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.

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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.

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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.

AtıfScopus39·WoS39·OpenAlex31

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