Late Cenozoic volcanism in the Almaludag region, Azerbaijan province, northwest Iran: Evidence for post-collisional extension. (December 2020)

• Record Type: Journal Article
• Authors: Khalatbari Jafari, Morteza; Salehi Siavashani, Nafiseh; Babaie, Hassan A.; Xiao, Wenjiao; Faridi, Mohammad; Ao, Songjian
• Is Part Of: Journal of geodynamics. Volume 141/142(2020)
• Publication Date: 2020-12
• Subjects: Post-collision extension -- Adakite -- Trachydacite -- Cinder -- Basalt -- Shoshonite -- Northwest Iran; Geodynamics -- Periodicals; Earth movements -- Periodicals; Rock deformation -- Periodicals; Earth -- Internal structure -- Periodicals; 551.1
• DOI: 10.1016/j.jog.2020.101779
• Languages: English
• ISSNs: 0264-3707

Abstract

Abstract: We discuss the geology, petrology, and major and trace element geochemistry of Late Cenozoic volcanic rocks in the Almaludag region in the Western Azerbaijan province, northwest Iran. Geology of this region evolved through the northward subduction of the Neotethyan oceanic lithosphere and subsequent collision of the Arabian and Eurasian plates during the Alpine-Himalayan orogeny. Two different Late Cenozoic periods of volcanic activity are recognized: Episode I produced pyroclastic deposits and trachydacitic lava (1.47 Ma, U-Pb dating) and Episode II generated mafic lava and scoria cones (including spatter/cinder). Geochemical data indicate that Episode I lavas have high-silica adakitic compositions, similar to the post-collisional and continental adakites, that formed from the partial melting of the thickened lower crust. Episode II lavas vary in composition and fall into two distinct geochemical groups. The first group includes picrobasalt-basanite and tephrite compared to the more evolved trachybasalt and basaltic trachyandesite of the second group. Both of these groups show alkaline to shoshonitic affinities. The binary geochemical plots of the Episode II samples display compositional trends that indicate magmatic processes such as fractional olivine ± clinopyroxene crystallization. The major and minor elemental variations of these samples reflect a mantle source heterogeneity and minor crustal contamination. The REE (rare earth elements) patterns and spider diagrams indicate enrichment of the large ion lithophile elements (LILE) and depletion of the high field strength elements (HFSE) relative to the heavy rare earth elements (HREE), and reveal an enriched lithospheric mantle source which was previously metasomatized by subduction components. The mantle source of the Episode II lavas was enriched by fluids and melts which were released from a subducted slab between Late Mesozoic and Early Cenozoic in northwest Iran. The Si-undersaturated lavas of the first group of Episode II probably originated in the garnet stability field in the lithospheric mantle with carbonate residue or veins, suggesting that the mantle source probably underwent carbonate metasomatism. Geochemistry of the SiO2 rich lavas of the second group of Episode II is consistent with a melt extracted from a peridotitic mantle source. The compositional variation from the rocks of the first group to those in the second group suggests a diminishing degree of metasomatic veins-wallrock interactions. The Late Cenozoic mafic rocks in the Almaludag region probably formed through extension in a post-collision, post-orogenic setting. The extension was likely the result of the delamination of the thickened subcontinental lithospheric mantle (SCLM) and ensuing asthenospheric upwelling after the collision of the Arabian and Eurasian plates.