Geochemical characteristics of a pre-Middle Jurassic oceanic crust fragment from the Central Pontides in northern Turkey: Geodynamic implications on intra-oceanic subduction initiation

摘要: Abstract The Central Pontides (northern Turkey) is one of the key localities to understand geodynamic evolution Palaeo- and Neotethyan oceans. It consists pre-Jurassic basement units, Early Jurassic Cretaceous accretionary complexes, widespread Middle continental arc magmatics Late Tertiary cover units. complex represented by Pontide Structural Complex includes oceanic which were metamorphosed during Cretaceous. Apart from these a few metaophiolite serpentinite fragments have been recognized within may represent remnants an older ocean. pre-Middle Devrekani Metaophiolite largest fragment tectonically intercalated within/between Metamorphics Cangaldag Metamorphic Complex. mainly composed harzburgites, dunites with chromite veins metagabbros, cut metabasaltic andesites metadacites. Petrographically, gabbro plagioclase clinopyroxene, displays phaneritic/porphyritic texture. In contrast, andesite mica phenocrysts fine-grained groundmass. Also, metadacite predominantly quartz, plagioclase, minerals. Two different magmatic groups belonging completely tectono-magmatic settings geochemically determined based on immobile trace element systematics. metadacites are akin characterized negative Nb Ta anomalies depleted HFSE relative Th La contents. However, metagabbro samples display geochemical signatures boninitic rocks highly depletion in HFSEs REEs N-MORB. another remnant crust generation can be north-eastward continuation Permian-aged Almacik Bogazkoy western Sakarya Composite Terrane. intrusions extensive magmatism after its imbrication unit. presence units indicate that Paleozoic ocean survived as Intra-Pontide Ocean between Scythian Platform Terrane Mesozoic time. Thus, Suture normally include Palaeozoic long-lived northward subducting Tethyan