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Geoscience Australia has been acquiring deep crustal reflection seismic transects throughout Australia since the 1960s. The results of these surveys have motivated major interpretations of important geological regions, contributed to the development of continental-scale geodynamic models and improved understanding about large-scale controls on mineral systems. Under the Onshore Energy Security Program, Geoscience Australia has acquired, processed and interpreted over 5000 km of new seismic reflection data. These transects are targeted over geological terrains in all mainland states which have potential for hydrocarbons, uranium and geothermal energy systems. The first project was undertaken in the Mt Isa and Georgetown regions of North Queensland. Interpretations of these results have identified several features of interest to mineral and energy explorers: a previously unknown basin with possible hydrocarbon and geothermal potential; a favourable setting for iron oxide uranium-copper-gold deposits; and, a favourable structural setting for orogenic gold deposits under basin cover. Other geophysical data were used to map these features in 3D, particularly into areas under cover. Seismic imaging of the full thickness of the crust provides essential, fundamental data to economic geologists about why major deposits occur where they do and reduces risk for companies considering expensive exploration programs under cover.

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Contained in: Proceedings of papers presented at an industry workshop held in Perth, 20 June 2002. Edited by K.F. Cassidy (See link)

Contained in: Proceedings of papers presented at an industry workshop held in Perth, 20 June 2002. Edited by K.F. Cassidy (See link)

One's understanding of the crustal architecture of Australia's Archaean Yilgarn Craton has increased greatly over the last few years with the collection a range of different seismic data types. The seismic data collected range from broadband seismic studies using distant earthquakes to study lithospheric scale problems, receiver function studies to obtain crustal velocity variations, deep seismic reflection transects to image province to mine scale studies on specific structural problems within the top few kilometres of the crust. At the craton scale, broadband deployments, recording P-wave, S-wave and surface wave variations, have been used to develop 3D velocity models of the craton. These velocity models allow researchers and the Yilgarn Craton mineral industry to understand the larger picture variations within the craton. An interesting feature of the data, easily identified in 3D, is the presence of a fast S-wave velocity anomaly (> 4.8 km.s-1) within the upper mantle. This anomaly is east-dipping and has a series of step-down offsets that coincide approximately with terrain boundaries. Receiver function results show significant variation in crustal and upper mantle velocities across the craton. The receiver function results for the depth to the Moho are consistent with the deep seismic reflection data; both show an increase in depth to the east. Refraction results have provided the framework for the construction of a 3D crustal architecture of the Eastern Yilgarn Craton that suggests the dominant geodynamic process involved the development of a foreland basin with its associated contractional folding and thrusting events. This contractional event were separated by equally important extension events, with the seismic reflection data suggesting that extensional movement on shear zones was more common that previously thought. The seismic reflection suggests that the dominant mineral systems operating involved fluid flow up along crustal-penetrating shear zones. These seismic data have proved invaluable in constraining the crustal geometry of the Yilgarn Craton and in developing three-dimensional models of the crust and upper mantle of the Yilgarn Craton, Australia. In all these data sets, ANSIR, the Australian National Seismic Imaging Facility, is acknowledged for its part in the provision of equipment and expertise and in the data collection phases of the work

A recent passive seismic survey to investigate the variations in crustal structure across the Yilgarn craton has shown significant contrasts in seismic models between neighbouring terranes/superterranes. The Eastern Goldfields showed a unique variability in crustal structure in agreement with a recent reinterpretation of terrane boundaries within the Yilgarn craton. We further investigate the Eastern Goldfields region using a 3-way approach which combines conventional passive seismic analysis with innovative seismic noise-correlation methods and constraints from active source data. The conventional passive seismic analysis enables the receiver function S-velocity structure, and hence composition, of the lower crust to be constrained. The noise-correlation analysis allows seismic model in the 5-15 km depth range to be determined and provides medium resolution coverage across regions not previously explored using active seismic methods. Where active source data have been acquired, shallow structure and deeper seismic velocity determinations are added, providing an unprecedented combination of seismic constraints on the structure of this complex and economically important region. We find that, although some individual terrane boundaries within the new Eastern Goldfields reinterpretation are open to question, the concept of the multi-terrane amalgamation is substantially justified by the exceptional variability of the lower crustal structure. Upper crustal structure is often characterised by seismic discontinuities which may represent detachment surfaces or layered structure that varies between terranes over a sub-100 km length scale. The accretionary history of the superterrane and associated regional tectonic setting of numerous formations of economic significance would now appear to be beyond question.

Legacy product - no abstract available

Seismic stack data available in SEGY format. Data were acquired under the Continental Margins Program in 1985 and processed in-house at AGSO. Hardcopy sections also available on request