ASEG Extended Abstracts - ASEG2006 - 18th Geophysical Conference, 2006

Proterozoic rocks of the Isa Superbasin in northern Australia host globally-significant Pb-Zn-Ag deposits as well as a series of Cu, Cu-Au and U deposits. This numerical modelling study explores fluid flow patterns during the shortening deformation event associated with the initial stages of the structural inversion of the Isa Superbasin at ca. 1575 Ma. We have simulated the following scenarios of coupled deformation and fluid flow processes: 1) fundamental basin fluid flow in a basin-inversion environment subject to shortening; 2) syn-tectonic dehydration-related fluid production; 3) the incorporation of hydrofracturing and permeability creation; 4) aquifer permeability changes with depth; 5) the effect on fluid flow of a buried fault versus an open fault.

In a scenario only considering the interaction of deformation and fluid flow during basin inversion, intense upward flow along basin-scale faults and strong lateral flow along the well-connected segments of major aquifer horizons dominate the fluid flow field. The combinations of deformation features, aquifer geometry and fault distribution result in different fluid flow patterns across the simulated section, suggesting some fluid compartmentalization, and mineralisation variations in the region. The incorporation of dehydration fluid production and permeability creation both significantly facilitates fluid flow, expressed as greater fluid fluxes and volumes along faults and aquifer units.

Since the development of mass spectrometric techniques for U-series dating some 20 years ago, fundamental breakthroughs have been made in Quaternary climatic and archaeological studies. In this presentation I will summarise research highlights in U-series dating of palaeoclimatic and archaeological indicators achieved at the University of Queensland over the past five years. These include speleothem records from Australia and China covering the Last Interglacial, the Last Deglaciation and the Holocene periods, coral records in the South China Sea and other sites and Homo erectus and Homo sapiens sites in China.

The usual practice of resistivity imaging using standard electrode arrays, such as Schlumberger, Wenner or dipole-dipole, is based on the pseudosection section for ease of interpretation. However, the resistivity inversion technique has been more and more applied for interpretation of electrical resistivity data. With such a technique, it is not necessary to follow the rules of the standard electrode arrays. Also the technique requires more data to obtain more accurate and ore reliable results. With this in mind a new prototype multi-channel and multi-electrode, full waveform resistivity acquisition system which permits such a recording strategy has been developed. It allows for significant data collection capacity and flexibility and is therefore suitable for 2D or 3D surface or cross-hole tomography and for monitoring.

We present a new numerical scheme for 2D/3D direct current resistivity modelling. This method co-operatively combines the solution of the variational principle of the partial differential equation, Gaussian global quadrature abscissae and local cardinal functions so that it has the main advantages of the finite element method and the spectral method. The formulation shows that the method is close to the spectral element method, but it does not require the element mesh or the element integrations, and it makes it much easier to deal with geological models having a 2D/3D complex topography than the traditional numerical methods. It can achieve a similar convergence rate to the spectral element method. We show it transforms the 2D/3D resistivity modelling problem into a sparse and symmetric linear equation system, which can be solved by an iterative or matrix inversion method.