Mineralogy, geochemistry and tectonic setting of metabasites from Gasht metamorphic complex (west Rasht)

Gasht metamorphic complex is situated in the Talesh mountains of western Alborz range. This metamorphic complex consists mainly of metapelite and metabasite. Metabasites display metamorphic conditions of amphibolite and greenschist facies. Mineralogical paragenesis of greenschists are amphibole, feldspar and epidot and clinopyroxene occures as accessory minerals. The amphibolites of Gasht metamorphic complex are both granular and foliated types. Rock forming minerals are andesin and magnesiohornblende and accessory minerals contain sphene, ilmenite and clinopyroxene. Biotite formed as a result of amphibole altration. Thermobarometry results, that calculated by different thermobarometry methods, show temperature rangs between 550 to 750°C and pressure between 6 to 8 Kb that are nearly equivalent to geothermal gradient of 30°C/Km. These metamorphic conditions and geothermal gradient are resemble to the adjacent metapelites. Whole rock chemistry of metabasites from Gasht metamorphic complex display geochemical characteristics of subduction setting basic magmas. Probably, greenschists and amphibolites of Gasht metamorphic complex are indicative of basic magmatic arc products that resulted of Paleotethys oceanic basin subduction beneath edge of  the Turan plate and has experienced continental active margin or collision metamorphism.