The Basement Elements of Tasmania

Abstract

A new compilation of magnetic data over onshore and offshore Tasmania plus existing geological mapping and gravity data has provided the basis for the production of a map illustrating the geometric distribution of the main basement units that comprise Tasmania Significant items of the new interpretation map include the delineation of the widespread sub-surface granite occurrences in Tasmania, identification of more extensive occurrences of Proterozoic rocks than previously known, mapping of the extent of the Dundas Trough and extensive northwestern and southeastern continuations of the Beaconsfield ultramafics, definition of the areal distribution of Mesozoic sedimentary basins and the control of Proterozoic lineaments, in particular the Arthur Lineament, on the development of the Mesozoic basins. The use of filtering techniques to suppress the magnetic effects of shallow magnetic sources proved particularly valuable for mapping deeper structures obscured by basalt flows and dolerite dykes and sills.

Inherited crustal deformation along the East Gondwana margin revealed by seismic anisotropy tomography

“…In support of this hypothesis, the orientation of the fast anisotropy axes here, particularly at 5 s period, is congruent with the strike of the deep igneous body beneath Bass Basin (40°S and 146.5°E). Its geometry suggests that magma emplacement might have been controlled by northeasterly extension, with the intrusion being generated as extension progressed and then terminated when the breakup failed [ Gunn et al , ; Müller et al , ]. This pattern of anisotropy is in stark contrast with that observed in adjacent mainland Australia but appears to partially propagate into northern Tasmania.…”

Crustal architecture of central Victoria: results from the 2006 deep crustal reflection seismic survey

“…This north-dipping fault also coincides with the northeastern boundary of a broad but thin sheet of deeply buried, magnetic rocks beneath the Melbourne Zone (McLean et al 2010), a boundary that can be traced southwards towards Waratah Bay. We suggest that this fault may be a northern continuation of the Arthur Lineament of Tasmania (Gunn et al 1997;Rawlinson et al 2006). If so, the deeper parts of the Selwyn Block west of this buried structure in Victoria may be equivalent to the Rocky Cape Block and King Island crust, whereas parts to the east may be equivalent to the Tyennan Block.…”

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

“…In particular, one belt can be clearly traced without apparent dislocations from offshore western Tasmania to the Mornington Peninsula in Victoria. The corresponding outcrops have been studied in southeastern King Island and led several authors to consider it as a strong evidence of an extension of the Tasmanian crust towards Victoria (Gunn et al, 1997a(Gunn et al, , 1997bVandenBerg et al, 2000;Cayley et al, 2002;Meffre et al, 2004;Calver, 2007;Moore et al, 2013). Other belts of high magnetic character, including the Togari Group, Rocky Cape Group and Arthur Lineament, appear to be cross-cut by a younger high magnetic anomaly almost in the middle of Bass Strait, coincident with the position of 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.…”