| Summary: | This Thesis deals with the study of the rifting and seafloor spreading processes in backarc basins using swath-bathymetry and geophysical data. The geophysical methods used are mainly magnetics and gravity, although other methods, such as seismic reflection and submersible data are also presented in some chapters. Three areas were selected for this study: The Central and Eastern Bransfield Basins, northwest Antarctic Peninsula, and the Central Spreading Ridge and the South Pandora-Tripartite Ridges in the North Fiji Basin, southwest Pacific. The Bransfield Basin is a narrow and elongated active backarc basin located between the Antarctic Peninsula and the South Shetland Islands, at the southwestem edge of the Scotia Arc (Fig. 1 a). The Bransfield Basin is composed of three small basins, Western, Central and Eastern, separated respectively by Deception and Bndgeman Islands. The last two were surveyed by the GEBRA 93 cruise during which full swath-bathymetric coverage, single-channel seismic reflection and magnetic profiles were acquired. The Central Bransfield Basin (Fig. la) is 60 km wide, 230 km long and 1950 m deep, and the structures mainly trend N55-60. The basin morphology is dominated by six large seamounts (labelled A to F) that crop out from the sedimented seafloor of the Central Bransfield Basin and align with the basin axis. The seamounts present circular, semi-circular and elongated morphologies. Moreover, the Eastern Bransfield Basin (Fig. la) is 42 km wide, 150 km long, deeper than 2700 m and trends N40-45. The basin is charactensed by four deep en échelon troughs showing a lozenge shape, and small, scattered volcanic cones mainly located in the southwestern half basin. A total of 119 submarine volcanoes are observed in these two basins, with a predominance of higher edifices (over 150 m high) in the Central Basin. Magnetic anomalies are difficult to identify in the Bransfield Basin, although a positive alignrnent well correlated with the submarine volcanic edifices of the Central Bransfield Basin ...
|
|---|