Interpretation of aeromagnetic data from the Ellsworth Mountains-Thiel Mountains ridge, West Antarctica

Over 12000 km of new aeromagnetic data, gathered during periods free from auroral disturbances, are presented for an area of 290 000 km2 in West Antarctica, including the majority of the Ellsworth-Whitmore Mountain crustal block. Selection of an appropriate line spacing (20 km) and rigorous diurnal control allowed interpretation of isolated magnetic anomalies by two-dimensional modellìng. Anomalies of 50–500 nT amplitude extend for over 100 km, predominantly with an east-west orientation. They attain their greatest amplitudes over scattered exposures of Middle Jurassic granite, but the measured magnetizations of these rocks (J <0.1 Am−1) are insufficient to match the observed anomalies. It was necessary during modelling to invoke deeper, magnetite-rich, probably mafic plutons (J >0.5 Am−1) beneath the granites. The intrusions probably form part of a widespread bimodal igneous suite created during early stages of continental fragmentation.