On the basis of about 12500 depth measurements of which 6700 were taken from r/v Profesor Siedlecki, 1300 from r/v Polarstern and the remainder from British navigation charts, a bathymetric chart of the Bransfield Strait in the scale 1:500 000 has been prepared. Within the assumed boundaries the total area of the Bransfield Strait covers 65308.6 square kilometres, of which the Western Basin covers 23.5%, Central Basin — 47.3%, and Eastern Basin 29.2%. Capacity of the whole Bransfield Strait amounts to 38451 km3 . The average depth of the Bransfield Strait is 592 m.
The Polish Geophysical Expedition to West Antarctica in 1979-1980 was carried out by the Institute of Geophysics, Polish Academy of Sciences. Beside deep seismic soundings, 12 multi-channel seismic profiles, with a total length of ca 1000 km have been recorded north and east of the South Shetland Islands and in the Bransfield Strait, but they have never before been completely interpreted and published. All profiles have been processed with modern processing flow including time migration. Profiles crossing the South Shetland Trench revealed distinct reflector inside continental slope, which has been interpreted as border between buried accretionary prism and overlying slope sediments of glacial-marine origin. Profiles in the Bransfield Strait show traces of the Last Glacial Maximum (LGM) in the form of glacial foreground valleys, with some of them used as weak spots for young age volcanic intrusions. This paper is the first comprehensive geological interpretation of collected dataset and differences between results from other expeditions are discussed.
During the Polish Antarctic Geodynamic Expeditions, 1979-91, a wide geophysical and geological programme was performed in the transition zone between the Drake and South Shetland microplates and the Antarctic Plate, in West Antarctica. In the Bransfield Strait area, and along passive continental margin of the Antarctic Peninsula, 20 deep seismic sounding profiles were made. The interpretation yielded two - dimensional models of the crust and lithosphere down to 80 km depth. In the coastal area between the Palmer Archipelago and the Adelaide Island, the Earth's crust has a typical continental structure. Its thickness varies from 36 to 42 km in the coastal area, decreasing to about 25-28 km toward Pacific Ocean. In the surrounding of Bransfield Strait, the Moho boundary depth ranges from 10 km beneath the South Shetland Trench to 40 km beneath Antarctic Peninsula. The crustal structure beneath the Bransfield Strait trough is highly anomalous. Presence of a high-velocity body, with longitudinal seismic wave velocities Vp > 7,0 km/s, was detected there in the 6-32 km depth range. This inhomogeneity was interpreted as an intrusion, coinciding with the Deception-Bridgeman volcanic line. 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° towards the southeast, indicating the direction of subduction of the Drake Plate lithosphere under the Antarctic Plate. Basing on the results of four Polish Geodynamic Expeditions, the map of crustal thickness in West Antarctica is presented.
During the Polish Antarctic Geodynamical Expeditions in 1979-91, deep seismic sounding measurements were performed in the transition zone between the Drake and South Shetland Microplates and the Antarctic Plate in West Antarctica. For the Bransfield Strait area, the seismic records of five land stations in South Shetland Islands and two stations at the Antarctic Peninsula were used. The interpretation yielded two—dimensional models of the crust and lithosphere down to 80 km depth. In the uppermost crust, the unconsolidated and poorly consolidated young sediments with velocities of 1.9 — 2.9 km/s cover the layers 4.0—4.2 and 5.6—5.9 km/s. The crustal structure beneath the trough of Bransfield Strait is highly anomalous. The presence of a high velocity body, with longitudinal seismic wave velocities vp > 7.0 km/s, was detected in the 6 — 30 km depth range. This inhomogeneity was interpreted as an intrusion, coinciding with the Deception—Bridgeman volcanic line. For the uppermost crust, a qualitative comparison was made between the results from the reflection profiles (GUN) and deep seismic sounding profiles (DSS). In the study area, the Moho boundary depth ranges from 10 km beneath the South Shetland Trench 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 Drake Plate lithosphere 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.