Mapping Undercover: Using Integrated Potential Field Interpretation, Inversion and 3D Modelling to Assess Basin Prospectivity.

Abstract:

Potential field interpretation and three-dimensional modelling combined with geochemical analyses are used to examine the subsurface below the poorly exposed Paleoproterozoic Yerrida Basin in central Western Australia. Past geodynamic processes and tectonic activity are revealed through imaging the structure of this region. Direct observation of basement and intrusive rocks is impossible due to overlying cover and sedimentary strata, thus geophysical imaging and modelling can reveal much under cover. This study finds that high amplitude density anomalies around the basin cannot be reconciled with current geological understanding, inferring that the density anomalies represent a possible abundance of buried and high-density material that is not indicated by the surface rocks. A hypothesis suggesting the causitive source for these high-density anomalies is the presence of intrusive and extrusive mafic volcanic rocks. Geochemistry also reveals that the magmatic history of the basin is more complicated than previously thought. In additional, sulphur isotopic data indicates no Archean signature to the mafic rocks, a somewhat surprising result given the basement to the basin is Archean cratonic rocks. It is proposed the mafic rocks were sourced from vents or sub-basins located to the north. The utility to the approach described here is examined for application to cratonic sag-basin environments. This result highlights the value in geophysics and geochemistry to reveal complexity in the earlier geodynamic evolution of the basin that may be indiscernible from surface geology, but may have high importance for the tectonic development of the region and its mineral resources.