Investigating the mineral chemistry of amphibole and petrogenesis of the appinite-granite rocks from SW Naghadeh-NW Iran

The Zagros orogeny occurred with the opening of Neotethys, subduction and closure of ocean between Arabian and central Iranian microplate. The Sanandaj-Sirjan Zone is a metamorphic–magmatic belt, associated with the Zagros Orogeny as parts of the Alpine. The dominant plutonic rocks in the Sanandaj-Sirjan zone are considered to be a response to the subduction of the Neotethys. This paper discusses the mineral chemistry of amphibole and feldspar in the appinitic and granitic rocks which are exposed in SW of Nagadeh area. The appinite rocks consist of a group of coeval plutonic rocks, ranging from ultramafic to felsic in composition in which hornblende and feldspar are the dominant minerals, and typically occurs both as large prismatic phenocrysts and in the finer grained matrix. The composition of minerals in the appinitic and granitic rocks are similar,  and the composition of amphibole is magnesiohornblende and feldspars is orthoclase. Both magmas have calc alkalic characteristics with arc continental tectonic setting. They have derived from the crustal-mantle mixed sources and high magmatic oxygen fugacity. The appinitic rocks and granites have not coeval. Thermobarometric estimates using amphibole data show that the appinitic-granitic magmas crystallized in two storage zones at pressures of 3-5 kbar (shallow crust) and 1-3 kbar (upper crust). The appinitic rocks were derived from partial melting of lithospheric mantle that had been metasomatized by slab-derived fluids, in the shallow crust during Neo-Tethyan slab breakoff. Generally, it is difficult for the hydrous basaltic magmas to ascend through the continental crust, therefore the underplating of the crust by these magmas supplied sufficient heat and water to facilitate the partial melting of the overlying crust to produce the granites associated with the appinite.