Fig. 4: Model of the effect of the SPA impact on the deep mantle and the subsequent formation of the CE6 basalt.
From: Ultra-depleted mantle source of basalts from the South Pole–Aitken basin
a, Formation of the SPA basin at around 4.33 Ga (ref. 34). Hydrocode models suggest that the upper approximately 250 km of the lunar interior was melted47 and that melts gathered at the bottom of the SPA basin to form an approximately 50-km-thick melt sheet after impact47,48. However, the heating effect of the SPA impact on the underlying mantle remains poorly understood. The dashed lines represent the isotherms of the lunar mantle based on constraints from ref. 48. b, Eruption of the CE6 basalt at around 2.8 Ga (ref. 8). The rheological barrier refers to the base of the lithosphere. Removal of the thermally insulating megaregolith/crust in the SPA basin could have resulted in a faster cooling rate and a deeper rheological barrier49. The mantle source of the CE6 basalt may have undergone melt extraction or it may have remained unaffected.
