Petrogenetic and petrographic investigation of Kumrat Granite, Kohistan Island arc, Northwestern Pakistan

The granitic rocks in Kumrat Valley of Kohistan Island Arc have been studied in terms of their petrographic and geochemical characteristics. Field relationship and petrographic studies display coarse-grained to porphyritic texture and classifying it as a two-mica granite. Alkali feldspar, quartz, plagioclase and biotite make the essential minerals whereas muscovite apatite, zircon, titanite and chlorite are the accessory contributions. The modal mineralogy and colour index plots depict calc-alkaline and leucocratic character of the studied rocks. The CaO/(FeO+MgO+TiO2) versus CaO+FeO+MgO+TiO2 and Al2O3/TiO2 versus CaO/Na2O plots show per-aluminous nature and pelitic to psamtic source for this granite. SiO2 versus A/CNK discrimination diagram depicts its S-type origin. Haplogranite system plot also suggests that this granite is formed by partial melting of sedimentary rocks under water deficient conditions. The Harker plots of major element reveal early fractionation of feldspars and biotite from the system The tectonic discrimination plots predict collisional island arc type of tectonic environment during the formation and emplacement of Kumrat Granite.