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ABSTRACT

The E-W–trending Izmir-Ankara-Erzincan suture zone in northern Anatolia represents a major Neotethyan suture zone separating the Eurasian and Gondwana continental domains in the Eastern Mediterranean region. It connects with the Vardar suture in the Balkan Peninsula to the west and with the Sevan-Akera suture zone in the Lesser Caucasus to the east, making up one of the longest fossil oceanic tracts within the broader Alpine-Himalayan orogenic system. The Izmir-Ankara-Erzincan suture zone includes intact and dismembered ophiolite complexes, ophiolitic mélanges, metamorphic soles, and locally well-developed island-arc sequences. Mélange occurrences in the western and eastern parts of the Izmir-Ankara-Erzincan suture zone and structurally below the ophiolites include clasts and blocks of oceanic rocks and platform carbonates in a muddy-silty matrix, and these are generally related to the emplacement of ophiolites onto underplated passive margins. The Ankara mélange in the central Izmir-Ankara-Erzincan suture zone contains blocks and megablocks of seamounts, ocean plate stratigraphy, and high- to medium-pressure (P) rocks in a sheared serpentinite and/or graywacke matrix. These seamount, ocean plate stratigraphy, and high-P rock assemblages indicate an important contribution of plume-related magmatism during the rift-drift, seafloor spreading, and subduction zone evolution of the northern Neotethys. Seamount volcanic rocks range from enriched (E) and plume (P) mid-ocean-ridge basalt (MORB) to ocean-island basalt (OIB) in their geochemical affinities, and they are interlayered with hemipelagic sedimentary rocks and carbonates. Partially subducted seamount volcano-sedimentary rocks were subjected to high-P metamorphism and were then exhumed in a subduction channel. The Ankara mélange thus locally represents a fossil subduction channel of an arctrench system. The oldest ophiolitic rocks within the Izmir-Ankara-Erzincan suture zone are MORB-type crustal units with ages ranging from 208 Ma to 179 Ma, which mainly occur in the northernmost sections of the suture zone, near the Sakarya terrane. These ophiolites have a deformed epiclastic cover with biostratigraphic and detrital zircon ages of 153 Ma to 128 Ma. Younger ophiolites and ophiolitic units (Late Jurassic–Cretaceous) within the suture zone and in the Ankara mélange in the central Izmir-Ankara-Erzincan suture zone display a clear geochemical progression from MORB-like to island-arc tholeiite, calc-alkaline, and boninitic affinities, and they become younger in age toward the south. These ophiolites developed in an incipient arc-forearc setting of the extended upper plate of a southward-retreating Neotethyan slab. A mid- to Late Cretaceous intra-oceanic island arc was constructed above this slab and on (across the deformed) displaced Neotethyan oceanic lithosphere and the Ankara mélange. The late-stage, southward displacement and imbrication of the Izmir-Ankara-Erzincan suture zone units above the Eocene flysch deposits are a manifestation of the collision tectonics between the Sakarya terrane (Eurasia) and the Anatolide-Tauride continental block (Gondwana) in the Paleogene.

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