Petrogenetic evolution of dumlupinar volcanic units and its geodynamic relation with Eskişehir ─ Afyon ─ Isparta lineament

Volcanic products that occurred in western Anatolian extensional province since Oligocene display calc-alkaline, shoshonitic, ultrapotassic and mildly alkaline character. Southward-younging magmatism has typical geochemical signatures of the arc and orogenic affinity, which have been primarily explained by mantle metasomatism processes. To the eastern part of the extensional province, N-S-trending alkaline and ultrapotassic volcanic rocks occurred since Middle Miocene are followed along the Eskişehir-Afyon-Isparta lineament, having geochemical traces of asthenospheric input. The lineament has been widely attributed to the development of slab tearing events on the subducted African oceanic slab. Volcanic rocks that comprise four separate outcrops on the western side of the lineament have been described in terms of geochemical and petrogenetic characteristics and grouped as Dumlupınar volcanic unit. It overlies the Early Miocene fluvial deposits and consists of Kozviran Dacite, Akçadere Trachydacite, Balcıdamı Trachyte, Çepni Trachyandesite and associated pyroclastic rocks. Dacites consist of quartz, plagioclase, sanidine, biotite and kersutite phenocrysts. Akçadere Trachydacite have much more sanidine and high silica content close to rhyolite composition. Balcıdamı Trachyte and Akçadere Trachydacite are lacking quartz as phenocrysts and high quartz contents can be linked to the groundmass composition. Çepni Trachyandesites include plagioclase, sanidine, biotite, kaersutite, augite and iddingsitized olivine phenocrysts within a hyalopilitic matrix. Balcıdamı Trachytes differ from Akçadere Trachyandesites by the absence of olivine and scarcity of augite crystals. Balcıdamı Trachytes differ from Akçadere Trachyandesites by the absence of olivine and scarcity of augite crystals. Petrographic descriptions indicate that Kozviran Dacite, Balcıdamı Trachyte and Çepni Trachyandesite magmas have similar mineralogical compositions to each other while Akçadere Trachydacites slightly differ with their geochemically higher quartz contents. Akçadere Trachydacite, Balcıdamı Trachyte and Çepni Trachyandesite rocks are alkaline in character while dacites are high-K and calc-alkaline. Kozviran Dacites have relatively lower alkali content with respect to other volcanic rocks. On Harker diagrams calc-alkaline and alkaline rocks display positive array in Al2O3, Na2O, K2O, Rb, Th, Zr, Nb and U contents while Fe2O3, MgO, CaO, TiO2, P2O5, Pb, Ni, Ba, Sr, Y and V have negative trends. Alkaline rocks are depleted in Na2O, K2O, Ba, Rb, Sr, Th, Zr, Nb and U, differing from the calc-alkaline rocks. Dumlupınar volcanic unit has 87Sr/86Sr and 143Nd/144Nd ratios of 0.704989¬0.706662 and 0.512492−0.512595, respectively. Petrographic, geochemical and isotopic data point out a metasomatized mantle origin. Furthermore crustal contamination, assimilation-fractional crystallisation, fractional crystallisation and magma mixing processes played a substantial role in calc-alkaline and alkaline magmas; fractional crystallization was more prominent in alkali volcanic rocks. Keywords: Dumlupınar Volcanics, alkaline, calc-alkaline volcanics, geochemistry, Sr-Nd isotope geochemistry, fractional crystallisation, crustal contamination, magma mixing, metasomatised enriched lithospheric mantle.