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

Abstract

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