Neogene and active shortening offshore the reactivated Levant margin in Lebanon: results of the SHALIMAR cruise

HR: 1340h
AN: T53B-0490 [Abstracts]
TI: Neogene and active shortening offshore the reactivated Levant margin in Lebanon: results of the SHALIMAR cruise
AU: Briais, A
EM: anne.briais@cnes.fr
AF: Observatoire Midi-Pyrenees, 14 Av Edouard Belin, Toulouse, 31400 France
AU: * Singh, S C
EM: singh@ipgp.jussieu.fr
AF: Laboratoire de Geoscience Marines, IPG Paris, 4 Place Jussieu, Paris, 75252 France
AU: Tapponnier, P
EM: tappon@ipgp.jussieu.fr
AF: Laboratoire de Tectonique, IPG Paris, 4 Place Jussieu, Paris, 75252 France
AU: Elias, A
EM: elias@ipgp.jussieu.fr
AF: Laboratoire de Tectonique, IPG Paris, 4 Place Jussieu, Paris, 75252 France
AU: Elias, A
EM: elias@ipgp.jussieu.fr
AF: CNRS, Bhannes, B.P. 16-5432, Beyrouth, 5432 Lebanon
AU: Sursock, A
EM: asursock@cnrs.edu.lb
AF: CNRS, Bhannes, B.P. 16-5432, Beyrouth, 5432 Lebanon
AU: Jomaa, R
EM: rjomaa@cnrs.edu.lb
AF: CNRS, Bhannes, B.P. 16-5432, Beyrouth, 5432 Lebanon
AU: Carton, H
EM: carton@ipgp.jussieu.fr
AF: Laboratoire de Geoscience Marines, IPG Paris, 4 Place Jussieu, Paris, 75252 France
AU: Daeron, M
EM: daeron@ipgp.jussieu.fr
AF: Laboratoire de Tectonique, IPG Paris, 4 Place Jussieu, Paris, 75252 France
AU: King, G
EM: king@ipgp.jussieu.fr
AF: Laboratoire de Tectonique, IPG Paris, 4 Place Jussieu, Paris, 75252 France
AU: Jacques, E
EM: Eric.Jacques@eoast.u-strasbg.fr
AF: IPG Strasbourg, 5 Rue Descartes, Strasbourg, 67084 France
AB: The objectives of the SHALIMAR cruise were to study recent deformation of the Mediterranean seafloor west of Mt Lebanon. We collected multibeam bathymetry and back-scatter images, reflection seismic profiles - surface and deep-towed, 3.5 kHz echo-sounder data, gravity and magnetic data over an 80 km-wide zone offshore the entire Lebanese coast. The bathymetry reveals a very steep slope between Beyrouth and Batroun, with a water depth of 1500 m only 5 km offshore. Between Saida and Tripoli (33.5N to 34.5N), both the bathymetry and seismic lines show a series of ramp anticlines affecting Plio-Quaternary deposits and a seismically transparent layer with variable thickness corresponding to the Messinian evaporites (5.6 Ma). This fold-and-thrust belt is the offshore expression of shortening related to the formation of Mt Lebanon. It is limited westwards by a prominent fold front 30 km from shore. Some ramps appear to be submarine continuations of faults documented ashore (e.g., Aabde and Tripoli thrusts). The strikes of fold axes are consistent with WNW-ESE shortening and slip-partitioning along the 30$^ų$ Lebanese bend of the Levant fault. North of Tripoli and south of Saida, the continental margin displays a wider shelf (20 km) and gentler slope. In the south, at 1200-1500 m depth small, closely spaced, NE-trending scarps attest to young, distributed dip-slip faulting, although deformation is much less than north of Beyrouth. At the southern extremity of our survey, NW-trending normal fault scarps roughly aligned with the Mt Carmel-Haifa fault vanish 50 km offshore in the Levant basin. Bouguer gravity anomalies, estimated by removing from free-air gravity data the effect of bathymetry, display a very steep gradient between Beyrouth and Tripoli, marking the passage from thickened Mt Lebanon crust to thin crust in the Levant basin. Gravity anomalies also outline large, NE-SW trending steps between the basin crust and thinned continental crust near and south of Beyrouth. The particularly large negative anomalies in the north likely reflect flexure of the lithosphere due to subduction under Cyprus and underthrusting beneath Lebanon. The SHALIMAR data suggest that local compression induced by the bend in the Dead Sea Transform reactivated faults of the Mesozoic Levant margin into lateral ramps and thrusts whose evolution may lead to subduction. It is possible that the shorter distance between the transform and margin in central Lebanon (35 km) than in Syria (65 km) is one measure of continental shortening. That the oceanic lithosphere is strong may explain why the Carmel and Roum faults did not extend into the Levant basin.
DE: 8005 Folds and folding
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
DE: 3025 Marine seismics (0935)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting