Early Miocene granite formation by detachment tectonics or not? A case study from the northern Menderes Massif (Western Turkey)

Abstract

The northern border of the Menderes Massif is dominated by gneiss–schist–marble association and metagranites. The high-grade units of the massif are tectonically overlain by a meta-platform sequence of the Afyon Zone and the Cretaceous-early Tertiary HP/LT Tavşanlı Zone. The Simav Magmatic Complex, comprising the shallow-seated, I-type, calc-alkaline, post-collisional Eğrigöz and Koyunoba granites, and associated subvolcanic-volcanic sequences crosscuts the Menderes Massif, Afyon Zone and tectonic contact between them. In this paper, the age relation between gneisses, metagranites of the Menderes Massif and the Eğrigöz and Koyunoba granites was evaluated by isotope dating. 207 Pb/ 206 Pb evaporation ages between 607 and 501 Ma and U–Pb zircon ages of 543 ± 10 and 30.04 ± 0.56 Ma were obtained for two gneiss samples and a metagranite in the Menderes Massif, respectively. U–Pb zircon analyses yield crystallization ages of 21.7 ± 1.0 Ma for the Koyunoba granite and 19.4 ± 4.4 Ma for the Eğrigöz granite. A cooling age of 18.77 ± 0.19 Ma for the Eğrigöz granite was obtained by Rb–Sr (whole rock, biotite) analyses. Field occurrences, geochemical characteristics and geochronological data obtained from the Eğrigöz and Koyunoba granites show close similarities with other Oligo-Miocene granitoids in northwestern Anatolia indicating that they emplaced along an E-W trending regional magmatic belt and are not individual bodies related to local, north-dipping, low-angle detachment faults as suggested in previous papers.