-RXUQDORI$VLDQ(DUWK6FLHQFHV ²
Contents lists available at ScienceDirect
Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes
Middle Permian–early Triassic magmatism in the Western Pontides, NW Turkey: Geodynamic significance for the evolution of the Paleo-Tethys ⁎
Namık Aysala, , Sabah Yılmaz Şahina, Yıldırım Güngöra, Irena Peytchevab, Sinan Öngena a b
İstanbul University-Cerrahpaşa, Engineering Faculty, Department of Geological Engineering, İstanbul, Turkey Bulgarian Academy of Sciences, Geological Institute, Sofia, Bulgaria
A R T I C L E I N FO
A B S T R A C T
Keywords: Istranca Massif İstanbul Zone Peraluminous-metaluminous granites U-Pb dating Paleo-Tethys Back-arc setting
Permian-Triassic magmatic rocks are widely exposed in different tectonic terranes and continental blocks in the Aegean region. This study is focussed on the İstanbul Zone and the Istranca (Strandja) Massif, which are located in the Western Pontides of NW Turkey. The Kırklareli and the Tepecik plutons intruded into the metamorphic basement rocks of the Istranca Massif, and the Sancaktepe pluton is emplaced into the İstanbul 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 Kırklareli 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, calc-alkaline to shoshonitic granitoids with aluminum saturation index (ASI) values between 0.9 and 1.3, which define them as peraluminous and slightly metaluminous. 87Sr/86Sr(i) values for the studied plutons range between 0.701123 and 0.707704. 143Nd/144Nd(i) ratios calculated for crystallization ages are between 0.512052 and 0.512431, and εNd(i) values vary from −4.71 to 2.22. TDM 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 Kırklareli 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.
1. Introduction Granitic rocks are important in understanding continental growth. Granites can be derived from different sources (i.e., mantle and crust) that may provide granitoids of varied chemical signatures (e.g., M-, I-, S-, and A-type). Similarly, granitic magmas carry geochemical records of their tectonic setting (i.e., subduction, collision, and/or rift related) from which they were derived. For example, metaluminous granites are generally associated with subduction zones, whereas peralkaline and alkaline granites occur in post-collisional or within-plate tectonic settings (Bonin, 2007; Martin, 1987; Wedepohl, 1991; Peng et al., 2015). Permian–Triassic magmatic rocks are observed in different tectonic terranes and continental blocks such as the Istranca Massif, İstanbul Zone, Menderes Massif, and Kazdağ Massif in Turkey; in the Balkanides, they are observed in the Serbo-Macedonian Massif (SMM), Hellenides, and Aegean Islands in the eastern Mediterranean region. Some re-
⁎
Corresponding author. E-mail address:
[email protected] (N. Aysal).
https://doi.org/10.1016/j.jseaes.2018.06.026 Received 23 January 2018; Received in revised form 10 June 2018; Accepted 11 June 2018 $YDLODEOHRQOLQH-XQH 3XEOLVKHGE\(OVHYLHU/WG
searchers have proposed that Permian–Triassic magmatic rocks formed in a volcanic-arc/continental margin or in post-collisional tectonic settings (Zidarov et al., 2007; Peytcheva et al., 2009; Tatar Erkül et al., 2008), whereas others argue that these magmatic rocks are related to rift zones and the opening of the Permian–Triassic oceans, for example, in the Central Balkanides (Georgiev et al., 2013), the Arnea, and the Kerkini regions in the Vertiskos unit/SMM (Christofides et al., 2007; Poli et al., 2009); in the Pelagonian Zone (Anders, et al., 2007); and in the Attic Cycladic Belt (Liati et al., 2013). Recently, detrital zircon studies of the metasedimentary rocks have shown that they are enriched in Permian–Triassic magmatic zircons in the Sakarya Zone (Ustaömer et al., 2016) and in Crete (Zulauf et al., 2015). In this study, we present new geochemical data from representative granitic plutons in the Istranca Massif and the İstanbul Zone in order to constrain their sources, petrogenesis, and geodynamic setting.
