Abstract We report new U–Pb zircon ages, major and trace element data, mineral chemistry, and Sr–Nd isotopic analyses of the mafic–intermediate dykes and intrusions in the İstanbul Zone. Mafic dykes are represented by calc-alkaline to alkaline lamprophyre and diabase. Intermediate dykes and subvolcanics are andesitic to dacitic in composition and calc-alkaline in character, while intrusive rocks (stocks and small plutons) are granodioritic and dioritic in composition. New zircon U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) dating yielded ages from 72.49 ± 0.79 (Upper Cretaceous–Campanian) to 65.44 ± 0.93 Ma (Lower Paleocene–Danian) for the intermediate dykes, and 58.9 ± 1.8 Ma (Upper Paleocene–Thanetian) for a small granodiorite stock. 87 Sr/ 86 Sr (i) values of the mafic and intermediate dykes and small stocks span a range from 0.703508 to 0.706311, while their 143 Nd/ 144 Nd (i) values vary from 0.512614 to 0.512812 and eNd (i) values from 5.09 to 1.24. Nd TDM model ages range between 0.46 and 0.77 Ga. Dykes are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) relative to high field strength elements (HFSEs). Normal-type mid-ocean ridge basalt (N-MORB)-normalized multi-element spidergrams of the majority of the mafic and intermediate dykes display a clear subduction signature, except a subset, which cut the Palaeozoic of İstanbul and the upper part of the Upper Cretaceous volcanics in the north of İstanbul (i.e. feeder dykes of the Kısırkaya Formation) and show a clear ocean island basalt (OIB) signature indicating that the melts feeding the dyke system during the Upper Cretaceous–Paleocene period were derived from two contrasting mantle sources: (1) initially a lithospheric mantle modified by subducted slab-derived melts which sourced the magmas with a clear subduction signature; and (2) followed by an asthenospheric mantle from which basic magmas with OIB signature. Petrological models indicate the interaction of these two discrete magma series via magma-mixing processes. Geothermometric calculations based on the composition of amphiboles are in the range of 769–953 and 938–994°C. Geobarometric calculations indicate crystallization depths ranging over an interval between 3.0 and 20.2 km, implying a polybaric crystallization. The oxygen fugacity (logƒO 2 ) values vary between −10.10 and −13.07 bar in the dykes cutting the Upper Cretaceous volcanics, and from −8.71 to −10.33 bar in intermediate dykes cutting the İstanbul Palaeozoic unit. H 2 O melt contents change between 4.91–6.89 and 4.82–7.51%, respectively implying that the dykes were emplaced at mid to shallow crustal levels. Dyke complexes of the İstanbul zone are interpreted to have been emplaced in a rifted volcanic arc margin related to the opening of the Black Sea during the Late Cretaceous–Paleocene period. Supplementary material: Tables of representative analyses are available at https://doi.org/10.6084/m9.figshare.c.3841276

ABSTRACT The Intra-Pontide suture is the boundary between the İstanbul Zone and the Sakarya Continent in northwest Turkey. Our new paleontological and stratigraphic data show that the subduction of the Intra-Pontide Ocean was still going on between the late Cretaceous and the early Tertiary. This is in contrast to the recently reported Santonian closure of the Intra-Pontide Ocean. We have gathered much of the earlier published stratigraphic, paleontological, and radiogenic data on both the metamorphic units and the unmetamorphosed sedimentary basins along and near the Intra-Pontide suture. Our analysis shows two successive accretionary prisms were formed along the western and the central segments of the suture zone: (1) an Upper Cretaceous blueschist-eclogite facies metamorphic prism in the Biga Peninsula, and (2) an Upper Jurassic–Lower Cretaceous greenschist-epidote amphibolite facies metamorphic prism between the Armutlu Peninsula and Almacik Mountains. However, in the eastern third segment, Middle Jurassic and Middle to Upper Cretaceous high-pressure–low temperature (HP-LT) and low-pressure–low temperature (LP-LT) subduction-accretion complexes cover a large area, creating the Central Pontide Supercomplex. Between the late Cretaceous and late Paleocene, when the Rhodope-Pontide arc was evolving, an Upper Cretaceous–Paleocene forearc basin (the Kocaeli Basin) consisting of Upper Santonian–Campanian volcanogenics and overlying Upper Campanian–Selandian pelagic limestones also formed over the İstanbul Zone, which formed the hinterland. The paleontological data suggest that collision between the İstanbul Zone and the Sakarya Continent must have occurred later than the early Ypresian. An Upper Cuisian molasse covers all the older units, suggesting a possible medial Cuisian closure (ca. 51 Ma). This closure age can also be correlated with the similar, previously published fission-track uplift ages along the Intra-Pontide suture. Following the medial Cuisian closure of the Intra-Pontide Ocean, a wedge-shaped transtensional intramontane basin, the Thrace molasse basin, opened while the westerly escaping fragments of the Intra-Pontide suture tore off a piece of the Strandja system during the medial Eocene–Oligocene interval.

Abstract Before the Late Cretaceous opening of the Black Sea, the Central Pontides constituted part of the southern margin of Laurasia. Two features that distinguish the Central Pontides from the neighbouring Pontide regions are the presence of an extensive Lower Cretaceous submarine turbidite fan (the Çağlayan Formation) in the north, and a huge area of Jurassic–Cretaceous subduction–accretion complexes in the south. The Central Pontides comprise two terranes, the Istanbul Zone in the west and the Sakarya Zone in the east, which were amalgamated before the Late Jurassic (Kimmeridgian), most probably during the Triassic. The basement in the western Central Pontides (the Istanbul Zone) is made up of a Palaeozoic sedimentary sequence, which ends with Carboniferous coal measures and Permo-Triassic red beds. In the eastern Central Pontides, the basement consists of Permo-Carboniferous granites and an Upper Triassic forearc sequence of siliciclastic turbidites with tectonic slivers of pre-Jurassic ophiolite (the Küre Complex). The Küre Complex is intruded by Middle Jurassic granites and porphyries, which constitute the western termination of a major magmatic arc. Upper Jurassic–Lower Cretaceous shallow-marine limestones (the İnaltı Formation) lie unconformably over both the Istanbul and Sakarya sequences in the Central Pontides. Two new measured stratigraphic sections from the İnaltı Formation constrain the age of the İnaltı Formation as Kimmeridgian–Berriasian. After a period of uplift and erosion during the Valanginian and Hauterivian, the İnaltı Formation is unconformably overlain by an over 2 km-thick sequence of Barremian–Aptian turbidites. Palaeocurrent measurements and detrital zircons indicate that the major part of the turbidites was derived from the East European Platform, implying that the Black Sea was not open before the Aptian. The Çağlayan turbidites pass northwards to a coeval carbonate–clastic shelf exposed along the present Black Sea coast. In the southern part of the Central Pontides, the Lower Cretaceous turbidites were deformed and metamorphosed in the Albian. Albian times also witnessed accretion of Tethyan oceanic crustal and mantle sequences to the southern margin of Laurasia, represented by Albian eclogites and blueschists in the Central Pontides. A new depositional cycle started in the Late Cretaceous with Coniacian–Santonian red pelagic limestones, which lie unconformably over the older units. The limestones pass up into thick sequences of Santonian–Campanian arc volcanic rocks. The volcanism ceased in the middle Campanian, and the interval between late Campanian and middle Eocene is represented by a thick sequence of siliciclastic and calciclastic turbidites in the northern part of the Central Pontides. Coeval sequences in the south are shallow marine and are separated by unconformities. The marine deposition in the Central Pontides ended in the Middle Eocene as a consequence of collision of the Pontides with the Kırşehir Massif. Supplementary material: The palaeontological data (foraminifera, nannofossil and pollen) are available at: https://doi.org/10.6084/m9.figshare.c.3842359

Abstract The Black Sea is a 423,000-km 2 (163,000-mi 2 )-large Cretaceous-Tertiary basin surrounded by Alpine fold belts. It consists mainly of two large subbasins separated by the northwest-southeast-trending mid-Black Sea ridge (Figure 1 ). The west Black Sea basin is floored by oceanic crust overlain by more than 3-km (1.8-mi)-thick flat-lying sediments probably of Cretaceous and younger age ( Letouzey et al., 1977 ; Finetti et al., 1988 ; Okay et al., 1994 ; Robinson, 1996 ). Thenorthwest-trending east Black Sea basin has a thinned continental or oceanic crust overlain by less than 10-km (6-mi)-thick sediments, which are intersected by a large number of faults. It is generally accepted that the Black Sea opened during the Mesozoic as a back-arc basin above the northward-subducting Tethyan oceanic lithosphere (e.g., Bocceletti et al., 1974 ; Şengör and Yilmaz, 1981 ). A kinematic model for the opening of the Black Sea, based largely on data from onshore areas, was suggested in 1994 by Okay et al. The model involved separate mechanisms for the origin of the west and east Black Sea basins. The west Black Sea basin was believed to have opened by orthogonal rifting of a continental fragment from the odessa shelf starting in the Albanian-Cenomonian ( Okay et al., 1994 ). This continental fragment, called the Istanbul zone (Figure 1 ), drifted south, bounded by two major strike-slip faults, opening the oceanic west Black Sea basin in the north and closing the Tethyan Ocean in the south (Figure 2 ). During the early Eocene, the Istanbul zone collided with the Sakarya zone in the south, thereby causing a change-over from extension to compression in the Black Sea. Okay et al. (1994) suggested that the eastern half of the Black Sea, including the east Black Sea basin, mid-Black Sea ridge, and the easternmost part of the west Black Sea basin (Figure 1 ), opened through the anticlockwise rotation of a large continental block around a pole situated in Crimea (Figure 2 ). Such a mode of opening explained the Tertiary compression in the Caucasus, which diminishes northwestward toward the pole of rotation, as well as the segmented southern boundary of the eastern Black Sea. The rotation was believed to have been contemporaneous with the rifting in the west Black Sea basin (Figure 2 ).

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 Abstract: We review the Palaeozoic-Early Mesozoic evolution of the Eastern Mediterranean-Balkan region with special reference to Anatolia, and provide new isotopic data on the Palaeozoic magmatic and metamorphic rocks. The pre-Alpide evolution of the region involves episodic growth of Laurussia by accretion of oceanic terranes and Gondwana-derived microcontinents. Terrane accretion, associated with deformation, magmatism and regional metamorphism, took place in the Late Ordovician-Early Silurian, Carboniferous, Late Triassic-Early Jurassic and Mid-Jurassic. The Late Ordovician-Early Silurian accretion is inferred from strati-graphic and faunal records in the Pontides; other evidence for it is buried under young cover on the northern margin of the Black Sea. The Carboniferous orogeny is related to southward subduction and continental collision on the southern margin of Laurussia. It is marked in the Pontides by high-grade regional metamorphism, north-vergent deformation and post-orogenic latest Carboniferous- Early Permian plutonism. The latest Triassic-Early Jurassic Cimmeride orogeny involved the collision and amalgamation of an oceanic plateau to the southern margin of Laurasia. It is represented by voluminous accretionary complexes with Late Triassic blueschists and eclogites. Late Jurassic regional metamorphism and deformation is confined to the Balkans, and is the result of continental collision between the Rhodope-Serbo-Macedonian and Strandja blocks in the Late Jurassic. The Palaeozoic geological history of the Balkans and the Pontides resembles that of Central Europe, although the similarities end with the Mesozoic, as a consequence of the formation of Pangaea.