East Antarctic sources of extensive Lower–Middle Ordovician turbidites in the Lachlan Orogen, southern Tasmanides, eastern Australia

• Published in: Australian Journal of Earth Sciences
• Main Authors: Glen, R. A., Fitzsimons, I. C. W., Griffin, W. L., Saeed, A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2017
• Subjects: Detrital zircon dating; U–Pb; Hf isotopes; turbidites; sediment sources; Antarctica; Lachlan Orogen; Tasmanides; Antarc*; Antarctic; Dronning Maud Land; East Antarctica
• Online Access: https://researchers.mq.edu.au/en/publications/1b1f059a-633a-46eb-8ea4-61513cc5a324; https://doi.org/10.1080/08120099.2017.1273256; http://www.scopus.com/inward/record.url?scp=85015233780&partnerID=8YFLogxK

Lower to upper Middle Ordovician quartz-rich turbidites form the bedrock of the Lachlan Orogen in the southern Tasmanides of eastern Australia and occupy a present-day deformed volume of ∼2–3 million km 3 . We have used U–Pb and Hf-isotope analyses of detrital zircons in biostratigraphically constrained turbiditic sandstones from three separate terranes of the Lachlan Orogen to investigate possible source regions and to compare similarities and differences in zircon populations. Comparison with shallow-water Lower Ordovician sandstones deposited on the subsiding margin of the Gondwana craton suggests different source regions, with Grenvillian zircons in shelf sandstones derived from the Musgrave Province in central Australia, and Panafrican sources in shelf sandstones possibly locally derived. All Ordovician turbiditic sandstone samples in the Lachlan Orogen are dominated by ca 490–620 Ma (late Panafrican) and ca 950–1120 Ma (late Grenvillian) zircons that are sourced mainly from East Antarctica. Subtle differences between samples point to different sources. In particular, the age consistency of late Panafrican zircon data from the most inboard of our terranes (Castlemaine Group, Bendigo Terrane) suggests they may have emanated directly from late Grenvillian East Antarctic belts, such as in Dronning Maud Land and subglacial extensions that were reworked in the late Panafrican. Changes in zircon data in the more outboard Hermidale and Albury-Bega terranes are more consistent with derivation from the youngest of four sedimentary sequences of the Ross Orogen of Antarctica (Cambrian–Ordovician upper Byrd Group, Liv Group and correlatives referred to here as sequence 4) and/or from the same mixture of sources that supplied that sequence. These sources include uncommon ca 650 Ma rift volcanics, late Panafrican Ross arc volcanics, now largely eroded, and some <545 Ma Granite Harbour Intrusives, representing the roots of the Ross Orogen continental-margin arc. Unlike farther north, Granite Harbour Intrusives between ...