Early Precambrian basic rocks of Australia

Abstract

Australia has many geological similarities with the other fragments of the former supercontinent Gondwanaland (India, Africa, South America, Antarctica), and the Archaean of Australia is most similar to that of southern Africa (Chapter 16). Parts of the Yilgarn Block (Figure 14.1) contain greenstone belts unconformably overlying older gneisses, and to this extent are similar to Peninsular India (Chapter 15). The recent discovery of Archaean high-grade sapphirine + quartz assemblages in South Australia points to similarities with the Napier Complex in Antarctica (Oliver and Purvis, 1986; Harley and Black, 1987). Most of the early Proterozoic rocks of Australia occur in folded, deformed ‘mobile belts’ (Figure 14.1) (e.g. Etheridge et al, 1987), which appear to be a world-wide phenomenon. Although some Archaean rocks also occur in mobile belts, most of the Archaean mafic rocks of Australia occur within granitegreenstone terranes, known in Australia as ‘blocks’. A considerable thickness of Archaean basalt also occurs in the gently folded Hamersley Basin (Pidgeon, 1984; Blake and Groves, 1987). Post-tectonic suites of dykes and sills occur commonly both in the mobile belts and in the Archaean blocks, and extensive sills occur in the epicratonic Kimberley Basin (Bofinger, 1967).