We present a seismic reflection section acquired across the western margin of the Lake George Basin near Geary's Gap which images the stratigraphy of the basin sediments and the interaction between faults and these sediments. When coupled with high resolution topographic data, key aspects of the evolution of the Lake George Basin may be deduced. The Lake George Basin formed as the result of west-dipping reverse faulting and associated fault propagation folding at the eastern margin of the Lake George Range in the interval between ca. 3.93 Ma and the present. Assuming that elevated gravels in Geary's Gap and to the west along Brooks Creek are correlative with similar lithology at the base of the basin (as suggested by previous workers), vertical displacement in the order of 250 m has occurred in this time interval. This is one of the larger rates of displacement recorded for an Australian intraplate fault, averaged over a timescale of several million years. Three prominent angular unconformities, separating packages of approximately parallel strata, indicate that deformation was episodic, with up to 1 million years separating active periods on the fault. The ~75 km active length of the Lake George Fault is consistent with a MW7.4 characteristic earthquake. An event of this magnitude has the potential to cause significant damage to the Australian Capital Territory, given that the surface trace of the fault approaches to within 25 km of Parliament House. Assuming periodic recurrence, a characteristic event might be expected every ~3040 kyr. However, the evidence for temporal clustering suggests that such events might be much more tightly spaced in time (perhaps by an order of magnitude) in an active period on the fault. This neotectonic activity is allied to the Late Pliocene to Pleistocene `Kosciuszko Uplift, which may be responsible for adding several hundred metres of relief to the Eastern Highlands of Australia. Few crustal fault systems which might have accommodated such large-scale uplift have yet been characterised. Consequently, the seismic hazard of the Eastern Highlands, which is based largely upon the short historic record of seismicity, is likely to be underestimated. Nearby candidate faults for similar activity include the Queanbeyan, Murrumbidgee, Shoalhaven, Crookwell, Mulwaree, Binda, Tawonga, Khancoban-Yellow Bog and Jindabyne faults.

Numerous disparate and, in many cases, mutually inconsistent models for the Proterozoic amalgamation and evolution of the Australian continent have been published over the past ~15 years. Most of the models involve large-scale relative movements between pre-existing cratonic blocks, as well as accretion of relatively juvenile crust to cratonic margins, via modern style subduction-tectonics. As such, improved geological understanding of the margins of the major constituent cratonic blocks is critical to testing between contrasting evolutionary models. Both the northern and eastern margins of the Gawler Craton, South Australia, are characterised by shear zones with strike lengths of several hundred kilometres; the Karari Shear Zone in the north, and the Kalinjala Shear Zone in the east. Each of these structures preserves evidence for very significant strike-slip motion, but also juxtaposes rocks from different crustal levels indicating significant dip-slip motion. Recently-acquired deep seismic transects across each of these cratonic margins, together with new U-Pb and 40Ar/39Ar geochronology are interpreted to indicate that the Karari Shear Zone was likely active in at least three episodes through the Paleo- and Mesoproterozoic, and currently preserves an overall north-dipping thrust geometry that dates from the early Mesoproterozoic (~1580 - 1450 Ma). In contrast, on the eastern margin of the craton, the northern part of the Kalinjala Shear Zone preserves an east-dipping bulk extensional geometry that dates from the Paleoproterozoic (~1800 - 1740 Ma). The temporal evolution of the margins of the Gawler Craton provides constraints on models invoking tectonic interaction with other parts of Proterozoic Australia.

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.

The magma-poor southern Australian rifted margin formed as a result of a long history of lithospheric extension that commenced in the Middle Jurassic. Breakup with Antarctica was diachronous, commencing in the west at ~83 Ma and concluding in the east at ~34 Ma. Initial NW-SE ultra-slow to slow seafloor spreading (83-45 Ma), followed by N-S fast spreading (45 Ma-present), resulted in a broad threefold segmentation of the margin: a long E-W oriented divergent margin segment (Bight-western Otway basins); a NW-SE trending transitional segment (central Otway-Sorell basins); and a N-S oriented transform margin (southern Sorell-South Tasman Rise). Segmentation appears to have been strongly controlled by the pre-existing basement structure. The divergent and western transitional margin segments are characterised by a broad region of lithospheric thinning and thick extensional basin development. In this region, a well-developed ocean-continent transition zone includes basement highs interpreted as exhumed sub-continental lithospheric mantle. Mapping of stratigraphic sequences provides insights into the processes that took place at the evolving margin, including the timing of mantle exhumation, and the diachronous nature of crustal thinning and breakup. The orientation and segmentation of the western and transitional margin segments suggests that initial spreading is likely to have been accommodated by short, extension-parallel transform segments. In the easternmost part of transitional zone, lithospheric thinning is not as marked and the continent-ocean boundary is interpreted to comprise both rift and long transform elements. Here, roughly N-S oriented extension resulted in the development of strongly transtensional basins.

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.

A short article describing the outcomes of the Tasman Frontier Petroleum Industry Workshop held at Geoscience Australia on 8 and 9 March 2012.

A deep seismic reflection and magnetotelluric survey, conducted in 2007, established the architecture and geodynamic framework of north Queensland, Australia. Results based on the interpretation of the deep seismic data include the discovery of a major, west-dipping, Paleoproterozoic (or older) crustal boundary, interpreted the Gidyea Suture Zone, separating relatively nonreflective, thick crust of the Mount Isa Province from thinner, two layered crust to the east. East of the Mount Isa Province, the lower crust is highly reflective and is subdivided into three mappable seismic provinces (Numil, Abingdon and Agwamin) which are not exposed at the surface. To the west of Croydon, a second major crustal boundary also dips west or southwest, offsetting the Moho and extending below it. It is interpreted as the Rowe Fossil Subduction Zone. This marks the boundary between the Numil and Abingdon seismic provinces, and is overlain by the Etheridge Province. The previously unknown Millungera Basin was imaged below the Eromanga-Carpentaria basin system. In the east, the Greenvale and Charters Towers Provinces, part of the Thomson Orogen, have been mapped on the surface as two discrete provinces, but the seismic interpretation raises the possibility that these two provinces are continuous in the subsurface, and also extend northwards to beneath the Hodgkinson Province, originally forming part of an extensive Neoproterozoic-Cambrian passive margin. Continuation of this passive margin at depth beneath the Hodgkinson and Broken River Provinces suggests that these provinces (which formed in an oceanic environment, possibly as an accretionary wedge at a convergent margin) have been thrust westwards onto the older continental passive margin. The Tasman Line, originally defined to represent the eastern limit of Precambrian rocks in Australia, has a complicated geometry in three dimensions, which is related to regional deformational events during the Paleozoic.

Introduction: As part of the Offshore Energy Security Program (2007-2011), Geoscience Australia (GA) undertook an integrated regional study of the deepwater Otway and Sorell basins to improve the understanding of the geology and petroleum prospectivity of the region. The under-explored deepwater Otway and Sorell basins lie offshore of southwestern Victoria and western Tasmania in water depths of 100-4,500 m. The basins developed during rifting and continental separation between Australia and Antarctica from the Cretaceous to Cenozoic and contain up to 10 km of sediment. Significant changes in basin architecture and depositional history from west to east reflect the transition from a divergent rifted continental margin to a transform continental margin. The basins are adjacent to hydrocarbon-producing areas of the Otway Basin, but despite good 2D seismic data coverage, they remain relatively untested and their prospectivity poorly understood. The deepwater (>500 m) section of the Otway Basin has been tested by two wells, of which Somerset 1 recorded minor gas shows. Three wells have been drilled in the Sorell Basin, where minor oil shows were recorded near the base of Cape Sorell 1. Structural framework: Using an integrated approach, new aeromagnetic data, open-file potential field, seismic and exploration well data were used to develop new interpretations of basement structure and basin architecture. This analysis has shown that reactivated north-south Paleozoic structures, particularly the Avoca-Sorell Fault System, controlled the transition from extension through transtension to a dominantly strike-slip tectonic regime along this part of the southern margin. Depocentres to the west of this structure are large and deep in contrast to the narrow elongate depocentres to its east. ...

Detrital zircon age patterns are reported for sandstones from the mid-Permian-Triassic part of the accretionary wedge forming the Torlesse Composite Terrane in Otago, New Zealand and from the early Permian Nambucca Block of the New England Orogen, eastern Australia. In Otago, the Triassic Torlesse samples have a major (64%) age group of Permian-Early Triassic components ca. 240, 255 and 280 Ma, and a minor age group (30%) with a Precambrian-early Paleozoic range (ca. 500, 600 and 1000 Ma). In Permian sandstones nearby, the younger group is diminished (30%), and the older group also contains a major (50%) and unusual, Carboniferous group (components at ca. 330-350 Ma). This trend is similar in sandstones from the Nambucca Block, an early Permian extensional basin in the southern New England Orogen, in which Permian zircons are now minor (<20%), and the age patterns are also dominated (40%) by similar Carboniferous age components, ca. 320-350 Ma.

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.