Geochemistry and tectonics of the Formation of SahandDacitic Dome, Southeast of Tabriz (Northwest of Iran)

Sahand volcanic-sub-volcanic Dome, along with several other magmatic domes in northwest Iran and the southern part of Tabriz Fault show adakitic geochemical characteristics. Sahand Dome has mainly dacitic composition. The SiO₂ content and Mg number of Sahand Dome range from 64 to 73 wt% and 27 to 57 respectively. Sahand Dome can be classified as High Silica Adakitic (HSA) type. The rocks studied have porphyritic texture and phenocrysts with plagioclase, sanidine, amphibole, biotite and quartz. Based on geochemical data and multi elements pattern, these rocks are medium to high K calc-alkaline suite and show LILE and LREE enriched normalized multi-element patterns, and Nb and Ti deplated. Chondrite normalized REE patterns of the studied volcanic rocks display a decrease from LREE to HREE without any Eu anomaly and formed in subduction zone in an active continental margin. The geochemical characteristics of Dome demonstrate that it has been formed in a post-collision setting. Given the generative model and the formation environment of these rocks, the upper Miocene age of Sahand Dome and middle Miocene closure age of Neo-Tethys, the genesis of these rocks can be associated with Neo-Tethys geodynamic processes, in a way that with complete closure of Neo-Tethys in the middle to upper Miocene, the collision of Arabian plate with Iranian central plate caused crustal thickening at the collision zone in the early upper Miocene. Post-collision stretching forces caused stretching of lithosphere and delimination of the lower crust at the collision zone. Partial melting of deliminated lower crust and its relative contamination with mantle materials caused the formation of Sahand Dacitic Dome.