The structural evolution of George VI sound, Antarctic Peninsula
George VI Sound, 400 km long and between 25 and 90 km wide, separates Alexander Island from the Antarctic Peninsula. The straight parallel sides of its northern section and sub-parallel normal faulting observed in exposed rock on adjacent parts of Alexander Island and Palmer Land indicate a history of rifting. Subglacial topography, revealed through radar sounding of ice thickness in Palmer Land, shows deep areas which owe their presence to two major fault zones parallel to the main N-S trend. One of these is probably the western escarpment of the Palmer Land plateau and the eastern boundary of the rift system. Bedrock relief suggests that transverse block faulting has differentially raised and lowered the mountains on the eastern side of the sound. A seismic profile through George VI Ice Shelf (which occupies most of George VI Sound) confirms that the “W”-shaped cross-section of the bedrock observed by plumb-line at the northern edge of the ice shelf is also found 250 km further south. The shape may be due entirely to glacial erosion, but it is more likely to be a structural feature subsequently glacially modified. These features are consistent with a model of George VI Sound as a region of Tertiary intra-arc extension within the Mesozoic and Cenozoic magmatic arc of the Antarctic Peninsula and Alexander Island.