HR: 1330h
AN: T12A-0435    [PDF]
TI: The Porcupine Basin (west of Ireland): Asymmetric Detachment Tectonics and Mantle Serpentinisation. Implications for the Structure and Evolution of Conjugate Non-Volcanic Rifted Margins
AU: * Gaw, V
EM: vgaw@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Reston, T J
EM: treston@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Klaeschen, D
EM: dklaeschen@geomar.de
AF: GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Stubenrauch, A
EM: Alan.Stubenrauch@conoco.com
AF: CONOCO (UK) Ltd, Rubislaw House, Aberdeen, AB15 6FZ United Kingdom
AU: Walker, I
EM: ian.walker@conoco.com
AF: CONOCO (UK) Ltd, Rubislaw House, Aberdeen, AB15 6FZ United Kingdom
AB: The Porcupine Basin, south-west of Ireland, provides an opportunity to investigate the symmetry and temporal development of extension processes leading to continental breakup. The axial stretching factors derived from subsidence increase from 1.5 (typical values of the North Sea) in the north of the basin up to values greater than 6 (typical for continental margins) in the south. Actual stretching factors are likely to be even larger if the mantle underlying the crust has been partially serpentinised. For this reason a series of seismic profiles across the basin can show how a rift evolves to a completely developed continental margin. Furthermore, both sides of the basin may be imaged during one survey, allowing the investigation of symmetry/asymmetry of extension. We have addressed these issues by pre-stack depth migration selected seismic profiles to provide depth images across the basin at different latitudes. These allow structural analysis of the effects of progressive extension. Together with the analysis of reflection characteristics (polarity, waveform, amplitude) allows an integrated interpretation of the basin. A bright reflection (P) appears to represent a detachment fault, and may in part follow the top of partially serpentinised mantle. This is consistent with results from gravity modelling, and with the models of crustal embrittlement and mantle serpentinisation during extension. We infer that this detachment developed as part of a rolling hinge system, with late extension migrating westward. Although overall the basin remains symmetric, the consistent westward structural dip of the detachment implies that, at high stretching factors, extension was asymmetric. We might thus expect considerable differences in the late-stage evolution of conjugate margin pairs, such as Iberia and Newfoundland.
DE: 3025 Marine seismics (0935)
DE: 8015 Local crustal structure
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting