Effects of late accretion impacts on an argon-constrained crustal growth model

Abstract

As an important reservoir for incompatible elements, the growth of the continental crust profoundly influenced the composition of the mantle and the atmosphere. The co-evolution of the continental crust, mantle, and atmosphere throughout Earth history can be traced through the transfer of argon and potassium between these three reservoirs. While many argon-constrained crustal growth models have been proposed, none of them consider the effect of late accretion (bombardment by leftover planetesimals in the several hundred million years after the Moon formed) in detail. Our model is the first of its kind to simulate both the volatile delivery and the atmospheric erosion by impacting planetesimals. Whereas the relative fraction of impactor-derived argon in the present-day atmosphere depends on the assumed impactor composition and the starting atmospheric mass, the present-day atmospheric argon originates largely from mantle degassing and crustal processing. For a range of impact parameters, our model results indicate that the early rapid growth of continental crust is required to satisfy the argon budget of the mantle and atmosphere.