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

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