||Prof. Dr. Mehmet ARSLAN|
||Graduate School of Natural and Applied Sciences|
||Karadeniz Technical University, Turkey||
|Title of the Thesis:
||Petrography, Petrochemistry, 40Ar-39Ar Geochronology, Sr-Nd Isotope Geochemistry and Petrogenesis of the Ulubey (Ordu-NE Turkey) Area Tertiary Volcanics |
|Number of Pages:
Eocene (44.6-49.4 Ma) aged collisional volcanics and Miocene (15.1 Ma) aged post-collisional volcanics in the Ulubey (Ordu) area at the eastern Pontides are divided into four groups; Trachybasalt, Trachydacite-Dacite, Trachyandesite-Trachydacite-Rhyolite and Andesite-Trachyandesite suites.
The volcanics have tholeiitic-calkalkaline to mildly alkaline affinities, and medium to high-K contents. The petrochemical variations show the fractionation of plagioclase + clinopyroxene + hornblende + biotite ± magnetite ± apatite ± sanidine in the evolution of volcanics. N-Type MORB-normalized trace element patterns indicate enrichment in LILE, Th and Ce, and depletion in Zr, Y and TiO2. The chondrite-normalized REE patterns suggest a similar source for the volcanics. (87Sr/86Sr)i ratios (0.70435-0.70503) and εNdi values [(+2.7)(-0.9)]) of the rocks reveal a depleted mantle source region enriched by slab components. Besides, depletion in Nb and Ta relative to LILE, moderate LREE/HREE and high Th/Yb ratios, and Sr-Nd isotope geochemistry data suggest that the parental melts of the volcanics were derived from an enriched mantle, which had been previously metasomatized by fluids derived from subducted slab during Upper Cretaceous-Eocene time. In the studied area, Eocene aged intermediate-acidic volcanics derived lithospheric mantle source and Miocene aged basic volcanics derived asthenospheric mantle source should be related to the thinning of young lithosphere caused by transtantional extensional regime developed by slab break-off in the eastern Pontides.
Key Words: Petrography, Mineral Chemistry, Petrochemistry, Geochronology, Sr-Nd Isotopes, Geochemical Modelling, Volcanics, Ulubey (Ordu), Eastern Pontide, Turkey