A-type granite of the Hasan Robat area (NW of Isfahan, Iran) and its tectonic significance

The Late Precambrian Hasan Robat Granite occurs in the northwestern part of the Sanandaj-Sirjan Zone NW of Iran. The granitoid rocks are composed of biotite-bearing syenogranite, alkali-feldspar granite and minor amount of monzogranite. The main minerals are quartz, microcline, plagioclase (albite-oligociase), green biotite, and amphibole (ferrohornblende) with subsolvus to subordinate hypersolvus affinities. Chemically, the rock suite is characterized by high SiO2, Fe/Mg, total alkali (K2O, Na2O), Zr, Nb, Y, Hf, Ta. Ga/Al, and REE (except for Eu), and low contents of MgO, CaC, P2O5, and Sr. They display A-type characteristics, being ferroan, alkali-calcic to calc-alkalic and metaluminous to peraluminous with minor of peralkaline nature. Crystallization of such magmas has produced the iron-enrichment and alkali composition of the Hasan Robat Granite which likely occurred in an extensional environment. Low abundances of Ba, Sr, P, Ti, Eu, the positive correlation between Ba and Eu anomalies, and the negative correlation between Rb and K/Rb reveal fractional crystallization of alkali feldspar produced at the final compositions of these granites. The low ratios of Y/Nb (<1.2) as well as the ferroan composition of these rocks suggest that they are fractionation from mantle derived magma related to Within Plate Granite (WPG) field. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.