Insights from the basalts of SE Lebanon into the nature of the Middle East Cenozoic Volcanic Province
Abdel-Rahman, Abdel-Fattah M.; Kallas, Lara M.
published: Nov 1, 2013
ArtNo. ESP155027002006, Price: 29.00 €
A component of the vast Middle East Cenozoic Volcanic Province is represented by lavas from SE Lebanon, occurring at the Dead Sea transform. The lavas are phyric alkali basalts, consisting of 45-50 vol.% labradorite (An60-68), 30% clinopyroxene, 20% olivine, and minor opaque phases. They exhibit low silica values (ave. 46 wt% SiO2) and have a narrow range of major element compositions (Al2O3, 14.1-15.7 wt%; MgO, 5.9-8.9 wt%; CaO, 8.5-10.6 wt%). The rocks are alkaline in nature and are enriched in TiO2 (2.2-3.1 wt%), Zr (175-237 ppm), Nb (32-57 ppm) and REE, thus reflecting strong OIB affinities. The primitive mantle-normalized patterns are strongly fractionated [(La/Yb)N = 19.3] indicative of a garnet-bearing mantle source. The 87Sr/86Sr isotopic composition ranges from 0.70327-0.70339 and 143Nd/144Nd from 0.512848-0.512872 (εNd = 4.1 to 4.6). The basatltic magma was more likely generated via adiabatic decompression and melting occurred along fractures developed during the Plio-Quaternary. Modeling using a variety of mantle source materials and different degrees of partial melting indicates that the magma was produced by a small degree of batch partial melting (F = 0.5%) of a primitive, garnet-lherzolite fertile mantle source. Judging from the nature of the Levantine crust, along with elemental ratios such as K/P (2.85) and La/Nb (1.06), the magma was subjected to minimal crustal contamination. Changes in the Arabian plate motion as it rotated to the northeast with respect to the Levantine sub-plate during the Plio-Quaternary may have initiated localized transtensional forces, thus provoking the development of deep-seated fractures along which basaltic lavas have erupted.