Interpretation of the Capricorn deep seismic reflection survey has provided images which allow us to examine the geodynamic relationships between the Pilbara Craton, Capricorn Orogen and Yilgarn Craton in Western Australia. Prior to the seismic survey, suture zones were proposed at the Talga Fault, between the Pilbara Craton and the Capricorn Orogen, and at the Errabiddy Shear Zone between the Yilgarn Craton and the Glenburgh Terrane, the southernmost component of the Capricorn Orogen. Our interpretation of the seismic lines indicates that there is a suture between the Pilbara Craton and the newly-recognised Bandee Seismic Province. Our interpretation also suggests that the Capricorn Orogen can be subdivided into at least two discrete crustal blocks, with the interpretation of a suture between them at the Lyons River Fault. Finally, the seismic interpretation has confirmed previous interpretations that the crustal architecture between the Narryer Terrane of the Yilgarn Craton and the Glenburgh Terrane consists of a south-dipping structure in the middle to lower crust, with the Errabiddy Shear Zone being an upper crustal thrust system where the Glenburgh Terrane has been thrust to the south over the Narryer Terrane.

Granulite-facies paragneisses enriched in boron and phosphorus are exposed over a ca. 15 x 5 km area in the Larsemann Hills, East Antarctica. The most widespread are biotite gneisses containing centimeter-sized prismatine crystals, but tourmaline metaquartzite and borosilicate gneisses are richest in B (680-20 000 ppm). Chondrite-normalized REE patterns give two groups: (1) LaN>150, Eu*/Eu < 0.4, which comprises most apatite-bearing metaquartzite and metapelite, tourmaline metaquartzite, and Fe-rich rocks (0.9-2.3 wt% P2O5), and (2) LaN<150, Eu*/Eu > 0.4, which comprises most borosilicate and sodic leucogneisses (2.5-7.4 wt% Na2O). The B- and P-bearing rocks can be interpreted to be clastic sediments altered prior to metamorphism by hydrothermal fluids that remobilized B. We suggest that these rocks were deposited in a back-arc basin located inboard of a Rayner aged (ca. 1000 Ma) continental arc that was active along the leading edge the Indo-Antarctic craton. This margin and its associated back-arc basin developed long before collision with the Australo-Antarctic craton (ca. 530 Ma) merged these rocks into Gondwana and sutured them into their present position in Antarctica. The Larsemann Hills rocks are the third occurrence of such a suite of borosilicate or phosphate bearing rocks in Antarctica and Australia: similar rocks include prismatine-bearing granulites in the Windmill Islands, Wilkes Land, and tourmaline-quartz rocks, sodic gneisses and apatitic iron formation in the Willyama Supergroup, Broken Hill, Australia. These rocks were deposited in analogous tectonic environments, albeit during different supercontinent cycles.

Speculation is increasing that Proterozoic eastern Australia and western Laurentia represent conjugate rift margins formed during breakup of the NUNA supercontinent and thus share a common history of rift-related basin formation and magmatism. In Australia, this history is preserved within three stacked superbasins formed over 200 Myr in the Mount Isa region (1800-1750 Ma Leichhardt, 1730-1670 Ma Calvert and 1670-1575 Ma Isa), elements of which extend as far east as Georgetown. The Mount Isa basins developed on crystalline basement of comparable (~1840 Ma) age to that underlying the Paleoproterozoic Wernecke Supergroup and Hornby Bay Basin in NW Canada which share a similar tripartite sequence stratigraphy. Sedimentation in both regions was accompanied by magmatism at 1710 Ma, further supporting the notion of a common history. Basin formation in NW Canada and Mount Isa both concluded with contractional orogenesis at ~1600 Ma. Basins along the eastern edge of Proterozoic Australia are characterised by a major influx of sediment derived from juvenile volcanic rocks at ~1655 Ma and a significant Archean input, as indicated by Nd isotopic and detrital zircon data. A source for both these modes is currently not known in Australia although similar detrital zircon populations are documented in the Hornby Bay Basin, and in the Wernecke Supergroup, and juvenile 1660-1620 Ma volcanism occurs within Hornby Bay basin NW Canada. These new data are most consistent with a northern SWEAT-like tectonic reconstruction in a NUNA assembly thus giving an important constraint on continental reconstructions that predate Rodinia.

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.

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.

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

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 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.

Paleoproterozoic-earliest Mesoproterozoic sequences in the Mount Isa region of northern Australia preserve a 200 Myr record (1800-1600 Ma) of intracontinental rifting, culminating in crustal thinning, elevated heat flow and establishment of a North American Basin and Range-style crustal architecture in which basin evolution was linked at depth to bimodal magmatism, high temperature-low pressure metamorphism and the formation of extensional shear zones. This geological evolution and record is amenable to investigation through a combination of mine visits and outcrop geology, and is the principal purpose of this field guide. Rifting initiated in crystalline basement -1840 Ma old and produced three stacked sedimentary basins (1800-1750 Ma Leichhardt, 1730-1670 Ma Calvert and 1670-1575 Ma Isa superbasins) separated by major unconformities and in which depositional conditions progressively changed from fluviatile-lacustrine to fully marine. By 1685 Ma, a deep marine, turbidite-dominated basin existed in the east and basaltic magmas had evolved in composition from continental to oceanic tholeiites as the crust became increasingly thinned and attenuated. Except for an episode of minor deformation and basin inversion at c. 1640 Ma, sedimentation continued across the region until onset of the Isan Orogeny at 1600 Ma.

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.