Structure of the Mount Isa Region Inferred from Gravity and Magnetic Anomalies

Most of the Mount Isa Inlier lies within the Mount Isa Geophysical Domain, 800 km long and 150 to 250 km wide. This domain is inferred to have formed later than crust to the east and west, and earlier than the Tasman Orogenic System to the south, and the crust to the north. Most major features of the domain parallel the arcuate NNE to NNW trending domain margins. The domain can be longitudinally subdivided using geophysical anomalies into six zones. The zone boundaries broadly correlate with the faults forming the boundaries of the major geological blocks of Blake and Stewart, and bound the extent of some stratigraphic units and batholiths. There are changes in rocks and structures within some zones, in particular at a 20° bend in the domain at 21.5-22°S. Rocks and structures similar to those of the inlier are shown to extend 300 km to the north, and to the south under cover. The western part of the inlier is found to belong in part to the Arunta and Murphy Geophysical Domains. The geophysical anomalies support the interpretation of most Mount Isa rocks forming in an intra-cratonic rift setting, but they show that the lower crustal structure differs from most other Middle Proterozoic mobile belts in that the rift truncates structures on both sides.