HR: 1330h
AN: T12A-0438    [PDF]
TI: Crustal Structure and Continental Break-up Revealed From Multichannel Seismic Data Across the North Biscay Rifted Margin.
AU: * Bullock, A D
EM: ab397@soc.soton.ac.uk
AF: Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Minshull, T A
EM: tmin@soc.soton.ac.uk
AF: Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AB: The North Biscay margin is a non-volcanic rifted margin that extends for \mbox{$\sim$400 km} along strike between the Amorican margin to the east and the fossil Bay of Biscay triple junction and Goban Spur to the west. Rifting occured during the late Cretaceous \mbox{($\sim$100 Ma),} at the same time as Goban Spur in the north Atlantic. No syn-rift volcanism is observed and an abrupt transition to oceanic crustal spreading has been previously interpreted. A well defined reflector ('S') can be seen near the seaward tip of continental crust and is continuous for at least \mbox{160 km} along margin strike. Towards the eastern part of the margin 'S' can be identified in thinned continental crust up to \mbox{$\sim$15 km} thick. We present reprocessed data from a \mbox{200 km,} 24 fold multichannel seismic reflection line, CM13, acquired in 1977 over the western part of the margin. Stacking velocity analysis was performed every \mbox{2.5 km} and \mbox{tau-p} multiple removal applied pre-stack. Post-stack time migration was carried out based on a smoothed stacking velocity model. Tilted continental fault blocks are large (up to \mbox{30 km} wide) and draped by Tertiary to recent sediments. Clear pre- and syn-rift sediments are visible over the largest block which is bounded to the south by a strong reflector which rapidly flattens and is overlain by \mbox{1 s} TWT of seismically transparent basement, forming a broad zone \mbox{$\sim$40 km} wide. Beneath this, at \mbox{$\sim$9 s} TWT, is a continentward dipping package of reflectors that may represent the Moho. Further seaward lie three smaller \mbox{(10-15 km)} fault blocks, separated from the other continental blocks by the transparent basement. The bounding fault of the most seaward of these blocks soles out \mbox{0.4 s} TWT within basement at the 'S' reflector which is raised towards top basement and dips continentward. Overlying the southern portion of 'S' is thin upper basement \mbox{(1 s} TWT), seismically distinct from the adjacent thinned continental crust which may represent initial oceanic crust. A \mbox{-100 nT} magnetic anomaly marks this boundary and basement is magnetically quiet for \mbox{$\sim$80 km} until the first marine magnetic anomaly, 34, is reached.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935)
DE: 7218 Lithosphere and upper mantle
DE: 8100 TECTONOPHYSICS
DE: 9335 Europe
SC: Tectonophysics [T]
MN: 2003 Fall Meeting