Evolution of neogene calc-alkaline to alkaline volcanism in the Aliaga-Foca region (Western Anatolia, Turkey)

In the Foca Region, a complete Miocene volcano-sedimentary succession outcrops. This succession includes a well-developed central volcano gradually interdigitating with flank erruptions and a lacustrine sedimentary succession. The Dumanhdag volcano consists of three laterally and vertically interdigitating rock associations;. the Yuntdag volcanics. the Foca volcanics and the Aliaga limestones. The lowermost unit is the Yuntdag volcanics comprising dominantly andesitic and trachyandesitic lava flows. domes and dykes. and interbedded blocky pyroclastic flow deposits. These different facies together form a central volcano with a caldera structure surrounding its summit The andesitic volcanic succession grades laterally into and is overlain by the rhyolitic Foca volcanics that erupted along the fiawk of the Dumanhdag volcano and comprise a thick rhyolitic pyroclastic sequence with small rhyolite domes and dykes. In the uppermost parts. the Foca a volcanics include sporadic Occurrences of alkaline dykes and lavas. This volcanic sequence inter-fingers laterally with larustrine sedimentary rocks. The volcanism was calc-alkaline during the formation of the Yuntdag volcanics and controlled by NE-SW-trending,. regional-scale weakness zones. Along these fault or fracture zones. three linearly aligned volcanic vents developed. The volcanism was dominated by flank eruptions in the later stages, and both subaerial and lacustrine volcano-sedimemtry deposits of the Foca volcanics; were formed. During: the latest phase, volcanism was bimodal and alkaline trachyandesitic to phonolitic lavas and dykes coevally formed with the calc-alkaline rhyolitic volcanics along NE-SW-trending fracture zones. The flank of the Dumanhdag, volcano and extensive areas in western Anatolia were covered by shallow lakes. and widespread lacustrine limestones were deposited. Field studies and geochemical characteristics of the volcanic rocks indicate that the volcanism. tectonic activity and the sedimentary deposition were progressive without any pronounced interruption and were controlled by NW-SE-trending extension throughout the formation of the Miocene succession. (C) 2004 Elsevier Ltd. All rights reserved.