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Abstract

The Cooper Bay Dislocation Zone (CBDZ) represents a major NW-SE trending tectonic boundary within the island of South Georgia that juxtaposes components of a Middle Jurassic to mid-Cretaceous island-arc and back-arcbasin system. New detailed structural data from the southern end of the dislocation zone reveal that earliest displacement along the boundary appears to have been associated with dip-slip reverse shear, characterised by widespread proto-to meso-mylonitic granitic rocks within the basement assemblage exposed to the southwest of the shear zone. Along the northeast margin, highly sheared and mylonitised metasedimentary and metabasic rocks reveal sinistral strike-slip kinematics and a sub-horizontal mineral lineation. Narrow zones of sinistral shear are locally superimposed within the basement rocks along the SW margin, that together with the presence of brittle sinistral faults suggest that the strike-slip component of deformation postdates the dip-slip. Comparison with the tectonic history of the Rocas Verdas Marginal Basin, Fuegian Andes, suggests that the sinistral shear event preserved along the CBDZ maybe be related to Late Cretaceous, main Andean orogenic transpression, although a Cenozoic event cannot to ruled out.

South Georgia and Gondwana's Pacific Margin: Lost in translation?

“…The Drygalski Fjord and Larsen Harbour complexes were tectonically emplaced along the Cooper Bay Shear Zone, a NW-trending mylonitized fault zone with a complicated history of normal, reverse, oblique and left-lateral strike-slip or transtensional deformation (Storey and Macdonald, 1984;Curtis, 2007;Curtis et al, 2010). Dalziel (1981) suggested that some of these movements occurred in mid-Cretaceous times on the basis of observations on rocks in South America that he assumed to be near neighbours to South Georgia's.…”