Abstract

K–Ar and Rb–Sr age-determinations made on Australian Precambrian rocks up to 1967 are summarized and discussed. On present sampling, and subject to its possible bias, we distinguish broad periods of acid magmatism and high-grade metamorphism between: (I) 3050–2900 m.y., (II) 2750–2600 m.y., (III) 1900–1700 m.y., and (VI) 1100–950 m.y., plus relatively shorter periods between (IV) 1550–1500 m.y., (V) 1400–1350 m.y. and (VII) 700–650 m.y. Isolated granitic bodies were emplaced outside these periods; extensive acid volcanics in the range 2000–2200 m.y. may signify important plutonic activity of this age not yet discovered.With similar qualifications, we distinguish six Precambrian sedimentary successions of different ages and of varying geographical extent. Although the radiometric controls on their separate durations are not yet satisfactory, the overlap between different successions in time appears to be small or absent, and, in contrast with previous impressions, the sediments may document only about half the total time between the Cambrian and 3100 m.y.

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