Petrology and geochemistry of the Ouch-Pelang granitoid, northeastern Kashmar


The Tertiary Ouch-Pelang granitoid massif is located in the northeast of Kashmar city and tectonically belongs to the eastern Central Iran zone. The massif has been cut the Eocene volcanic rocks and, based on the field study, mineralogy and geochemistry, is mainly composed of granodiorite, quartz-monzonite and monzonite with some granite. The rocks show granular, porphyroid and rarely mirmikitic textures. SiO2 display a small range (from 62% to 70%) and show a positive correlation with Fe2O3, MgO, MnO, TiO2, CaO, Al2O3, P2O5, Cr, V, Co, Ni, Pb and Nd and a negative correlation with K2O, U, Zr, Y, Th, and Yb and remains invariable against Na2O and Cs, Rb and Ba. The regular variation of the Harker diagram could be related to the fractional crystallization and the scattered patterns may relate to the assimilation. This massif is a metaluminous to slightly peraluminous and typical of I-type granites. It belongs to high-K calk-alkaline series and displays geochemical characteristics typical of volcanic arc granites related to an active continental margin (e.g. a significant Nb, Ti, P and Sr depletion and K, Th, Rb and LREE restoration) which may perhaps connected to the subduction of the Neothethys under the Central Iran.