Composite volcanoes in the south-eastern part of İzmir–Balıkesir Transfer Zone, Western Anatolia, Turkey

Abstract

During the Early–Middle Miocene (Western Anatolia) several volcanic fields occur along a NE–SW-trending shear zone, known as İzmir–Balıkesir Transfer Zone. This is a deformed crustal-scale sinistral strike-slip fault zone crossing the Bornova flysch and extending along the NW-boundary of the Menderes Massif by accommodating the differential deformation between the Cycladic and Menderes core complexes within the Aegean extensional system. Here we discuss the volcanic activity in Yamanlar and Yuntdağı fields that is closely related to the extensional tectonics of the İzmir–Balıkesir Transfer Zone and in the same time with the episodic core complex denudation of the Menderes Massif.This study documents two composite volcanoes (Yamanlar and Yuntdağı), whose present vent area is strongly eroded and cut by a variety of strike-slip and normal fault systems, the transcurrent NW–SE being the dominant one. The erosional remnants of the vent areas, resembling a shallow crater intrusive complex, illustrate the presence of numerous dykes or variably sized neck-like intrusions and lava flows, typically associated with hydrothermal alteration processes (propylitic and argillic). Such vent areas were observed in both the examined volcanic fields, having ~6km in diameter and being much more eroded toward the south, along the NW–SE fault system. Lava flows and lava domes are sometimes associated with proximal block and ash flow deposits. In the cone-building association part, besides lava flows and remnants of lava domes, rare block and ash and pumice-rich pyroclastic flow deposits, as well as a series of debris-flow deposits, have been observed.The rocks display a porphyritic texture and contain various proportions of plagioclase, clinopyroxene, orthopyroxene, amphibole, rare biotite and corroded quartz. The examined rocks fall at the limit between calc-alkaline to alkaline field, and plot predominantly in high-K andesite and dacite fields and one is rhyolite. The trace element distribution suggests fractional crystallization processes and mixing in upper crustal magma chambers and suggests a metasomatized lithospheric mantle/lower crust source. This preliminary volcanological–petrological and geochronological base study allowed documenting the Yamanlar and Yuntdağı as composite volcanoes generated during post-collisional Early–Middle Miocene transtensional tectonic movements.