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

Abstract

A *400 km long deep crustal reflection seismic survey was acquired in central Victoria, Australia, in 2006. It has provided information on crustal architecture across the western Lachlan Orogen and has greatly added to the understanding of the tectonic evolution. The east-dipping Moyston Fault is confirmed as the suture between the Delamerian and western Lachlan Orogens, and is shown to extend down to the Moho. The Avoca Fault, the boundary between the Stawell and Bendigo Zones, is a west-dipping listric reverse fault that intersects the Moyston Fault at a depth of about 22 km, forming a V-shaped geometry. Both the Stawell and Bendigo Zones can be divided broadly into a lower crustal region of interlayered and imbricated metavolcanic and metasedimentary rocks and an upper crustal region of tightly folded metasedimentary rocks. The Stawell Zone was probably part of a Cambrian accretionary system along the eastern Gondwanaland margin, and mafic rocks may have been partly consumed by Cambrian subduction. Much of the Early Cambrian oceanic crust beneath the Bendigo Zone was not subducted, and is preserved as a crustal-scale imbricate thrust stack. The seismic data have shown that a thin-skinned structural model appears to be valid for much of the Melbourne Zone, whereas the Stawell and Bendigo Zones have a thick-skinned structural style. Internal faults in the Stawell and Bendigo Zones are mostly west-dipping listric faults, which extend from the surface to near the base of the crust. The Heathcote Fault Zone, the boundary between the Bendigo and Melbourne Zones, extends to at least 20 km, and possibly to the Moho. A striking feature in the seismic data is the markedly different seismic character of the mid to lower crust of the Melbourne Zone. The deep seismic reflection data for the Melbourne Zone have revealed a multilayered crustal structure that supports the Selwyn Block model.

Crustal architecture and geodynamics of North Queensland, Australia: Insights from deep seismic reflection profiling

“…14). Its trapezoid geometry is similar to that of the Selwyn Block in central Victoria, as imaged in recent seismic profiles Cayley et al, 2011); and it could have acted as a buttress, also similar to that proposed for the Selwyn Block (Cayley et al, 2002).…”

The nature of the Moho in Australia from reflection profiling: A review

“…To the east, the VT2 segment of the 2006 Victorian transect in the western Lachlan Fold Belt shows clear mid crustal reflections, which are inferred to be associated with the Proterozoic Selwyn Block (Cayley et al [29]). The reflection section is of high quality with clear thrust connection to surface ophiolites at CDP 8200 ( Fig.…”

“…Limestones in the west of the region had presented considerable problems with the older low fold procedures, but very high quality data was obtained with the vibrator sources in 2009. To the west the main reflection profile SD1 linked to the 2006 Victorian transect (Cayley et al [29]). …”

A unified model for gold mineralisation in accretionary orogens and implications for regional-scale exploration targeting methods

“…One example of this was the Western Lachlan Fold Belt in Victoria, where more recent seismic surveys have now confirmed the presence of extended Proterozoic basement underlying the orogen at depth (e.g. Willman et al 2010;Cayley et al 2011) Consistent with these observations, recent lithosphericmantle focused, integrated geophysical and geochemical studies have shown that juvenile arc-related lithosphere is, perhaps surprisingly, not a major component of accretionary orogens Belousova et al 2010;Griffin et al 2011). The reason for this relates to the fundamental processes of continental lithosphere formation, as summarised by Griffin et al (2009).…”

“…4 Schematic illustration of the conjunction of three independent parameters required to form a world-class gold deposit (of any deposit type) within an accretionary orogen Western Lachlan Fold Block of Victoria. These deposits are located above the inferred margins of the Selwyn Block, an underlying older basement domain that occurs locally within the orogen (Miller et al 2006;Cayley et al 2011). …”