Cretaceous and Triassic subduction-accretion, high-pressure-low-temperature metamorphism, and continental growth in the Central Pontides, Turkey

Abstract

Biostratigraphic, isotopic, and petrologic data from the Central Pontides document major southward growth of the Eurasian continental crust by subduction-accretion during the Cretaceous and Triassic Periods. A major part of the accreted material is represented by a crustal slice, 75 km long and up to 11 km thick, consisting of metabasite, metaophiolite, and mica schist that represent underplated Tethyan oceanic crustal and mantle rocks. They were metamorphosed at 490 °C and 17 kbar in mid-Cretaceous time (ca. 105 Ma). The syn-subduction exhumation occurred in a thrust sheet bounded by a greenschist facies shear zone with a normal sense of movement at the top and a thrust fault at the base. A fl exural foreland basin developed in front of the south-vergent high-pressure-low-temperature (HP-LT) metamorphic thrust sheet; the biostratigraphy of the foreland basin constrains the exhumation of the HP-LT rocks to the Turonian-Coniacian, ~20 m.y. after the HP-LT metamorphism, and ~25 m.y. before the terminal Paleocene continental collision. The Cretaceous subduction-accretion complex is tectonically overlain in the north by oceanic crustal rocks accreted to the southern margin of Eurasia during the latest Triassic-earliest Jurassic. The Triassic subduction-accretion complex is made up of metavolcanic rocks of ensimatic arc origin and has undergone a high pressure, greenschist facies metamorphism with growth of sodic amphibole. Most of the Central Pontides consists of accreted Phanerozoic oceanic crustal material, and hence is comparable to regions such as the Klamath Mountains in the northwestern United States or to the Altaids in Central Asia.

Thermal structure of low-grade accreted Lower Cretaceous distal turbidites, the Central Pontides, Turkey: insights for tectonic thickening of an accretionary wedge

“…An associated Albian arc is reported north of the Black Sea ( Figure 1; Nikishin et al, 2015). The CPS is locally unconformably overlain by an Upper Cretaceous volcanosedimentary sequence representing fore-arc deposits (Okay et al, 2006(Okay et al, , 2013Tüysüz and Tekin, 2007). The volcanosedimentary sequence passes upward a mélange-like unit consisting mainly of ophiolitic blocks.…”

“…The oceanic unit, known as the Domuzdağ Complex, consists mainly of eclogite to blueschist facies metabasite and micaschist with serpentinites, metagabbro, metachert, and marble representing deep levels of the subduction-accretionary complexes (Tüysüz, 1990;Ustaömer and Robertson, 1993, 1999Altherr et al, 2004;Okay et al, 2006Okay et al, , 2013Aygül et al, 2015a). 40 Ar/ 39 Ar phengite ages from the Domuzdağ Complex range between 114 and 92 Ma (Okay et al, 2006(Okay et al, , 2013Aygül et al, 2015a). An associated Albian arc is reported north of the Black Sea ( Figure 1; Nikishin et al, 2015).…”

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).…”

“…The 'Central Pontides' is a geographical term comprising the middle portions of the Sakarya Zone (Okay et al, 2006). This region, which includes the study area, is a place where an important continental growth occurred on the continental margin of Laurasia because of the subduction of the Tethys Ocean during the Mesozoic (Aygül & Okay, 2012).…”

Jurassic–Paleogene intraoceanic magmatic evolution of the Ankara Mélange, north-central Anatolia, Turkey

“…the Sakarya Continent (Duru et al, 2004;Okay et al, 2006;Nzegge et al, 2006;Topuz et al, 2007). These metamorphic basement rocks are intruded by the Carboniferous (295 Ma) granitoids (Çogulu et al, 1965;Delaloye and Bingöl, 2000).…”