Mineral Chemistry and Crystallization Pressure and Temperature of the Quartz-Diorites from the Takht-e-Soleyman Area, NW Iran

The igneous rocks of Takht-e-Soleyman area in the north western Iran crop out in association with the amphibolites. The contact between igneous rocks and amphibolites is sharp. Igneous rocks in the study area are mainly granodiorite, quartz-monzodiorite and quartz-diorite. Plagioclase and hornblende form dominant minerals of the igneous rocks. Titanite and epidote occur in rare amounts. Chemical compositions of the clinopyroxene, plagioclase, hornblende and titanite in quartz-diorites were analysed using EPMA. High Mg and Si contents accompanied by low Ti at the rim composition of the analysed amphiboles can be attributed to subsolidus cooling event. Magmatic crystallisation temperature for quartz-diorites is determined based on compositions of hornblende and coexisting plagioclase. Clinopyroxene composition was used to estimate crystallization pressure of the investigated rocks in the Takab area. Estimated temperature and pressure are consistent with 820±75oC and 8 kbar, respectively. Thermometry based on Ti content of the analysed hornblende gives temperature of 760oC. On the basis of chemical compositions of the analysed clinopyroxenes, sub-alkaline and I-type natures of the quartz-diorites in the study area can be concluded.