Abstract The Tasmanides of eastern Australia record the break-up of Rodinia, followed by the growth of orogenic belts along the eastern margin of Gondwana. Spatially, the Tasmanides comprise five orogenic belts, with an internal Permian-Triassic rift-foreland basin system. Temporally, the Tasmanides comprise three (super)cycles, each encompassing relatively long periods of sedimentation and igneous activity, terminated by short deformational events. The Neoproterozoic-earliest Ordovician Delamerian cycle began by rifting, followed by convergent margin tectonism and accretion of island-arc forearc crust and ?island arcs in the Middle-Late Cambrian. The Ordovician-Carboniferous convergent margin Lachlan supercycle consists of three separate cycles, each ending in major deformation. The Ordovician Benambran cycle includes convergent (island-arc) and transform margin activity terminated by terrane accretion in the latest Ordovician-earliest Silurian. The Silurian-Middle Devonian Tabberabberan cycle reflects development of a large back-arc basin system, marked by rift basins and granite batholiths, behind intra-oceanic arcs and an Ordovician-Early Devonian terrane that were accreted in the Middle Devonian. The Middle Devonian to Carboniferous Kanimblan cycle began by rifting, followed by continental sedimentation inboard of a major convergent margin system that forms the early part of the Late Devonian-Traissic Hunter-Bowen supercycle. This supercycle comprises a Late Devonian-Carboniferous continental arc, forearc basin and outboard accreted terranes and subduction complexes intruded by the roots of a Permian-Triassic continental margin arc. Complex deformation ended with accretion of an intra-oceanic arc in the Early Triassic. Key features of the Tasmanides are: continuity of cycles across and along its length, precluding growth by simple eastwards accretion; development of a segmented plate margin in the Late Cambrian, reflected by major rollback of the proto-Pacific plate opposite the southern part of the Tasmanides; rifting of parts of the Delamerian margin oceanwards, to form substrate to outboard parts of the Tasmanides; the presence of five major Ordovician terranes in the Lachlan Orogen; and the generation of deformations either by the accretion of arcs, the largely orogen-parallel ‘transpressive’ accretion of Ordovician turbidite terranes (in the Lachlan Orogen), or by changes in plate coupling.

The Tasmanides of eastern Australia

The well-known southwest-to-northeast younging of stratigraphy over a present-day cross strike distance of >1500 km in the southern Tasmanides of eastern Australia has been used to argue for models of accretionary orogenesis behind a continually eastwards-rolling paleo-Pacific plate. However, these accretionary models need modification, since the oldest (ca 530 Ma) outcrops of Cambrian supra-subduction zone rocks occur in the outboard New England Orogen, now ∼900 km east of the next oldest (520–510 Ma) supra-subduction zone rocks. This is not consistent with simple, continuous easterly rollback. Instead, the southern Tasmanides contain an early history characterised by a westwards-migrating margin between ca 530 and ca 520 Ma, followed by rapid eastwards rollback of the paleo-Pacific plate from 520 to 502 Ma that opened a vast backarc basin ∼2000 km across that has never been closed. From the Ordovician through to the end of the Carboniferous, the almost vertical stacking of continental margin arcs (withi...

Refining accretionary orogen models for the Tasmanides of eastern Australia

[1] The Ross-Delamerian orogenic belt formed along the early Paleozoic active Pacific margin of the newly merged Gondwana supercontinent. In its northernmost segment in the Townsville region of northeastern Australia, we have identified a short contractional phase of the Delamerian orogeny in the Argentine Metamorphics postdating formation of a mafic breccia with a U-Pb zircon age of 500 ± 4 Ma. Contraction was followed by widespread inferred extensional deformation with formation of flat-lying foliation, domal features, and amphibolite grade and greenschist retrograde metamorphism all synchronous with latest Cambrian to Early Ordovician extensional back-arc volcanism, sedimentation, and intrusions. One of these intrusions gives a U-Pb zircon age of 480 ± 4 Ma. Foliation related to the extensional deformation is crosscut by a late granodiorite dike with a U-Pb zircon age of 461 ± 4 Ma. Late east-west contractional deformation affected the higher-grade part of the assemblage. In contrast to the Ross-Delamerian orogenic belt in the Transantarctic Mountains and southeastern Australia, the orogenic belt in northeastern Australia was affected by a short episode of contraction at ∼495 Ma followed by long-lived back-arc extension from ∼490 Ma to 460 Ma with subsequent contractional deformation.

/pdf/structural-metamorphic-and-geochronological-constraints-on-3izy874dzx.pdf

Structural, metamorphic, and geochronological constraints on alternating compression and extension in the Early Paleozoic Gondwanan Pacific margin, northeastern Australia

During the last 20 years, seismic tomography has frequently been used to provide information on the structure of the lithosphere beneath the Australian continent. New tomographic models are presented using two complementary seismological techniques in order to illustrate the current state-of-knowledge. Surface wave tomography is the ideal method to obtain information of velocity variations across the whole continent. The latest models use data from over 13 000 source–receiver paths, allowing a higher resolution than in previous studies using the same technique. In Western Australia the results at 100 km depth clearly reveal the contrast in structure between the Pilbara and Yilgarn Cratons and the Capricorn Orogen. At greater depths, the Kimberley Block has a distinct fast velocity anomaly in comparison with the surrounding mobile belts. In the east of the continent, strong horizontal gradients in velocity indicate transitions in lithospheric structure, although the new high resolution models reveal a comp...

3-D structure of the Australian lithosphere from evolving seismic datasets

Arc–continent collision and orogenesis in western Tasmanides: Insights from reactivated basement structures and formation of an ocean–continent transform boundary off western Tasmania

Major advances have been made over the last decade in our understanding of the distribution, compositions, age and significance of Late Neoproterozoic and Cambrian rocks in Victoria.These advances have been driven mainly by the new generation of geological mapping carried out by the Geological Survey of Victoria, using detailed aeromagnetic, gravity and radiometric datasets covering much of the state. In addition, detailed work by universities over certain areas, particularly the Glenelg region in the far west and locally around Stawell, have made significant contributions to the knowledge of the Cambrian geology.
In western Victoria, Cambrian rocks comprise all the known
sedimentary and volcanic bedrock as well as numerous granites. Although there is some possibility of Proterozoic rocks occurring here, no dated rocks have returned ages older than Cambrian. The rock units and geological histories of the Glenelg, Grampians, Stavely and Stawell zones, which were poorly known until recently, are now much better understood. In central and eastern Victoria, the Cambrian rocks generally lie at deeper structural levels and are only exposed in the hanging walls of major faults. Important new information is available for the Glenelg River Complex in westernmost Victoria, the exposed and drilled volcanic belts in western Victoria, and the Cambrian greenstones around Pitfield and on Phillip Island.

Neoproterozoic and Cambriancontinental rifting, continent-arc collision and post-collisional magmatism

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Neoproterozoic and Cambriancontinental rifting, continent-arc collision and post-collisional magmatism