Talk by: Dr Peter Gunn, Consulting Geophysicist
The magnetic map of Australia shows numerous large magnetic anomalies with lateral dimensions of the order of tens and even hundreds of kilometres. Many of these anomalies spatially correlate with the depocentres of sedimentary basins and the axes of rift systems. Such anomalies have been interpreted as being due to large mid-crustal intrusions resulting from mantle plumes and crustal extension in associated rift systems and to be related to the formation of the basins and rifts.
Despite being at depths of the order of 10-15 km, the geometry of such features influence sedimentation and structuring at all stages of the development of the overlying rifts and basins. Areas of uplift and subsidence can be interpreted by mapping the intrusions. As a result it is possible to predict facies distributions.
Areas of crustal extension and structural highs can be inferred from the outlines of the anomalies. Major basin bounding faults, accommodation zones that could localise mineral deposits and sub-basin outlines can also be mapped using the anomalies.
Cases can be made that a knowlege of the geometry of the intrusions can be used to predict the the localities of exhalative Cu-Au-Pb-Zn-Au deposits and FeO-Cu-Au-REE deposits.
Various mafic-ultramafic intrusions of possible economic interest appear to be developed at shallower levels above the mid-crustal intrusions. The intrusions themselves appear to be of mafic-ultramafic composition and are themselves of economic interest in situations where they outcrop as a result of erosion or tectonic activity.