Latest Cretaceous “A2-type” granites in the Sakarya Zone, NE Turkey: Partial melting of mafic lower crust in response to roll-back of Neo-Tethyan oceanic lithosphere

Transition From Low‐K to High‐K Calc‐Alkaline Magmatism at Approximately 84 Ma in the Eastern Pontides (NE Turkey): Magmatic Response to Slab Rollback of the Black Sea

“…Our slab rollback model appears to be reasonable at explaining the spatial and temporal variation and compositional transition of the Late Cretaceous magmatism, as well as the presence of the approximately 81‐ to 73‐Ma A 2 ‐type alkaline granitoids with high zircon saturation temperatures (up to 862 °C) in the Pirnalli and Topcam area of the EP (Figure b, Karsli et al, ; Karsli, Caran, et al, ). However, we note that the validity of this model is subject to future work using the data of the coeval mafic rocks and the abundant geochronological data of the Late Cretaceous magmatism in the EP arc.…”

“…We note that a slab rollback model associated with the northward subduction of the northern branch of the Neotethys lithosphere has also been proposed to explain the generation of the Late Cretaceous magmatic rocks both in the EP (e.g., Çinku et al, ; Karsli et al, ; Karsli, Caran, et al, ) and the western Pontides (e.g., Aysal et al, ; Keskin & Tüysüz, ) on the basis of an assumed southward migration of magmatism that was inferred from the paleomagnetic data (Çinku et al, ). However, as discussed earlier, existing data indicate that the Late Cretaceous magmatism did not show a simple southward migration but covers a broader region not only in the northern zone (Ordu‐Güdül) but also in the southern zone (Gümüşhane‐Bayburt) of the EP (Figure b).…”

“…Such extensive Late Cretaceous magmatism was constrained previously by hornblende K‐Ar dating, including the granodiorites from İkizdere in the east of the arc (Figure b) that was dated at 79 Ma (Moore et al, ) and from the Dereli batholith in the central of the arc that were dated between 84 and 71 Ma (Moore et al, ). Farther to the west, the monzonites from Topcam (Figure b) have been dated at 72.8 ± 0.3 and 73.5 ± 0.3 Ma by LA‐ICP‐MS zircon U‐Pb dating (Karsli et al, ). Geochronological data reported here indicate that the plutonic rocks from Güdül to Torul were emplaced during the Late Cretaceous (91–78 Ma).…”

“…The presence of large‐scale ultramafic‐mafic bodies and the Late Cretaceous olistostromal mélanges in the axial zone, eastern part of the IAE (Figure a) (e.g., Adamia et al, ; Dilek & Whitney, ; Parlak et al, ; Robertson et al, ; Robertson & Dixon, ), has been considered as Jurassic to Late Cretaceous ophiolites representing the relics of the northern branch of the Neotethys lithosphere, and such oceanic branch is inferred to be subducted northerly beneath the EP (e.g., Boztuğ et al, ; Çelik et al, ; Dilek & Thy, ; Galoyan et al, ; Hässig et al, ; Karsli, Dokuz, Uysal, Aydin, Kandemir, et al, ; Okay & Sahinturk, ; Parlak et al, ). In this model, the Black Sea is regarded as a back‐arc basin of the northern branch of the Neotethys and is inferred to be opened during the Late Cretaceous‐Eocene (e.g., Karsli et al, ; Okay et al, ). In contrast, the presence of a narrow shelf (< 20‐km wide) with a steep apron in the present‐day configuration (Özsoy & Ünlüata, ) and Eocene giant east‐west trending south dipping reverse faults (Figure b) (e.g., Dewey et al, , ; Kazmin et al, ; Nikishin et al, ) in the southern coast of the Black Sea, and the southward migration and increasing potassium content of the Late Cretaceous magmatism (e.g., Bektaş et al, ; Eyuboglu et al, ; Eyuboglu, Chung, et al, ; Eyuboglu, Santosh, et al, ) led some authors to propose that the EP arc can be attributed to the southward dipping subduction of the Black Sea (Paleotethys) oceanic lithosphere since the Late Cretaceous.…”

“…Abbreviations: AP = Arabian Platform; EP = eastern Pontides; CP = central Pontides; WP = western Pontides; TAP = Tauride‐Anatolide platform; KM = Kırşehir massif; IAE = İzmir‐Ankara‐Erzincan belt; IT = Inner Tauride belt; BZ = Bitlis‐Zagros suture; NAF = north Anatolian fault; NEAF = northeast Anatolian fault. Age data in the literature are from Eyuboglu (), Eyuboglu et al (, ), Karsli, Dokuz, Uysal, Aydin, Chen et al (), Karsli, Caran, et al (), Karsli, Dokuz, et al (), Karsli et al (); Karsli, Caran, et al (), Kaygusuz and Aydincakir (), Kaygusuz and Sen (), Kaygusuz et al (, , , , , , , ), Moore et al (), Özdamar (), and Sipahi and Sadıklar ().…”