Strontium and neodymium isotopic evidence in the identification of a Carboniferous intracontinental rift at northern Iran

Abstract

The Tuyeh-Darvar intrusion (Eastern Alborz zone, northern Iran) has a Carboniferous age and comprises metaluminous, ferroan and alkalic monzonites and monzodiorites. Strontium and neodymium isotopic data - obtained at the UA in the scope of a post-graduate internship - had a major role in the characterization of this intrusion. The whole set of petrographic, geochemical and isotopic evidence shows that the Tuyeh-Darvar rocks may be classified as A-type granitoids (“A” stands for both “alkaline” and “anorogenic”). The initial 87 Sr/86Sr ratios of the studied rocks range from 0.70562 to 0.70678, whilst the initial ƐNd values vary between -1.1 and -1.5. These compositions plot in the an area of the Sr-Nd isotopic correlation diagram where the fields of ocean island basalts and continental basalts overlap and also relatively close to the composition of enriched mantle I (EM I) component. As such, the Tuyeh-Darvar granitoids seem to derive from magmas resulting from melting in enriched asthenospheric mantle below an intracontinental rift existing at the Alborz block in the Carboniferous times