Beginning in the Archean, the continent of Australia evolved to its present configuration through the accretion and assembly of several smaller continental blocks and terranes at its margins. Australia usually grew by convergent plate margin processes, such as arc-continent collision, continent-continent collision or through accretionary processes at subduction zones. The accretion of several island arcs to the Australian continent, through arc-continent collisions, played an important role in this process, and the geodynamic implications of some Archean and Proterozoic island arcs recognised in Australia will be discussed here.

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New geochronological data combined with existing data suggest that the Neoproterozoic period in Australia was reasonably well mineralised, with two major periods of mineralisation: (1) 850-800 Ma sediment-hosted Cu, unconformity U, and diamond deposits, and (2) 650-630 Ma epigenetic Au-Cu deposits. The early period appears to be associated with extension related to initiation of Rodinia break-up, whereas the geodynamic setting of the latter, more restricted, event is unclear.

Multiple new geophysical (airborne electromagnetics, borehole gamma and NMR), geospatial (LiDAR), sonic drilling and geochronological datasets have been used to map and resolve the nature of Quaternary fluvial deposition in the Lower Darling Valley (LDV), NSW. The LDV Cenozoic sequence contains Paleogene and Neogene shallow marine, fluvial and shoreline sediments overlain by Quaternary lacustrine, aeolian and fluvial units. In the LDV Quaternary fluvial sequence, multiple scroll-plain tracts are incised into higher, older more featureless floodplains. Prior to this study, these were respectively correlated to the Coonambidgal and Shepparton Formations of the Riverine Plain in the eastern Murray Basin and associated with the subsequently discarded Prior Stream/Ancestral River chronosequence of different climatically controlled depositional styles. In contrast to that proposition, we ascribe all LDV Quaternary fluvial deposition to lateral-migration depositional phases of one style, though with more variable stream discharges and channel and meander-scroll dimensions. Successively higher overbank-mud deposition through time obscures scroll traces and provides the main ongoing morphologic difference. A new morphostratigraphic unit, the Menindee Formation, refers to the mostly older and higher floodplain sediments, where scroll traces are obscured by overbank mud which continues to be deposited by the highest modern floods. Younger inset scroll-plain tracts, with visible scroll-plain traces, are still referred to the Coonambidgal Formation. Another new stratigraphic unit, the Willotia beds, refers to even older fluvial sediments, now above modern floodplain levels and mostly covered by aeolian sediments. This work provides important insights into hydrogeological processes and the nature of Australian Quaternary fluvial deposition.

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Detrital zircon from sandstone bodies intersected in three recent exploration wells on the North West Shelf were analysed and dated using the SHRIMP (Sensitive High Resolution Ion Microprobe) at Geoscience Australia to test the technique as a tool for understanding the provenance and sediment transport pathways of reservoir facies in the region. Chevron, Hess and Santos, the operating companies for exploration permits WA- 365-P, WA-390-P and WA-281-P respectively, collected 3-5 kg of cuttings from the wells Guardian-1 and Hijinx-1 (Triassic Mungaroo Formation on the Exmouth Plateau of the Carnarvon Basin) and Burnside-1 (Jurassic Brewster Sands from the Browse Basin). All three wells were drilled in 2009-2010. Samples were prepared at Geoscience Australia with 70-80 zircon grains randomly selected for analysis following standard data acquisition and processing procedures to provide a statistically meaningful representation of detrital ages in each sample.

Speculation is increasing that Proterozoic eastern Australia and western Laurentia represent conjugate rift margins formed during breakup of the NUNA supercontinent and thus share a common history of rift-related basin formation and magmatism. In Australia, this history is preserved within three stacked superbasins formed over 200 Myr in the Mount Isa region (1800-1750 Ma Leichhardt, 1730-1670 Ma Calvert and 1670-1575 Ma Isa), elements of which extend as far east as Georgetown. The Mount Isa basins developed on crystalline basement of comparable (~1840 Ma) age to that underlying the Paleoproterozoic Wernecke Supergroup and Hornby Bay Basin in NW Canada which share a similar tripartite sequence stratigraphy. Sedimentation in both regions was accompanied by magmatism at 1710 Ma, further supporting the notion of a common history. Basin formation in NW Canada and Mount Isa both concluded with contractional orogenesis at ~1600 Ma. Basins along the eastern edge of Proterozoic Australia are characterised by a major influx of sediment derived from juvenile volcanic rocks at ~1655 Ma and a significant Archean input, as indicated by Nd isotopic and detrital zircon data. A source for both these modes is currently not known in Australia although similar detrital zircon populations are documented in the Hornby Bay Basin, and in the Wernecke Supergroup, and juvenile 1660-1620 Ma volcanism occurs within Hornby Bay basin NW Canada. These new data are most consistent with a northern SWEAT-like tectonic reconstruction in a NUNA assembly thus giving an important constraint on continental reconstructions that predate Rodinia.

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Abstract for 34th IGC

In eastern Tasmania, Devonian granites intrude the Ordovician-Early Devonian quartz-rich turbidites of the Mathinna Supergroup. The earliest (~400 Ma) I-type granodiorites may be arc-related and pre-date the Tabberabberan Orogeny (~388 Ma), which appears to represent the juxtaposition of Eastern and Western Tasmanian. Subsequently, more felsic and finally strongly fractionated I- and S-type granites were emplaced until ~373 Ma. In western Tasmania, mostly felsic and fractionated I- and S-types were emplaced from ~374-351 Ma, possibly in response to post-collisional crustal extension, into a more diverse terrane with depositional ages extending back to the Late Mesoproterozoic. Granites from the two terranes are readily distinguishable by the age spectra of their inherited zircon, which resemble those of the detrital zircon from sedimentary successions in their respective terranes. Furthermore, within each terrane both I and S-types yield similar inheritance patterns. This is interpreted to indicate a pivotal role for the sedimentary successions in the petrogenesis of both types. Western Tasmanian granites are also enriched in ~1600 Ma zircon, which is essentially unrepresented in the exposed supracrustal succession. This might date an important deep crustal igneous source rock, or represents a detrital component in sedimentary rocks derived from the Gawler Range Volcanics or equivalent rocks. There is no convincing evidence for an additional deep crustal component (of any age) in eastern Tasmania. If present, however, it would be expected to be of mafic composition and to have contributed little if any zircon to the felsic magmas.