Head and Wilson 1992), due to the higher liquidus densities of basaltic magmas compared to that of the anorthositic crust, magmas could have been extruded to the surface preferentially in thin areas of the anorthositic crust. This is supported by the relationship between the crustal thickness and magma volumes within impact basins, suggesting that magma eruption could only occur in basins with small minimum crustal thicknesses (MCTs) (Taguchi et al. 2017). On the farside, the critical crustal thicknesses (Hc) is estimated to be ~12 km from the farside mare basin with the largest MCT (Ingenii) and the farside non-mare basin with the smallest MCT (Planck). On the nearside, the critical crustal thicknesses for magma eruption might be thicker than that of the farside. The mare basins, Nubium and Tranquillitatis, have a MCT of ~15 km, and the only nearside non-mare basin investigated here is Mutus-Vlacq, which has a MCT of ~20 km. Therefore, the critical crustal thickness of the nearside for magma eruption is Hc = 15–20 km.
In thicker crustal areas, it is expected that magma could not erupted to the surface and intruded in the crust. In this study, we investigated depth contaminated by basaltic intrusions using FeO contents of central peaks of large craters (Lemelin et al. 2015). Th results show that the lower part of crust is partially contaminated by basaltic intrusion with depth of 20-30 km. The areas with crustal thickness thicker than 30 km remain pristine crustal rocks, consistent with the global occurrence of pure anothosite (Ohtake et al. 2009; Yamamoto et al. 2012).