Özet:

In the middle Pontides, late Kretase-Eosen ancient volcanic rocks around Sinop-Samsun give clear traces. The late Kretase volcanoes are represented by the Hamsaros volcanoes near Sinop in the north, and the volcanoes within Yemişliçay Formation in Alaçam-Dikmen-Durağan in the south. The Eosen volcanoes are represented by the Tekkeköy Formation volcanoes, which flood in a wide area starting from Bafra to the east. In this study, the (sub)volcanic units within the Yemişliçay Formation will be presented with 40Ar/39Ar geocronology, mineral- and all-crowd geochemistry. The volcanoes of the Yemiliçay Formation contain plagioclass (An50-70), clinopirosine (ojit-diopsite), amphibol (magnezyo-hastingsite, rarely chermacite) phenocrystals and impacous minerals. The age of 40Ar/39Ar obtained from the volcanites indicates that volcanic activity is effective in two separate periods: Late Cretase (~71 Mile, reverse isocron age) and Eosen (~48 Mile, platonic age). While late Kretase volcanoes are considered to be a product of a same-age volcanism with Yemişliçay Formation, this formation is interpreted as an accompaniment of Eosen old volcanoes, which cuts it as thin intrusions. Late Kretase volcanoes are characterized by andezite/bazaltic and kalk-alkalen, Eosen volcanoes are characterized by basalt/trakiandezite and chosonite. The trace element patterns normalized according to N-MORB of all examined samples, which are typical for the loss-related volcanoes, indicate BIE (Rb, Ba, K, Sr), Th and HNTE (La, Ce) enrichment, manifest negative Nb-Ta-Ti and positive Pb anomalies. The shoshonic rockets are represented by the relatively high Ndi (εNd: +4) and low Sri (0.704634) isotopes, while the elevated rockets have the reverse low Ndi (εNd: -3) and high Sri (0.705203-0.706956) values. The geocronological and geochemical data obtained, when evaluated along with the published geological information, indicate that the Yemişliçay Formation volcanoes are formed in the Pontidic Magmatic Radiation in a foam-pre-environment.

Anahtar Kelimeler:

Özet:

In the Central Pontides, Late Cretaceous-Eocene volcanic rocks prominently outcrop around Sinop-Samsun. The Late Cretaceous volcanites are represented by the Hamsaros volcanites near Sinop in the north and volcanic units in the Yemişliçay Formation around Alaçam-Dikmen-Durağan in the south. The Eocene volcanites are represented by the Tekkeköy Formation outcropping in a large area from Bafra to the East. 40Ar/39Ar geochronology, mineral- and whole-rock geochemistry of the (sub)volcanic units in the Yemişliçay Formation will be presented in this study. The Yemişliçay Formation volcanites include plagioclase (An50-70), clinopyroxene (augite-diopside), amphibole (mainly magnesio-hastingsite, rarely tschermakite) phenocrysts and opaque minerals. 40Ar/39Ar ages from the volcanites show that volcanic activity occurred two different time as Late Cretaceous (~71 Ma, inverse isochron age) and Eocene (~48 Ma, plateau age). The Late Cretaceous volcanites were considered as products of the volcanism contemporaneous with the deposition of the Yemişliçay Formation, but as shallow intrusions in this formation, the Eocene volcanites were interpreted to be continuation of volcanites of the Tekkeköy Formation. The Late Cretaceous volcanites are andesite/basaltic andesite and calc-alkaline, but the Eocene volcanites basalt/trachyandesite and shoshonitic in character. N-MORB-normalized trace element patterns of all the volcanites are characterized by strong enrichments in LILE (Rb, Ba, K and Sr), Th and LREE (La, Ce), prominent negative Nb-Ta-Ti and positive Pb anomalies, all characteristic for subduction-related volcanites. The shoshonitic samples possess relatively high Ndi (εNd: +4) and low Sri (0.704634) isotopes whereas calc-alkaline rocks have low Ndi (εNd: down to -3) and high Sri (0.705203-0.706956) isotopes. The obtained geochronological and geochemical data together with the published geological information reveal that the Yemişliçay Formation volcanites formed in a fore-arc setting in the Pontide magmatic arc.