Geophysical investigations of P3 segment of the Phoenix Ridge in Drake Passage,Antarctica

Abstract

During the KARP 99/00 cruise, new swath bathymetry, gravity, and magnetic data were obtained in the P3 segment of the Phoenix Ridge in Drake Passage, Antarctica. The detailed bathymetry (including a deep valley, a 2500 m-high seamount, seabed faults and depressions) suggests that spreading rates in P3 varied with time, from an intermediate rate off the ridge axis to a slow rate when spreading ceased. Mantle Bouger anomalies reveal that several gravity lows are associated with the seamount and both flanks of the P3 axial valley, and that highs are found at the junction of the ridge axis and the Hero Fracture Zone. A synthetic magnetic model indicates that the positive anomaly on the axial seamount probably results from the seamount eruption and that it post-dates spreading. By removing the seamount effect, the cessation of P3 spreading is interpreted at about 3.6 Ma, earlier than the 3.3 Ma of previous studies.