HR: 11:20h
AN: T52B-05    [Abstracts]
TI: Passive-active margin inversion along the Levant plate-boundary: Subduction birth and growth of Mt Lebanon.
AU: * Tapponnier, P E
EM: tappon@ipgp.jussieu.fr
AF: Institut de Physique du globe de Paris - Laboratoire de Tectonique, 4 place Jussieu, Paris, 75252 France
AU: Daeron, M
EM: daeron@ipgp.jussieu.fr
AF: Institut de Physique du globe de Paris - Laboratoire de Tectonique, 4 place Jussieu, Paris, 75252 France
AU: Sursock, A
EM: asursock@cnrs.edu.lb
AF: Lebanese National Centre for Geophysics, Bhannes, B.P. 16-5432, Beirut, 1100-2040 Lebanon
AU: Jomaa, R
EM: rjomaa@cnrs.edu.lb
AF: Lebanese National Centre for Geophysics, Bhannes, B.P. 16-5432, Beirut, 1100-2040 Lebanon
AU: Briais, A
EM: anne.briais@cnes.fr
AF: institut de Physique du Globe de Strasbourg, 5 rue Descartes, Strasbourg, 67084 France
AU: Carton, H
EM: carton@ipgp.jussieu.fr
AF: Institut de Physique du Globe d e Paris - Laboratoire de G‚osciences marines, 4 place Jussieu, Paris, 75252 France
AU: Singh, S
EM: singh@ipgp.jussieu.fr
AF: Institut de Physique du Globe d e Paris - Laboratoire de G‚osciences marines, 4 place Jussieu, Paris, 75252 France
AU: Elias, A
EM: elias@ipgp.jussieu.fr
AF: Institut de Physique du globe de Paris - Laboratoire de Tectonique, 4 place Jussieu, Paris, 75252 France
AU: Elias, A
EM: elias@ipgp.jussieu.fr
AF: Lebanese National Centre for Geophysics, Bhannes, B.P. 16-5432, Beirut, 1100-2040 Lebanon
AU: King, G C
EM: king@ipgp.jussieu.fr
AF: Institut de Physique du globe de Paris - Laboratoire de Tectonique, 4 place Jussieu, Paris, 75252 France
AU: Jacques, E
EM: Eric.Jacques@eost.u-strasbg.fr
AF: Observatoire Midi-Pyr‚n‚es, 14 avenue Edouard Belin, Toulouse, 31400 France
AB: Evidence obtained during the SHALIMAR cruise clarifies the Miocene to Present tectonic evolution of the Lebanese segment of the Arabia/Africa plate boundary. A 90 km-long, 30 km-wide submarine fold and thrust belt deforms Neogene carbonates, Messinian evaporites and Plio-Quaternary turbidites offshore Mount Lebanon. The fold belt faces the broadest ($\approx$ 40 km) and highest ($\approx$ 3100 m) part of the mountain, and the steepest continental slope of the Levantine Basin margin, underwater continuation of the great Lebanese flexure. It is simply interpreted as a thin-skinned, foreland migrating thrust wedge, typical of active mountain piedmonts in the Alpine ranges of Eurasia. This belt is limited to the north by the Aabd\'e oblique thrust-ramp, and to the south by a left-stepping, offshore branch of the Roum lateral ramp. That neither of these ramps, or other faults cutting Miocene to Quaternary deposits extend farther into the Basin towards Cyprus indicates that the arcuate Mt Lebanon Thrusts and the Yammouneh fault, with which they connect north of Koubayate and south of Marjayoun, form a local, closed system. As they plunged down under the Lebanese flexure to merge at depth with the fault, the thrusts have governed the growth and rise of the mountain. Since the Mid-Miocene ($\approx$ 15 Ma), this thickening wedge of continental crust was extruded upwards, due to complete slip-partitioning in the Lebanese transpressive bend. Geological sections suggest that the total amount of shortening onshore and offshore is a few tens of kilometers. That the thickening offshore sediments are decoupled from the Levantine basin's basement implies that the mantle lithosphere and $\approx$10km-thick crust of that basin subduct beneath Mount Lebanon. The 25$\deg$CW Lebanese restraining bend and correlative inversion of the Levant passive margin into an active margin only offshore Lebanon result from the 180$\deg$ inversion of tectonic stresses between the Cretaceous and Miocene and propagation of the Dead Sea Transform. The NE-SW striking normal faults observed in Mt Lebanon and the Palmyrides are also clear in the Levant basin from the SHALIMAR bathymetric, gravity and magnetic data. They formed during the NW-SE late Jurassic extension event that led to the final opening of the Levant basin. As it propagated northwards in the Miocene, the left-lateral Dead Sea fault was likely deviated by one prominent Jurassic fault zone, the Damietta-Beyrouth line. This zone marks the southeastern margin of the deepest part of the Basin, with particularly thin (oceanic?) crust. The resulting clockwise swing of the fault, where it reached nearest to the basin margin, naturally led to fault perpendicular shortening, and to successful, runaway underthrusting of dense lithosphere under Mt Lebanon. This illustrates a mechanism for triggering subduction at passive margins reactivated by strike-slip faulting.
DE: 7230 Seismicity and seismotectonics
DE: 8100 TECTONOPHYSICS
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting