A unifying model of crust formation on the Hadean Earth by comparing zircon geochemical signatures with whole-rock petrology
There are only a few locations on Earth known to preserve records of Hadean (>4.0 Ga) crust formation. The >4.0 billion-year-old detrital Jack Hills zircons are the oldest known remnants of felsic crust formation on Earth, however, they represent a fragmentary record—the source rocks from which these zircon crystals were eroded were likely destroyed. Felsic rocks as old as the Jack Hills zircons have not been discovered despite extensive efforts to target the oldest domains of continental crust, and thus we must use this record of zircon minerals, that are without the context of their host rock, to make inferences about Earth’s earliest continents. Here, we propose a model for the formation of Hadean continental crust based on the oldest known terrestrial rock record. We do this by comparing geochemical signatures of the Jack Hills zircons with zircons from the oldest evolved terrestrial crust, the Canadian Acasta Gneiss Complex (4.0-3.6 Ga). The benefit of this comparison is that the Acasta rocks have been extensively characterized and are well-preserved, allowing a comparison to the fragmentary record represented by the Jack Hills zircons.