The study of P-T formation of Kolah Ghazi granitoid based on mineralogical relationships (southeast of Isfahan)

The Kolah Ghazi granitoid body is located in the south-southeast of Isfahan and lies in the Sanandaj-Sirjan zone. The pluton is predominately composed of monzogranite, granodiorite and syenogranite. Quartz, plagioclase, K-feldspar, biotite, tourmaline, cordierite andalusite, sillimanite, kyanite, spinel and garnet are major and minor minerals of the pluton. The presence of kyanite in granodiorite enclaves may be due to melting of the pelitic rocks of the area which gave rise to formation of alumina rich restite. The occurrence of sillimanite these granitoid rocks can be related to metasomatism process. The inclusion of biotite and sillimanite needles in the cordierite indicates that the alteration of these minerals, during congruent melting, is responsible for the origin of cordierite. Further, cordierite crystallized during anatexis conditions under 660-770 °C and 3.5 kbar condition. Growth of spinel around the aluminosilicates with symplectites texture represents conditions of high temperature, low content of SiO2, high ƒO2 in the Fe-enriched meta-argillite. The assemblages of cordierite, sillimanite, biotite and tourmaline with unusual common blue pleochroism in the Kolah Ghazi granitoids indicate the breakdown of tourmaline under temperature higher than 750 °C. The origin of the garnet with almandine component in the Kolah Ghazi granitoids is magmatic source and refers to the pressure of 4 to 5 kbar, corresponding to depth of more than 18 km and temperature less than 850 °C. As it may be observed from the mineralogical relationship, geochemistry of feldspar and Zr vs. SiO2 the pluton developed under 700-900 °C and over 2 kbar PH2O.