MINERALOGICAL AND PETROGRAPHICAL CHARACTERISTICS OF THE ORTAKÖY AMPHIBOLITES AND TREMOLITE-BEARING GNEISSES

Abstract

The amphibolites and tremolite-bearing gneisses, formed concordantly within metasediments around Ortaköy(Aksaray) area, are composed of mainly magnesio-hornblende, magnesio-hastingsite, plagioclase, sphene, diopsite, quartz, biotite ; and tremolite, actinolite, actinolitic hornblende, ilmenite respectively. It has ever been found out a preserved flowing texture, indicating subvolcanic origin for the amphibolite by this work. A strong zoning structure is determined in plagioclase (An 48 and An94) of the amphibolites by SEM studies. The andesine is indicated to be earlier than anorthite by existence of linear compositional variations in the amphiboles, lack of widespread metasomatic, hydrothermal alterations and migmatisation in the the amphibolites. The anorthite may be formed via breakdown of diopsite to hornblende. Coupled substitutions such as alumino-tschermakite, ferri-tschermakite and edenite had caused compositional variations in the amphiboles of amphibolites and tremolite gneisses. It has been suggested that the amphibolites and tremolite-bearing gneisses are of co-genetic as linear relations exists between their amphibole