Fig. 4: The geological processes involved in regolith evolution at the CE-6 landing site.
From: Impact-induced mixing generated the stratified soils of the Lunar South Pole Aitken Basin
The SPA impact melt sheet formed around 4.25 Ga46 and experienced fractional crystallization, producing stratified noritic layers. At ~3.98 Ga54, the Apollo impact event excavated these differentiated products. Around the same time, contemporaneous large-scale basin-forming events in the lunar highlands re-deposited crustal materials into the SPA basin floor. Subsequent impacts within the SPA dispersed noritic ejecta across the Apollo basin floor. This era also marked the onset of multiple episodes of mare volcanism. By ~3.3 Ga, low-Ti mare basalts were emplaced in the southern portion of the basin, followed by the accumulation of a thin paleo-regolith layer. At ~2.8 Ga, emplacement of the CE-6 basalts occurred. The overlying regolith subsequently evolved through a range of surface processes, including (1) the development of an early megaregolith; (2) physical mixing with noritic ejecta from Chaffee S crater; (3) fragmentation of fresh ejecta rocks by small-scale impacts at the landing site; (4) episodic replenishment of coarse regolith from nearby craters; and (5) progressive space weathering. Subsurface stratigraphy in the CE-6 landing site is modified from Gou et al.55.
