Early Cretaceous volcanism of the Coastal Ranges, NW Syria: Magma genesis and regional dynamics

Early Cretaceous volcanism in the present Coastal Ranges, NW Syria, dated at 106.3±0.2Ma and 103.4±0.3Ma (bulk-rock 40Ar/39Ar ages), represents the last instance of Mesozoic intraplate magmatism in the Levant region. On the basis of the petrography and chemistry of the lavas, the rocks can be divided into an ankaramite series and a transitional basalt series, which exhibit distinct isotopic compositions (ankaramites: εNd(t)=5.1–5.6, 87Sr/87Sr(t)=0.70293–0.70302, 187Os/188Os(t)=0.227–0.242; transitional basalts: εNd(t)=4.0–4.6, 87Sr/87Sr(t)=0.70320–0.70424, 187Os/188Os(t)=0.392). Fractional crystallisation and assimilation–fractional crystallisation modelling suggests minor roles for both processes, despite the generally high Os isotopic ratios and excepting that the ankaramites experienced small amounts of olivine, clinopyroxene and rare Cr-spinel fractionation. The modelling also precludes derivation of one lava series from the other, suggesting that the isotopic distinction as well as other chemical distinction between the ankaramites (lower SiO2, higher TiO2, Nb/U, Nb/Th, Nb/La and Ce/Pb) and the transitional basalts must be inherited from the source. It is interpreted that these chemical characteristics represent a significant component derived from metasomatic amphibole-rich veins in the source region. Both the ankaramites and transitional basalts were generated from this source which contained veins of metasomatic cumulates in a peridotitic host. A contribution from deeper mantle sources or an anomalously hot mantle (e.g. arrival of a mantle plume) is not required to explain the data, which is better considered a result of melting of a metasomatically hydrated lithospheric mantle at relatively low temperatures during times of Levant regional extension.