HR: 1340h
AN: T43B-1391    [Abstracts]
TI: What does the 3D Sedimentary Architecture tell us about Continental Breakup: the Example of the Southern Iberia Abyssal Plain.
AU: Peron-Pinvidic, G
EM: gwenn.peron-pinvidic@eost.u-strasbg.fr
AF: EOST-CGS, 1 rue Blessig, Strasbourg, 67084 France
AU: * Manatschal, G
EM: manatschal@illite.u-strasbg.fr
AF: EOST-CGS, 1 rue Blessig, Strasbourg, 67084 France
AU: Minshull, T
EM: tmin@soc.soton.ac.uk
AF: NOC, European way, Southampton, SO14 3ZH United Kingdom
AB: Most of the conceptual ideas concerning the sedimentary architecture and tectonic evolution and models quantifying isostasy at rifted margins are based on either continental rifts or proximal margins both of which underwent only small amounts of crustal thinning. However, the increase number of higher-resolution seismic and drill-hole data from the more distal margins clearly show that: (1) concepts and models used in proximal margins are ineffective at predicting the deformation history as well as the subsidence history in more extended distal margins; and (2) deeper margins show a strong heterogeneity along strike. The aim of our study is to resolve the evolution of rift structures in time and space in the most distal parts of the margins by mapping the 3D architecture of dated sedimentary units in the Southern Iberia Abyssal Plain (SIAP). We defined 6 seismic formations based on own observations and descriptions given by Wilson et al. (1996). In order to have the best possible resolution and to be able to correlate these seismic formations with ODP drill sites, we used all available seismic lines (CAM, GP, IAM9, ISE, LG12, Sonne). Of particular interest for our study was the distribution of the lowermost formation overlying the basement, here referred to as Formation 6. This formation has been dated at DSDP Site 398 as Valanginian-Hauterivian to late Aptian (Wilson et al., 1996), considered as syn-rift to early post-rift. Our results show that: (1) growth structures in the northern SIAP show a progressive younging oceanwards; and (2) the sediment architecture of Formation 6 changes across the SIAP from north to south. Whilst the sediments of Formation 6 occur in the north in classical fault bounded basins overlying tilted blocks, to the south they overlie either exhumed basement or onlap against extensional allochthons. The changing sedimentary architecture reflects a major change in the basin architecture along strike in the OCT from low-strain basins to the north, characterized by steep bounding normal faults and sedimentary wedges overlying a tilted hanging wall, to high-strain basins soled by detachment faults to the south. In later case, accommodation space increases dominantly by horizontal movement, the detachment faults expose deep crustal and mantle rocks at the seafloor, and the syn-exhumation sedimentary strata are parallel or sub-parallel to the low-angle top basement detachment faults. Based on our detailed mapped sedimentary architecture, and on the characterization of the basement structure throughout the distal margin, we propose a 3D schematic model for the evolution of the SIAP. This model suggests a general migration of active faulting towards the future ocean, i.e. from the east to the west, and a change in the mode of extension along strike with upward concave faults in the north to downward concave faults in the south. The increase in strain from north to south may reflect an overall rotation of Iberia during the northward propagation of the spreading centre.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 8000 STRUCTURAL GEOLOGY
DE: 8100 TECTONOPHYSICS
SC: Tectonophysics [T]
MN: Fall Meeting 2005