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Journal of the Geological Society

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

¹ British Antarctic Survey, NERC, High Cross, Madingley Road, Cambridge CB3 OET, UK
² Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-3000 Hannover 51, FRG

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.