The voluminous 2.81–2.71 Ga Goldfields Tholeiitic Super Event: Implications for basin architecture in the Yilgarn Craton and global correlations

Abstract

The time-interval between 2.8 and 2.7 Ga is associated with the worldwide appearance of thick tholeiite-komatiite successions. However, their origin and affiliation, if any, is poorly understood. The Eastern Goldfields Superterrane of the Yilgarn Craton, Western Australia, is dominated by the 2.7 Ga Kalgoorlie and Kurnalpi terranes, both of which consist of well-preserved mafic-ultramafic volcano-stratigraphy. On a local scale, these supracrustal sequences permit reconstruction of volcano-sedimentary environments, which provides important constraints to the local conditions of magmatism and/or deposition. Regionally, these observations can be used to test correlations between greenstone belts, constrain basin architecture and the extent of volcanism. Studies of this nature provide important insights to global, Archean volcano-sedimentary processes.Here we present an integrated field, geochemical and U-Pb geochronological study from the well-preserved West Laverton Greenstone Belt in the Kurnalpi Terrane and compare it to the relatively well constrained Kalgoorlie Terrane. The sequence comprises three volcanic ‘events’ consisting dominantly of low-Th tholeiitic basalt and komatiite derived from depleted mantle sources. Magmatism commenced after 2854 ± 4 Ma and ceased by 2717 ± 4 Ma. Prominent banded iron formations separate volcanic cycles, indicating an overall quiescent subaqueous setting.The West Laverton Sequence is correlated with volcanic events in the neighbouring Kalgoorlie Terrane, where pre-existing basement with remarkably similar character is documented near Norseman, over 360 km away. Both terranes contain basal paragneiss (2.96–2.93 Ga) and epiclastic sediments (∼2.93–2.85 Ga) that are overlain by three variably preserved and widespread tholeiite-dominated volcanic events, here defined as the 2.81–2.71 Ga ‘Goldfields Tholeiitic Super Event’. These correlations support an autochthonous setting for the Kalgoorlie and Kurnalpi terranes with the eruption of volcanic tholeiites onto submerged continental crust.Voluminous tholeiitic volcanism at 2.8–2.7 Ga was a global event. The Zimbabwe and Slave cratons preserve remarkably similar basement overlain by thick basaltic units, that are compositionally similar to the ‘Goldfields Tholeiitic Super Event’. This correlation indicates that a globally significant rifting event at 2.8–2.7 Ga affected much of the continental crust extant.