Paleoproterozoic increase in zircon δ18O driven by rapid emergence of continental crust

Abstract

Numerous geologic proxies for Earth system processes track dramatic changes at the atmosphere-lithosphere or atmosphere-ocean interface during the early Paleoproterozoic Era. The presence of a geodynamic driver for these changes and how this might have affected the deeper lithosphere is more cryptic. Here we present temporally constrained δ 18 O and εHf in detrital zircon from Paleoproterozoic sedimentary successions in Western Australia and Canada that chart a rapid change in the oxygen isotopic composition from <7.5‰ prior to Great Oxidation Event (GOE) to 9–11‰ by ∼2.3 Ga. Intriguingly, we show that the timing of this zircon δ 18 O isotopic shift directly coincides with the GOE and the rapid development of continental freeboard evidenced by the shift from predominantly subaqueous to subaerial large igneous provinces and a rapid decrease in Δ 17 O in shale. Importantly, no correlation exists between zircon δ 18 O and εHf or to known periods of enhanced tectonic reworking of sedimentary material (e.g. ∼2.3–2.2 Ga tectono-magmatic lull). We propose that the development of continental freeboard led to the appearance of an isotopically distinct sedimentary reservoir with high δ 18 O that was incorporated into subduction zone magmas. The sedimentary contamination of subduction zone magmas led to a globally rapid change in average continental composition as recorded by δ 18 O in zircon grains.