--> --> Structural Evolution and Active Tectonics of the Damour – Beit Ed Dine Fault Zone and the Southern Central Mt-Lebanon

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Structural Evolution and Active Tectonics of the Damour – Beit Ed Dine Fault Zone and the Southern Central Mt-Lebanon


The 25Km long Damour – Beit ed Dine fault (DBF) is the southernmost of a set of E – W faults dissecting the western flank of Mt. Lebanon, west of the plate bounding Yammouneh strike-slip fault. The DBF trace in the geology is a series of 4 – 10 Km long, WSW-ENE faults that separate different structural domains in the geology of Lebanon north and south of this fault zone. Growth faulting observed in the Upper Albian – Aptian sedimentary units around the fault segments suggest normal faulting during an early extensional phase of Mesozoic age. Mid-Miocene tectonic phase dominated by sinistral shear on the Yammouneh Fault, reactivated the secondary, right-lateral E – W faults in bookshelf deformation style with a counter clockwise rotation of the blocks bound by these faults. Offset geologic features, mapped on both sides of the DBF suggest ∼500m – 1000m dextral horizontal slip on this structure. Recent seismicity analysis as well as morphotectonic evidence – such as fresh fault scarps along several of its branches and frequent landslides over its length – are indicators of recent and ongoing tectonic activity. This activity can also explain special geomorphic traits of the drainage system in the region. Folding and thrusting, probably of mid-Miocene to present age, have retouched the original extensional fabric of the region and hints to deep seated active thrust faults accommodating part of the compressive stress on the Lebanese Restraining Bend. A set of smaler, 4 – 7Km long, NW – SE faults located on both sides of the DBF, are likely due to the same Mesozoic extensional phase. They seem to sole and fade in the Chouf-sandstone formation below, thus resembling recently discovered fault sets of same orientation in the Levantine basin offshore Mt-Lebanon, presumably of much younger age though. Detailed structural analysis of fault attributes astride the DBF suggests a 10° - 18° clockwise rotation of the faults north of the DBF relative to those located south of the fault. This is interpreted as an effect of a differential secondary clockwise block rotation due to dextral shear on the E – W faults present north of the DBF only. Thickness measurements of different formations from the Early Cretaceous in the Chouf area show large variations in magnitude and suggest important tectonic control on the depocenter of this region in Mesozoic times.