Mineral chemistry, magmatic series and geotectonic setting of Ghaidou monzogranite southeast of Khomein (Sanandaj-Sirjan zone)


Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran


The Ghaidou monzogranite in the southeast of Khomein constitute a part of rock complex from the northern part of the Sanandaj-Sirjan zone. This body intruded into the Jurassic micaschists and created a metamorphic aureole. Also, aplitic veins, tourmaline bearing pegmatitic dikes, felsic microgranular enclaves and surmicaeous enclaves are observed in this area. The predominant minerals of these rocks are K-feldspar (orthoclase and microcline), Na-plagioclase (Albite- oligoclase in the monzogranite and oligoclase in the felsic microgranular enclaves), quartz and black mica (Annite) -as the main minerals- with minor amount of tourmaline (schorle), garnet, white mica (phengite), sillimanite, kyanite, zircon, apatite and ilmenite. On the basis of biotites mineral chemistry, these phases are enriched in FeO and Al2O3 and relatively low in TiO2. These minerals are magmatic and primary and thermometry results yielded 660-690 ºC. According to the chemical composition of primary igneous biotites in the enclaves and monzogranites, these rocks have calc-alkaline, peraluminous and an orogenic continental collision affinity characteristics of S-type granites. Also, the biotite composition and the presence of ilmenite point to low oxygen fugacity and redox conditions during magma crystallization. Based on the available data, the generation of these rocks can be related to Arabian-Eurasia collision zone.