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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.

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