The eastern Mediterranean region within the Tethyan realm shows a high concentration of ophiolites with contrasting times of formation and emplacement along the belt: In the Balkans, the ophiolites formed during the early to medial Jurassic, and were obducted during the late Jurassic, whereas in Turkey and farther east, structurally intact Jurassic ophiolites are rare and Jurassic ophiolite obduction is unknown. Here we report a structurally intact, large ophiolite body of early Jurassic age from NE Turkey, the Refahiye ophiolite, located close to the suture zone between the Eastern Pontides and the Menderes-Taurus block. The Refahiye ophiolite forms an outcrop belt, 175 km long and 20 km wide, and is tectonically bound by the late Cretaceous ophiolitic mélange to the south, and by the North Anatolian Transform Fault against the Triassic low-grade metamorphic rocks to the north. Early to medial Jurassic very low-to low-grade metamorphic rocks, interpreted as intraoceanic subduction-accretion complexes, occur either beneath the ophiolite or as thrust slices within it. The ophiolite body within the studied section is made up of mantle peridotite (clinopyroxene-bearing harzburgite and minor dunite) crosscut by up to 20 cm thick veins of clinopyroxenite and later dikes/pods/stocks of gabbro ranging in size from 2 m to several hundreds of meters. The gabbro is represented by two distinct types: (i) cumulate gabbro, and (ii) non-cumulate gabbro with locally well-developed igneous foliation. Within the non-cumulate gabbro or enclosing peridotite, there are up to 5 m and 50 cm-thick veins of trondhjemite and pegmatitic gabbro, respectively. LA-ICP-MS dating on zircons from two trondhjemite samples yielded weighted mean ages of ϳ184 ؎ 4 Ma and 178 ؎ 4 Ma (2), respectively, suggesting formation during early Jurassic time. Formation in a suprasubduction-zone forearc setting is inferred from (i) wide-ranging pyroxene and spinel compositions in the peridotites as documented in most suprasubduction-zone ophiolites, (ii) arc tholeiitic signature of the non-cumulate gabbros, and (iii) association of the ophiolite with the coeval subduction-accretion complexes. Emplacement of a trapped forearc ophiolite above its own subductionaccretion complex as a backstop is proposed based on a series of field relationships such as (i) intimate association of the unsubducted suprasubduction-zone ophiolite with coeval accretionary complexes, (ii) absence of unambiguous relationship to the southern Atlantic-type continental margin, and (iii) absence of any stratigraphic indications for the ophiolite obduction in the southern Atlantic-type continental margin during Jurassic time. This is a clear difference from the Jurassic ophiolites in the Balkans that were obducted over the Atlantic-type continental margin. This difference in mode of emplacement is most probably related to the greater distance of the intra-oceanic subduction zone to the Atlantic-type continental margin than it was in the Balkans, which is commensurate with the greater width of...

The Late Cretaceous accretionary complex of the İzmir–Ankara–Erzincan suture zone, near Artova, is composed mainly of peridotites (variably serpentinized), amphibolite, garnet-micaschist, calc-schist, marble, basalt, sandstones, neritic limestones. The metamorphic rocks were interpreted as the metamorphic sole rocks occurring at the base of mantle tectonites, because: (i) amphibolites were observed together with the serpentinized peridotites suggesting their occurrences in the oceanic environment; (ii) foliation in amphibolites and serpentinized peridotites run subparallel to each other; (iii) all these metamorphic rocks and serpentinized peridotites are cross-cut by the unmetamorphosed dolerite dikes with island arc tholeiite-like chemistry. Geochemical characteristics of the amphibolites display enriched mid-ocean ridge basalt (E-MORB)- and ocean island basalt (OIB)-like signatures. The dolerite dikes, on the other hand, yield an island arc tholeiite-like composition. Geothermobarometric investigations of the metamorphic sole rocks suggest that the metamorphic temperature was ~650 ± 30°C and the pressure condition was less than 0.5 GPa. Dating of hornblende grains from amphibolite yielded age values ranging from 139 ± 11 to 157 ± 3.6 Ma (2σ). The oldest weighted average age value is regarded as approximating the timing of the intra-oceanic subduction. These cooling ages were interpreted to be the intra-oceanic subduction/thrusting time of the İzmir–Ankara–Erzincan oceanic domai

Two isolated metamorphic accretionary complexes of Jurassic age, the Refahiye and Kurtlutepe metamorphic rocks, crop out as tectonic slices within the coeval suprasubduction-zone ophiolite at the southern margin of the Eastern Pontides (NE Turkey), close to the İzmir-Ankara-Erzincan suture. The Refahiye metamorphic rocks are made up of greenschist, marble, serpentinite, phyllite and minor garnet amphibolite, garnet micaschist and metachert. The whole unit was metamorphosed under garnet-amphibolite-facies conditions and strongly retrogressed during exhumation. The Kurtlutepe metamorphic rocks consist of subgreenschist-facies metavolcanics, metavolcaniclastics, marble, calc-phyllite, and minor serpentinite and metachert. Metabasites in the Refahiye metamorphic rocks are represented by four distinct geochemical affinities: (i) cumulate "flavor," (ii) alkaline oceanic island basalt (OIB), (iii) enriched mid-ocean ridge basalt (E-MORB) and (iv) tholeiitic island arc basalt (IAB). On the other hand, the Kurtlutepe metavolcanic rocks display only tholeiitic to calc-alkaline island arc geochemical affinities. The metabasic rocks with OIB affinities were interpreted as parts of the accreted oceanic islands, and those with E-MORB affinities as parts of accreted ridge segments close to oceanic islands and/or plume-distal mid-ocean ridges with a mantle previously metasomatized by plume components. The metabasic rocks with IAB affinities might have been derived from the overlying suprasubduction ophiolite and/or arc domain by a number of tectonic or sedimentary processes including tectonic slicing of accretionary complex and overlying fore-arc ophiolite, juxtaposition of the magmatic arc with subduction zone by strike slip faults, submarine gravity sliding and debris flows or subduction erosion. However, totally recrystallized nature of the metabasic rocks together with field relations does not allow any inference on the processes involved. The Kurtlutepe metavolcanic rocks might represent collided and accreted oceanic island arc with the subduction zone. Attempted subduction of an intraoceanic island arc may also explain the magmatic lull during Late Jurassic-Early Cretaceous in the Eastern Pontides.

The late Cretaceous accretionary complex along the İzmir–Ankara–Erzincan suture zone, northern Turkey, includes various types of metamorphic rock together with radiolarite, sandstone, mudstone, serpentinite, basalt and limestone. Meta-plagiogranite blocks (up to 5 m in diameter) and a meta-gabbro slice (800 × 500 m) cross-cut by meta-plagiogranite are observed in a matrix of serpentinite, mudstone and radiolarian chert. These meta-gabbros and meta-plagiogranites show subduction-related geochemical characteristics. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of zircons from two meta-plagiogranites yielded 222.3 ± 1.5 and 227.2 ± 1.6 Ma crystallization ages. This study shows that the meta-gabbro and meta-plagiogranite from the accretionary complex are remnants of the metamorphosed equivalents of the late Triassic lower crustal rocks of the subducted Tethyan oceanic crust. They are the oldest lower crustal rocks observed in the İzmir–Ankara–Erzincan suture zone. Both the meta-gabbros and meta-plagiogranites have Na–Ca amphiboles, indicating blueschist facies metamorphism. However, phengites from a blueschist facies rock yielded an 40 Ar/ 39 Ar age of 104.3 ± 0.7 Ma, indicating that blueschist metamorphism occurred during the Albian. All these data suggest that the oceanic crust formed during the Norian, metamorphosed during the Jurassic to early Cretaceous and then dismembered during accretionary complex formation in the late Cretaceous. Supplementary material: A complete description of the analytical methods ( electron microprobe, LA-ICP-MS zircon U–Pb and 40 Ar/ 39 Ar age analyses, pseudo-section modelling and THERMOCALC) are available at https://doi.org/10.6084/m9.figshare.6509984 Thematic collection: This article is part of the ‘Tethyan ophiolites and Tethyan seaways collection’ available at: https://www.lyellcollection.org/cc/tethyan-ophiolites-and-tethyan-seaways