Deformational evolution of a Cretaceous subduction complex: Elephant Island, South Shetland Islands, Antarctica

New structural data from Elephant Island and adjacent islands are presented with the objective to improve the understanding of subduction kinematics i n the area northeast of the Antarctic Peninsula. On the island, a first def ormation phase, D-1, produced a strong SL fabric with steep stretching and mineral lineations, partly defined by relatively high pressure minerals, su ch as crossite and glaucophane. D-1 is interpreted to record southward subd uction along an E-W trench with respect to the present position of the isla nd. A second phase, D-2, led to intense folding with steep E-W-trending axi al surfaces. The local presence of sinistral C'-type sheer bands related to this phase and the oblique inclination of the L-2 stretching lineations ar e the main arguments to interpret this phase as representing oblique sinist ral transpressive shear along steep, approximately E-W-trending shear zones , with the northern (Pacific) block going down with respect to the southern (Antarctic Peninsula) block. The sinistral strike-slip component may repre sent a trench-linked strike-slip movement as a consequence of oblique subdu ction. Lithostatic pressure decreased and temperature increased to peak val ues during D-2, interpreted to represent the collision of thickened oceanic crust with the active continental margin. The last deformation phase, D-3, is characterised by post-metamorphic kink bands, partially forming conjuga te sets consistent with E-W shortening and N-S extension. The rock units th at underlie the island probably rotated during D-3, in Cenozoic times, toge ther with the trench, from an NE-SW to the present ENE-WSW position, during the progressive opening of the Scotia Sea. The similarity between the stra in orientation of D-3 and that of the sinistral NE-SW Shackleton Fracture Z one is consistent with this interpretation. (C) 2000 Elsevier Science B.V. All rights reserved.