A4 - Formation and evolution of large impact basins on the moon

Research area: Geophysics

Summary

Large impact basins are the most prominent landforms on the Moon. Basin-forming impactors delivered the majority of matter during the late-accretion phase of the early Earth-Moon system and those events, we have shown, leave a ubiquitous signature in rocks at the surface today. The basins are the oldest remaining morphological traces of this heavy bombardment, representing important time markers of the early history of the Earth-Moon system. In this continuation of our study, we wish to refine our knowledge of the full inventory of lunar impact basins by analysing the near-surface bulk density and porosity using LOLA and GRAIL data and we want to study deep structures in the basins through their Bouguer anomalies. We also want to improve our knowledge of basin formation and timing through understanding the origin of studied surface samples. This will be done by studying how the impact gardening process interacts with the emplacement of the maria (majority of collected samples were close to highland-maria boundary) and by considering the migration of material components carrying more enduring time signatures: namely U-Pb in zircons, in contrast to K-Ar, studied previously. Finally, we want to estimate the energy (and mass) of the impactors as well as understand the character of the lunar environment at the time the basins formed. The project will also significantly contribute to the petrological and geochemical evaluation and radiometric dating of critical lunar samples by providing constraints on the correlation of Apollo specimens to large basin-forming impact events and their ejecting and emplacement history.
 

Bulk density of lunar crust

Fig. 1: Bulk density of the lunar crust using high-resolution gravity of degree and order 1500 (approx. 4 km). Left: near side. Right: far side.

 

Map of the crustal thickness from GRAIL observations

Fig. 2: (a) map of the crustal thickness from GRAIL observations (Wieczorek et al., 2013); (a) comparison of the average crustal-thickness profiles for swath 1 to 4 derived from both the modeled crustal thickness and the crustal thickness derived from GRAIL observation (A). Deviations result from subsequent impacts such as SPA.