Emergence of continents above sea‐level influences sediment melt composition

Abstract

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 δ 18 O 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 highδ 18 O felsic magmas, temporally constrained zircon δ 18 O reveals an increase in δ 18 O at ~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 sedimentderived 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 δ 18 O that subsequently partially melted to generate the granitoids.

Composition of continental crust altered by the emergence of land plants

“…The widespread development of post-Archean continental freeboard 46,47 and the concomitant increase in continental weathering is inferred from an increase of mudrock δ 18 O throughout the Proterozoic 28 ; no equivalent secular change is apparent in post-Proterozoic mudrocks (Extended Data Fig. 1).…”

Whole-rock geochemistry and zircon O-Hf isotope compositions of ca. 2.35 Ga strongly peraluminous granites: Implications for increase in zircon δ18O values during the Paleoproterozoic

“…SPGs have recently been the focus of study to understand how surface weathering across the Archean-Proterozoic boundary may have changed and been imprinted on the chemistry of igneous rocks (Bucholz and Spencer, 2019;Bindeman, 2021;Libemann et al, 2021a, b). For example, Liebmann et al (2021a) documented a ~3.5‰ increase in zircon δ 18 O of SPGs from the late Neoarchean (~2.5 Ga) to late Paleoproterozoic (~1.93 Ga).…”