TY  - JOUR
A1  - Elmas, Ali
A1  - Koralay, Ersin
A1  - Duru, Olgun
A1  - Schmidt, Alexander
T1  - Geochronology, geochemistry, and tectonic setting of the Oligocene magmatic rocks (Marmaros Magmatic Assemblage) in Gokceada Island, northwest Turkey
T2  - International Geology Review
N2  - Through the zmir-Ankara-Erzincan and the Vardar oceans suture zones, convergence between the Eurasian and African plates played a key role in controlling Palaeogene magmatism in north-western Anatolia, northern Aegean, and eastern Balkans. LA-ICP-MS dating of U and Pb isotopes on zircon separates from the tuffs of the Harmankaya Volcanic Rocks, which are inter-fingered with the lower-middle Eocene deposits of the Gazikoy Formation to the north of the Ganos Fault and the Karaaac Formation in the Gelibolu Peninsula, yielded a late Ypresian (51Ma) age. The chemical characteristics suggest that the lavas and tuffs of the Harmankaya Volcanic Rocks are products of syn- or post-collision magmas. These volcanic rocks show also close affinities to the subduction-related magmas. In addition to the already known andesitic volcanic rocks, our field observations in Gokceada Island indicate also the existence of granitic and rhyolitic rocks (Marmaros Magmatic Assemblage). Our U-Pb zircon age data has shown that the newly discovered Marmaros granitic plutons intruded during late Oligocene (26Ma) into the deposits of the Karaaac Formation in Gokceada Island. LA-ICP-MS dating of U and Pb isotopes on zircon separates from the Marmaros rhyolitic rocks yielded a late Oligocene (26Ma) crystallization age. Geochemical characteristics indicate that the more-evolved Oligocene granitic and rhyolitic rock of the Marmaros Magmatic Assemblage possibly assimilated a greater amount of crustal material than the lower Eocene Harmankaya Volcanic Rocks. Geochemical features and age relationships suggest increasing amounts of crustal contamination and a decreasing subduction signature during the evolution of magmas in NW Turkey from the early Eocene to the Oligocene. The magmatic activity developed following the northward subduction of the zmir-Ankara-Erzincan oceanic lithosphere and the earliest Palaeocene final continental collision between the Sakarya and Anatolide-Tauride zones.
KW  - U-Pb geochronology
KW  - geochemistry
KW  - granitoids
KW  - rhyolites
KW  - post-collision
KW  - Eocene-Oligocene
KW  - Gokceada Island
KW  - Northwestern Turkey
Y1  - 2016
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/55235
SN  - 0020-6814
SN  - 1938-2839
VL  - 59
IS  - 4
SP  - 420
EP  - 447
PB  - Taylor & Francis Group
CY  - Philadelphia
ER  -