AUSTRALIA/Tasman Orogenic Belt 249 Figure 10 Plate tectonic reconstructions at (A) 400 380 Ma and (B) 365 340 Ma Adapted and reprinted, with permission, from the Annual Review of Earth and Planetary Sciences, Volume 28, ß 2000 by Annual Reviews, www.annualreviews.org The plate positions and continental outlines were calculated and drawn using data in Paleogeographic Information System/MacTM verison June 7, 1997 by MI Ross & CR Scotese (PALEOMAP Project, Arlington Texas) During this time large turbidite fans grew off the shore of the Ross–Delamerian mountain chain and spread onto the mafic crust of the developing marginal ocean (Figure 9B) Some thousands of kilometres off shore subduction had initiated within the oceanic plate, leading to the development of a volcanic arc complex at about 485 Ma, now represented by the Ordovican shoshonites in the eastern Lachlan Orogen, and an associated accretionary complex at about 445 Ma (Narooma Accretionary Complex), exposed in south-eastern New South Wales Back-arc Basin Closure (450–420 Ma): Evolution of the Lachlan Orogen The Lachlan Orogen formed by amalgamation of a series of thick turbidite-dominated thrust wedges and volcanic-arc terranes in a tectonic setting similar to that of the Philippine, Mulucca, and New Guinea sectors of the western Pacific today (Figure 9C) The Lachlan Orogen resulted from the closure of a small ocean-basin–arc system situated along the Pacific margin of Gondwana, inboard of a larger major long-lived Palaeozoic subduction system that is now exposed in the New England Orogen (Figure 10A) The total amount of subducted oceanic lithosphere was relatively small (less than 1000 km) Basin closure involved Woodlark Basin-style double divergent subduction (Figure 9C), inferred from the multiple subduction-related thrust systems (Figure 6) and the presence of the blueschist blocks in the serpentinite-matrix me´ lange along major faults (Figure 7) The thrust systems developed by duplexing