Beginning in the Archean, the continent of Australia evolved to its present configuration through the accretion and assembly of several smaller continental blocks and terranes at its edges. Australia grew usually by convergent plate margin processes, such as arc-continent collision, continent-continent collision or through accretionary processes at subduction zones. The accretion of several island arcs to the Australian continent, through arc-continent collisions, played an important role in this process, and the geodynamic implications of some Archean and Proterozoic island arcs recognised in Australia will be discussed here.

The origins of high heat production (HHP) granites - with high concentrations of the heat-producing elements Th, U and K (HPE) - is controversial, particularly large areas of such rocks. To constrain possible controls on HHP granites, we have investigated temporal changes in Th, U and K contents of Paleoarchean to Mesozoic granites in Australia, and how these relate to peri-ods of HHP magmatism. Australian HHP granites range in age from Mesoarchean to Triassic, but are most abundant in the Neoarchean, the Paleoproterozoic - early Mesoproterozoic, and the Carboniferous. HHP magmatism ranges from relatively short lived (<30 Ma) geographically-restricted events in the Neoarchean and Carboniferous, to geographically widespread, (possibly unrelated) repetitive events over an extended time period (ca. 1800 to 1500 Ma) for the Proterozoic.

Until recently, tectonic reconstructions have been limited by (1) the assumption that tectonic plates do not deform, or (2) the inability of software packages to simulate deformation. The assumption that plates do not deform is based on the earliest ideas about plate tectonics. This assumption has led workers dealing with plate tectonic reconstructions to introduce new micro-plates to explain the inconsistencies observed in different place circuits (e.g. the Somalian plate). However, we now know that the oceanic and continental crust deform. Therefore, tectonic reconstructions must begin to address this point, without the need to invoke more and more micro-plates to resolve inconsistencies in rigid plate circuits. The second point, that software cannot simulate plate deformation is no longer an issue after the development of Pplates. Pplates is an open-source tectonic reconstruction package that allows geologists to build both classical (rigid) plate reconstructions as well as deformable plate reconstructions. To do this, the software uses one or meshes to move data back and forth in time. Each of these meshes is deformable in order to simulate deformation of the crust. This software also allows geologists to import and deform GIS data. Here we report the initial results of a deformable reconstruction of the Australian and Antarctic plates, from the timing of rifting prior to Gondwana break-up, to the present. This reconstruction also shows the timing of major fault development in the sedimentary basins along Australia's southern margin. Future work aims to simulate development of major crustal features on the Australian and Antarctic plates, and to incorporate palaeogeographical interpretations from the sedimentary record. Our ability to simulate extensional deformation associated with continental break-up has implications for both global tectonic reconstructions as well as reconstructions of individual sedimentary basins

Summary of forward gravity and flexure modelling of the New Caledonia Trough to highlight temporal variations in lithospheric rigidity during its evolution.

Over the last fifteen years, Geoscience Australia, through its Onshore Energy Security Program, in conjunction with Primary Industries and Resources South Australia (PIRSA), the Geological Survey of New South Wales (Industry & Investment NSW), the Australian Geodynamics Cooperative Research Centre, and the Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC), has acquired several deep seismic reflection profiles, which, when combined, form an east-west transect about 870 km long in southeastern Australia. The seismic data vary from low-fold, dynamite-source to higher-fold, vibroseis-source data. The combined seismic profiles, from the western Eyre Peninsula to the Darling Basin, provide a near complete cross-section of the crust across the Gawler Craton, Adelaide Rift System, Curnamona Province, Koonenberry Belt and Darling Basin. The entire region is dominated by east-dipping faults, some of which originated as basin-bounding extensional faults, but most appear also to have a thrust sense of movement overprinting the extension. In the Gawler Craton, an inferred shallow, thin-skinned thrust belt occurs to the west of an inferred thick-skinned thrust belt. The boundary between the two thrust belts, the Kalinjala Mylonite Zone, was active at least during the Kimban Orogeny, with possible extensional movement at that time. The thrust movement possibly occurred during the ~1600 Ma Olarian Orogeny.

No abstract available

This record outlines models for the tectonic evolution of Australian Proterozoic terranes, and the mineral systems that are likely to have operated in particular regions at particular times.

This report documents a study into the Late Jurassic to Recent breakup and drift history of southern Australia, Antarctica and New Zealand , and the relationship between these tectonic events and the stratigraphy and drainage history of these areas. The study was conducted between March 1999 and August 2000. Many of the goals have been achieved, but the plate reconstructions still need to be put into a proper geo-referenced kinematic framework. The purpose behind the study was to lay the framework for understanding the palaeogeography, lithofacies, tectonics and geomorphology of these areas in a reconstructed palinspastic setting; something that had not been accomplished before. The methodology has been to first of all compile structural elements maps for the southern Australian and conjugate Antarctic margins. An updated ocean age map was also prepared as a basis for a first-pass reconstruction. Then the stratigraphy was summarised for three representative cross sections in the Great Australian Bight, Otway and Gippsland Basins, and these were displayed as detailed chronostratigraphic sections in order to demonstrate the stratigraphic responses to the breakup history. One of the vital predictive conclusions was to try and understand the structure and stratigraphy under the lower continental margins; the prime tools for this part of the study were deep-penetration seismic lines shot by AGSO under the Law of the Sea and Continental Margins programs. Finally, a set of 18 plate reconstruction maps were compiled for the period from the Oxfordian to the Present Day, with elements of the tectonics and stratigraphy plotted on them. Because of time constraints and the inability to work the appropriate plate kinematic software, the reconstructions presented here were prepared with scissors and tape from the ocean age map and hence must be regarded as indicative cartoons of the plate positions. This situation is obviously not ideal but is considered justified by the need to understand the geological relationships between the various terrains before going to a rigorous kinematic reconstruction. AGSO supported this study as a Collaborative Research Project, providing both data and support with expenses. In addition, this work has been shown at various stages to a large number of people, all of whom helped by making comments and suggestions, and their contributions are gratefully acknowledged. Some of those involved were:- Kevin Hill (La Trobe University) Nick Hoffman (La Trobe University) Mark Smith (Petroleum Consultant) Alan Partridge (La Trobe University) Heike Struckmeyer (AGSO) Jennie Totterdell (AGSO) Howard Stagg (AGSO) Jacques Sayers (AGSO) Russell Korsch (AGSO) Colin Pain (AGSO) Paul O'Sullivan (Syracuse University, NY) Meredith Orr (Monash University) Mike Hall (Monash University) Steve Gallagher (Melbourne University) Guy Holdgate (Melbourne University) Barry Kohn (Melbourne University) Dietmar Muller (U. Sydney) Mike Gurnis (Caltech) Chris Adams (NZIGNS) Tom Bernecker (VDNRE) Andrew Constantine (VDNRE) David Moore (VDNRE) Ross Cayley (Geol. Survey Victoria) Cliff Ollier (ANU) Graham Taylor (University of Canberra)

The northeastern part of the Archaean Pilbara Craton is characterised by an ovoid dome and basin pattern of domal granites separated by synformal greenstones (supracrustal rocks). This ovoid pattern is variably preserved at various structural and stratigraphic levels, with the most deeply eroded domes being granite dominated, and the least eroded domes being greenstone dominated. The North Pole Dome (NPD) is an example of a relatively high-level dome that has a flanking syncline preserving some of the youngest rocks of the craton (Fortescue Group) to be involved in the doming process. At the apex of the NPD is a small intrusive granite that was considered by some workers to be the top of a large underlying domal granite batholith. The NPD comprises mostly dense basaltic greenstones that range in age from ca. 3500 Ma to 2700 Ma. The ca. 3460 Ma North Pole Monzogranite, a volumetrically insignificant intrusive granite body, intrudes the greenstones in the apex of the dome. No marginal shear zones occur around the intrusion. A new model, based on a detailed gravity traverse across the monzogranite, suggests that the granite intrusion is plug-like, up to 1.5 km thick and does not represent the exposed top of a larger underlying domal batholith. Results from potential field modelling show that the dome is relatively flat bottomed, with a base and around 5.5-6.5 km deep. The NPD has no significant granitic material within the dome, but like all greenstones, is underlain by felsic crust (granite) below its base. The development of the NPD (and flanking syncline) was a multistage process. The first stage of doming involved relatively minor doming/tilting, possibly associated with the emplacement of the monzogranite, because palaeocurrents of synchronous volcanic rocks flowed radially outward from the dome. It is likely that this doming was minor as there are no recorded unconformities in the Warrawoona Group (in the NPD) above these volcanic rocks. A major dome-forming event (tilting >20?) occurred in the period between 3240 Ma and 2772 Ma, and was unrelated to the emplacement of the small granite plug (diapirism). Regional folding and refolding from horizontal compression deformed the area into a domal shape (Type I fold interference pattern). Uplift and erosion of the dome was superseded by extension and deposition of flood basalts (Fortescue Group) that flowed towards the dome. Three further stages of shortening folded the regional unconformity and the underlying and overlying units, further amplified the underlying dome, developed the flanking Marble Bar syncline, as well as fold interference patterns in the Fortescue Group. The NPD was developed over a 800 Ma time frame, ostensibly by a process of fold interference due to multiple stages of horizontal compression. This work shows that diapirism was not the cause of the development of the domal geometry of the NPD, and its flanking syncline, rather folding and refolding due to horizontal compression was the principal controlling factor.

Introduction to a thematic issue of AJES on the Tasmanides. Most papers were originally presented at the 15th Australian geological Convention in Sydney, 3-7 july 2000.