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.

AtıfScopus7·WoS7·OpenAlex5

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Aktağ, Alican; Önal, Ayten Öztüfekçi; Sayit, Kaan

The East Anatolian Accretionary Complex (EAAC) comprises an ideal example of post-collisional volcanism within the Africa-Eurasia collision zone. The Miocene mafic Tunceli Volcanics, as a part of this post-collisional volcanic system, are located in the western termination of EAAC. The mafic Tunceli Volcanics are characterized by mildly alkaline and tholeiitic basalts, in which olivine, clinopyroxene and plagioclase characterize the main mineralogy. The role of fractional crystallization (FC) and assimilation combined with fractional crystallization (AFC) processes appear to be negligible in the petrogenesis of the primitive mafic Tunceli Volcanics. Relative enrichment in large ion lithophile elements (LILE), Th and La over high field strength elements (HFSE) and heavy rare earth elements (HREE) suggest contribution from a metasomatized mantle source. The wide range of ratios displayed by these elements also calls for some asthenospheric input for the genesis of these volcanics. The metasomatizing agents can be attributed to a past subduction event, probably during the closure of Neotethys. Considering also the geophysical constraints, which limits the lithospheric thickness to about 70–75 km around the region, a melt mixing between lithospheric and asthenospheric melts generated at different depths appear to be an important process in the petrogenesis of these lavas. The combined geochemical and geophysical data, therefore, necessitate a geodynamic model with some remnant lithospheric mantle underlying the Eastern Anatolian region.

AtıfScopus10·WoS11·OpenAlex13

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