Mineral chemistry and P-T estimations of Grt-Cpx amphibolites, SE Qarehaghaj-East Azerbaijan province

The study area is located in the Central Iran Zone, in the view of tectonic subdivisions of Iranian terrains. The main outcropping rock types are metabasites and amphibolites having Precambrian age. The amphibolites have been classified as Ep-amphibolite, normal amphibolite, Grt-amphibolite and Grt-Cpx amphibolite, considering characteristic mineral assemblages. The main textures are granoblastic and porphyrogranobastic. Mineral chemistry of Grt-Cpx amphibolites have been investigated in this contribution. The results have been used to estimate metamorphic P-T conditions. The compositions of amphiboles are pargasite and hornblende. Clinopyroxne is diopside. Plagioclases are rich in An content (An73.50-95.90) and Ab content is low (Ab3.90-24.70). Garnet have compositions as Alm (%45.90-%59.10)¡ Prp (%5.6-%16.1)¡ Sps (%10.90-%23.50)¡ GAU (%13.20-%23.70) . Garnet composition is non-uniform as increasing of Fe and Mg contents where Mn and Ca contents are decreased from the core to the rim. The peak metamorphic T-P obtained as 670 oC to 705 oC at 8.5 Kbar respectively. The estimated pressure is consistent with the depth of ~25Km correspending to the lower crustal condition. The recorded mid P-T conditions of Grt-Cpx ampgibolites belonge to Barrovian type regional metamorphism. On the basis of geological and petrological studies from the SE Qarehaghaj and the analogies with comparable rocks from adjucent Precambrian terrains, it seems that the Pan-African Orogeny is the phase causing metamorphism and consolidation of the basement rocks. The Precambrian metabasites and amphibolites have been probably formed in this regard. The subsequent mid P-T metamorphism of the metabasites under upper amphibolite facies (Barrovian type metamorphism) have been most likely recorded related to continental collision between the Arabian plate and the Central Iranian micocontinent correspending to the Alpian Orogeny during Cenozoic.