oa South African Journal of Geology - Middle Proterozoic evolution of the Mt Isa Inlier, north-western Queensland, Australia : a synthesis

Volume 89 Number 2
  • ISSN : 1012-0750
  • E-ISSN: 1996-8590



Within the Mount Isa Inlier, crystalline basement rocks, older than about 1840 Ma, are overlain unconformably by Middle Proterozoic cover sequences dated at 1810 ro 1670 Ma or possibly 1600 Ma. These cover rocks are many kilometres thick, and represem predominantly shallow-water sediments and largely subaerial bimodal volcanics. They were probably laid down in an intracratonic setting, rather than at an active continental margin, during an essentially tensional tectonic regime, when subsidence more or less kept pace with deposition. Complex folding, faulting, and thrusting, and regional metamorphism lo greenschist and amphibolite fades took place between about 1620 and 1550 Ma. Pre-tectonic and post-tectonic granites and several generations of mafic dykes intrude the cover sequences. The felsic igneous rocks include both I and A-types, and the mafic igneous rocks are mainly of continental tholei ite type.

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