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British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
It has long since been recognised that the Ellsworth-Whitmore mountains (EWM) crustal block possesses an anomalous structural and stratigraphic history relative to its neighbouring West Antarctic crustal blocks, and the Transantarctic Mountains. This has led to uncertainties in the original pre-break-up position of the EWM within Gondwana. Positions vary from along the East Antarctic margin, west of the Pensacola Mountains, to within the Natal embayment region between Africa and Antarctica. The original position of the EWM within Gondwana has important implications, as its subsequent transposition has to be accounted for during the tectonic evolution of the Weddell Sea region.
Several geological features have been identified within the EWM as potential constraints on Gondwana reconstructions. These include a Grenvillian age basement devoid of mineral reset ages; an apparently continuous stratigraphic succession from Cambrian to Permian times; Middle-Upper Cambrian extension-related volcanic rocks; no Ross age deformation; and a dextral transpressive component to the Early Mesozoic Gondwanide deformation. Based on a consideration of these key geological features, and comparisons between the Ellsworth Mountains and the palaeo-Pacific margins of Gondwana, we conclude that the EWM displays geological affinities with both the Antarctic and South African margins, and that it was located outboard of both. A prerequisite of this conclusion is that rotation and translation of the EWM must be included in models of early Weddell Sea tectonic evolution.
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