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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, B02401, doi:10.1029/2004JB003154, 2005

Tectonic evolution of the west Scotia Sea

Graeme Eagles

Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany


Roy A. Livermore

British Antarctic Survey, Cambridge, UK


J. Derek Fairhead

GeTECH, University of Leeds, Leeds, UK


Peter Morris

British Antarctic Survey, Cambridge, UK


Abstract

Joint inversion of isochron and flow line data from the flanks of the extinct West Scotia Ridge spreading center yields five reconstruction rotations for times between the inception of spreading prior to chron C8 (26.5 Ma), and extinction around chron C3A (6.6–5.9 Ma). When they are placed in a regional plate circuit, the rotations predict plate motions consistent with known tectonic events at the margins of the Scotia Sea: Oligocene extension in Powell Basin; Miocene convergence in Tierra del Fuego and at the North Scotia Ridge; and Miocene transpression at the Shackleton Fracture Zone. The inversion results are consistent with a spreading history involving only two plates, at rates similar to those between the enclosing South America and Antarctica plates after chron C5C (16.7 Ma), but that were faster beforehand. The spreading rate drop accompanies inception of the East Scotia Ridge back-arc spreading center, which may therefore have assumed the role of the West Scotia Ridge in accommodating eastward motion of the trench at the eastern boundary of the Scotia Sea. This interpretation is most easily incorporated into a model in which the basins in the central parts of the Scotia Sea had already formed by chron C8, contrary to some widely accepted interpretations, and which has significant implications for paleoceanography and paleobiogeography.

Received 26 April 2004; accepted 12 November 2004; published 2 February 2005.

Keywords: Drake Passage; Scotia Sea; plate tectonics; gateways; Antarctica; plate motion.

Index Terms: 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); 8157 Tectonophysics: Plate motions: past (3040); 9310 Geographic Location: Antarctica (4207); 9360 Geographic Location: South America; 4999 Paleoceanography: General or miscellaneous.

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Citation: Eagles, G., R. A. Livermore, J. D. Fairhead, and P. Morris (2005), Tectonic evolution of the west Scotia Sea, J. Geophys. Res., 110, B02401, doi:10.1029/2004JB003154.