Petrogenesis and Ar-40/Ar-39 geochronology of the volcanic rocks of the Usak-Gure basin, western Turkiye

In spite of much research over the past 30 years, the dynamic evolution, origin of the volcanism and geometrical-stratigraphical relations of the NE-SW-trending basins in western Anatolia are poorly understood. The Usak-Gure basin is one of the prominent NE-SW-trending basins developed on the northern part of the Menderes Massif core complex. Three distinct volcanic successions are found in the Usak-Gure basin: (1) the Beydagi volcanic unit composed of shoshonite, latites and rhyolitic lavas followed by dacitic and andesitic pyroclastic deposits; (2) the Payamtepe volcanic unit composed of potassic intermediate composition lavas (latites and trachytes); and (3) the Karaagac dikes composed of andesite and latite. The Beydagi volcanic unit occurs in three different NE-SW-trending volcanic centers Beydagi, Itecektepe and Elmadag calderas from southwest to northeast, respectively. The oldest radiometric ages for the Beydagi volcanic unit are from the Elmadag volcanic center in the north and range from 17 to 16 Ma. The data indicate that volcanism was active during the latest early Miocene. The youngest radiometric age for the Beydagi volcanic unit is obtained from the Beydagi caldera located (12 Ma) in the south. The data indicate that Beydagi volcanism was active in the late middle Miocene and migrated from north to south with time. Ar-40/Ar-39 ages of the Payamtepe volcanic unit are restricted to a short period between 16.0 and 15.9 Ma. Volcanic rocks of the Usak-Gure basin are characterized by strong enrichment in LILE and LREE and depletions of Nb-Ta and Ti on MORB-normalized multi-element diagrams. Geochemical features of the volcanic rocks suggest that they experienced mixing processes between mafic and felsic end-members and also fractional crystallization of dominantly plagioclase and pyroxenes from mixed magma compositions. Crustal contributions to the magma sources may also have occurred during magmatic evolution. These processes have resulted in scattered major and trace element variations with respect to increasing silica contents. Geochemical features of the most mafic samples agree with the results of previous studies from other volcanic areas in western Anatolia, suggesting that the volcanic rocks in the region were derived from a mainly lithospheric mantle source that had been heterogeneously metasomatized by previous subduction events during convergence between the African and Eurasia plates. The volcanic activity in the region, which developed synchronously with the formation of the Menderes Massif core complex, is best explained by delamination of lithospheric mantle slices that were heterogeneously enriched by previous subduction-related processes. (C) 2010 Elsevier B.V. All rights reserved