In easternmost Australia, the New England Orogen contains a geological record dominated by subduction-related rocks, with plate convergence during the Late Devonian to Triassic being related to a west-dipping subduction system, assuming present-day orientation, at the boundary of eastern Gondwanaland and the Panthalassan Ocean. A well-preserved Late Paleozoic accretionary wedge contains deep-marine turbidites deposited as trench fill, plus infaulted slices of oceanic crust. The turbidites are mostly first-cycle, immature, quartz-poor, volcanic-derived sedimentary rocks, some of which contain detrital hornblende, along with less-common quartz-rich sandstones to the east. In this study, detrital zircons from sandstones in various tectonic blocks of the New England Orogen are dated by the U-Pb SHRIMP and LA-ICPMS techniques and detrital hornblendes by the Ar-Ar technique to constrain the age and provenance of sedimentary rocks in the accretionary wedge. All samples, except two quartz-rich sandstones from the northern Shoalwater Formation, have maximum depositional ages of 355-316 Ma, indicating that the accretionary wedge evolved over a period of at least 40 Ma, with principal sources from a contemporaneous active continental margin volcanic arc. Quartz-rich sandstones from the easternmost part of the accretionary wedge (Shoalwater Formation and eastern Beenleigh Block) contain a greater range of individual detrital zircon ages from Late Paleozoic to Archean (several individual grains >3000 Ma). These ages indicate that, although detritus from Carboniferous volcanic arc sources was involved, quartz-rich detritus mostly derived from the continental interior dominated the depocentres. We suggest that these quartz-rich sandstones accumulated from longitudinal transport along the trench, like the modern-day Barbados Ridge accretionary wedge, along with breaching of the marginal arc by streams draining the continental interior.
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New England Orogen;
Document Type: Research Article
Onshore Energy and Minerals Division, Geoscience Australia, Canberra, ACT, Australia
GNS Science, Lower Hutt, New Zealand
Department of Geological Sciences, University of Florida, Gainesville, FL, USA
Geological Survey of Queensland, Indooroopilly, Qld, Australia
ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents, Department of Earth and Planetary Sciences, Macquarie University, NSW, Australia
Publication date: 2009-07-01