Petrology, Geochemistry, Petrogenesis and Reactivation of Volcanic Tuffs at Dair El-Kahif Area, NE-Jordan

Abstract

The volcanism in the western Arabian plate extends from the Red Sea through the Harrat Ash-shaam system to western Syria. The aforementioned volcanic activity produced large quantities of alkali olivine basalts and tuffaceous materials. The stratovolcano (7km) NE of Dair El-Kahif, NE Jordan has been investigated. The results show that dominant mineral phases are olivine, augite, plagioclase, magnetite and ilmenite. Chemical analysis of the whole rock tuff samples confirms alkali olivine magma origin. Low concentrations of Li and Rb in tuff samples are used as an argument against the contamination of the basaltic magma during its journey to the surface. The MgO and Mg-values (Mg/Mg+Fe²+) in samples from volcanic tuff exhibit different degrees of fractionation, which are indicated by the varying concentrations of incompatible trace elements (Ba, Rb, Sr). The thermometric evaluation of tuff determined by using pyroxene thermometers revealed a temperature range between 1022-1083°C and a pressure of 5-10 kbars. The low Mg-ratio (Mg/Mg+Fe²+) is due to fractional crystallization of olivine and pyroxene in tuff samples. The variations of incompatible elements imply derivation from a peridotite source in the upper mantle with low degree of melting (<20%). The volcanic activity took place in phases corresponding to rifting associated with the sinistral movement along the Dead Sea Transform and the later reactivation processes.