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- MakaleYalnız künye2020Scopus SJRQ1Geochemical characteristics of the adakite-like Dodurga Pluton (Central Pontides, N Turkey): implications for Middle Triassic continental arc magmatism in southern Black Sea region
Çimen, Okay
The tracing of Triassic arc magmatism is much-debated for a long time along the Sakarya Composite Terrane in Turkey and the southern Black Sea region. The Dodurga Pluton is located in the Central Pontides (N Turkey), one of the most complicated regions around the Black Sea region, and represents the first documented middle Triassic continental arc in the region. This pluton comprises of dacite porphyry and granodiorite, and displays calc-alkaline signatures, which is in agreement with arc-related and I-type magmas. The PM-normalized multi element and CN-normalized REE patterns are akin to volcanic arc granites, and characterized by LILEs and LREEs enrichments relative to HFSEs and HREEs coupled with negative Nb anomalies, which confirm derivation in a subduction-related tectonic setting. Moreover, the major and trace element systematics of the samples including higher Sr/Y ratios (22.93–101.36) and lower Yb contents (0.31–1.30 ppm) are consistent with those from adakitic melts compared to classical arc magmas. Therefore, this pluton also represents the first middle Triassic adakite-like magmatic occurrence in Turkey. Overall petrographic and geochemical signatures reported here indicate that the Dodurga Pluton might have been derived from a heterogeneous source, mixed by melts from subducted oceanic slab and lower continental crust in an active continental margin. Based on the Tethyan evolution in the Anatolian realm, three geodynamic scenarios are possible for its formation, and it could have been formed as a result of northward or southward-subduction of the Paleotethys Ocean or northward-subduction of the northern branch of Neotethys Ocean during the middle Triassic.
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İncele - MakaleYalnız künye2020Scopus SJRQ1Geochemical characteristics of a pre-Middle Jurassic oceanic crust fragment from the Central Pontides in northern Turkey: Geodynamic implications on intra-oceanic subduction initiation
Çimen, Okay
The Central Pontides (northern Turkey) is one of the key localities to understand the geodynamic evolution of the Palaeo- and Neotethyan oceans. It consists of the pre-Jurassic basement units, the Early Jurassic and the Early Cretaceous accretionary complexes, the widespread Middle Jurassic continental arc magmatics and the Late Jurassic to Tertiary cover units. The Early Cretaceous accretionary complex is represented by the Central Pontide Structural Complex and includes the Middle Jurassic oceanic units, which were metamorphosed during the Early Cretaceous. Apart from these oceanic units, a few metaophiolite and serpentinite fragments have been recognized within the basement units, which may represent the remnants of an older ocean. The pre-Middle Jurassic Devrekani Metaophiolite is the largest oceanic fragment and tectonically intercalated within/between the Devrekani Metamorphics and the Çangaldağ Metamorphic Complex. It is mainly composed of harzburgites, dunites with chromite veins and metagabbros, and cut by metabasaltic andesites and metadacites. Petrographically, the gabbro consists mainly of plagioclase and clinopyroxene, and displays phaneritic/porphyritic texture. In contrast, the metabasaltic andesite includes plagioclase and mica phenocrysts within a fine-grained groundmass. Also, the metadacite is composed predominantly of quartz, plagioclase, and mica minerals. Two different magmatic groups belonging to completely different tectono-magmatic settings have been geochemically determined based on the immobile trace element systematics. The metadacites and metabasaltic andesites are akin to continental arc magmatics and characterized by negative Nb and Ta anomalies and depleted HFSE relative to Th and La contents. However, the metagabbro samples display the geochemical signatures of boninitic rocks and characterized by highly depletion in HFSEs and REEs relative to N-MORB. The Devrekani Metaophiolite in the Central Pontides may represent another remnant of pre-Middle Jurassic oceanic crust generation and can be north-eastward continuation of the Permian-aged Almacık complex and the Boğazköy Metaophiolite fragment in the western Sakarya Composite Terrane. It may have been cut by intrusions of the extensive Middle Jurassic continental arc magmatism after its imbrication within the basement unit. The presence of pre-Middle Jurassic oceanic units may indicate that the Paleozoic ocean may have survived as the Jurassic Intra-Pontide Ocean between the Scythian Platform and Sakarya Composite Terrane during the Mesozoic time. Thus, the Intra-Pontide Suture may normally include the Palaeozoic and Mesozoic remnants of the long-lived northward subducting Tethyan ocean.
AtıfScopus7WoS7OpenAlex5İncele - MakaleAçık Erişim2019Scopus SJRQ1Petrology and 40Ar-39Ar dating of paragneisses from the Devrekani Massif (Central Pontides, Northern Turkey): Implications for the Jurassic high-T metamorphism in an extensional tectonic environment
Gücer, Mehmet Ali; Arslan, Mehmet; Çimen, Okay; Sherlock, Sarah C.
The Devrekani Massif in the northern part of the Central Pontides (Northern Turkey) provides important clues to the regional tectonics and geodynamic processes associated with Jurassic high grade metamorphic conditions. This study reports new paragenetic assemblages, mineral compositions, whole-rock geochemistry and 40Ar-39Ar geochronological data from the paragneisses in the massif, and, discusses the P–T conditions and geodynamic implications of the Jurassic metamorphism during continental extension in the Central Pontides. Upper amphibolite to lower granulite facies paragneisses form one of the main lithological units in the massif. Within these, there are five different mineral parageneses with diagnostic mineral assemblages of: quartz, K-feldspar (An0-1Ab4-26Or73-96), plagioclase (An18-35), biotite [XPhl: 0.28–0.57; Mg/(Mg + Fe2+): 0.33–0.61], sillimanite, cordierite [Mg/(Mg + Fe2+): 0.48–0.71] and garnet (Alm43-80Grs0-18Prp5-23And0-4Sps10-33) with minor hercynite. Based on Na-in-Crd thermometry and GASP barometry results, the peak metamorphic conditions are 775 ± 25 °C and 6 ± 1 kbar in the massif. The field relations, petrography and bulk chemical data suggest that the paragneisses, derived from shale-wackestone and pelitic sedimentary protoliths, are typical rock lithologies of an active continental margin. They display enrichments in LILE over HFSE, coupled with negative Nb and Ti anomalies, which are geochemical signatures of subduction-related sources. It is likely that the peak metamorphism took place during the Middle–Upper Jurassic period (ca. 174–156 Ma), suggesting that the metamorphic rocks cooled to 300–350 °C at ca. 156 Ma. The mineral assemblages reveal that the prograde history passed from sillimanite zone conditions up to the cordierite-garnet-K-feldspar zone. The petrological and geochronological data indicate that the protoliths are related to multiple sources such as volcano-sedimentary successions. We conclude that the Devrekani Massif represents the products of pre-Jurassic sedimentation, and Permo-Carboniferous continental arc magmatism, overprinted by Jurassic metamorphism.
AtıfScopus9OpenAlex6İncele - MakaleAçık Erişim2018Scopus SJRQ1New zircon U-Pb LA-ICP-MS ages and Hf isotope data from the Central Pontides (Turkey): Geological and geodynamic constraints
Çimen, Okay; Göncüoğlu, M. Cemal; Simonetti, Antonio; Sayit, Kaan
The Central Pontides in northern Anatolia is located on the accretionary complex formed by the closure of Neotethyan Intra-Pontide Ocean between the southern Eurasian margin (Istanbul-Zonguldak Terrane) and the Cimmerian Sakarya Composite Terrane. Among other components of the oceanic lithosphere, it comprises not yet well-dated felsic igneous rocks formed in arc-basin as well as continent margin settings. In-situ U-Pb age results for zircons from the arc-basin system (öangaldağ Metamorphic Complex) and the continental arc (Devrekani Metadiorite and Granitoid) yield ages of 176 ± 6 Ma, 163 ± 9 Ma and 165 ± 3 Ma, respectively. Corresponding in-situ average (initial) 176Hf/177Hf initial ratios are 0.28261 ± 0.00003, 0.28267 ± 0.00002 and 0.28290 ± 0.00004 for these units and indicative of a subduction-modified mantle source. The new U-Pb ages and Hf isotope data from these oceanic and continental arc units together with regional geological constraints support the presence of a multiple subduction system within the Intra-Pontide Ocean during the Middle Jurassic.
AtıfScopus39OpenAlex32İncele - MakaleAçık Erişim2017Scopus SJRQ1Whole rock geochemistry, Zircon U–Pb and Hf isotope systematics of the Çangaldağ Pluton: Evidences for Middle Jurassic Continental Arc Magmatism in the Central Pontides, Turkey
Çimen, Okay; Göncüoğlu, M. Cemal; Simonetti, Antonio; Sayit, Kaan
The Central Pontides (Turkey) includes several igneous complexes, which are predominantly Permo-Carboniferous and Middle Jurassic in age. The Çangaldağ Pluton is one of the largest igneous bodies located in the northern Central Pontides, whose age and tectono-magmatic evaluation is important to constrain the geological evolution of the Northern Neotethys. The pluton tectonically overlies the Çangaldağ Metamorphic Complex, which represents an arc–back-arc complex of Middle Jurassic age. The Çangaldağ Pluton consists mainly of non-metamorphic gabbroic diorite, dacite porphyry, and lesser amount of granitic rocks. Geochemically, the various rock types are akin to volcanic arc magmas displaying Th/Nb and light rare earth element/heavy rare earth element enrichments. In-situ U–Pb age results of zircons from dacite porphyry and granite samples yield ages of 161 ± 5 Ma and 170 ± 2 Ma, respectively. Corresponding in-situ average 176Hf/177Hf initial ratios are 0.28287 ± 0.00004 and 0.28213 ± 0.00002 for the dacite porphyry and granite samples, respectively. These results are consistent with derivation from a subduction-modified mantle source. Based on Hf isotope compositions, TDM model ages vary between 624 and 1512 Ma and suggest that the arc magmatism associated with the Çangaldağ Pluton may have involved partial melting of Neoproterozoic/Mesoproterozoic crustal rocks, a common feature in Gondwana-derived terranes. The geochemical, Hf isotope, and geochronological data reported here confirm the presence of a continental arc system during the Middle Jurassic in the Central Pontides, and suggests that the Çangaldağ Pluton formed during northward subduction of the Intra-Pontide branch of the Northern Neotethys.
AtıfScopus35OpenAlex32İncele - MakaleAçık Erişim2016Scopus SJRQ1Geochemistry of the metavolcanic rocks from the Çangaldağ complex in the central pontides: Implications for the middle jurassic arc-back-arc system in the neotethyan intra-pontide ocean
Çimen, Okay; Göncüoğlu, M. Cemal; Sayit, Kaan
The Cangaldağ Complex in northern central Turkey is one of the main tectonic units of the Central Pontide Structural Complex that represents the remains of the poorly known Intra-Pontide branch of the Neotethys. It comprises low-grade metamorphic rocks of intrusive, extrusive, and volcaniclastic origin displaying a wide range of felsic to mafic compositions. Petrographically the complex consists of basalts-andesites-rhyodacites and tuffs with minor amount of gabbros and diabases. On the basis of geochemistry, the Cangaldağ samples are of subalkaline character and represented by both primitive and evolved members. All rock types are variably depleted in Nb compared to LREEs, similar to the lavas from subduction-related tectonic settings. In N-MORB normalized plots, the primitive members are separated into 3 groups on the basis of levels of enrichment. The first group is highly depleted and displays characteristics of boninitic lavas. The second group is relatively enriched compared to the first group but still more depleted than N-MORB. The third group, however, is the most enriched one among the three, whose level of enrichment is around that of N-MORB. The overall geochemical features suggest that the Cangaldağ Complex has been generated with the involvement of a subductionmodified mantle source. The chemistry of the primitive members further indicates that the melts generated for the formation of the Cangaldağ Complex probably occurred in both arc and back-arc regions above an intraoceanic subduction within the Intra-Pontide branch of the Neotethys.
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