Geology and Petrology of the Kösedağ Metavolcanic Rocks to the south of Tosya

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Jeoloji Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2015

Tezin Dili: İngilizce

Öğrenci: Faruk BERBER

Danışman: Kaan Sayıt

Özet:

The Kösedağ Metavolcanics crops out in the southern Central Pontides as a NE-SW trending belt to the south of Tosya. This unit is characterized by a low-grade metavolcanic assemblage interbedded with metasedimentary lithologies. While these metavolcanics are bounded to the north by the North Anatolian Fault Zone, they structurally overlie the metacarbonates of the Dikmen Formation in the south.

Petrographically, the Kösedağ Metavolcanics are characterized by metadacites, metaandesites and metabasalts. The metadacites within this unit include abundant quartz phenocrysts, whereas the metaandesites are plagioclase-phyric. The metabasalts, on the other hand, consists of clinopyroxene and plagioclase as the dominant primary phases. All these metavolcanics have been influenced by low-grade metamorphism. In addition, the Kösedağ Metavolcanics appear to have been affected by mylonitic deformation along the NAFZ.

The Kösedağ Metavolcanics are characterized by a wide range of chemical compositions including basalts, andesites and dacites. The Kösedağ Metavolcanics are subdivided into two groups as Type 1 and Type 2 based on trace element systematics. The Kösedağ Metavolcanics display enrichment in Th and LREE relative to HFSE, and characterized by negative Nb anomalies, suggesting involvement of subduction component. The high Zr/Nb, low Zr/Y and Nb/Y signatures of the Kösedağ Metavolcanics indicate that they have derived from a depleted mantle source similar to N-MORB source.

Geochemical signatures of the Kösedağ Metavolcanics suggest that they have formed above a subduction zone. Considering also their geological characteristics, the Kösedağ Metavolcanics appear to represent remnants of an island arc within a Neotethyan branch during the Late Cretaceous.

Keywords: Central Pontides, metavolcanic rocks, geochemistry, island arc.