Petrogenesis, Mineral Chemistry, and Thermobarometry of Back-Arc Basin Metabasites from the Ghoulan Area, East Azerbaijan, NW Iran

Abstract

Amphibolites from the Ghoulan area in the East Azerbaijan province, NW Iran are metabasites containing plagioclase and hornblende as main phases also rutile and opaque minerals as accessory phases. They are spatially associated with different magmatic intrusions from the Shahjahan batholith and their relationship is sharp. These metabasites are located between three main suture zones such as Sevan-Akera suture zone in Armenia, Bitlis-Portugal suture zone in Turkey and Zagros suture zone in Iran, so their geodynamic features will help us to reconstruction paleo-geodynamic of Neotethys Ocean especially in the North West of Iranian microplate. Based on whole rock, major and trace element geochemistry of the amphibolites, they are formed from sub-alkaline basalt to andesite-basalt with tholeiitic affinity which originated from high rate partial melting (more than 10%) of mantle with spinel lherzolite to spinel-garnet lherzolite composition, they do not show any negative Ti, Nb and Ta anomaly in the different normalized spider diagrams which indicate their generating is not related to the subduction tectonic setting but they are enrichment in large ionic lithophile and LREE elements such as Rb, Sr, U, Th and Cs rather than HREE and HFSE. The geochemical composition of studied metabasites show sialic back arc basin tectonic setting. Based on plagioclase and amphibole mineral chemistry, the amphibole minerals show metamorphic and calcic features also Edenite in composition and plagioclase are andesine in composition. Thermobarometry based on amphibole composition in amphibolites shows 697-778oC temperature and 3.5- 5.5 Kbar pressure for these metabasites which can be correlate with LP-HT metamorphic facies that confirm their generation in the extensional tectonic setting. Although any age dating on these metabasites is not reported yet but due to high similarities between these metabasites and studied metabasites in the Khoy metamorphic complex (NW Iran) from petrogenesis and geochemical viewpoints, we propose that these metabasites can be correlate together and generated from a single tectonic event at a same geological time, so we propose the Paleocene –Eocene possibility time for metamorphism of studied amphibolites and closure of the back arc basin.