An assessment of the gravity signature of the Windmill Islands, East Antarctica

Abstract

A gravity survey was conducted on the Windmill Islands, East Antarctica, during the 2004-05 summer season. The aim of the study was to investigate the subsurface geology of the Windmill Islands area. Ninety-seven gravity stations were established. Additionally, 49 observations from a survey in 1993-94 were re-reduced and merged with the 2004-05 data. A three-dimensional subsurface model was constructed from the merged gravity dataset to determine the subsurface geology of the Windmill Islands. The main country rock in the Windmill Islands is a Garnet-bearing Granite Gneiss. A relatively dense intrusive charnockite unit, the Ardery Charnockite, generates the dominant gravity high of the study area and has been modelled to extend to depths of 7-13 km. It has moderate to steep contacts against the surrounding Garnet-bearing Granite Gneiss. The Ardery Charnockite surrounds a less dense granite pluton, the Ford Granite, which is modelled to a depth of 6-12 km and creates a localized gravity low. This granitic pluton extends at depth towards the east. The modelling process has also shown that Mitchell Peninsula is linked to the adjacent Law Dome ice cap by an 'ice ramp' of approximately 100 m thickness.