Proterozoic – Early Palaeozoic rocks and the Tyennan Orogeny in central Victoria: The Selwyn Block and its tectonic implications

Evolution of a Cambrian active continental margin: The Delamerian–Lachlan connection in southeastern Australia from a zircon perspective

“…In the Cambrian, an oceanic realm developed resembling the modern western Pacific Ocean with island arcs, backarc basins and boninitic-tholeiitic successions (Crawford et al, 2003). In contrast, the Melbourne Zone is underlain by a northward continuation of the basement rocks of western Tasmania called the 'Selwyn block' (Cayley et al, 2002;Cayley, 2011;Moore et al, 2013) as shown by magnetic connections across Bass Strait. Western Tasmania is thought to have reached its present location with respect to East Gondwana by the Early Ordovician (Li et al, 1997).…”

“…Ar/Ar ages from the Moorambool Metamorphic Complex in the western Stawell Zone indicate exhumation of garnet amphibolites at ~500 Ma from this west-dipping Delamerian subduction zone (Miller et al, 2005). Cayley (2011) has reinterpreted the tectonic development of the Delamerian Fold Belt in western Victoria as an active east-facing margin developed in the Early to Middle Cambrian with intensification of deformation in the Late Cambrian associated with collision of an outboard microcontinent, "Van Dieland", that includes Tasmania and its inferred northern subsurface continuation, the Selwyn Block forming a deeply buried metamorphic basement to much of central Victoria (Cayley et al, 2002).…”

Illite crystallinity and the b-spacing values of white micas and their implications for gold mineralisation in the Lachlan Orogen

“…Others suggested that the correlation of field and aeromagnetic data between mainland Australia and Tasmania supports the existence of a Proterozoic/Paleozoic basement block, termed the Selwyn Block, beneath the eastern half of the Bendigo and Melbourne Zones (Cayley et al 2002). The age-boundary and magnetic character (Cayley et al 2002) between the Early and Late Devonian plutons are parallel to the inferred western edge of the Selwyn Block (Figure 2). This 'pluton-age' boundary has previously been used to infer a change in basement terrane across the Stawell and Bendigo Zones (Chappell et al 1988) (dashed line in Figure 1).…”

“…This inferred underlying Proterozoic/Paleozoic block beneath the Bendigo and Melbourne Zones would be expected to influence the temperature of metamorphism of the overlying turbidites, as it would insulate heat flow from the mantle to the upper crust. While the western margin of the inferred basement block has an overall northeast-trend, the boundary is poorly defined and has previously been drawn as a relatively smooth contact (Cayley et al 2002). In this contribution we reinvestigate the change in 'illite crystallinity' observed by Offler et al (1998) and try to relate it to the existence of the Selwyn Block and its western margin, and the implications for gold mineralisation in the Lachlan Orogen.…”

“…The presence of the Selwyn Block therefore accounts for the observed Kü bler Index and b-spacing changes if it acted as a protective (insulating) basement beneath the eastern Bendigo and Melbourne Zones during deformation. East-west compression in the Benambran Orogeny shortened the Cambrian-Ordovician sedimentary basin between the Selwyn Block and the continental crust beneath the Stawell Zone by about 70% (Gray & Willman 1991;Cayley et al 2002). The sediments to the west of the Selwyn Block would have had no strong, rigid basement to them, only imbricated oceanic basalts, and hence became easily deformed as a series of eastwardtransported duplexes between the advancing Selwyn Block and the stable Proterozoic basement block that is part of the Australian Craton (Figure 14c).…”