Stratigraphy of the Agnew-Wiluna Greenstone Belt: review, synopsis and implications for the late Mesoarchean to Neoarchean geological evolution of the Yilgarn Craton

Our ability to understand the geological evolution of Archean cratons is fundamentally dependent on stratigraphic reconstructions across greenstone belts. Here, we integrate published stratigraphic, geochemical and geochronological data to produce a revised stratigraphic model for the Agnew-Wiluna Greenstone Belt of the Yilgarn Craton. The Agnew-Wiluna Greenstone Belt records ca 130 m.y. of magmatism that occurred between ca 2820 and 2690 Ma and can be divided into three cycles. Cycle 1 is marked by ca 2820-2740 Ma mafic-ultramafic volcanic rock successions. Cycle 2 is associated with ca 2740-2720 Ma felsic volcanic rocks, associated fragmental deposits and contemporaneous mafic-ultramafic intrusions. Cycle 3 consists of ca 2720-2690 Ma mafic-ultramafic volcanic rock successions and co-magmatic intrusions. Exhumation and reworking of these continental rift basin successions after ca 2690 Ma resulted in two younger, additional, depositional cycles in the Agnew-Wiluna Greenstone Belt. Cycle 4 is associated with intermediate to felsic volcanoclastic rocks and epiclastic rocks erupted/deposited between ca 2690 and 2665 Ma. Cycle 5 is associated with the deposition of polymict conglomerates and sandstones in localised depocentres between ca 2665 and 2655 Ma. The stratigraphic scheme identified at the scale of the Agnew-Wiluna Greenstone Belt is the local expression of craton-wide tectono-thermal events. Our revised stratigraphic model for the Agnew-Wiluna Greenstone Belt and proposed correlations at the craton scale support a para-autochthonous model whereby crust from a proto-Yilgarn continental mass was extended/thinned, favouring the activation of translithospheric pathways associated with the ca 2720-2690 Ma Kalgoorlie Large Igneous Province. Inversion of this intra-cratonic rift basin after ca 2680 Ma led to the protracted activation of shear zones and multiple shifts in sedimentary depocentres. The widespread occurrence of previously unidentified fragments of ca 2820-2720 Ma substrate within the Kalgoorlie-Kurnalpi Rift has significant implications for craton-scale stratigraphic reconstructions and challenges existing terrane and domain boundaries.

Automated summary

This study provides a revised stratigraphic model for the Agnew-Wiluna Greenstone Belt by integrating published stratigraphic, geochemical, and geochronological data. The stratigraphic record in this belt spans approximately 130 million years and can be divided into three cycles. In addition, two younger depositional cycles were identified after ca 2690 Ma. The findings challenge existing terrane and domain boundaries and have significant implications for craton-scale stratigraphic reconstructions.