Middle Permian-early Triassic magmatism in the Western Pontides, NW Turkey: Geodynamic significance for the evolution of the Paleo-Tethys

Abstract

Permian-Triassic magmatic rocks are widely exposed in different tectonic terranes and continental blocks in the Aegean region. This study is focussed on the Istanbul Zone and the Istranca (Strandja) Massif, which are located in the Western Pontides of NW Turkey. The Kirklareli and the Tepecik plutons intruded into the metamorphic basement rocks of the Istranca Massif, and the Sancaktepe pluton is emplaced into the Istanbul Paleozoic sedimentary sequences. We present new geochemical data for these plutons, in order to interpret their petrogenesis and time of emplacement and use this information for geodynamic interpretation. The zircon U-Pb crystallization ages are 268.3 +/- 2.1 Ma for the Kirklareli pluton, 249.4 +/- 1.5 Ma for the Tepecik pluton and 257.3 +/- 1.5 Ma and 253.7 +/- 1.75 Ma for the the Sancaktepe pluton. They are high-K, talc-alkaline to shoshonitic granitoids with aluminum saturation index (ASI) values between 0.9 and 1.3, which define them as peraluminous and slightly metaluminous. Sr-87/Sr-86((i))) values for the studied plutons range between 0.701123 and 0.707704. Nd-143/Nd-144((i))) ratios calculated for crystallization ages are between 0.512052 and 0.512431, and epsilon Nd-(i)) values vary from -4.71 to 2.22. T-DM model ages range between 0.83 and 1.41 Ga. These plutons are enriched in LILEs and LREE and depleted in HFSEs with negative Eu anomalies, indicating that the melts were derived from mafic crustal sources. Our new data suggest that the Kirklareli pluton was generated in a subduction-related magmatic arc, and the highly fractionated Sancaktepe and Tepecik plutons were formed in a back-arc setting in response to the northward subduction of the Paleo-Tethys Ocean during the Mid Permian-Early Triassic.