3450-m.y.-old volcanics in the Archaean layered greenstone succession of the Pilbara Block, Western Australia

Abstract

Zircon U-Pb systems from a single block sample of columnar dacite from the early Archaean Warrawoona Group from the layered “greenstone” succession of the Pilbara Craton, Western Australia, indicate an age of3452 ± 16 (2σ) m.y. This is interpreted as the age of the dacite, and is the oldest age so far determined from the Archaean of Australia. This confirms the antiquity of the Warrawoona Group and suggests a close age relationship between the Warrawoona Group in the Pilbara and the Onverwacht Group in South Africa. The Rb-Sr whole rock systems of the dacite have been disturbed since emplacement and indicate apparent ages that have no direct geological significance. This is in accord with previous published accounts of resetting of Rb-Sr whole rock ages determined on acid metavolcanics.