New Perspectives Workshop, September 2014
Presented by AIG Victoria and AusIMM Central Victoria Branch, Romsey Victoria
W.J. Collins*
NSW Institute for Frontiers Geoscience, University of Newcastle, Newcastle NSW, Australia
G. Rosenbaum
School of Earth Sciences, University of Queensland, St Lucia Queensland, Australia
S.E. Bryan
School of Earth & Environmmental Science, Queensland University of Technology, Brisbane Qld, Australia
C. Verdel
School of Earth Sciences, University of Queensland, St Lucia Qld, Australia
A.C. Hack
NSW Institute for Frontiers Geoscience, University of Newcastle, Newcastle NSW, Australia
R. Hegarty
Geological Survey of New South Wales, Maitland NSW, Australia
D Purdy
Geological Survey of Queensland, Brisbane Qld, Australia
This project is a collaboration between three universities and two geological surveys, with Geoscience Australia also involved through major geophysical and drilling programs. It is one of the key initial projects of the national geoscience exploration initiative, UNCOVER.
A key unexposed region in eastern Australia is the central Tasmanides, an area straddling the NSW-Qld border (Fig. 1). In this region, the Southern Thomson Orogen (STO) links the southern with the northern Tasmanides, and hence plays a key role in understanding Tasmanides geodynamics. It is one of the most poorly exposed and least understood regions in eastern Australia.
The origin and evolution of the Tasmanides have traditionally been explained in the context of a palaeo- Circum-Pacific convergent margin, which was oriented ~N-S (in present coordinates) and mostly involved W-dipping subduction (eg., Veevers, 1984; Fergusson et al , 1986; Collins, 2002; Glen, 2005). Such models explain the general N-S structural grain of the Tasmanides, but have difficulty in explaining orthogonal (~E-W) tectonic features. The STO is the major, arcuate E-W oriented structure in the Tasmanides, extending ~750 km broadly parallel to the NSW-Qld border. The interplay with Paleozoic deformation within the Australian craton is just beginning to be investigated (eg. Cayley, 2012; Veevers, 2013), but to date, little consideration has been given to how orthogonal (N-S oriented) tectonic forces have impacted on Tasmanides development. As such, the origin of the STO is an unanswered question, resolution of which may change the way we understand the geodynamic evolution of the Australian continent during the Paleozoic.
Fig 1. Map showing location of Southern Thomson Orogen (STO), which lies below the extensive cover of the Eromanga Basin. Only 1% of the STO crops out in the field area. Note the enigmatic E-W boundary with the Lachlan Orogen. (From Glen et al 2013).
Contrasting models of the central Tasmanides
Three hypotheses have recently been suggested for the origin and evolution of the STO:
Predictions of and tests for each model
Fig. 2. TMI map of Southern Thomson Orogen showing major geophysical E-W anomalies plus location of drillholes available for sampling (yellow dots). Traverses for proposed MT and AEM surveys, and for AEM array also shown. Drilling program will largely follow the geophysical surveys, plus areas of shallow basement.
Implications For Resource Potential
Cu deposits in BIF-like metamorphosed metasediments might be expected if Anakie equivalents exist in the basement (Model 1).
VHMS base metal deposits, and Ni in ultramafic schists (eg., Culgoa Magnetic Lineament) if the Warraweena volcanics are of Cambrian age. Similarly, it is likely that the Cobar Basin extends northward at least to the Olepoloko Fault, and possibly to the Culgoa Lineament(linear magnetic feature in central- east of Fig 2).
Porphyry copper-gold deposits might be expected if the arc is a correlative of the Macquarie arc.
Orogenic gold deposits are likely to occur in the deformed extensive turbidite piles to the N of the arc system, given the potential correlations with the Bendigo-Ballarat zone (models 2 and 3).
Volcanic or sediment-hosted Cu deposits equivalent to Girilambone group copper deposits are predicted by model 3 for sediments located south of the arc system.
Intrusion-related gold deposits associated with ~430 Ma granites are already recognised in the Tibooburra region, and along-strike to the east.
Tin deposits have been discovered in the 420 Ma old Brewarrina granite, and similar syn-kinematic granites are predicted from the geophysical maps of the region.
Burton, G. R.(2010) ‘New structural model to explain geophysical features in northwestern New South Wales: implications for the tectonic framework of the Tasmanides, AJES 57: 23-49.
Cayley, R. 2012. Oroclinal folding in the Lachlan Fold Belt: Consequence of SE-directed Siluro-Devonian subduction rollback superimposed on an accreted arc assemblage in eastern Australia. In: Selywn Symposium 2012. Geol. Soc. Aust. Abst, 103, 34-43.
Collins W.J. 2002. Nature of extensional accretionary orogens. Tectonics 21 (4);1258-1272 (10.1029/2000TC001272).
Fergusson et al.., 1986 Fergusson, C.L., Gray, D.R. and Cas, R.A.F., 1986, Overthrust terranes in the Lachlan Fold Belt, southeastern Australia: Geology, 14, 519-522.
Glen, R.A., 2005. The Tasmanides of eastern Australia. Geological Society Special Publication, 246, p. 23–96.
Glen R.A., et al. (2013) Geodynamic significance of the boundary between the Thomson Orogen and the Lachlan Orogen, northwestern New South Wales and implications for Tasmanide tectonics, AJES 60, 371-412,
Hegarty, R. 2010. Preliminary geophysical–geological interpretation map of the Thomson Orogen. In: Thomson Orogen—Release of Provisional and Preliminary Information June 2010. DVD, Geological Survey of New South Wales.
Veevers, J.J. (Ed.), 1984. Phanerozoic Earth History of Australia. Clarendon Press, Oxford, pp. 418.
Veevers, J.J., 2013 Pangea: Geochronological correlation of successive environmental and strati-tectonic phases in Europe and Australia. Earth-Science Reviews 127, 48–95
Professor Bill Collins is the Director of the NSW Institute for Frontiers Geoscience at the University of Newcastle. He has focussed his research on the interplay between magmatism and tectonics, using the integrated information to highlight the role of protracted extensional tectonics in the origin of the Tasmanides. More recently, he has been using Hf isotopes in zircon to provide new avenues to understand Tasmanides tectonics, and is applying this isotopic approach to understand global geodynamics. He was a member of the implementation committee for progressing the UNCOVER initiative, which has a focus on exploration geoscience in Australia. He will be discussing how he has used the UNCOVER initiative to gain Australian Research Council (ARC) linkage project success.