Modeling an impact-generated Hadean felsic crust

Abstract:

Exploring Earth’s “Dark Ages” (the first 500 Myr) was identified by the National Research Council as one of the fundamental questions driving the geological and planetary sciences. Due to Earth’s constant resurfacing, any presence of early crust during the Hadean has inevitably been recycled; leaving no trace of information regarding its composition or abundance. Although modern continental crust formation tends to be associated with plate tectonics, in the absence of a plate tectonic regime a different mechanism is required to produce an evolved crust. One such possible mechanism on early Earth is the processing of the surface through impact melting. Investigating the geochemistry within multiple portions of fractionated impact melt sheets from preserved terrestrial craters, we can explore how the crust can be processed into more evolved compositions through impact events. By scaling the enrichment of isotopic and bulk chemical analyses from these terrestrial impact melt sheets we can apply the estimated size-frequency distribution of early impactors and fractionation parameters of the resulting impact melt through hydrocode modeling to examine the expected enrichment of a primitive early crust. This correlation can increase our understanding of early planetary formation and accretion during the first 500 Myr and provide a mechanism for the formation of a felsic component during the Hadean and in the absence of a plate tectonic regime. Preliminary results suggest abundant evolved crust due to impact melting is generated early in the Hadean, adding evidence to support the paradigm shift in our understanding of Earth’s formation.