Ductile thrusting within subduction complex rocks on Signy Island, South Orkney Islands
A model involving repeated NNW-directed ductile thrusting in subduction complex rocks on Signy Island. South Orkney Islands, accounts for the consistent NNW-trending alignment of fold axes, stretching and shearing directions. In the absence of major discrete thrust planes, stratigraphic control or younging criteria, the evidence for consistent ductile thrusting is more cryptic and is found in folding/stretching relations, porphyroblast rotations and mylonite fabrics. Early fold axes parallel to stretching, syn-tectonic garnet rotations, augen lineations and sheath folds all support NNW-directed thrusting as do a common late shear-band foliation and minor shear zones. Development of late open folds with axes parallel to stretching may be due to constrictional deformation, a lateral ramp or differential movement during thrusting.
The structures described from Signy Island may characterize the type of deformation in deep-level ductile thrust zones at the base of an accretionary wedge or in a zone of subcretion. The thrusting direction on Signy Island is inferred to be parallel to the direction of subduction in the South Orkney Islands in the early Jurassic: plate reconstructions suggest that this direction was at a high angle to the arcuate trend of the Antarctic Peninsula continental margin.