Unearthing the marginal terranes of the South Australian craton: keystone of Proterozoic Australia.
An ARC funded Linkage project - LP0882000
Martin Fairclough (PIRSA)
Doctor Peter Betts (Monash University)
Doctor Bruce Schaefer (Monash University)
This collaborative project between Monash University, PIRSA and the CMXUC was awarded funding by the Australian Research Council in October 2007 and will begin in early 2008. Total funding for the project is $630,000 comprising $430,000 from the ARC and $200,000 plus in-kind contributions from PIRSA. The funding includes a three-year ARC APD(I) fellowship for Doctor Graham Baines.
The geological structure and evolution of unexposed basement of the South Australian Craton is poorly constrained yet holds the keys to understanding the Proterozoic amalgamation of continental Australia. This project will use geophysical data to constrain the three dimensional (3D) structure of the crust and rock samples obtained during a scientific drilling program to constrain the rock types, petrophysical properties, provenance and age of the basement. This project will define the architecture of the major crustal blocks, and determine their geological evolution. The results will underpin models for terrane accretion, continental growth and reorganization, and provide a framework for mineral exploration.
The primary aim of the project is to understand the architecture and tectonic evolution of the buried and exposed terranes along the margins of the South Australian Craton to understand and develop on conceptual models of continental amalgamation during the Proterozoic, To achieve this aim, the following will be addressed:
- Characterizing the marginal terranes of the South Australian Craton in terms of their geophysical signature, component rock types, and their ages.
- Determination of the architecture and geometry of the boundaries of the marginal terranes of the South Australian Craton in 3D, including the boundary between the South Australian Craton and the Musgrave Block.
- The constraining of the provenance of rocks within the margin terranes.
- The constraining of the orogenic evolution including the age of deformation and metamorphism, the structural style, and the role of major faults and shear zones.
- The development of a more sophisticated higher resolution tectonic models that build on first order geodynamic models for Precambrian amalgamation of the building blocks of Australia.
These results will enable the determination of the geological processes responsible for the amalgamation of Australia during the Proterozoic and will have immediate impact on understanding: (i) crustal architecture of Australia; (ii) Australia in a global Proterozoic context; and (iii) conceptual tectonic models for mineralization of this period including the vast Pb-Zn belts of northern Australia and Fe-oxide Cu-Au mineral belt of eastern Proterozoic.
A fundamental aspect of this project will be to define the 3D architecture of the marginal terranes and their bounding structures using a combination of potential field analysis, seismic interpretation, and geological data collected from drill holes and field mapping. This has not been done before in the marginal terranes of the South Australian Craton.
Geophysical analysis will involve a combination of interpretation of seismic reflection data, integrated interpretation of aeromagnetic and bouguer gravity grids, and combinations of forward, inversion and 3D modeling to constrain the internal architecture of the marginal terranes and determine the location and geometry of the terrane boundaries.
Potential field analysis will be the primary tool used in this study because excellent aeromagnetic and gravity data available in South Australia are the only geophysical data that have the necessary spatial coverage and resolution to constrain the 3D structure of the basement. These data also allow interpretation of geological maps, enables extrapolation of geological provinces over vast distances, and effectively images structure in the crust because these faults and shear zones often juxtapose packages of rocks of different rock property character, or are locations of intense fluid flow which alters rock properties within the fault zone. Potential fields are therefore useful for mapping out structure and associated overprinting relationships. Geophysical analysis will be used to determine the internal architecture of the marginal terranes to assess vergence directions and internal fault architecture. This analysis will provide constraints on the transport direction and fault kinematics during amalgamation events. Potential field also allow the sources of the signal to be filtered out and are thus very good data to determine the crustal architecture at different depth.
Drilling Program and Fieldwork
The proposed drilling program will access geological terranes that were identified from geophysical data. A number of drill-holes have penetrated basement in the region and been analysed but these data are of limited value given that drilling was undertaken by exploration companies, with a particular focus. The proposed scientific drilling program will follow the planned seismic transect and thus provide direct geological data that will add significant value to the results of this project. Results from this scientific program of drilling will provide samples that will be assessed for rock type, rock property analysis, isotope and geochronology analysis. The resultant datasets will potentially triple the available geologic constraints within these terranes. Drill sites will be located along the seismic transect and selected to penetrate representative basement in each basement terrane. This contrasts available drill hole data which has been collected by the minerals sector which will have targeted anomalous rock types.