Abstract The Pontides forming the southern continental margin of the Black Sea consist of the Strandja, İstanbul and Sakarya zones. The Zonguldak-Ulus Basin, located in the NE part of the İstanbul Zone, has traditionally been viewed as opening during the Barremian and deepening until the Albian under the control of normal faults. New outcrop data indicate that the southern and eastern parts of this basin facing towards the Intra-Pontide Ocean in the south were already open during the Berriasian or earlier. Uplift and erosion of the Zonguldak-Ulus Basin during the Cenomanian is attributed to collision of the İstanbul and the Sakarya zones along the Intra-Pontide Suture. The Sinop Basin in the Sakarya Zone opened during Hauterivian–Barremian time. Sedimentation in this basin continued in a deepening environment until the development of the Pontide Magmatic Belt during the Turonian. The contact between the İstanbul and the Sakarya zones is represented by a shear zone that consists of siliciclastic distal turbidites, debris-flow deposits and radiolarian cherts imbricated with Middle Jurassic–Lower Cretaceous magmatic arc fragments. This shear zone is interpreted as being the eastern continuation of the Intra-Pontide Suture, separating the İstanbul and the Sakarya zones. The Western Black Sea Basin to the north of the Pontides possibly opened in two stages. In the first stage, coeval with the opening of the Zonguldak-Ulus Basin, the rifting was a wide-rift style and caused thinning of the continental crust. During the Turonian–Santonian, the Pontide Magmatic Belt started to develop as an extensional arc, and caused break-up of the already thinned crust and the start of oceanic spreading in the Western Black Sea Basin.

Abstract The Western Pontide Magmatic Belt consists of two different magmatic series corresponding to two distinct periods of intense volcanism, separated by a pelagic limestone marker horizon resting on a regional unconformity. The first stage of magmatism and associated extensional tectonic regime prevailed in the region between the Middle Turonian and Early Santonian. During the first stage, magmas were derived from a depleted mantle source containing a clear subduction signature. The extrusives intercalated with marine clastic sediments and pelagic carbonates associated with thick debris-flow horizons and olistoliths. Based on geochemistry and depositional features, the first stage is interpreted as an extensional ensialic arc setting developed in response to northwards subduction of the Tethys Ocean beneath the southern margin of Laurasia. During the Late Santonian, the volcanism stopped and the whole region suddenly subsided with the deposition of a thin, but laterally continuous, pelagic limestone horizon. This subsidence may imply the break-up of the Laurasian continental lithosphere and the beginning of oceanic spreading in the Western Black Sea Basin. The intensified extension is interpreted to be linked to the southwards rollback of the subducting slab. During the second stage in the Campanian, magmas were derived from two contrasting mantle sources: (1) a depleted lithospheric mantle enriched by a subduction component; and (2) an enriched asthenospheric mantle which is similar to that of the ocean island basalts (OIB). The depleted lithospheric source may be linked to the subcontinental lithospheric mantle of Laurasia, which was metasomatized by the previous Tethyan subduction event rather than by an active arc magmatism. Lavas derived from the depleted source are abundant throughout the stratigraphic column, whereas those from the enriched source dominate the end of the second stage. The presence of the alkaline lavas may indicate thinning of the lithosphere and upwelling of the asthenospheric mantle in the matured stages of rifting. We argue that the main cause of both rifting and temporal change in magma generation was the steepening and rollback of the northwards subducting slab of the Tethys Ocean. The aforementioned rollback also caused the Istanbul Zone to be moved to the south, and colliding with the Sakarya Zone in the south during the Maastrichtian. Based on geochemical, stratigraphic, palaeontological and sedimentary data, we suggest that the oceanic Western Black Sea Basin opened as an intra-arc basin during Turonian–Santonian time. Supplementary material : The full geochemical dataset in MS Excel workbook format is available at https://doi.org/10.6084/m9.figshare.c.3841255

Abstract Middle Eocene magmatic rocks (MEMR) (49.3±2 to 38.1±1.9 Ma) formed an east–west trending belt after continental collision and rest unconformably on pre-Middle Eocene units as a common cover. The origin and tectonic setting of MEMR are controversial as both arc and post-collisional settings are proposed. We present new geological and petrological data from the western part of the belt, between the Armutlu Peninsula and the Almacık Mountains. The MEMR are represented by basic to intermediate volcanic rocks, dykes and coeval granites. The lavas exhibit a continuous trend from basalt to dacite. The MEMR as a whole display low- to medium-K subalkaline (to rarely mildly alkaline) affinities and a calc-alkaline trend. On N-type Mid Ocean Ridge Basalt-normalized spidergrams these rocks display relative enrichment in large ion lithophile elements, slight enrichment in light rare earth elements, but depletion in Ta and Nb. Geochemical data and Sr, Nd, Pb and δ 18 O isotope compositions, coupled with ɛNd (T) values, reveal that the MEMR magma was of hybrid type, with both depleted sub-continental lithospheric mantle and crustal components. We conclude that the MEMR was produced in a post-collisional setting, and we favour a slab-breakoff mechanism to explain this as it is consistent with the known Middle Eocene tectonic evolution of northwestern Turkey.

Abstract This chapter describes the internal divisions and the orogenic evolution of the Pontides, the northernmost tectonic division of Turkey. The Pontides are an east-west-trending orogenic belt, representing an amalgamated tectonic entity in which three tectonostratigraphically different sectors can be distinguished: the Western Pontides, the Central Pontides, and the Eastern Pontides. The Western Pontides consist of the Istranca Massif, the istanbul-Zonguldak Zone, the Armutlu-Almacik Zone, and the Sakarya continent. The Eastern Pontides are represented by the following east- west-trending tectonic zones: a magmatic belt, a fore-arc basin fill, a belt of metamorphic massif, an ophiolitic suture zone, and a remnant basin fill. The Central Pontides represent a tectonic knot where the eastern Pontide units and the western Pontide units have been tectonically juxtaposed. The Pontides represent segments of the Tethyside system that carry the record of Cimmeride and Alpide orogenic events. The Cimmeride orogeny resulted from the elimination of Paleotethys and her dependencies such as the Karakaya marginal basin, which existed during the Triassic. The Paleotethyan Ocean was located to the north of the Cimmerian continent, parts of which form the basement of the Pontides. During the closure of the Paleotethys, an Andean-type magmatic belt was developed on the Cimmerian continent due to the southward subduction of the Paleotethyan Ocean floor. During this period, the Neotethys began to open, possibly as a back-arc basin, behind the Cimmerian continent. In the Dogger assemblage, while the collision between the Scythian platform of Laurasia and Cimmerian continent took place in the north and eliminated most of the Paleotethys Ocean floor, the Neotethys continued to grow in the south. The late Cretaceous witnessed the elimination of the Neotethys due to its northward subduction under the Pontides. This created a new active conti-nental margin arc. The closure of the Neotethys resulted in the collision between the Pontides arc and the Tauride-Anatolide Platform. Its effects con-tinued until the middle Eocene. The present mountain regions began to elevate as a giant horst block during the late Miocene.

Abstract The southern continental margin of the Black Sea back-arc basin is represented predominantly by a thick clastic sequence of Aptian to Recent age. Potential source, reservoir, and cap rocks are common in various Stratigraphic levels of this sequence. The most prospective source and reservoir rocks appear to have been deposited in the synrift stage of the basin. During this stage, the rift trough was probably relatively shallow and restricted from free interchange with the Neotethys Ocean in the south. During the postrift stage, a thick sequence of volcaniclastic turbidites and subordinate pelagic limestones, with limited source and reservoir potential, accumulated. This accumulation was interrupted at the end of the early Eocene by compressional tectonics, which resulted from the closure of the Neotethys. The postrift sedimentation probably carried the earlier source rocks into the hydrocarbon generation window, while the Eocene compressional tectonics generated the main prospective traps.