A study of enclaves in Astaneh plutonic complex and comparison with enclaves from other plutonic bodies in the northwest of Sanandaj-Sirjan zone

The Astaneh Plutonic body is located at SW of Arak city in the Sanandaj – Sirjan belt . It is composed of granodiorite and tonalite and minor monzogranite. The enclaves in this body consist of mafic microgranular enclaves, hornfelsic enclaves, andalusite xenocrysts and tourmaline nodules. Variations in major and trace elements of microgranular mafic enclave and host rock are the same. The variety of enclaves in the Astaneh plutonic body is less in comparison to enclaves of the Qorveh, Alvand (Hamedan), Malayer and Aligoudarz plutonic bodies. The origin of the enclaves is often magma mixing, with the exception of Aligoudarz, that enclaves are chilled margin of the magma reservoir, which were broken off in later stages and dispersed within the host rock. The nature of the shape and size of the enclaves in these bodies are nearly similar but the border of the enclaves with the host rock in the Astaneh body is sharp, but in other bodies, there are also gradual to ambiguous boundaries. Intergranular and poikilitic textures, and presence of zoned and sericitic plagioclase and mafic nature of enclaves in contrast to their hosts is the same in bodies. The shape of the enclaves of the Astaneh body vary from roughly angular to rounded. According to the chondrite normalized diagrams which show negative anomalies of niobium, phosphorus and titanium. The geotectonic setting of the enclaves is often related to the subduction zones according to the chemistry of biotite, plagioclase, amphibole, tourmaline and chlorite minerals.