A Late Palaeozoic‐Early Mesozoic marginal basin along the actives sourthern continental margin of Eurasia: Evidence from the central Pontides (Turkey) and adjacent regions

Abstract

Remnants of two ‘Palaeotethyan’ oceanic basins are exposed in the Central Pontides of northern Turkey, separated by a continental sliver and an oceanic arc. The southern basin corresponds to the main Tethys (‘Palaeotethys’), which partially closed in Early Mesozoic time following northward subduction under the southern, active continental margin of Eurasia. The northern basin (Küre Complex) opened above the ‘Palaeotethyan’ subduction zone as a marginal basin, following rifting of a continental fragment (Istanbul fragment) from Eurasia. Marginal basin opening apparently dates from the Late Palaeozoic in the east (Küre basin) and from the Triassic in the west (Kocaeli basin). Basin closure was achieved by southward subduction‐accretion, in pre‐Late Jurassic times, leaving ‘Neotethys’ open to the south. Counterparts of the Küre Complex are found in the adjacent Crimea (Taurian Series), Istranca (Zabernevo Complex), Dobrogea (Nalbant flysch) and Caucasus (pre‐Late Jurassic Southern Slope Basin) regions. Basin opening was accompanied by oceanic crust genesis, at least in the Pontides and Caucasus. Closure before Mid‐Jurassic time was achieved by subduction‐accretion processes, whereby oceanic crust and deep‐sea sediments (including sulphides) were detached and structurally assembled, while oceanic basement was subducted. Marginal basin opening and closure is seen as one in a series of events along a long‐lived, active south Eurasian continental margin.

Geochronology of the Karadere basement (NW Turkey) and implications for the geological evolution of the Istanbul zone

“…It is well known that the Palaeozoic and Mesozoic rocks of the Istanbul zone differ in metamorphic, magmatic and stratigraphic history from rocks of the adjacent Sakarya and the Strandja zones (Şengör et al 1984Robertson and Dixon 1984;Yilmaz and Şengör 1985;Ustaömer and Robertson 1995;Göncüoǧlu 1997;Ustaömer and Robertson 1997;Yilmaz et al 1997). Therefore, the Istanbul zone is interpreted as a rifted continental fragment of the Eurasian continental margin, which became isolated from this margin during the Mid-to Late Cretaceous and then has moved to the south during opening of the western Black Sea basin (Ustaömer and Robertson 1993;Okay et al 1994Okay et al , 1996. Closure of the Intra-Pontide Ocean and final collision of the Istanbul zone with the Sakarya continent during latest Cretaceous/ Palaeocene led to the present-day plate tectonic assembly in NW Turkey (Okay et al 1994(Okay et al , 1996Yiǧitbaş et al 1999;Okay and Satir 2000).…”

“…The Istanbul zone (Okay 1989(Okay , 2000Okay et al 1994) also referred to as Istanbul nappe (Şengör and Yilmaz 1981) or Istanbul fragment (Ustaömer and Robertson 1993), NW Turkey, lies within the western Pontide tectonic belt (Ketin 1966). It consists of pre-Early Palaeozoic crystalline basement, which is overlain by relatively undeformed Palaeozoic (Ordovician to Carboniferous), Mesozoic (Jurassic-Cretaceous) and Cainozoic (Eocene) sedimentary successions.…”

Genesis of Au-containing magmatic deposits of the non-ferrous metals in island-arc structures (Lesser Caucasus and East Pontids), data on inclusions and isotopic investigations

“…), they consist of ultrabasic tectonic "plates", intermittent clay shales and basalts covers represented by island arc and oceanic tholeiites as well as by rocks of depleted mantle. According to Ustaömer, Robertson (1993), geological pattern similar to Cyprus is observed in places of ore mineralization manifestation: serpentinized peridotites have been known in the lower part of section over which gabbro, dyke doleritic complex and greenstone changed pillow-lavas of basaltes have been manifested. The lavas including doleritic dykes have been overlapped by clay shales.…”

Subduction-related Late Cretaceous high-K volcanism in the Central Pontides orogenic belt: constraints on geodynamic implications

“…The Central Pontides is bordered by the Black Sea in the north and separated from the Izmir-Ankara-Erzincan suture zone and Central Anatolian Crystalline Complex in the south. The Central Pontides comprising of İstanbul and Sakarya Zones encountered during the Eocene and younger units lie in the north; it also contains Black Sea marginal basin deposits (Cretaceous-Eocene volcano-sedimentary sequences) bordered by the Black Sea in the farther north (Okay et al, 2006;Tüysüz, 1990;Ustaömer & Robertson, 1993;Yılmaz & Şengör, 1985;Figure 1(b)). These zones started to exist alongside each other together with the tectonic opening of the Black Sea basin in the Early Cretaceous Period (Tüysüz, 1999) and were formed by the tectonic mixing of the Cimmerian and Eurasian continental remanents with Paleotethys Ocean remnants (Yilmaz, Tüysüz, Yiğitbaş, Genç, & Şengör, 1997).…”