Western Anatolia has experienced thickening and orogenic collapse subsequent to the Eocene continent-arc collision. The early stage of the post-collisional volcanism in the region was thought to have produced widespread lavas and pyroclastic deposits of calc-alkaline basaltic andesite to rhyolite composition. However, in the Selendi Basin, one of the NE-trending basins in western Anatolia, there are two distinct volcanic unit compositions associated with the Lower Miocene sedimentary rocks: (1) a calc-alkaline, high-potassic felsic unit; and (2) alkaline, ultrapotassic lamproitic units, i.e. both are bimodal in character. The calc-alkaline felsic volcanic rocks (Eğreltidağ volcanic unit) are composed of wide-spread pyroclastic rocks and lava flows, whilst the ultrapotassic-lamproitic mafic rocks (Kuzayır lamproite) consist of small-volume syn-sedimentary lava flows. The geochemical characteristics of the Kuzayır lamproite are similar to those of the ´Mediterranean lamproites` that were widely produced in post-orogenic tectonic settings. A temporal and spatial association between these volcanic units clearly describes a post orogenic bimodal volcanic activity. The data also imply that the continental extensional tectonic regime in western Anatolia began, at least, in the Early Miocene, and produced not only calc-alkaline felsic activity but also mantle-derived alkaline, ultrapotassic volcanic rocks.
Western Anatolia, lamproite, ultrapotassic volcanism, bimodal volcanism, continental extension
ERSOY, YALÇIN and HELVACI, CAHİT (2007) "Stratigraphy and Geochemical Features of the Early Miocene Bimodal (Ultrapotassic and Calc-alkaline) Volcanic Activity Within the NE-trending Selendi Basin, Western Anatolia, Turkey," Turkish Journal of Earth Sciences: Vol. 16: No. 2, Article 1. Available at: https://journals.tubitak.gov.tr/earth/vol16/iss2/1