In 2009, as part of its Onshore Energy Security Program, Geoscience Australia, in conjunction with the Northern Territory Geological Survey, acquired 373 km of vibroseis-source, deep seismic reflection, magnetotelluric and gravity data along a single north-south traverse from the Todd River in the south to nearly 30 km north of the Sandover Highway in the north. This traverse, 09GA-GA1, is referred to as the Georgina-Arunta seismic line, extends from the northeastern Amadeus Basin, across the Casey Inlier, Irindina and Aileron provinces of the Arunta Region and Georgina Basin to the southernmost Davenport Province. Here, we report the results of an initial geological interpretation of the seismic and magnetotelluric data, and discuss some preliminary geodynamic implications.

We present new paleoseismicity data for the 30 km long and 2.5 m high Hyden fault scarp in Western Australia, which, when combined with the results of previous research, provides the most extensive record of surface rupturing earthquakes yet assembled for an "active" Australian intracratonic fault. The data indicate that four to five surface rupturing earthquakes have occurred on the Hyden Fault during the Quaternary (E1: ca. 20 ka, E2: ca. 50-55 ka, E3: ca. 90-100 ka, and two events E4 and E5, >200 ka). Activity is episodic, with single seismic cycle slip rates varying from 0.03 mm/yr to less than 0.01 mm/yr. Palaeo-earthquake magnitudes are estimated to have been in the order of M 6.8. The identification of a similar fault scarp immediately northwest of the Hyden scarp, and of two air-photo lineaments to the west of the Hyden scarp, indicates that strain is distributed amongst a family of faults in this region. The presence of multiple nearby active faults suggests that the recurrence of severe ground shaking in the Hyden region is more frequent than indicated by the palaeoseismic data presented here.

A two-dimensional crustal velocity model has been derived from 1997 wide-angle seismic profiling across the Lachlan Transverse Zone (LTZ) in the eastern Lachlan Orogen. The LTZ is considered to be a significant early tectonic feature controlling structural evolution in eastern Australia. The 364 km north-south profile passed from Ordovician volcanic and volcaniclastic rocks (Molong Volcanic Belt of the Macquarie Arc) in the north across the LTZ into Ordovician turbidites and Early Devonian intrusive granitoids in the south. The velocity model highlights significant lateral variations in sub-surface crustal architecture within the upper and middle crust. In particular, there is a higher P-wave velocity (6.24-6.32 km/s) unit identified in the upper crust under the arc at 5 to15 km depth that is not seen south of the LTZ. Near-surface P-wave velocities within the LTZ are markedly less than those along other parts of the profile and these are attributed to mid-Miocene volcanic centres. In the middle and lower crust there are also poorly defined velocity features that we also interpret to be related to the LTZ. The interpreted Moho depth increases from 37 km in the north to 47 km in the south above an underlying upper mantle with a P-wave velocity of 8.19 km/s. The seismic data indicate significant differences in crustal architecture between the northern and southern parts of the profile within the upper and middle crust, with associated strong indications that the LTZ may also have through-going crustal features to Moho depths.

Previous investigators in the area have interpreted the Nerrima Dome as a dome closed by folding (Wade, 1936), a dome closed against a transverse fault at the eastern end (Kraus, 1942), and as a westward plunging anticlinal fold probably closed by transverse faulting (Reeves, 1949). The purpose of the present survey is to determine by detailed geological mapping the true structure of the Nerrima Dome.

In a unique study, 44 land-based recorders distributed throughout Tasmania, SE Australia, were deployed to record seismic energy from an encircling array of marine normal-incidence reflection shot lines. We invert refraction and wide-angle reflection traveltimes for crustal structure, with the principal outcome being a map of the Tasmanian Moho. Key tectonic inferences from this map include: (1) the Arthur Lineament metamorphic belt in NW Tasmania overlies a major change in crustal thickness (over 5 km) and probably represents the NW limit of deformation in Tasmania during the Mid-Late Cambrian Tyennan Orogeny, (2) thickening of the crust beneath central northern Tasmania may be associated with the juxtaposition of the Eastern and Western Terranes during the Mid-Devonian Tabberabberan Orogeny, and (3) the difference in crustal thickness between the east and west coasts reflects the presence of differing strain regimes during the Cretaceous break-up of Gondwana. No evidence is found for thin-skinned deformation.

The Lesi structure, situated near the coast of the Gulf of Papua, about 100 miles north-west of Port Moresby, was surveyed by plane table. A full account of this survey work is set down in this report. The general characteristics, physiography, and regional geology of the area are described. A detailed account of the geology of the Lesi structure is given, including descriptions of the lithology, palaeontology, stratigraphy, and geological structure. The structure's relation to adjoining structures and the possibility of oil accumulation are discussed. An extract from a micropalaeontological report, geological plans, and photographs of the area are appended.

This report is a record of field work carried out by B.H. Flinter and G.E. McInnes during January-February, 1949. The area covered extends south from Queanbeyan and Mt. Stromlo to 3 miles beyond Williamsdale and represents an easterly extension of the work carried out by W.J. Orme and H.M. Harris in 1948 (Record 1948/031). The investigation was essentially of a regional character and little detailed mapping or close examination of sediments or igneous rocks was attempted. The stratigraphy, igneous rocks, structural observations, and physiography of the area are described in this report. Accompanying geological sketch and section plans are included.

No abstract available

The Palaeozoic rocks of the Bonaparte Basin outcrop at the head and along the western side of Joseph Bonaparte Gulf and extend across the border between Western Australia and the Northern Territory. The Bonaparte Basin is the least known Palaeozoic basin in Australia, due partly to the remoteness of the area and the discouraging results of early coal explorations, and partly to the fact that the stratigraphical extent of the Palaeozoic sequence was only discovered in the last ten years. The Palaeozoic sequence so far established includes Cambrian, Ordovician, Devonian, Carboniferous and Permian sediments which rest on a pre-Cambrian basement and which are overlain in places by a mantle of Lower Cretaceous sediments. The authors intend in this paper to give an account of Carboniferous and Permian sediments of the Basin, as far as present knowledge permits, with briefer mention of the Lower Palaeozoic and Mesozoic sediments of the area.

No abstract available