Geochemistry of Fe-rich tholeiites from the Georgetown Inlier, North Queensland: implications for relationship with the Broken Hill and Mt Isa sequences

Abstract

Mafic igneous rocks in the Georgetown Inlier of north Queensland are found within the Palaeoproterozoic Etheridge Group, and comprise the extrusive Dead Horse Metabasalt and intrusive Cobbold Metadolerite. This study presents new major, trace and rare earth element data for the mafic rocks, and compares them to existing data from similarly aged mafic rocks of other Palaeoproterozoic terranes in eastern Australia. Based on the geochemical and limited geochronological evidence, both suites of mafic rocks are relatively evolved low-K tholeiites with strong Fe-enrichment trends (Fe2O3(t) 6.81-21.11 wt%), and were emplaced between ca. 1700 and 1650 Ma. Despite pervasive metamorphism and recrystallization, the rocks appear geochemically similar to basic gneisses of the Broken Hill Block and mafic rocks of the Mt Isa Eastern Succession, particularly the Toole Creek Volcanics. This relationship is of regional significance, as it may point to a tectonic relationship between the terranes, and hence help place the Georgetown Inlier within the Proterozoic framework of northern Australia.