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).

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.

We present a 3‐D inversion of magnetotelluric data acquired along a 340‐km transect in Central Australia. The results are interpreted with a coincident deep crustal seismic reflection survey and magnetic inversion. The profile crosses three Paleoproterozoic to Mesoproterozoic basement provinces, the Davenport, Aileron, and Warumpi Provinces, which are overlain by remnants of the Neoproterozoic to Cambrian Centralian Surperbasin, the Georgina and Amadeus Basins, and the Irindina Province. The inversion shows conductors near the base of the Irindina Province that connect to moderately conductive pathways from 50‐km depth and to off‐profile conductors at shallower depths. The shallow conductors may reflect anisotropic resistivity and are interpreted as sulfide minerals in fractures and faults near the base of the Irindina Province. Beneath the Amadeus Basin, and in the Aileron Province, there are two conductors associated strong magnetic susceptibilities from inversions, suggesting they are caused by magnetic, conductive minerals such as magnetite or pyrrhotite. Beneath the Davenport Province, the inversion images a conductive layer from ∼15‐ to 40‐km depth that is associated with elevated magnetic susceptibility and high seismic reflectivity. The margins between the different basement provinces from previous seismic interpretations are evident in the resistivity model. The positioning and geometry of the southern margin of the crustal conductor beneath the Davenport Province supports the positioning of the south dipping Atuckera Fault as interpreted on the seismic data. Likewise, the interpreted north dipping margin between the Warumpi and Aileron Province is imaged as a transition from resistive to conductive crust, with a steeply north dipping geometry.

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.

<div>The city of Lae is Papua New Guinea (PNG)’s second largest, and is the home of PNG’s largest port. Here, a convergence rate of ~50 mm/yr between the South Bismarck Plate and the Australian Plate is accommodated across the Ramu-Markham Fault Zone (RMFZ). The active structures of the RMFZ are relatively closely spaced to the west of Lae. However, the fault zone bifurcates immediately west of the Lae urban area, with one strand continuing to the east, and a second strand trending southeast through Lae City and connecting to the Markham Trench within the Huon Gulf. </div><div>The geomorphology of the Lae region relates to the interaction between riverine (and limited marine) deposition and erosion, and range-building over low-angle thrust faults of the RMFZ. Flights of river terraces imply repeated tectonic uplift events; dating of these terraces will constrain the timing of past earthquakes and associated recurrence intervals. Terrace riser heights are typically on the order of 3 m, indicating causative earthquake events of greater than magnitude 7. </div><div>Future work will expose the most recently active fault traces in trenches to assess single event displacements, and extend the study to the RMFZ north of Nadzab Airport. These results will inform a seismic hazard and risk assessment for Lae city and surrounding region.</div> Presented at the 2023 Australian Earthquake Engineering Society (AEES) Conference