Seismic structure of the lithosphere across the zone of subducted Drake plate under the Antarctic plate, West Antarctica

During the third Polish Antarctic Geodynamical Expedition in 1987–88, deep seismic sounding measurements were performed in the transition zone between the Drake plate and the Antarctic plate in West Antarctica. 30 shots were fired in the sea along profile DSS-17 of 310 km length. The interpretation was made with the use of seismic records of four land stations in the South Shetland Islands and Antarctic Peninsula. The interpretation yielded a 2-D model of the lithosphere down to 80 km depth. The crustal structure beneath the trough of Bransfield Strait is highly anomalous. The presence of a high-velocity body, with longitudinal seismic wave velocities v_p>7.0 km s⁻¹, was detected in the 6–30 km depth range. This in-homogeneity was interpreted as an intrusion, coinciding with the Deception-Penguin-Bridgeman volcanic line. The Moho boundary depth ranges from 10 km in the South Shetland Trench area to 40 km under the Antarctic Peninsula. In the transition zone from the Drake Passage to the South Shetland Islands, a seismic boundary in the lower lithosphere occurs at a depth ranging from 35 to 80 km. The dip of both the Moho and this boundary is approximately 25°, and indicates the direction of subduction of the lithosphere of the Drake plate under the Antarctic plate. The results obtained were compared with earlier results of seismic, gravity and magnetic surveys in West Antarctica. A scheme of geotectonic division and a geodynamical model of the zone of subduction of the Drake plate under the Antarctic plate is compared with subduction zones in other areas of the circum-Pacific belt.