BUCHITE FROM FESHARK AREA NORTHEAST ISFAHAN CENTRAL IRAN: A PRELIMINARY STUDY

Buchitic glassy rocks appear within the skarn of contact metamorphic aureole of Feshark intrusive complex situated 30 km northeast of Isfahan. Intrusive complex is a multistage intrusion . Noritic gabbro is the first inttrusion which is invaded later on by a granitic melt. Granitic melt has metasomatically altered the gabbro and as a consequence a suite of hybrid rocks like monzogabbro, monzodiorite, and diorite has been formed. A remnant of the original rocks in buchite is biotite bearing feldspathic quartzite or biotite gneissic rock, by fusion of which a granitic melt is forrned. Subsequent supercooling of this melt resulted in glassy buchitic rock. Buchites of Feshark have a glassy, columnar jointed character at bothcontacts with the skarn host rock and a semiglassy character with contorted foliation in the middle part. Buchites are generally very rich in glass, in which minute, very rare, fine crystals of high disordered sanidine, high disordered oligoclase, mullite, orthopyroxene, Fe-Ti oxides, corundum and biotite have been recognized. This mineral assemblage strongly reflects the condition of sanidinite or spurrite-merwinite facies [14] which implies the existence of spurrite-merwinite facies assemblages in skarn host rock. The lack of such an assemblage is interpreted as resulting from the rnetasomatic and retrogressive effect of granite intrusion which reverted very high grade assemblages of spurritemerwinite facies to normal pyroxene hornfels assemblages in host skarn rock. It is probable that the buchitic melt originated in thedeeperpart of the contact metamorphic aureole and was injected into fractures of a higher level