The Thermal Evolution of Mercury Over the Past ∼4.2 Ga as Revealed by Relaxation States of Mantle Plugs Beneath Impact Basins

Abstract

AbstractWe investigated the relaxation states of 11 large impact basins on Mercury based on an updated crustal thickness map, finding that the pre‐Tolstojan basins have comparable instead of varied relaxation states, suggesting that Moho temperature (TempMoho ) did not decrease substantially from ∼4.2 to 3.8 Ga. At the same time, mantle uplift beneath the Caloris basin is the least degraded, therefore implying a sharp decrease of TempMoho ∼ 3.8 Ga. These findings contrast with our thermal evolution models that predict a fast decrease of TempMoho between ∼4.2 and 3.8 Ga. Therefore, the discrepancies in the cooling rate suggest that the relatively elevated bombardment history between ∼4.2 and 3.8 Ga might have input additional energy to Mercury and substantially decreased the cooling rate.