Geochronology of the Archean of Australia

Abstract

The Archean eon is a chronometrically defined subdivision of the Precambrian that extends from 3800 to 2500 Ma. In the Australian continent, Archean rocks (i.e. those with sedimentary deposition or igneous crystallisation ages confidently interpreted to be older than 2500 Ma) occur in the Pilbara and Yilgarn Cratons of Western Australia, the Mulgathing and Sleaford Complexes in the Gawler Craton of South Australia and as minor inliers in the Pine Creek Orogen of the Northern Territory. Metamorphosed lithological components with igneous or sedimentary precursors inferred to be of Archean age also occur in the Browns Range Dome and Billabong Complexes of the Tanami Inlier, Northern Territory, and possibly also in the Broken Hill Inlier. This contribution outlines aspects of the historical development of geochronological methods applied to the Archean of Australia, the respective strengths and weaknesses of these methods and how our understanding of the continent's Archean geology and tectonics was related to this development. The geological formation of the Yilgarn and Pilbara Cratons is investigated using a new statistical approach based on the distribution of SHRIMP U–Pb zircon and monazite dates obtained from rock samples that may have complex mineral age populations. Spatial and temporal characteristics of the magmatic episodes identified in the Yilgarn and Pilbara granite–greenstone terranes are atypical of rift/collision processes attributable to tectonic-plate interactions, but are consistent with their interpretation as a response to major mantle convection events. The strengths of this geochronology-based approach are demonstrated by its application to the Narryer Gneiss Complex of the northwestern part of the Yilgarn Craton. It is shown that this approach offers unique insights into geological events that may be under-represented at the outcrop scale due to later crustal re-working.