Petrogenesis of the post-collisional Eocene volcanic rocks from the Central Sakarya Zone (Northwestern Anatolia, Turkey): Implications for source characteristics, magma evolution, and tectonic setting

Abstract

Eocene volcanic rocks from the Central Sakarya Zone in the north of the A degrees zmir-Ankara suture zone (IASZ) are predominantly intermediate-acidic lava flows and pyroclastics that crop out with a W-E orientation. The volcanic rocks include Bozani double dagger lavas, agglomerates, A degrees AYdir lavas, and KapA +/- kaya tuffs. The Bozani double dagger lavas contain plagioclase, hornblende, clinopyroxene, and biotite, whereas the A degrees AYdir lavas consist of plagioclase, hornblende, biotite, and quartz. According to the total alkali-silica (TAS) diagram, the Bozani double dagger lavas are mainly composed of andesite and dacite, with one sample of trachyandesite, whereas the A degrees AYdir lavas mainly contain dacite and minor andesite. Bozani double dagger and A degrees AYdir lavas exhibit moderate- to high-K calc-alkaline character. Major oxide and trace element variations suggest the effects of fractional crystallization in the evolution of the volcanic rocks. N-type mid-ocean ridge basalt (MORB) normalized trace element patterns of the lavas exhibit enrichment in large ion lithophile elements (LILEs; K, Rb, Ba, Th) and depletion in high field strength elements (HFSEs; Zr, Ti, Y). In addition, the chondrite-normalized rare earth element (REE) plots of the rocks show moderately enriched and nearly concave-shaped patterns (La-N/Yb-N = 5.4-17.6 for the Bozani double dagger lavas and 6.5-13.1 for the A degrees AYdir lavas), suggesting clinopyroxene (Cpx) and hornblende dominated fractionation. Negative Eu anomalies in the acidic lavas reveal plagioclase fractionation. Some trace element ratios of the lavas demonstrate a subduction signature and crustal contamination in the generation of the parent magma(s). Multi-dimensional tectonic discrimination diagrams suggest that the studied volcanic rocks have developed in a collisional setting.