Geochemistry of Sarvabad basic igneous rocks from northern Sanandaj - Sirjan Magmatic Arc, Iran

Sanandaj - Sirjan Magmatic Arc (SSMA) as a segment of Alpine -Himalayan magmatic belt embrace a wide spectrum of igneous rocks, both volcanic and plutonic, from basic to felsic compositions. The igneous rocks which are mainly calc-alkaline are attributed to the subduction of Neotethyan oceanic slab beneath central Iranian plate in Mesozoic time (Berberian and Berberian, 1981; Omrani et al., 2008). In the present study the focus is made on the geochemistry and petrography of igneous rocks from northwestern end of the SSMA, in Sarvabad area, in order to elucidate their geodynamic setting. A set of 30 rock samples were analyzed for major and selected trace elements. Mafic igneous bodies from northern SSMA are regarded as post - collisional plutonic bodies of Eocene - Oligocene age (Ghasemi and Talbot, 2006). Azizi and Moinevaziri (2009) considered the igneous rocks from the northern SSMA, at Sonqor - Baneh area, as the products of subduction that continued to the Paleogene time. Investigations carried out in the course of present study demonstrate that the Sarvabad basic igneous rocks, shown on the magmatic map of Iran (Emami et al., 1993) as gabbroic plutons, are composed of volcanic, subvolcanic and plutonic rocks of basic composition. The silica and Mg number of the rocks vary in the ranges 49-52 wt. % and 54-68, respectively. The volcanic rocks are vitrophyric to porphyritic with some plagioclase, olivine and clinopyroxene microphenocrysts. In the subvolcanic and plutonic bodies, plagioclase, clinopyroxene and some amphibole and Fe-Ti oxides are the major constituents. These igneous rocks indicate tholeitic affinity and cover the typical mantle array on a Zr/Nb vs. Y/Nb plot. Occurrences of a few ultramafic bodies found as metric - size isolated lenses in the basic igneous rocks highlight the spatial characteristic of these rocks; the existence of an ophiolitic rock assemblage nearby. Located toward the southwest of Sarvabad basic igneous rocks, is a Cretaceous ophiolitic assemblage occupying a crucial terrain between Sanandaj - Sirjan structural zone at north and Zagros Folded - Thrust Belt at south. The ophiolitic assemblage is attributed to the continent - continent collision that resulted in the closure of Neotethyan Ocean (Hasssanipak et al., 1996). The ophiolite includes sub-alkaline and alkaline basic volcanic rocks and peridotites. Further scrutinies of the geochemistry of Sarvabad basic igneous rocks help reconstruct a better picture of the geodynamic evolution of Sanandaj - Sirjan arc orogeny. References: Azizi, H., Moinevaziri, H., 2009. Review of the tectonic setting of Cretaceous to Quaternary volcanism in northwestern Iran. J. Geodyn. 47, 167-179. Berberian, F., Berberian, M., 1981. Tectono-plutonic episodes in Iran. eodynamics Series (Delany, F. M. and Gupta, H. K., eds.), 5-32, Am. Geophys. Union. Ghasemi, A., Talbot, C.J., 2006. A new tectonic scenario for the Sanandaj-Sirjan Zone (Iran). J. Asian Earth Sci. 26, 683-693.