Evolution of seawater continentally-sourced Nd isotopic composition prior to and during the Great Oxidation Event

An ongoing debate concerns what initiated the Great Oxidation Event (GOE) and associated glaciation between similar to 2.45 and 2.2 Ga. One possibility is the emergence of continental landmasses and the increase of subaerial igneous province weathering during the Late Archean. We test this hypothesis in the Hamersley Basin by reporting Nd-isotope data from a succession of iron formations (IFs), mudstone/siltstones and glacial diamictites from the Boolgeeda Iron Formation and overlying Turee Creek Group deposited during the GOE. In a Sm-147/Nd-144 - epsilon Nd-(t) diagram, the data define a negative trend indicating the contribution of a high epsilon Nd-(t) similar to +3 hydrothermal component and a strongly negative epsilon Nd-(t) similar to -9 crustal component, which is compatible with the Nd-isotope composition of the upper continental crust but also of the underlying felsic volcanics of the Woongarra Rhyolite and crustally-contaminated mafic volcanics of the Fortescue Group. A less pronounced negative trend originating from the same hydrothermal source but correlated with non-contaminated ultramafic Fortescue volcanics (epsilon Nd-(t) similar to -2) is observed for the older Joffre, Dales Gorge and Marra Mamba IFs. As Nd-isotopes are not sensitive to redox conditions, the major shift of Nd-isotopic compositions at similar to 2.45 Ga cannot be linked to a change in the weathering regime, rather to a change in the nature of the continental surface exposed to weathering. One explanation is that the Sm-Nd sources for sediments deposited before and during the GOE were locally derived from the underlying subaerial LIPs, reflecting a change in the geodynamic context of deposition and/or hydrographic network and catchment areas. Another explanation could be a significant change in the nature of fluid-rock interactions due to the increase role of weathering processes associated with the emergence of continental landmasses. Additional Nd isotope data from different cratons worldwide are needed, however, to infer as to whether or not the marked shift in Nd isotope compositions recorded in the Turee Creek Group reflect a change in the global hydrological cycle. Our data support the role of large subaerial magmatic provinces as triggers of the rise of atmospheric oxygen and the onset of glaciations at the beginning of the Proterozoic.

Automated summary

The study examines the hypothesis that the emergence of continental landmasses and increased subaerial igneous province weathering triggered the Great Oxidation Event. The Nd-isotope data confirm the influence of crustal and hydrothermal components during this period, suggesting a significant role in the rise of atmospheric oxygen and the onset of glaciations.