Petrography and geochemistry of myionitic granite from GhaIeh-Dezh, NW Azrta, Sanandaj-Sirjan zone, Iran

摘要

We have carried out a petrographic and geochemical investigation of the Ghaleh-Dezh granitic pluton in southwestern Iran. Petrographic studies show myionitic fabrics and microstructures in these rocks. Asymmetrical core-and-mantle structure is the most characteristic fabric in these rocks. The Ghaleh-Dezh myionitic granite is generally coarse-grained, contains mainly quartz, alkali feldspar, plagioclase, biotite and muscovite. Based on collected geochemical data, the granites have a pronounced A-type affinity: they are mostly metaluminous with high concentrations of Na_2O+K_2O, Rb, HFSE, REE (except Eu), high K_2O/Na_2O and Fe/ (Fe+Mg) ratios, and very low concentrations of MgO, CaO, P_2O_5, and Sr. Moreover, the granites plot in the range of post-collision granites and belong to the A2-type. The decreasing concentrations of A1_2O_3, TiO_2, Zr, Sr, Ba and, maybe Ga with increasing SiO_2 may be related to fractional crystallization of mainly biotite, K-feldspar, plagioclase, titanite and zircon. Based on the isotope data (Rb-Sr and Sm-Nd), the Ghaleh-Dezh plutonic rocks are derived from a mantle source with the magma undergoing coupled crustal assimilation-fractionation during uprising through continental crust.