Structure And Development Of The Powell Basin (Ne Antarctic Peninsula)

Abstract

Powell Basin is one of the few present-day examples of a small ocean basin largely surrounded by blocks of continental crust. The western and eastern margins are conjugate passive margins having a transitional crust in the continent-ocean boundary. The distinct characteristics of these two margins suggest a degree of asymmetry in their development. A possible origin of asymmetrical extension during the initial rifting stage may be the occurrence of a shear zone with an eastwards dipping component. A spreading ridge, located in the central part of the basin, split into two crests that may be interpreted as two segments of an overlapping spreading centre (OSC). The rifting episode could have begun about 35-40 Ma. A maximum age of Early Oligocene (29 Ma latest Early Oligocene) is proposed for the ocean basin spreading, that appears to have ceased during the Early Miocene (23 Ma). The eastward motion of the South Orkney Microcontinent relative to the Antarctic Peninsula created this basin. A pullapart origin, related to a dextral fault system, has been proposed for the basin development. However, a possible alternative is to consider that the transcurrent fault bounding the basin has opposite kinematics (sinistral the northern one and dextral the southern one). In this model, the continental crust at the north of the Powell Basin remains fixed in relation to the Antarctic Peninsula.