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

The provenance of detrital zircons in nineteen littoral and sedimentary dep osits in eastern Australia is determined in terms of their isotopic ages me asured by Sensitive High Resolution Ion MicroProbe (SHRIMP). Principal comp onent analysis of the age data reveals four 'age groupings' whose occurrenc e and distribution have wider implications for regional tectonics and gener al provenance studies. A 100-175 Ma age grouping is correlated with Jurassi c/Cretaceous volcanism along the eastern Australian margin. A 225-350 Ma ag e grouping is correlated with the New England Orogen. A 350-500 Ma age grou ping is correlated with magmatism in the Lachlan Orogen. The ultimate sourc e of the Pacific-Gondwana 500-700 Ma age grouping is enigmatic, but is tent atively identified as a Neoproterozoic orogeny along the eastern Antarctic margin. The geochronology of detrital zircon reveals a strong regional vari ation 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 secto r, and then a New England Orogen age grouping in the north. The Pacific-Gon dwana 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 favoura ble sedimentary pathway can have greater control over provenance than proxi mity. The other example occurs with Jurassic/Cretaceous age grains are prom inent in the Murray Basin, around 1200 km from the protosource along the ea stern margin, but not in sediments now accumulated on that same margin. (C) 1999 Elsevier Science B.V. All rights reserved.