Geochemical characteristics of a pre-Middle Jurassic oceanic crust fragment from the Central Pontides in northern Turkey: Geodynamic implications on intra-oceanic subduction initiation |
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| Institution: | 1. Department of Geological Engineering, Gümü?hane University, 29000 Gümü?hane, Turkey;2. Department of Geological Engineering, Bal?kesir University, 10145 Bal?kesir, Turkey;3. Department of Mining Engineering, Gümü?hane University, 29000 Gümü?hane, Turkey;4. Department of Geological Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey;1. Kocaeli Üniversitesi, Mühendislik Fakültesi, Jeoloji Mühendisli?i Bölümü, 41380 Kocaeli, Turkey;2. University of Geneva, Section des Sciences de la Terre et de l''Environnement, CH-1205 Geneva, Switzerland;3. Dipartimento di Geoscienze, Università di Padova, and IGG-CNR, 35100 Padova, Italy;4. University of Auburn, Department of Geology and Geography, 117 Petrie Hall, Auburn, AL, USA;5. ?stanbul Teknik Üniversitesi, Avrasya Yer Bilimleri Enstitüsü, 34469 Maslak, ?stanbul, Turkey;1. Middle East Technical University, Department of Geological Engineering, 06800 Ankara, Turkey;2. General Directorate of Mineral Research and Exploration, Department of Geological Research, 06800 Ankara, Turkey;3. Department of Geological Engineering, Hacettepe University, 06532 Ankara, Turkey;4. Selcuk University, Department of Geological Engineering, 42075 Konya, Turkey;1. Department of Geological Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey;2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;3. School of Earth Science and Mineral Resources, China University of Geosciences, 29 Xue-Yuan Road, Haidian District, Beijing 100083, China |
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| Abstract: | 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 Çangalda? 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 Almac?k complex and the Bo?azköy 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. |
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| Keywords: | Pre-Middle Jurassic Oceanic crust Subduction initiation Volcanic arc Central Pontides |
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