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.

Cross-sectional anatomy and geodynamic evolution of the Central Pontide orogenic belt (northern Turkey)

“…This younger age of the Kapanboğazı Formation is confirmed in the Central Pontides by stratigraphic sections immediately west of our study area that have nannoplankton assemblages of Santonian age, possibly extending down to Coniacian (Okay et al 2006) and also by nannoplankton assemblages of Santonian-Lower Campanian age in sample 96C (Figs. 2, 3; Table 1).…”

“…In the Kargı Massif, south of Boyabat ( Fig. 1), rocks classically interpreted as Middle Triassic to Lower Jurassic schists, metabasites and serpentinites (e.g., Şengör et al 1984;Okay 1989;Uğuz et al 2002), provided metamorphic ages indicating subduction and collision of an oceanic plateau (Domuzdağ complex) during the Early Cretaceous (Okay et al 2006. Our study area is located in the Central Pontides north of the Kargı Massif and in the Sakarya Zone (Fig.…”

“…The inset shows the main tectonic elements of the Black Sea region (modified after Robinson et al 1996;Robinson 1997;Okay and Tüysüz 1999). The Domuzdağ complex is part of a Lower Cretaceous accretionary wedge (Okay et al 2006). The Boyabat flysch basin and its western prolongation the Ulus flysch basin are interpreted as forearc basins.…”

“…1). Much of the crust of Anatolia formed by accretion of Gondwana-derived microcontinents to the southern margin of Eurasia during the closure of the Paleotethyan and the Neotethyan oceans from Jurassic to Eocene time (e.g., Şengör and Yılmaz 1981;Okay and Tüysüz 1999;Okay et al 2006;Ustaömer and Robertson 1997;Pourteau et al 2010). Behind the north-dipping Neotethyan subduction zone, the Black Sea opened as a back-arc basin from Cretaceous to Paleocene time (Hsü et al 1977;Letouzey et al 1977;Şengör and Yılmaz 1981;Zonenshain and Le Pichon 1986;Görür 1988;Okay et al 1994;Robinson et al 1996;Stephenson and Schellart 2010;Graham et al 2013;Nikishin et al 2015).…”

Blueschists of the Amassia-Stepanavan Suture Zone (Armenia): linking Tethys subduction history from E-Turkey to W-Iran

“…Dating of HP rocks from the Kargi massif ( Fig. 1) provided mean 40 Ar/ 39 Ar phengite age of 104.5 ± 7.2 Ma (Okay et al 2007), while ages between 101 and 85 Ma were obtained with the same method in the NW part of the Izmir-Ankara suture (Okay et al 1998;Sherlock et al 1999). In contrast, Mid Paleocene to Eocene ages were obtained in the southwest Izmir suture (Rimmelé et al 2003).…”