Geochemical classification of Palaeoproterozoic oceanic volcanic front and backarc basin remnants of the Granites-Tanami Orogen, Australia

Abstract

The Granites-Tanami Orogen (GTO) is a lower-greenschist to amphibolite facies succession of >1840 Ma backarc basalts and volcaniclastic-sedimentary rocks that was metamorphosed (~1850–1840 Ma), and later intruded by granites and granodiorites (~1825–1791 Ma) during assembly of the Kimberley Craton, proto-Northern Australia Craton, and the Arunta Region.The data presented here show geochronological, sedimentological, petrographic, and geochemical evidence for the existence of a volcanic arc (‘Tanami Arc’) in the GTO at ~1912 Ma. Furthermore, the combination of volcanic structures, including fiamme and hyaloclastites, and a mafic HFSE geochemical signature of the pyroclastic and volcaniclastic-sedimentary turbidite successions suggests a syndepositional volcanic front within an oceanic arc-backarc system during deposition of the Dead Bullock Formation (and equivalents). Geochemical vectors applied to existing stratigraphic interpretations indicate a trend towards more felsic composition with younging, providing an alternative proxy for relative stratigraphy and a tool for exploration and correlation across the GTO. The localisation of the volcanic arc within the N-NNE dipping arc-continent collision zone has important implications for the debated Palaeoproterozoic amalgamation of the North Australia Craton.