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Geological Society, London, Special Publications; 2007; v. 290; p. 285-303;
DOI: 10.1144/290.10
© 2007 Geological Society of London

Restraining bends, transpressional deformation and basement controls on development

Strain partitioning of active transpression within the Lebanese restraining bend of the Dead Sea Fault (Lebanon and SW Syria)

F. Gomez1, T. Nemer1, C. Tabet2, M. Khawlie3, M. Meghraoui4 & M. Barazangi5

1 Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211, USA (e-mail: fgomez{at}missouri.edu)
2 Lebanese National Council for Scientific Research, Beirut, Lebanon
3 Lebanese National Center for Remote Sensing, Beirut, Lebanon
4 EOST, Institut de Physique du Globe, UMR 7516, Strasburg, France
5 Institute for the Study of the Continents, Snee Hall, Cornell University, Ithaca, New York 14853, USA

Recent neotectonic, palaeoseismic and GPS results along the central Dead Sea fault system elucidate the spatial distribution of crustal deformation within a large (c.180-km-long) restraining bend along this major continental transform. Within the ‘Lebanese’ restraining bend, the Dead Sea fault system splays into several key branches, and we suggest herein that active deformation is partitioned between NNE–SSW strike-slip faults and WNW–ESE crustal shortening. When plate motion is resolved into strike-slip parallel to the two prominent NNE–SSW strike-slip faults (the Yammouneh and Serghaya faults) and orthogonal motion, their slip rates are sufficient to account for all expected strike-slip motion. Shortening of the Mount Lebanon Range is inferred from the geometry and kinematics of the Roum Fault, as well as preliminary quantification of coastal uplift. The results do not account for all expected crustal shortening, suggesting that some contraction is probably accommodated in the Anti-Lebanon Range. It also seems unlikely that the present kinematic configuration characterizes the entire Cenozoic history of the restraining bend. Present-day strain partitioning contrasts with published observations on finite deformation in Lebanon, demonstrating distributed shear and vertical-axis block rotations. Furthermore, the present-day proportions of strike-slip displacement and crustal shortening are inconsistent with the total strike-slip offset and the lack of a significantly thickened crust. This suggests that the present rate of crustal shortening has not persisted for the longer life of the transform. Hence, we suggest that the Lebanese restraining bend evolved in a polyphase manner, involving an earlier episode of wrench-faulting and block rotation, followed by a later period of strain partitioning.