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 Izmir–Ankara suture zone (IASZ) are predominantly intermediate-acidic lava flows and pyroclastics that crop out with a W–E orientation. The volcanic rocks include Bozanic lavas, agglomerates, Igdir lavas, and Kapikaya tuffs. The Bozanic lavas contain plagioclase, hornblende, clinopyroxene, and biotite, whereas the Igdir lavas consist of plagioclase, hornblende, biotite, and quartz. According to the total alkali–silica (TAS) diagram, the Bozanic lavas are mainly composed of andesite and dacite, with one sample of trachyandesite, whereas the Igdir lavas mainly contain dacite and minor andesite. Bozanic and Igdir 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 (LaN/YbN = 5.4–17.6 for the Bozanic lavas and 6.5–13.1 for the Igdir 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.