HR: 15:10h
AN: T53E-07    [Abstracts]
TI: Structure of the NE-Rockall Trough from Wide-Angle Seismic Data Modelling: The Role of Pre-break-up Extension on the Formation of Continental Margins
AU: * Klingelhoefer, F
EM: fklingel@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 20280 France
AU: Edwards, R A
EM: rae@soc.soton.ac.uk
AF: Challenger Division, National Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: England, R W
EM: rwe5@leicester.ac.uk
AF: Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH United Kingdom
AU: Hobbs, R W
EM: r.w.hobbs@durham.ac.uk
AF: University of Durham, South Road, Durham, DH1 3LE United Kingdom
AB: The Rockall Trough is a 250 km wide and up to 3 km deep bathymetric basin separating the Irish and UK continental shelves from the Rockall and Hatton Banks. It is one of a series of rift basins that formed prior to the opening of the present day North Atlantic Ocean. Two wide-angle seismic lines located in the northeast Rockall Trough were acquired in May 2000. One Line crosses the Trough from the Hebrides continental shelf to oceanic crust west of Lousy Bank in a NW-SE direction. The other line intersects the first, crosses the Wyville-Thomson Ridge in a SW-NE direction and ends in the Faroe-Shetland Trough. Sonobuoy data and expanding-spread profiles acquired in the same area have been remodelled. Analysis of the seismic data using travel-times and amplitudes reveals an up 5 km thick sedimentary layer including an up to 1.5 km thick basaltic layer present in most of the trough. Beneath the sediments is highly stretched continental crust of ca. 13 km thickness. The crust thickens to about 24 km beneath Lousy Bank, which is interpreted to be of continental nature. Beneath the Hebrides continental shelf a three layer continental crust 26 km thick is modelled. A high-velocity layer up to 12 km thick is observed underneath the ocean-continent boundary west of Lousy Bank and is interpreted as magmatic underplating resulting from excess volcanism during rifting. The modelled wide-angle profiles show that the Rockall and Faroe Shetland Troughs have stretching factors of between 2 and 6. Stratigraphic data suggests that rifting in these Troughs took place in early to mid-Cretaceous times (c. 120 Ma), some 60 Ma before the opening of the NE Atlantic. Consequently, at the time of continental break-up at about 55 Ma, the lithosphere beneath the Troughs was dominated by strong mantle lithosphere, making them resistant to further rifting. They remained strong as N Atlantic rifting gave way to ocean floor spreading and they do not show evidence of extension (e.g. faulting) of Early Paleogene age. Rifting to form oceanic crust took place along an axis to the east of the Troughs, through the relatively unextended and potentially weaker lithosphere of the Hatton Bank, Lousy Bank and Faroes Bank regions. The magmatic underplating may have played a role in the final stages of continental break-up but its distribution suggests that it does not appear to play a significant role in modifying the crustal structure on a large scale to promote break-up.
DE: 3025 Marine seismics (0935, 7294)
DE: 3075 Submarine tectonics and volcanism
DE: 8105 Continental margins: divergent (1212, 8124)
SC: Tectonophysics [T]
MN: Fall Meeting 2005