Evidence for stabilization of the Pilbara Block, Australia

Abstract

The stabilization of continental crust to form cratons represents one of the major features of Earth history¹. Major structural, geochemical^2,3 and, to a lesser extent, sedimentological changes⁴ associated with the development of stable crustal blocks are recorded mainly around 2,500 Myr ago¹. This change, however, appears to have been globally diachronous and cratonic sequences as old as 3,100 Myr are recorded⁵. I now present the results of a recent regional stratigraphical and sedimentological study on the ∼2770 Myr old lower Fortescue Group^6,7 (previously classified lithologically as Proterozoic⁸, but following the recent recommendation of a 2,500-Myr Archaean/Proterozoic chronological boundary⁹ is referred to as Archaean) in the Pilhara Block¹⁰, Western Australia. A major stabilization of the underlying granitoid–greenstone terrain appears to have pre-dated Fortescue basin formation. This event, which available geochronology suggests was relatively rapid, marked a major changing point in the tectonic evolution of the Pilhara Block.