Comparison of young volcanic associations of western and eastern Anatolia formed under a compressional regime: a review

Abstract

Turkey is characterised by widespread post-Oligocene volcanism. In western Anatolia, volcanic activity began during the Late Oligocene — Early Miocene in a compressional regime. A widespread suite of andesitic and dacitic calc-alkaline rocks was erupted in this period. They were accompanied by locally-developed high-level granitic intrusions. The abrupt change from N — S compression to N — S stretching in the middle Miocene was accompanied by a gradual transition to alkali basaltic volcanism. In eastern Anatolia, the collision-related compressional tectonics and associated volcanic activity began in the Late Miocene to Pliocene and continued almost without interruption into historical times. One minor and two major volcanic phases may be distinguished. An initial minor eruptive phase of basic and intermediate alkaline rocks was followed by widespread eruptions of andesitic and dacitic calc-alkaline rocks during the Pliocene. Partly penecontemporaneous with this, a second, more important major phase of volcanism, involving alkaline and transitional lavas, began and continued during the Quaternary. The calc-alkaline lavas of both regions were erupted at a time when the compressional regime led to crustal thickening. These lavas display many geochemical and isotopic signatures that may be interpreted in terms of contamination of magma involving continental crustal materials. The alkaline lavas in both regions began during the final stage of the compressional regime and form two groups. One group is geochemically and isotopically similar to the calc-alkaline rocks and the other is more typically alkaline. The volcanic evolution of these two regions of Turkey followed a somewhat similar pattern producing highly contaminated calc-alkaline lavas at the beginning and evolving towards uncontaminated alkaline lavas at the end.