U–Pb zircon, zircon Hf and whole-rock Sm[sbnd]Nd isotopic signatures on the evolution of Late paleozoic bimodal magmatism in Gharebagh area, NW Iran

Abstract

The Gharebagh area consists of a suite of mafic to acidic rocks located in northwestern Iran, in the Sanandaj-Sirjan zone (SSz), which is part of the Zagros orogenic belt. In this paper, we present a detailed petrological, geochronological, and isotopic study of representative rocks of Late Paleozoic igneous activity in NW Iran. LA-ICP-MS dating of zircons shows that the Gharebagh intrusive body (GIB) was formed in a tight time frame of 300 Ma. Geochemical analyses as well as isotopic studies of LuHf on zircon and SmNd on whole-rock were used to determine the petrogenesis of these rocks and develop a tectonic model. Crustal-model ages (Hf-tNC) of 0.57 to 1.02 Ga indicate the contribution of older Neoproterozoic crust to the formation of these rocks. The partially melted lower crust was one part of the magma together with a mafic melt formed by differentiation of the depleted mantle. The GIB suite was presumably formed by an anorogenic magmatic event (continental rift) that included extensive mantle upwelling and partial melting of the lower crust. So the gabbroid and granitoid rocks are coeval with the 300 Ma but not co-magmatic origin.