HR: 1340h
AN: T23D-1654    [Abstracts]
TI: The Algerian Margin: an Example of a Reactivation in Compression of a Complex Cenozoic Passive Margin
AU: * Domzig, A
EM: anne.domzig@univ-nantes.fr
AF: LPG-UMR 6112, Universite de Nantes, 2 rue de la Houssiniere, BP 92205, Nantes Cedex 3, 44322, France
AU: Deverchere, J
EM: jacdev@univ-brest.fr
AF: Universite de Bretagne Occidentale, IUEM-CNRS UMR6538, Technopole Brest Iroise, Plouzane, 29280, France
AU: Yelles, K
EM: kyelles@yahoo.fr
AF: CRAAG, Route de l'Observatoire, B.P. 63, Bouzareah, 99999, Algeria
AU: Govers, R
EM: govers@geo.uu.nl
AF: Faculty of Earth Sciences, Utrecht University, P.O. Box 80.021, Utrecht, 3508, Netherlands
AU: Wortel, R
EM: wortel@geo.uu.nl
AF: Faculty of Earth Sciences, Utrecht University, P.O. Box 80.021, Utrecht, 3508, Netherlands
AU: Petit, C
EM: carole.petit@lgs.jussieu.fr
AF: Laboratoire de Tectonique, Universite Pierre et Marie Curie, 4 place Jussieu, Paris, 75252, France
AU: Cataneo, A
EM: antonio.cattaneo@ifremer.fr
AF: Laboratoire Geosciences Marines, Ifremer, Centre de Brest, Plouzane, 29200, France
AU: Kherroubi, A
EM: aziz_kherroubi@yahoo.fr
AF: CRAAG, Route de l'Observatoire, B.P. 63, Bouzareah, 99999, Algeria
AU: teams, M
EM: 0
AB: The Western Mediterranean underwent a complex Cenozoic history involving subduction of the Tethys Ocean as well as subduction roll-back and associated opening of back-arc basins. During the Oligo-Miocene, the subduction roll-back to the south led to the collision of the Kabylies into the African plate, but subduction continued towards west, causing the Alboran slab to migrate towards the Gibraltar Arc. Northern Africa is at the southern border of this system and is therefore a major study area in the context of slow convergent plates to study the reactivation in compression of a Cenozoic passive margin but also the records of past geodynamic processes. This work aims to characterize the multi-scale structure of the offshore Algerian margin, based on the MARADJA'03 and MARADJA2/SAMRA'05 cruises data (multibeam bathymetry, seismic-reflection, side-scan sonar, backscattering, CHIRP, gravimetry). Tectonic (geomorphology, folds, faults) records reveal large recent and active structures as well as the geological inheritance of the margin. In western Algeria, slab roll-back is likely to have been accompanied by lithospheric tearing (STEP fault) as it has been modelled at a regional scale (Govers and Wortel, 2005): we provide first evidence for the presence of such structure(s) offshore Algeria. The geodynamical conditions have now changed, and we are facing new types of structures. Two main tectonic styles are identified: reverse to the centre and east; and strike-slip to the west. In Central Algeria, the compressional structures are active blind thrusts (Plio-Quaternary) verging to the north (opposite to pre-existing features) expressed as asymmetrical folds, sub-perpendicular to the convergence direction and often en echelon. These faults may all trigger M=6-7.5 earthquakes (e.g. Khair al Din fault near Algiers). Among them, the fault associated with the 2003 Boumerdes event (Mw=6.8) would continue to the surface by flats and ramps creating piggy-back basins or rollovers. From our estimate of sub-surface shortening on Quaternary structures, a significant part of the deformation resulting from Africa-Eurasia convergence (about 5 mm/yr at the longitude of Algiers) appears to be accommodated at the foot of the Algerian margin, which could indicate, with the compressional flexure of the deep basin, a future subduction inception.
DE: 8104 Continental margins: convergent
DE: 8106 Continental margins: transform
DE: 8107 Continental neotectonics (8002)
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting