Geochronology of basin phases in the western Mt Isa Inlier, and correlation with the McArthur Basin∗

Zircon geochronology—using U‐Pb SHRIMP methods—has been applied to investigate the Palaeoproterozoic history of basin development and sedimentation in the western Mt Isa Inlier and eastern McArthur Basin. Ages of the sediment packages have been measured using the abundant felsic volcanics in lower parts of the sequences, and overlying sediments have been dated through the use of zircons in sparse, concordant tuff beds that punctuate these successions. The earliest volcanic phases north and south of the Murphy Inlier are close to 1725 Ma, and may be part of a much larger extensional tectonic regime now identified in the central and eastern Mt Isa Inlier. A somewhat younger episode of volcanism took place in the central Lawn Hill Platform (Fiery Creek Volcanics and Bigie Formation) at about 1710 Ma, approximately coeval with volcanism throughout much of the McArthur Basin. The most southerly volcanic suite below the Mt Isa Group is 30–40 million years younger, closer to the ca 1650 Ma age of overlying strat...