Petrography and mineral chemistry of the east Nabar volcanic rocks (southwest of Kashan)


Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran


The east Nabar volcanic rocks with Eocene age are located in the southwest of Kashan and Uromieh-Dokhtar magmatic belt. These rocks are composed of basaltic andesite, andesite, dacite and rhyolite. Plagioclase, amphibole, clinopyroxene, biotite and quartz are the essential minerals of these rocks. Very few apatites are observed in some plagioclases. Epidote, calcite, chlorite, sphene and opaque are secondary minerals. Porphyritic, glomeroporphyric, microlitic and poikilitic textures are common textures in these rocks. On the base of microprobe analyses the composition of plagioclase ranges from oligoclase to labradorite, the clinopyroxenes are diopside and the amphiboles are magnesio-hornblende and tremolite. The chemistry of clinopyroxenes show that these rocks belong to sub-alkaline series and volcanic arcs. On the base of barometry of clinopyroxenes, the study rocks formed in medium to low pressure during their ascending. The volume of water in the crystallization environment of clinopyroxenes was high and the rocks studied formed in high oxygen fugacity. The thermometry of clinopyroxenes reveals the temperature of 975 oC for their crystallization. The amphiboles thermobarometry shows the pressure of 2.97 kbar and the temperature of 700-750 oC.