Petrology of the Quaternary lavas in the east of Mahabad

Executor of project: Dr. Morteza Khalatbari Jafari 

2017 

This report presents the field geology, petrography and geochemical data of young lavas in Almaludagh-Kuh Soltan area, southeast of Mahabad in west Azerbaijan province. These lavas form part of Iranian-Turkish Cenozoic orogeny plateau. The volcanic area consists two parts: the lower part is dacitic-rhyolitic in composition and form main volume of Almaludagh-Kuh Soltan Mountains. It seems that these lavas are older than Quaternary basaltic lavas, so according to stratigraphy studies are related to Plio-Quaternary. The upper part consists of Quaternary basaltic lavas which expose as cinder cones and lava flows in the west side of Almaludagh-Kuh Soltan. According to petrography and geochemical studies, the composition of Plio-Quaternary lavas is rhyodacite and Quaternary lavas composition include picrobasalt, trachybasalt, basanite, basaltic trachyandesite and tephrite. The microscopic texture of Almaludagh-Kuh Soltan sides’ rocks is porphyric with hyalo-microlithic to hyalomicrocrystalline groundmass and the summit rocks have porphyritic with microcrystalline groundmass texture. The textures of Quaternary lavas are phyric-vesicular with glassy groundmass, microlithic flow and intersertal. In tectono-magmatic discrimination diagrams, rhyodacitic lavas of Almaludagh-Kuh Soltan have been plotted in volcanic arc, within plate and syn-collision granites fields. The geochemical results show that in addition to partial melting of crustal source, the crustal contamination have affected the generation of these lavas. The parental magma of Quaternary lavas is alkaline to shoshonitic. The Chondrite normalized rare earth elements’ pattern and the primitive mantle normalized trace elements’ diagram show some amounts of LILE enrichment and slight depletion of HFSE, which can attribute to crustal contamination of paternal magma. Considering variation diagrams of major and trace elements vs. SiO2 indicate magmatic differentiation, which is occurred by fractional crystallization and magmatic contamination, is an important process for evolution of region's quaternary basaltic magmas. In the tectono-magmatic discrimination diagrams, they have been plotted in the field of OIB and within plate basalts. Geochemical considerations of rare elements suggest that the source of main magma is enriched mantel which is similar to EM1 and EM2 and has incurred the partial melting. The ratios of Ta/Yb and Ba/La in the studied lavas are different from the amounts of these elements in volcanism of subduction zones. Therefore, it can be said that subduction component has not had affected the evolution of quaternary lavas of west of Almaludagh. Changes of incompatible elements in quaternary magmas show the presence of mantle but heterogeneous source in their generation. It seems that after collision between central Iran block and Arabian plate, the thickness of crust in Almaludagh area has been increased. The results of this event are delamination of lithospheric root and the ascent of asthenosphere, which has locally occurred in a post-collision extensional basin.