The opening of Powell Basin was part of the regional response to N55Wrelative plate motion of South America away from Antarctica, which led tothe formation of Drake Passage during the Eocene and Oligocene.Restoration of microplates around the basin using gridded magneticanomalies from its margins illustrates the pre-break-up continuity of thePacific Margin Anomaly magnetic high associated with a Mesozoicarc-batholith. Newly compiled magnetic anomaly data over Powell Basinshow subdued linear seafloor spreading type anomalies. These are used,together with marginal and regional geology, to constrain the openinghistory of the basin. Magnetic reversal modelling suggests that slowspreading in Powell Basin probably occurred between 29.7 and 21.8 Ma,following rifting of Mesozoic continental crust with associated break-upvolcanism. A simple, two-phase model for the rotation of the South OrkneyMicrocontinent away from the Antarctic Peninsula accounts for the patternof magnetic reversals recorded in Powell Basin, and for the structure ofits margins.