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Journal of the Geological Society; 1998; v. 155; issue.6; p. 941-956;
DOI: 10.1144/gsjgs.155.6.0941
© 1998 Geological Society of London

Article

Tectonics and sedimentary environment of the North Scotia Ridge region revealed by side-scan sonar

ALEX P. CUNNINGHAM1, PETER F. BARKER1 & JEREMY S. TOMLINSON1,2

1 British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK (e-mail: a.cunningham{at}bas.ac.uk)

The North Scotia Ridge is a series of islands and submarine ridges extending 2000 km from Tierra del Fuego to South Georgia in the western South Atlantic. The ridge forms the elevated northern tectonic margin of the Scotia Sea, and accommodates E–W sinistral strike-slip motion at the South American–Scotia plate boundary. Existing studies have shown that the northern flank of the North Scotia Ridge is a large and continuous accretionary prism, formed during presumed mid–late Cenozoic N–S convergence. In this study, we present long-range side-scan sonar (GLORIA) images and seismic reflection profiles which show the structural style of the accretionary prism for the first time. The youngest accreted sediments show a uniform fabric of initial deformation (symmetric–gently asymmetric folds of 1–4 km wavelength), which has been subsequently disrupted at shallower depths by additional shortening and uplift. Between 52º45'W and 50º30'W, the deformation front is exposed at the sea floor, and the Falkland Trough retains the appearance of an active convergent margin. Elsewhere, however, the deformation front is buried beneath younger, undeformed drift sediments indicating that convergence has ceased. GLORIA sonographs also show geological features consistent with current-control of sedimentation, non- deposition, and erosion beneath the Antarctic Circumpolar Current. In particular, this study describes current-influenced sedimentation in the Falkland Trough, and steep-sided, eroded depressions and diffuse slope-parallel fabric on the elevated Falkland Plateau.

Key Words: GLORIA • Scotia Ridge • South Atlantic • accretionary wedges




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