From seafloor spreading to obduction: Jurassic–Cretaceous evolution of the northern branch of the Neotethys in the Northeastern Anatolian and Lesser Caucasus regions

Description

We present arguments for an innovative tectonic set-up just prior to the Northern Neotethys obduction event in the NE Anatolian and Lesser Caucasus area. Along the Northern Neotethyan suture (the Ankara–Erzincan–Amasia–Sevan–Akera suture zone), relicts of the northern branch of the Neotethys oceanic domain outcrop as preserved unmetamorphosed slivers obducted over the northern edge of the South Armenian Block (SAB) and Taurides–Anatolides Platform (TAP) margins. Recent studies have shown that the ophiolitic bodies are formed of similar lithologies of Middle Jurassic age, all bearing mid-ocean ridge basalt chemical compositions enriched in large ion lithophile elements. This extensive database supports a model in which these ophiolites are derived from a single obducted nappe. This model is supported by the metamorphic pressure–temperature–time paths of the sole lithologies under the outcrops of the suture zone ophiolites. Palaeontological dating of sediment deposits directly under or sealing the obduction contact also support this model by temporally linking the emplacement of distant ophiolite outcrops. General emplacement during early Late Cretaceous time has been determined. A south-dipping subduction under the SAB shortly predating obduction has recently been proposed from the metamorphic and magmatic evolution preserved in the SAB crystalline basement, founding a model featuring opposite-direction subduction from at least late Middle Jurassic to Early Cretaceous times. The emplacement of alkaline pillow basalts directly on the oceanic crust is dated as Early to mid-Cretaceous. These dates argue the existence of abnormal mantle heat flows which may be responsible for a decrease in the density of the 80 Ma-old oceanic lithosphere prior to its obduction onto the SAB–TAP. We present a detailed review of recent data to further constrain the structural and geodynamic evolution of this sector and to define the tectonic set-up just prior to the obduction event.

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