Petrology of Mesr granitoid complex (NE of Isfahan Province)

The Mesr granitoid complex situated in the NE of Isfahan Province and from structural viewpoint belongs to Central Iran. In this area, three granitoid phases and one pegmatite phase with the age of Middle Jurassic, cross cut the ophiolite and metamorphic rocks. The phases 3 and 1 present the maximum and the minimum volume of intrusive bodies, restectively. Also, the phases 4 and 1 present the youngest and the oldest intrusive bodies respectively. There are quartz, K-feldspar, plagioclase, and muscovite in all the studied rocks. Biotite exists in only phases 1, 2 and 3. Tourmaline belongs to the phases 2 and 4 and garnet is limited in phase 3. The geochemistry of the major elements in the granitoid complex points to the descending trend of MgO, Al2O3, Fe2O3, FeO, TiO2, P2O5, MnO, CaO and ascending trend of K2O vs. silica, which can be related to plagioclase crystallization (Al2O3, CaO) and precipitation of titanite (TiO2, FeO). The magma that produced these rocks have calc-alkaline nature with weakly to strongly peraluminous to metaluminous. According geochemical diagrams, the samples of the study area are recognized syncollision and the type of magma is recognized as hybrid. Geothermometric investigations were carried out using two-feldspar composition and the given temperatures are lower than the temperature of igneous environments. Thus, we can conclude that the feldspars composition have changed by the subsolidus effects and mylonitization. Biotite thermometry yields a temperature of 642-718 °C for biotites in phase 1 suggesting the magmatic environment temperature.