R.W.H.Butler1 & S. Spencer2
1 School of Earth Sciences, The University of Leeds, Leeds LS2 9JT,
United Kingdom
2 Department of Geology, American University of Beirut, Bliss Street,
Beirut, Lebanon
Abstract.
The Yammouneh Fault is commonly considered to be the principal active strand of the Dead Sea Transform in Lebanon - an inference reached primarily from interpretations of the geomorphological expression of the fault on satellite images. However, new geological field observations show the Yammouneh Fault to be sealed stratigraphically by the Homs basalt, dated using new K-Ar ages at 5.2-6.5 Ma. Drainage systems which link to the pre-Homs basalt palaeosurface show evidence of fault disruption. Those valleys incised into the basalt show no evidence for transcurrent offsets. The inferred c. 45km of left-lateral displacement on the Dead Sea transform that post-dates the Homs basalt is presumed to have by-passed to the west of Mount Lebanon. These linked geological and geomorphological studies indicate that landscape evolution can be exceptionally slow in northern Lebanon. Facetted spurs, poljes and offset drainage along the Yammouneh Fault across Mount Lebanon, evident on satellite images, are interpreted as being of Miocene age and are not indicative of Plio-Quaternary displacements on the fault. Thus much of the Lebanese tectonic landscape has remained stable for many millions of years, although locally incised during large-scale uplift of the Mount Lebanon range. Presumably landscape insensitivity reflects the arid climatic conditions together with inhibited run-off because of the regional karst system.
Complete reference: Butler, R.W.H. & Spencer, S. 1999. Landscape evolution and the preservation of tectonic landforms along the northern Yammouneh Fault, Lebanon. In: Uplift, erosion and stability: geological and geomorphological perspectives on landscape evolution. (ed. B.J. Smith, W.B. Whalley, & P.A. Warke) Spec. Publ. Geol. Soc. Lond. 162, 143-156