Tectonics of an extinct ridge-transform intersection, Drake Passage (Antarctica)

• Main Authors: Maldonado, Andrés, Carlos Balanyá, Juan, Barnolas, Antonio, Galindo-Zaldívar, Jesús, Hernández, Javier, Jabaloy, Antonio, Livermore, Roy, Martínez-Martínez, José Miguel, Rodríguez-Fernández, José, Sanz de Galdeano, Carlos, Somoza, Luis, Suriñach, Emma, Viseras, César
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Kluwer Academic Publishers 2000
• Subjects: Drake Passage; Shackleton; Shackleton Fracture Zone; West Scotia Ridge; Antarc*; Antarctica
• Online Access: http://nora.nerc.ac.uk/id/eprint/20641/; https://doi.org/10.1023/A:1004762311398

New swath bathymetric, multichannel seismic and magnetic data reveal the complexity of the intersection between the extinct West Scotia Ridge (WSR) and the Shackleton Fracture Zone (SFZ), a first-order NW-SE trending high-relief ridge cutting across the Drake Passage. The SFZ is composed of shallow, ridge segments and depressions, largely parallel to the fracture zone with an `en echelon' pattern in plan view. These features are bounded by tectonic lineaments, interpreted as faults. The axial valley of the spreading center intersects the fracture zone in a complex area of deformation, where N120° E lineaments and E–W faults anastomose on both sides of the intersection. The fracture zone developed within an extensional regime, which facilitated the formation of oceanic transverse ridges parallel to the fracture zone and depressions attributed to pull-apart basins, bounded by normal and strike-slip faults. On the multichannel seismic (MCS) profiles, the igneous crust is well stratified, with numerous discontinuous high-amplitude reflectors and many irregular diffractions at the top, and a thicker layer below. The latter has sparse and weak reflectors, although it locally contains strong, dipping reflections. A bright, slightly undulating reflector observed below the spreading center axial valley at about 0.75 s (twt) depth in the igneous crust is interpreted as an indication of the relict axial magma chamber. Deep, high-amplitude subhorizontal and slightly dipping reflections are observed between 1.8 and 3.2 s (twt) below sea floor, but are preferentially located at about 2.8–3.0 s (twt) depth. Where these reflections are more continuous they may represent the Mohorovicic seismic discontinuity. More locally, short (2–3 km long), very high-amplitude reflections observed at 3.6 and 4.3 s (twt) depth below sea floor are attributed to an interlayered upper mantle transition zone. The MCS profiles also show a pattern of regularly spaced, steep-inclined reflectors, which cut across layers 2 and 3 of the oceanic crust. ...