Structural field studies and geochemical and age analyses of the Eldivan ophiolite, which is dismembered within the Ankara Mélange, indicates that it developed as a supra-subduction zone basin within the İzmir-Ankara-Erzincan Ocean, which later subducted to form the İzmir-Ankara-Erzincan suture zone through continental block collision. Whole-rock and mineral geochemical evidence show a supra-subduction zone tectonomagmatic affinity for the ophiolitic crust and mantle, revealing that this basin formed in the upper plate of an intra-oceanic subduction zone. Structural restoration of the sheeted dike complex reveals that the supra-subduction zone spreading ridge of the Eldivan ophiolite was nearly parallel to the Sakarya-Pontide continental margin. U/Pb age analyses of detrital zircon in sandstone within the mélange and in the unconformably overlying Karadağ Formation indicate maximum depositional ages for the units of 143.2 ±2 Ma, and 105.2 ±5 Ma, respectively. Thus, thrust imbrication of the ophiolite and the development of serpentinite mélange were mostly complete by 105 Ma, as indicated by an angular unconformity between the ophiolitic units and the overlying Karadağ Formation. These results reveal how and when the Eldivan ophiolite was constructed, destructed, and incorporated into the serpentinite Ankara Mélange and İzmir-Ankara-Erzincan suture zone. The tectonic evolution of the İzmir-Ankara-Erzincan Ocean is similar to that of the Philippine Sea and Banda Sea ocean basins.

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.

Abstract The Central Anatolian Crystalline Complex (CACC) or Kırşehir Block is part of the metamorphosed leading edge of the Tauride–Anatolide Carbonate Platform. It contains oceanic remnants derived from the Neotethys Ocean (İzmir–Ankara–Erzincan branch) which separate it from the Sakarya microcontinent. Two tectonic units are distinguished: an amphibolite facies Mesozoic ‘basement’, dominated by platform marbles, over which is thrust a younger fragmented Upper Cretaceous ophiolite sequence. Three metabasite horizons were sampled to reconstruct the development of the oceanic components: (1) fragmented Upper Cretaceous (90–85 Ma) stratiform ophiolitic members comprising gabbros, sheeted dykes, basalt lavas and pelagic sediments thrust over all other units; (2) a tectonised admixture of basite, ultramafic and felsic blocks in an ophiolitic mélange (Upper Cretaceous matrix) thrust over the basement metamorphic rocks; and (3) amphibolites concordant with ‘basement’ marbles and minor pelagics of the largely (?)Triassic Kaleboynu Formation in the lower part of the carbonate platform. Metabasalts and metagabbros from isolated fragments of the stratiform ophiolites form geochemically coherent groups and indicate the influence of a subduction component during their development. It is considered that the suprasubduction zone ophiolites record the association of a tholeiitic arc and an adjacent back-arc basin with more mid-ocean ridge basalt (MORB)-like compositions. Metabasite blocks within the tectonised ophiolitic mélange slice are MORB like, together with minor ocean island basalt (OIB) and island arc basalts, and may be tectonically related to ophiolitic units within the accretionary wedge of the Ankara Mélange. Concordant amphibolites of the Kaleboynu Formation are largely OIB types and reflect an early ensialic rifting stage of the Tauride–Anatolide Carbonate Platform. Small ocean basins also developed at this time, as recorded by the presence of MORB and associated pelagics. The CACC block, together with parts of the Ankara Mélange, are considered to represent oceanic lithosphere (comprising both early spreading centre and latter subduction-influenced crust) and continental carbonate platform that were subsequently ejected from an accretionary–subduction complex on collision with the Sakarya microcontinent.

Abstract The Tauride–Anatolide continent, stretching for c . 900 km across western and central Turkey, is one of the world's best example of a subducted, exhumed passive margin within a collisional orogen. Twelve widely separated areas were studied and correlated to develop a new plate-tectonic model. A metamorphosed, rifted continental margin of Triassic–Lower Cretaceous age (Tauride–Anatolide platform) is overlain by Upper Cretaceous (Cenomanian-Lower Maastrichtian) pelagic sediments and then by both tectonic melange (subduction complexes) and sedimentary melange (foredeep gravity complexes). The melanges are overthrust by unmetamorphosed ophiolitic rocks, commonly peridotites with swarms of diabase/gabbro dykes, and are underlain by metamorphic soles. New geochemical evidence from basaltic blocks in the melange indicates predominantly subduction influenced, within-plate and mid-ocean ridge-type settings. The dykes cutting the ophiolites were probably intruded during early-stage intra-oceanic arc genesis. The metamorphosed continental margin, melanges and ophiolites in the north (Anatolides) are correlated with unmetamorphosed equivalents in the Taurides further south (e.g. Beyşehir and Lycian nappes). Oceanic crust of Triassic–Late Cretaceous age formed between the Gondwana-related Tauride–Anatolide continent in the south and the Eurasia-related Sakarya microcontinent in the north. Following Late Triassic–Early Cretaceous passive margin subsidence, the continental margin was covered by Cenomanian-Turonian pelagic carbonates ( c . 98–90 Ma). Ophiolites formed in an intra-oceanic subduction zone setting in response to northward subduction, probably within a two-stranded ocean, with the Inner Tauride ocean in the SE and the İzmir–Ankara–Erzincan ocean in the north/NW. Metamorphic soles relate to intra-oceanic subduction ( c . 95–90 Ma). Oceanic sedimentary/igneous rocks accreted to the advancing supra-subduction oceanic slab. The Tauride–Anatolide continental margin then underwent diachronous collision with the trench ( c . 85 Ma), deeply subducted and metamorphosed at HP/LT ( c . 80 Ma). Accretionary, ophiolitic and exhumed HP/LT rocks were gravity reworked into a southward-migrating flexural foredeep and progressively overridden ( c . 70–63 Ma). Slices of the upper part of the platform and its margin detached and were thrust southwards as the (Tauride) Lycian and Beyşehir nappes, together with regional-scale ophiolites. The continental margin and melange were simultaneously exhumed during Maastrichtian–Early Paleocene (70–63 Ma) and transgressed by shallow-water sediments, beginning in the Late Maastrichtian in the east ( c . 64 Ma) and the Mid?-Late Paleocene ( c . 60 Ma) further west. Remnant oceanic crust was consumed during Early Cenozoic time, followed by Mid Eocene (45–40 Ma) diachronous continental collision and a second phase of regional deformation. Rather than being progressive there were two stages of collision: first, Upper Cretaceous ophiolite emplacement driven by continental margin-subduction trench collision, and secondly Eocene collision of the Tauride and Sakarya/Eurasian continents.

Abstract The Ankara–Erzincan suture zone includes large bodies of ophiolite and ophiolitic melange in northeastern Anatolia. The ophiolitic bodies are (1) Refahiye (Erzincan), (2) Şahvelet (Erzurum), (3) Karadağ (Erzurum) and (4) Kırdağ (Erzurum). The ophiolite-related units include well-preserved sections of oceanic lithospheric and accretionary melanges with local blueschist assemblages. The ophiolite-related units in NE Anatolia are unconformably overlain by Campanian–Maastrichtian-aged sediments that were later imbricated with the ophiolitic rocks. Geochemical data for the individual ophiolite sections indicate a tholeiitic composition, depletion in Nb, enrichment in large ion lithophile elements, parallel to slightly depleted high field strength element patterns (compared with normal-mid ocean ridge basalt), and slightly light rare earth element-depleted to parallel rare earth element trends. These features suggest progressive source depletion towards island arc tholeiites and finally boninites. A fore-arc setting is proposed for the generation of the ophiolites. In contrast, the volcanic rocks from the mélange units exhibit tholeiitic to alkaline compositions and either depletion or enrichment of rare earth element and high field strength elements. Seamount-type alkaline and subduction-related tholeiitic basaltic rocks were apparently juxtaposed during subduction/accretion. Models involving either a single north-dipping subduction zone or two north-dipping subduction zones may be applicable. Both models involve the generation of supra-subduction zone-type ophiolites in a forearc setting, an accretionary prism (with blueschists) and a volcanic arc during the Late Cretaceous. The ophiolites, ophiolitic melange and related blueschists were emplaced either northwards onto the Pontide margin or southwards over the passive margin of the Tauride platform.

Abstract The Izmir–Ankara–Erzincan suture zone (IAESZ) in the Central and the Eastern Pontides comprises a stack of thrust sheets of mainly Late Cretaceous–Early Cenozoic age that are restored as: (1) a subduction–accretion complex; (2) a continental-margin magmatic arc, plus an associated forearc basin; (3) a back-arc basin and its mainly sedimentary fill. Northward thrusting affected all of the Late Cretaceous units during latest Cretaceous (Campanian–Maastrichtian) time. This was followed by regional southward thrusting to form the present thrust stack during Mid-Eocene time. Alternative tectonic models are considered in the light of sedimentary, igneous geochemical and structural evidence, and global comparisons. We infer that the Northern Neotethys was subducted northwards beneath the Eurasian active margin during the Late Cretaceous. Subduction was associated with the genesis of a magmatic arc and a related forearc basin. The subduction zone retreated oceanwards, associated with the opening of a back-arc basin along the Eurasian margin, floored by oceanic crust and overlain by mixed terrigenous and volcaniclastic deep-marine sediments. Ophiolite genesis in a continental margin back-arc setting is suggested by the presence of screens of basement-type metamorphic rocks within an ophiolite-related sheeted dyke complex in the Eastern Pontides. During the latest Cretaceous closure of the inferred back-arc basin resulted in northward emplacement of ophiolitic and related units onto the Eurasian margin, as well exposed in the Central Pontides. In addition, accretionary mélange, volcanic arc, forearc and ophiolitic units were emplaced southwards onto the Tauride continent, represented by the Munzur platform in the Eastern Pontides, also during latest Cretaceous time. This incipient (‘soft’) collision was followed by widespread Paleocene–Early Eocene deposition of Nummulitic shelf carbonates and coarse clastic sediments on deformed and emplaced accretionary mélange, arc and ophiolitic units. Final closure (‘hard collision’) of the Northern Neotethys occurred during the Mid-Eocene, resulting in large-scale southward imbrication, together with northward backthrusting in some areas. Suture tightening and Plio-Quaternary strike-slip ensued.

Abstract New radiolarian ages for blocks of radiolarian cherts associated with other blocks of distal pelagic facies and ophiolitic lithologies within the Lycian Mélange, SW Turkey, indicate deposition during Mid-Jurassic to Early Cretaceous time. Radiolarites overlying pink pelagic limestones of an allochthonous carbonate unit accumulated during the Mid- to Late Jurassic. On the basis of structural evidence the Lycian Mélange is inferred to have been rooted within the Northern Neotethys, to the north of the Tauride–Anatolide microcontinent. The Lycian radiolarites can be compared with other dated radiolarites from the Izmir–Ankara suture, the root zone of the Northern Neotethyan ocean. Based on all the available radiolarian data it is inferred that radiolarites accumulated within the Northern Neotethys in western Turkey from Late Triassic (Mid-Carnian to Late Norian) to Mid-Cretaceous (Cenomanian) time. The radiolarites were later detached from their inferred oceanic basement and accreted within a subduction complex during the Late Cretaceous (Turonian–Maastrichtian) and emplaced over the northern margin of the Tauride–Anatolide continent together with slices of continental margin and ophiolitic lithologies.