Provenance of Late Cambrian-Ordovician sedimentary rocks in western, north-eastern Tasmania and southern Victoria: Constraints from U/Pb dating, zircon geochemistry and εHf isotope

Habib, Umer1, Meffre, Sebastien1, Kultaksayos, Sitthinon1, Berry, Ron1

1Centre of Ore-Deposit Geology and Earth Sciences, University of Tasmania, Hobart, Australia

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The sedimentary sequences in western, north-eastern Tasmania and southern Victoria preserves an excellent record of distinctive Cambrian to Ordovician deposition environments and sediment provenance.  Here we integrate new and already published U/Pb detrital age data, field observations, zircon geochemistry, and Hf isotope data to establish the sediment source and tectonostratigraphic history of these rocks. Overall, the detrital age spans from 2.6 Ga to 0.476 Ga, which includes some major Precambrian and Cambrian age peaks. The 1.8-1.2 Ga peaks for Western Tasmania are consistent with derivation from the Tyenna region which incorporate sediments derived from granitoids in Laurentia (North America) and Baltica. A small population of detrital ages from 1.5-1.1 Ga from north-eastern Tasmania and southern Victoria is suggested to have Grenville provenance, possibly from central Australia or other parts of the Grenvillian Orogen. The 850-545 Ma detrital ages occur in all sedimentary rocks and are from the widely represented Pacific-Gondwana Phanerozoic sediments of south eastern Australia. These 850-545 Ma detrital ages are rare in the Owen Group, relative to the overlying Middle-Late Ordovician Pioneer Sandstone, implying a sharp shift in provenance in western Tasmania in the Early Ordovician. The Pioneer Sandstone is very similar to Early Ordovician sandstones from Waratah Bay in southern Victoria and Ordovician sandstone from eastern Tasmania. Also present in the samples are 480-520 Ma zircons. However, the proportions of these in the sedimentary rocks are variable. The Th/U ratios from the Cambrian zircons in western Tasmania support a proximal source from the Mt Read Volcanics. The Cambrian zircons in eastern Tasmania and southern Victoria have much lower Th/U ratios, implying a different provenance. The εHf isotope signatures and statistical analysis, along with sedimentological and paleocurrent data from previous studies, support a local derivation from Precambrian and Cambrian detrital sources for the western Tasmanian rock units, indicating deposition in a segmented basin-margin fault system. The eastern Tasmanian and southern Victorian sandstone were deposited in a basin offshore from the Tyennan-Delamerian Orogen during the Ordovician. 

Keywords. Western Tasmania, U-Pb dating, Tectonic configuration, Palaeozoic


Umer has done his Honors and masters degree in geology from Pakistan and worked for MOL from 2013-2015. He joined Codes in 2018 to persue his PhD.

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