Gravity and magnetic modelling of crustal structure in central Victoria: what lies under the Melbourne Zone?

Linking mainland Australia and Tasmania using ambient seismic noise tomography: Implications for the tectonic evolution of the east Gondwana margin

“…Moreover, three narrow belts of high shear velocity extend from Proterozoic northwestern Tasmania, beneath Bass Strait, to south-central Victoria. This concurs with previous interpretations using magnetic and gravity data (Cayley et al, 2002;McLean et al, 2010;Moore et al, 2013), and supports the interpretation of Proterozoic continental crust at least as far north as the Victorian coastline. Other tomography studies in Victoria (Rawlinson and Kennett, 2008;Rawlinson et al, 2011;Young et al, 2013a) and Tasmania (Rawlinson et al, 2006;Young et al, 2013b) have not recognised the presence of such a feature.…”

“…An alternative explanation for the high velocities is that they are associated with the presence of the Selwyn Block. Recent magnetic and gravity modelling (Cayley et al, 2002;McLean et al, 2010) have suggested that the exotic Proterozoic crust may extend beneath the Melbourne Zone and be delimited by the Governor Fault on its eastern margin. If this was the case, the Selwyn Block may extend south of Melbourne and be overprinted by the low wavespeeds that underpin the Bass Basin.…”

“…A diverse range of techniques have so far been exploited to infer information on crustal structure and composition beneath Bass Strait, mainly in studies focusing on similarities recognised in the geology (Crawford and Berry, 1992;Powell and Baillie, 1992;Reed, 2001;Cayley, 2011) and in geophysical, geochemical and other types of data in Tasmania and/or mainland Australia. Geophysical methods include potential field imaging and modelling (e.g., Leaman et al, 1994;Gunn et al, 1997aGunn et al, , 1997bMorse et al, 2009;McLean et al, 2010), seismic reflection profiling (Drummond et al, 2000;Cayley et al, 2011) and seismic tomography (Rawlinson and Kennett, 2008). Palaeomagnetic evidence in the form of magnetic remanence (Li et al, 1997) has also been used.…”

Backarc basin and ocean island basalts in the Narooma Accretionary Complex, Australia: setting, geochemistry and tectonics

“…By contrast, the Melbourne Zone had a continental substrate continuous with Tasmania and has most likely undergone northward translation along the East Gondwana margin (Cayley 2011). Emplacement of middle Cambrian supra-subduction ophiolite in Tasmania was attributed to east-dipping subduction (Berry & Crawford 1988) and was probably associated with emplacement of inferred ophiolite fragments in the eastern Melbourne Zone interpreted as responsible for magnetic highs reflecting a source at depths of 25-10 km (McLean et al 2010). The boninitic-tholeiitic-ultramafic associations of the eastern Bendigo Zone and southwest Tabberabbera Zone reflect initial formation in an arc-forearc associated with subduction followed by generation of the tholeiitic basalts in a backarc basin (Crawford et al 2003a).…”

Long-wavelength magnetic anomalies as a guide to the deep crustal composition and structure of eastern Australia

“…Given the arguments for contrasting continental and oceanic basement in the Tasmanides, it seems reasonable to assign continental middle to lower crust to the low-regional-field domains (the Proterozoic, East Lachlan, western New England, and eastern Thomson domains), and oceanic mid/lower crust to the Central Magnetic High and Eastern New England domains. Support for this interpretation comes from deep seismic reflection surveying across central Victoria, which indicates a stacked basement of mafic volcanics under the Stawell and Bendigo zones (Cayely et al, 2011), from a potential field model of the Selwyn Block basement below the Melbourne Zone, which has been interpreted to represent a large ophiolitic body (McLean et al, 2010), and from recent teleseismic results from northeastern NSW that imply high velocity, presumably Proterozoic, lithosphere below the western New England domain (Rawlinson, 2013).…”