Emergence Of Continents Above Sea-Level Influences Sediment Melt Composition

The Archean-Proterozoic transition heralded a number of fundamental changes on Earth, including the oxygenation of the atmosphere, a marked emergence of continents above sea-level, and an increase in delta O-18 of felsic magmas. The potential drivers for the latter are changes in the composition of supracrustal material or increased crustal reworking. Although the onset of subduction-induced continental collision and associated enhanced crustal recycling could produce high-delta O-18 felsic magmas, temporally constrained zircon delta O-18 reveals an increase in delta O-18 at similar to 2.35 Ga that predates the oldest widely recognized supercontinent. In this work, we use the O and Hf isotope ratios of magmatic zircon crystals in Archean and Proterozoic sediment-derived granitoids of the North China Craton to track the incorporation of supracrustal material into magmas. The results are consistent with a Paleoproterozoic increase of continental freeboard producing sedimentary reservoirs with comparatively elevated delta O-18 that subsequently partially melted to generate the granitoids.