Devonian magmatism in the western Sakarya Zone, Karacabey region, NW Turkey

Abstract

The Karacabey Pluton is a large magmatic body in the northwestern Turkey overthrust by the probable Triassic metamorphic rocks of the Lower Karakaya Complex. Both the metamorphic rocks and the Karacabey Pluton are unconformably overlain by a Lower Jurassic and younger sedimentary sequence. The Karacabey Pluton was regarded as a Carboniferous intrusion based on the previous K-Ar biotite geochronological data. Here, we provide new geological, geochemical and geochronological data from the Karacabey Pluton. Zircon U-Pb results from two samples yielded ages of 393.8 +/−2.7 to 395.9 +/−4.09 Ma, suggesting that the granitoids intruded in the crust throughout the Early to Middle Devonian. The Karacabey Pluton consists mainly of biotite and locally hornblende bearing granitoid with lesser amounts of S-type leucocratic granodiorite, all of which are cut by pegmatitic bodies. It belongs to the high-K calc-alkaline series with distinct Nb and Ta anomalies in multi-element spider diagram. Sr and Nd isotopes' initial values are 0.709-0.712 and 0.511-0.512, respectively. εNd(i) values range between −7.8 and −9.4. The isotopic characteristics of the rocks indicate lower crustal sources of both metapelitic and metaigneous origin. Geochemical features of the rocks suggest that they developed in an arc-related environment, along with the other Devonian granitoids described from the Biga Peninsula in northwest Turkey. The granitoid shows a low-temperature alteration/metamorphism marked by recrystallization of quartz, sericitization of the feldspar and formation of late chlorite, epidote and muscovite. Possibly because of these, the Ar-Ar biotite ages are scattered with a possible concentration at around Permo-Carboniferous boundary. Zircon (U-Th)/He geochronology suggests that after the granitoid was reburied during Early Jurassic to Early Cretaceous sedimentation, there was renewed uplift and erosion during the Late Cretaceous (Turonian), which is possibly related to the closure of the Intra-Pontide Ocean in the north.Keywords: Karacabey Pluton; Sakarya Zone; geochemistry; zircon U-Pb, biotite Ar-Ar and zircon (U-Th)/He ages IntroductionThe Sakarya Zone of the Pontides is an E-W trending belt bounded by Istanbul Zone in the north and by the Izmir-Ankara Suture in the south (Figures 1 and 2). It consists of a complex basement overlain by Jurassic and younger sedimentary sequence. The basement rocks of the Sakarya Zone can be divided into two separate parts: 1. Paleozoic plutonic and metamorphic rocks possibly related to the Variscan orogeny and 2. Triassic accretionary complexes with blueschists and eclogites, called as the Karakaya Complex (Okay & Göncüoğlu, 2004;Okay & Tüysüz, 1999;Okay, Satır & Siebel, 2006).Most of the plutonic rocks in the basement of the Sakarya Zone are of Carboniferous age (350-320 Ma, Figure 1). These can traced from the Kazdağ Massif in the Biga peninsula (308-329 Ma, Okay et al., 1996, through west of Ankara (~290 Ma, Okay et al., 2006, 319-327 Ma;Robertson, 2012) and Central Pontides (275-295 Ma, Nzeg...

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Striking Variation in the Provenance of the Lower and Upper Cretaceous Turbidites in the Central Pontides (Northern Turkey) Related to the Opening of the Black Sea

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U-Pb zircon geochronology of intrusive rocks from an exotic block in the Late Cretaceous – Paleocene Taraklı Flysch (northern Turkey): Constraints on the tectonics of the Intrapontide suture zone

“…Undeformed plutonic rocks of Paleozoic age occur in both the SK and IZ terranes (Okay and Topuz, 2017). In the SK terrane, most of the unmetamorphosed granitoids are Devonian and crop out in the western part of the Sakarya zone as tectonic slices generally occurring within the Triassic subduction-accretion complexes (Karakaya Complex), (Okay et al, 1996(Okay et al, , 2006Aysal et al, 2012;Sunal, 2012). These intrusives, which are mainly granodiorites, monzogranites and monzodiorites show geochemical and petrographic features of continental arc magmas (Aysal et al, 2012).…”