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

Abstract

Over 12000 km of new aeromagnetic data, gathered during periods free from auroral disturbances, are presented for an area of 290 000 km 2 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.