Palaeogeographic reconstructions of the Australian and Antarctic margins based on matching basement structures are commonly difficult to reconcile with those derived from ocean floor magnetic anomalies and plate vectors. Following identification of a previously unmapped crustal-scale structure in the southern part of the Delamerian Orogen (Coorong Shear Zone), a revised plate reconstruction for these margins is proposed. This reconstruction positions the Coorong Shear Zone opposite the Mertz Shear Zone and indicates that structural inheritance had a profound influence on the location and geometry of continental breakup, and ocean fracture development. Previously, the Mertz Shear Zone has been correlated with the Proterozoic Kalinjala Mylonite Zone in the Gawler craton but this means that Australia is positioned 300-400 km too far east relative to Antarctica prior to breakup. Differences in the orientation of late Jurassic-Cretaceous basin-bounding normal faults in the Bight and Otway basins further suggest that extensional strain during basin formation was partitioned across the Coorong Shear Zone following an earlier episode of strike-slip faulting on a northwest-striking continental transform fault (Trans-Antarctic Shear).

The evolution of the Paleo- and Mesoproterozoic of Australia is controversial. Early tectonic models were largely autochthonous, in part driven by the chemical characteristics of Proterozoic felsic magmatism: overwhelmingly potassic, often with elevated Th and U contents, and with evolved isotopic signatures, consistent with crustal sources and the implication they were not generated within continental arcs. This model has been increasingly challenged over the last 30 years, driven by the recognition of the diversity of Proterozoic magmatism, of linear magmatic belts often with subduction-compatible geochemistry and juvenile isotopic signatures, and of across-strike trends in isotope signatures, all consistent with continental margin processes. These, and other geological evidence for crustal terranes, suggest subduction-related tectonic regimes and collisional orogenesis. Current tectonic models for the Australia Proterozoic invoke such processes with varying number of continental fragments and arcs, related to assembly/break-up of the Nuna Supercontinent. Problems still exist however as the observations of early workers still largely hold-much Proterozoic magmatism was intracratonic, and interpreted backarc magmatism largely lacks obvious related arcs. This has led to more recent hybrid arc-plume models. No one model is completely satisfactory, however, reflecting ambiguity of geochemical data and secular arguments (when did modern-style tectonics actually begin).

Although there is general agreement that the western two-thirds of Australia was assembled from disparate blocks during the Proterozoic, the details of this assembly are difficult to resolve, mainly due to ambiguous and often conflicting data sets. Many types of ore deposits form and are preserved in specific geodynamic environments. For example, porphyry-epithermal, volcanic-hosted massive sulfide (VHMS), and lode gold deposits are mostly associated with convergent margins. The spatial and temporal distributions of these and other deposits in Proterozoic Australia may provide another additional constraints on the geodynamic assembly of Proterozoic Australia. For example, the distribution of 1805-1765 Ma lode gold and VHMS deposits in the North Australian Element, one of the major building block of Proterozoic Australia, supports previous interpretations of a convergent margin to the south, and is consistent with the distribution of granites with subduction-like signatures. These results imply significant separation between the North and South Australian elements before and during this period. Similarly, the distribution of deposits in the Halls Creek Orogen is compatible with convergence between the Kimberly and Tanami provinces at 1865-1840 Ma, and the characteristics of the deposits in the Mount Isa and Georgetown provinces are most compatible with extension at 1700-1650 Ma, either in a back-arc basin or as a consequence of the break-up of Nuna.

Presentation delivered on 8 March 2012 at the Tasman Frontier Petroleum Industry Workshop, 8-9 March 2012, Geoscience Australia, Canberra.

Australian Governments over the past decade have acquired thousands of kilometres of high-quality deep-seismic reflection data. The deep-seismic reflection method is unique among imaging techniques in giving textural information as well as a cross sectional view of the overall crust, including the character of the middle crust, lower crust, Moho, and any upper mantle features. Seismic reflection data can be readily integrated with other geophysical and geological data to provide an unsurpassed understanding of a region's geological history as well as the mineral and energy resource potential. Continental Australia is made up of four main elements (blocks), separated by orogens. Most boundaries between the elements are deeply rooted in the lithosphere, and formed during amalgamation of Australia. Major boundaries within the elements attest to their individual amalgamation, mostly prior to the final construction of the continent. Many of Australia's mineral and energy resources are linked to these deep boundaries, with modern seismic reflection providing excellent images of the boundaries. All of the seismic surveys have provided new geological insights. These insights have significantly advanced the understanding of Australian tectonics. Examples include: preservation of extensional architecture in an otherwise highly shortened terrane (Arunta, Yilgarn, Mt Isa and Tanami), unknown deep structures associated with giant mineral deposits (Olympic Dam, Yilgarn, Gawler-Curnamona), as well as the discovery of unknown basins, sutures and possible subduction zones (Arunta, North Queensland, Gawler-Curnamona). These new insights provide not only an improved tectonic understanding, but also new concepts and target areas for mineral and energy resources.

This database contains information on faults, folds and other features within Australia that are believed to relate to large earthquakes during the Neotectonic Era (i.e. the past 5-10 million years). The neotectonic feature mapping tool allows you to: * search and explore Australian neotectonic features * create a report for a feature of interest * download feature data and geometries as a csv file or kml file * advise Geoscience Australia if you have any feedback, or wish to propose a new feature.

Preserved within the Glenelg River Complex of SE Australia is a sequence of metamorphosed late Neoproterozoic-early Cambrian deep marine sediments intruded by mafic rocks ranging in composition from continental tholeiites to mid-ocean ridge basalts. This sequence originated during breakup of the Rodinia supercontinent and is locally host to lenses of variably sheared and serpentinised mantle-derived peridotite (Hummocks Serpentinite) representing the deepest exposed structural levels within the metamorphic complex. Direct tectonic emplacement of these rocks from mantle depths is considered unlikely and the ultramafites are interpreted here as fragments of sub-continental lithosphere originally exhumed at the seafloor during continental breakup through processes analogous to those that produced the hyper-extended continental margins of the North Atlantic. Subsequent to burial beneath marine sediments, the exhumed ultramafic rocks and their newly acquired sedimentary cover were deformed and tectonically dismembered during arc-continent collision accompanying the early Paleozoic Delamerian Orogeny, and transported to higher structural levels in the hangingwalls of west-directed thrust faults. Thrust-hosted metasedimentary rocks yield detrital zircon populations that constrain the age of mantle exhumation and attendant continental breakup to be no later than late Neoproterozoic-earliest Cambrian. A second extensional event commencing ca. 490 Ma overprints the Delamerian-age structures; it was accompanied by granite magmatism and low pressure-high temperature metamorphism but outside the zone of magmatic intrusion failed to erase the original, albeit modified, rift geometry. This geometry originally extended southward into formerly contiguous parts of the Ross Orogen in Antarctica where mafic-ultramafic rocks are similarly hosted by a deformed continental margin sequence.

Abstract: Compressional deformation is a common phase in the post-rift evolution of passive margins and rift systems. The central-west Western Australian margin, between Geraldton and Karratha, provides an excellent example of a strain gradient between inverting passive margin crust and adjacent continental crust. The distribution of contemporary seismicity in the region indicates a concentration of strain release within the Phanerozoic basins which diminishes eastward into the cratons. While few data exist to quantify uplift or slip rates, this gradient can be qualitatively demonstrated by tectonic landforms which indicate that the last century or so of seismicity is representative of patterns of Neogene and younger deformation. Pleistocene marine terraces on the western side of Cape Range indicate uplift rates of several tens of metres per million years, with similar deformation resulting in sub-aerial emergence of Miocene strata on Barrow Island and elsewhere. Northeast of Kalbarri near the eastern margin of the southern Carnarvon Basin, marine strandlines are displaced by a few tens of metres. A possible Pliocene age would indicate that uplift rates are an order of magnitude lower than further west. Relief production rates in the western Yilgarn Craton are lower still - numerous scarps (e.g. Mount Narryer) appear to relate individually to <10 m of displacement across Neogene strata. Quantitative analysis of time-averaged deformation preserved in the aforementioned landforms, including study of scarp length as a proxy for earthquake magnitude, has the potential to provide useful constraints on seismic hazard assessments in a region containing major population centres and nationally significant infrastructure.

The Mulgathing Complex within the Gawler Craton, South Australia, preserves evidence for magmatism, sedimentation and metamorphism spanning the transition between the Neoarchean and Paleoproterozoic (c. 2555 - 2410 Ma). Prior to this study, limited data has been available to constrain the timing of these tectonothermal events. Consequently there has been uncertainty regarding the timing of sedimentation and magmatism relative to the pervasive deformation and metamorphism that has affected this region. We report SHRIMP zircon U-Pb dating of metamorphosed sedimentary and magmatic rocks from the Mulgathing Complex, central Gawler Craton. The data show that etasedimentary gneisses (Christie Gneiss) preserve an inferred maximum depositional age of ca. 2480 Ma, in contrast to previous studies that have suggests deposition had occurred ca. 2510 Ma. The oldest metamorphic zircons in our data are ca. 2465 Ma, thus indicating there was a time interval of less than 15 Myr between the cessation of sedimentation and the occurrence of metamorphism at high metamorphic grade. Metamorphic zircons have a range of ages, from ca. 2465 and ca. 2415 Ma, consistent with a period of ca. 50 Myr during which high-grade metamorphism occurred. Mafic and felsic intrusions have ages that range from ca. 2520 Ma to 2460 Ma, indicating magmatism occurred during sedimentation and continued during the early stages of metamorphism and deformation of these rocks. The abundance of mafic intrusions and its temporal overlap with the sedimentation within the Mulgathing Complex may indicate that the overall tectonic regime involved some form of iithospheric extension. The Mulgathing Complex shows temporal similarities with only a few terranes in particular the Saask Craton, Canada, regions within the North China Craton, and to some extent cratonic regions within northern Australia.

New SHRIMP U/Pb zircon ages of 472.2 ± 5.8 Ma and 470.4 ± 6.1 Ma are presented for the age of peak metamorphism of Barrovian migmatite units. Magmatic advection is thought to have provided significant heat for the Barrovian metamorphism. Published U/Pb emplacement ages for Grampian-age igneous units of Scotland and Ireland define a minimum age range of c. 473.5 to c. 470 Ma for Barrovian metamorphic heating. The new U/Pb ages are consistent with attainment of peak Barrovian metamorphic temperatures during Grampian magmatism. U/Pb-calibrated 40Ar/39Ar ages for white mica from the Barrovian metamorphic series vary systematically with increasing metamorphic grade, between c. 465 Ma for the biotite zone and c. 461 Ma for the sillimanite zone. Microstructural work on the timing of metamorphism in the Barrovian metamorphic series has shown that peak metamorphism occurred progressively later with increasing peak-metamorphic grade. Younging metamorphic age with increasing metamorphic grade across the Barrovian metamorphic series requires that the sequence was cooled in the lower-grade regions while thermal activity continued in the high-grade regions. This thermal scenario is well explained by the presence of a large-scale extensional detachment that actively cooled units from above while the Barrovian metamorphic heating continued at greater depth in the footwall. The spatio-temporal thermal pattern recorded by the Barrovian metamorphic series is consistent with regional metamorphism during crustal extension.