Mineralogy of amphibolites and epidote amphibolites from south of Salmas, NW of Iran; determination thermodynamic conditions of epidote amphibolite to amphibolite sub-facies transformation

Amphibolites and epidote amphibolites are the main exposures of metabasites in south of Salmas area. Mineral chemistry of these two rock groups is different، and shows differences in the P-T conditions during prograde metamorphism. Study of amphibole chemistry show increases of tschermakite and crossite end members in amphiboles from epidote amphibolites toward amphiboles within the amphibolite samples، while increasing of the edenite content during transformation from epidote amphibolite to amphibolite is negligible. On the basis of mineral chemistry، rising of temperature was more effective than rising of pressure in transformation of epidote amphibolites to amphibolites in the studied samples. According to geothermobarometeric studies، epidote amphibolites and amphibolites were metamorphosed at 500±20ºC، 2-5 (commonly less than 5) Kbar and 600±20ºC، 6-8 Kbar conditions، respectively.