Tracing provenance through the isotope ages of littoral and sedimentary detrital zircon, eastern Australia

Abstract

The provenance of detrital zircons in nineteen littoral and sedimentary deposits in eastern Australia is determined in terms of their isotopic ages measured by Sensitive High Resolution Ion MicroProbe (SHRIMP). Principal component analysis of the age data reveals four 'age groupings' whose occurrence and distribution have wider implications for regional tectonics and general provenance studies. A 100-175 Ma age grouping is correlated with Jurassic/Cretaceous volcanism along the eastern Australian margin. A 225-350 Ma age grouping is correlated with the New England Orogen. A 350-500 Ma age grouping is correlated with magmatism in the Lachlan Orogen. The ultimate source of the Pacific-Gondwana 500-700 Ma age grouping is enigmatic, but is tentatively identified as a Neoproterozoic orogen along the eastern Antarctic margin. The geochronology of detrital zircon reveals a strong regional variation along the eastern coast with the Lachlan Orogen age grouping stronger in the south, mixing with the 500-700 Ma age grouping in the central sector, and then a New England Orogen age grouping in the north. The Pacific-Gondwana age grouping on the central coast is derived from the Middle Triassic Hawkesbury Sandstone of the Sydney Basin. This distribution of the Pacific-Gondwana age grouping via the Sydney Basin is one example of how a favourable sedimentary pathway can have greater control over provenance than proximity. The other example occurs with Jurassic/Cretaceous age grains are prominent in the Murray Basin, around 1200 km from the protosource along the eastern margin, but not in sediments now accumulated on that same margin.