Volcanological evolution of Mount Erciyes stratovolcano and origin of the Valibaba Tepe ignimbrite (Central Anatolia, Turkey)

Mount Erciyes (3917 m) is the largest stratovolcano of Central Anatolia (Turkey). The volcanological evolution of Mount Erciyes from Pliocene–Quaternary to historical times exhibits two distinct stages: (1) Koç Dağ and (2) Erciyes. During the Koç Dağ stage, basaltic and andesitic lava flows were emitted from the cinder cones of Kızıl Tepe and Topakkaya Tepe. Then, Koç Dağ pyroclastics were emplaced, leading to a caldera collapse of 14×18 km in diameter with a volume estimated at 110 km3. Two eruption phases separated by scoria fall and mud flow deposits are recognised associated with the caldera forming event. During Phase 1, plinian fall and pumice flows were emplaced on the eastern part of the volcano. Plinian fall deposits occur more than 50 km away from the source area. The volume of tephra is estimated at 63.3 km3 (16 km3 dense rock equivalent (DRE)), including 62 km3 of plinian fall and 1.3 km3 pumice flow deposits. Phase 2 mainly consists of pyroclastic flow deposits (two pumiceous flow units and Valibaba Tepe Ignimbrite (VTI)). The pumiceous flow deposits (4.2 km3 DRE) extend 30 km from the inferred source area towards the north and northeast. The final pyroclastic flows of Phase 2 occurred 2.8 Ma ago and produced the VTI. The VTI is a low aspect ratio welded ignimbrite and its volume is estimated at 40 km3 DRE. Plinian fall deposits (0.8 km3 DRE) preceded the VTI and are only observed on the eastern part of the volcano, covering an area of 1500 km2. During the Erciyes stage, two eruptive cycles are defined. The first cycle (2.6–0.17 Ma) is characterised by effusive, extrusive and weakly explosive activity with emplacement of andesitic lava flows, dacitic dome flows, basaltic andesite lava flows, and andesitic cones. The second cycle involved dacitic extrusive and explosive activity, located at the summit area, and produced block-and-ash flows derived from rhyodacitic domes. Plinian fall, surge and pumice flow deposits were emplaced prior to rhyodacitic dome extrusions. The last event was the emplacement of debris avalanche deposits related to sector collapse caldera.