Evolution of the Adelaidean Basin
Project InvestigatorsDoctor Guillaume Backé
Doctor Wolfgang Preiss (PIRSA)
Damien Dhont (University of Pau)
Stéphane Brusset (University of Toulouse)
University of Pau
University of Toulouse
This project is a collaborative initiative between the University of Adelaide, Primary Industries and Resources of South Australia (PIRSA), with support from Geosciences Australia, and the French Universities of Pau and Toulouse.
The architecture of the Adelaide Geosyncline will be reconstruted in four dimensions, from the earliest stages of Neoproterozoic rifting to the final phase of shortening during the Cambrian Delamerian Orogeny. The reconstruction will be obtained using a combination of field mapping, remote sensing, potential field interpretation and modelling, seismic and magneto-telluric analysis to constrain the present geometry of the basin, and then reconstruct the various stages of basin evolution by unfolding the belt in three dimensions. This will be the first time that such a study has been attempted on the Adelaide Geosyncline and is only now possible due to the convergence of the multiple datasets required to constrain the geometry in three dimensions. These datasets include compilations of detailed mapping conducted over the past 40 years, high resolution satellite imagery and potential field data (magnetic and gravimetric data) collected in the last 10 years and seismic and magneto-telluric studies planned to coincide with this project.
This project is part of a broader and long-term project between the different organisations aiming to improve the scientific knowledge and economic potential of South Australia. This project will be divided into four interdependent modules. Modules 1 and 2 will be run during 2007 with funding from the Center for Mineral eXploration Under Cover (CMXUC) and will focus on the interpretation and modelling of available data in conjunction with research partners in France. Modules 3 and 4 will be run in 2008 and will focus on the building of a 3D/4D geological model of the Adelaide Geosyncline and the initiation of the collection, processing and interpretation of new magneto-telluric dataset.
Module 1: Surface geology
The Northern and Central Flinders area has good exposure, which will enable the direct observation of the relationship between the Pre-Adelaidean basement and the Neo-Proterozoic-Middle Cambrian sedimentary cover. These observations will later be used to constrain geological models of the basement in areas without exposure.
The program will begin with the compilation of all the available surface and sub-surface data for the Flinders Range area into a single GIS database. Using this database together with the analysis of remote sensing images (Landsat images and DEM imagery) and field work will enable (1) the production of a comprehensive regional tectonic map of the Northern and Central Flinders which will offer a general understanding of the Delamerian deformation processes and enabling the determination of the different structural domains which will offer strong structural constraints for both the 2D and the 3D models; (2) quantify how strain was accommodated during the Delamerian orogeny; and (3) reconstruct the tectonic evolution of the area. These observations will enable the production of a set of cross-sections across the Flinders Ranges and along the OEI seismic line using the industry package 2D Move (Midland Valley), which will be used as templates for the potential field forward modelling. This module will benefit greatly from the contribution from the Partner Investigator (PI) Wolfgang Preiss about the stratigraphy and tectonic evolution of the Adelaide Geosyncline, and from the Overseas Investigators Damien Dhont and Stéphane Brusset in remote sensing and field data analysis and balancing of cross-sections.
Module 2: Potential field Interpretation and Modelling
This module, realized totally within the CMXUC group of the University of Adelaide, will involve the use of gravimetric and magnetic data in order to constrain the geometry of the structures at depth and to perform a regional-scale study of the basement geometry.
Potential field analysis
The analysis of the potential field data will enable (1) the determination of crustal boundaries at different depths and reveal steep structures not expressed through other data; (2) resolve overprinting relationships of structures and facilitate regional tectonic reconstruction for each crustal unit; and (3) provide a regional context for other sub-surface geophysical acquisitions.
The available potential field grid will be filtered in order to enhance and/or remove particular wavelengths or to perform trend analysis. Filtering of the grid will highlight features or trends that might not be apparent in the original datasets. Extended Euler deconvolution applied to both magnetic and gravity data will objectively identify the location, dip, depth and susceptibility/density contrast of anomaly sources. This method makes no assumptions about the type or geometry of the source, can be applied directly to both gravity and magnetic data and can be readily adjusted to vary the depths over which it is sensitive. This technique is commonly used to determine the depth to the magnetic basement. The resultant geometrical model from this process will be compared to the balanced cross sections constructed from module 1.
Potential field modelling
The 2D modelling of the geological cross-sections constructed previously will be the inital focus, before moving towards an integrated 3D model. This approach is more numerically and conceptually robust than attempting to directly produce a 3D model.
The balanced cross-sections from modules 1 and 2 will be used as a template for the potential field modelling. This initial 2D model will be interactively and iteratively refined by forward modelling in 2.75 dimensions by a combination of both potential field modelling using GM-SYS and cross-section balancing techniques using 2D Move. This process allows the calculation of the geophysical response in the profile and can include along-strike variations within geological structures. Calculated anomalies will be compared with the observed anomalies from field acquisitions. If a mismatch is observed we will have the possibility either to change the geometry of the section or to modify the bulk properties of the rocks (e.g. density or magnetic susceptibility) before the field can be recalculated. The adjustments of the geometry and rock properties of modelled source bodies will be repeated iteratively until a geologically reasonable match between the observed and calculated geophysical responses is reached.
Modules 1 and 2, to be completed by the end of 2007, will result in a set of balanced cross-sections across the Flinders Ranges and along the planned OEI seismic line.
Module 3: Onshore Energy Initiative – GA Seismic lines
The planned OEI seismic lines will add significantly to the knowledge of the geological structures at depth. The propagation of seismic waves is dependant of variations in the impedance and orientation of the different geological layers. Reflection seismic data allow producing detailed images of the Earth which can be interpreted in terms of geological structures at depth. However, the processing of seismic data is a complex process which can result in seismic images leading to very different interpretations. Modules 1 and 2 of this project will offer valuable guidelines for both the acquisition and interpretation of the seismic lines in the Adelaide Geosyncline and Stuart shelf as they will result in an independent 3D geological model. In return, this geological model will be challenged by the final seismic reflexion images when available in 2008. The timeframe of our project is very favourable because of GA’s commitment to perform the acquisition and processing of the seismic line by the end of 2007-beginning of 2008. In addition, GA’s support is a warranty of the high level of integration of this project in the Auscope and OEI initiatives.
Module 4: Magneto-Telluric data
In addition to the interpretation of the forthcoming OEI seismic lines, we propose to add new magneto-telluric (MT) stations in the vicinity of the seismic lines as a complement to the OEI and GA efforts. MT method is a technique for probing the electrical conductivity structure of the Earth to depth up to 600 km. This module will therefore provide good constraints about the thickness of the sedimentary cover and the depth to basement in the Adelaide Geosyncline. Furthermore, we will be able to investigate the location of major conductive structures and the nature of the mid-lower crust, and anisotropy in the MT response will indicate strain relative to conductive structures. The joint analysis and modelling of field data, potential field data, seismic data and MT data have been very successful to determine the geometry of structures at depth in various tectonic contexts. This module will be done in collaboration with the MT specialist group of the University of Adelaide.
The main aim of this project is to build a 3D/4D geological model of the Adelaide Geosyncline. This model will be crucial for the development of mining and geothermal resources. In addition, reconstructing the Adelaide Geosyncline history stage will offer a better understanding of its tectonic and sedimentary evolution as well as precious information about Neoproterozoic tectonics in general.
This project will be an opportunity to create a long term research relationship between the University of Adelaide and the French universities of Pau and Toulouse. In addition, the collaborative work between the two OI’s has led to the development of a 3D modelling methodology in fold and thrust belt from surface data and reconstruction techniques. The complementary approach developed by the research groups in Adelaide, Pau and Toulouse will greatly benefit to the success of the project.
- The resources required to complete this project will be provided by the Centre for Mineral eXploration Under Cover (CMXUC) of the University of Adelaide. The University of Adelaide houses all the facilities necessary for the accomplishment of the project both the computing and softwares resources and the necessary magneto-telluric data acquisition and processing facilities.
The co-existence at the University of Adelaide of different research groups with a sound interest in the tectonic evolution of the South Australian craton (ie, the Continental Evolution Research Group, CERG) along with geophysical and metamorphic geology exploration expertise will provide a stimulating intellectual environment for the duration of the project.
- The different National and South Australia programs launched in 2006 (Auscope, Onshore Energy Initiative, PACE) will provide the scientific and mineral resources exploration communities with a wealth of data crucial to achieving a better understanding of the geology of Australia. It is therefore essential to develop a coherent scientific approach to best use these data. This project fits perfectly into this framework, as it aims to use the expertise and facilities of various partners (Primary Industries and Resources of South Australia, the University of Adelaide, Geosciences Australia, Auscope and Earth Imaging and Structure) to gain fundamental information about the Australian plate, from its basic structure and evolution to its mineral and petroleum systems. The commitment of various Australian institutions (PIRSA, GA) other than the Host organisation clearly reflects integration of this project in the frame of the Australian geosciences community.
- UNESCO has declared 2008 as the International Year of the Planet. The worldwide effort to make this year a success has to be echoed in Australia and different initiatives coordinated by the National Committee for Earth Sciences will greatly contribute to this. This project would also fit into this framework as well as it will contribute to the National Research Priority Goal: An Environmentally Sustainable Australia (Developing Deep Earth Resources) and to the 2003 National Strategic Plan for the Geosciences. In particular, this study will provide the geosciences community with a regional 3D/4D model for the Adelaide Geosyncline. This model will be a major improvement for the future planning of mining and geothermal energy exploration in this area as well as a great improvement of the tectonic framework and evolution of South Australian Craton.
The better understanding of the Neoproterozoic plate tectonics from the break-up of continent to mountain building, arising from this study should then be used as a case-study in other cratonic areas both in Australia and overseas.