Convergent margin tectonic settings involving accretion of large turbidite fans represent important sites of growth and regeneration of continental crust. The newly accreted continental crust consists of an upper crustal layer of recycled crustal detritus (turbidites) underlain by a lower crustal layer of tectonically imbricated oceanic crust, and/or rifted and thinned continental crust, along with underplated magmatic materials; the new lower crust represents additions to continental crustal volume differentiated from the mantle. This two-tiered crust is of average continental crustal thickness and is isostatically balanced near sea level, resulting in remarkable stability. The Paleozoic Tasman orogen of eastern Australia is the archetypal example of this style of orogeny, representing continental growth rates of cubic kilometers per year of material that does not return to the mantle by oceanic plate-tectonic recycling. The Neoproterozoic Pan-African Damara orogen of SW Africa is a similar orogen, whereas the Mesozoic Rangitatan orogen or Rakaia wedge of New Zealand illustrates the transition of the convergent margin from a Lachlan-type to more recognizable “ring of fire”-type orogen. These orogens illustrate continental growth from the shortening of deep marine successions and their oceanic crustal basement involving subduction-accretion. The spatial and temporal variations in deformation, metamorphism, and magmatism across these orogens illustrate how large volumes of monotonous turbidites and their relict oceanic basement eventually become stable continental crust. The timing of deformation and metamorphism reflect the crustal thickening phase, whereas the posttectonic granitoids and surficial volcanic deposits give the timing of cratonization. The turbidites represent fertile sources for crustal melting and are the main sources for the S-type granites.

Deformation in accretionary orogens, such as the eastern Australian Tasmanides, is clearly partitioned either as thin-skinned thrusting or thick-skinned faulting, with structural style dependent on the nature and stratal thicknesses of the sequences involved. The thin-skinned thrust systems consist of either detachment-related folds and thrust sheets within attenuated passive margin sequences or thrust sheets of chevron-folded turbidites with leading imbricate-fan geometry that are developed within former submarine fans overlying back-arc basin oceanic lithosphere. Thick-skinned belts consist of major thrust faults that root into the seismic reflection Moho with no apparent common décollement and cause crustal-scale imbrication of former arc, forearc, submarine fan, and accretionary complex elements. The Tasmanides are a composite orogenic system made up of three distinct orogenic belts whose character and structural style have resulted from the deformation of different tectonic components; the former rifted passive margin to make the Delamerian Orogen, a turbidite fan system(s) in a back-arc setting to make the Lachlan Orogen, and an arc-subduction complex that includes some older accreted components to make the New England Orogen. The inboard Delamerian Orogen consists of an external, craton-vergent thrust belt with foreland-style, detachment-related folds and thrusts linked to a high-T/low-P metamorphic complex. The centrally located Lachlan Orogen is made up of three separate thrust systems largely developed in submarine turbidite fans and incorporates a shear-zone-bounded high-T/low-P metamorphic belt. The outermost New England Orogen is constructed from craton-vergent, fore-arc and magmatic arc sequences, subduction complexes, and ophiolite fragments.

Abstract The preservation of diverse ophiolitic rocks in the Tasmanides of eastern Australia reflects a period of complex oceanic crust formation off the east Gondwana margin from c. 560 to 495 Ma. This involved development of oceanic crust possibly at a spreading ridge (now preserved as the c. 560 Ma Marlborough ophiolite, New England Orogen), development of forearc crust in a suprasubduction zone between c. 530 and 515 Ma (Tyennan-Delamerian ophiolites), possible synchronous formation of suprasubduction zone crust further outboard (southern New England Orogen ophiolites), emplacement of Tyennan-Delamerian ophiolites onto the Gondwana margin at c. 515 Ma, followed by development of new forearc and backarc crust between c. 505 and 495 Ma (Lachlan Orogen). Tasmanide orogenesis has resulted in the production of both Tethyan-type and Cordilleran-type ophiolites. Tethyan types are represented by the Tyennan (Tasmanian) and possibly Delamerian Orogen ophiolites that were emplaced onto the passive continental margin. The Tasmanian ophiolite has been interpreted as having been emplaced as one or more thrust sheets, concurrent with the development of a metamorphic sole. In contrast, Lachlan Orogen ophiolites were emplaced within major fault zones by accretionary processes such as offscraping, underplating, and duplexing via underthrusting and basin closure during Late Ordovician to Silurian times. Cordilleran-type ophiolites, for example the Lachlan Orogen ophiolites, are dominated by disrupted upper oceanic crustal stratigraphies, whereas Tethyan-types tend to be dominated by mantle and gabbroic sequences, or preserve more complete stratigraphies.