Kelly Large Igneous Province, 3350–3315 Ma

Abstract

Unconformably overlying thick continental crust, the Kelly Group comprises three formations, in ascending stratigraphic order: the 3350–3335 Ma Euro Basalt, up to 9 km thick, and composed of komatiite, basaltic komatiite, and tholeiite; the 3325–3315 Ma Wyman Formation, up to 2 km thick, and composed of rhyolite flows and subvolcanic rhyolite intrusions; and the undated Charteris Basalt, up to 2 km thick, and containing komatiite, basaltic komatiite, and tholeiite. With an average stratigraphic thickness of 4 km, and erupted across at least 100,000 km2 of the Pilbara Craton, the Euro Basalt forms the main part of a Paleoarchean large igneous province, the Kelly LIP. The plume-related ultramafic–mafic–felsic volcanic cycle that commenced with eruption of the Euro Basalt ended with eruption of the felsic volcanics of the Wyman Formation. However, unlike the Euro Basalt the Wyman Formation is restricted to the eastern half of the East Pilbara Terrane and was derived from partial melting of older felsic crust. Eruption of the Wyman Formation was accompanied by numerous granodiorite and monzogranite intrusions of the Emu Pool Supersuite. Geochronology indicates that in some of the East Pilbara domes there was a ten-million-year interval between eruption of the Euro Basalt and Wyman Formation, during which time some parts of the Euro Basalt were folded and eroded. The undated Charteris Basalt is lithologically similar to the Euro Basalt and might form part of a second volcanic cycle.