Petrology of late cretaceous volcanits in Artvin and Borçka region (NE-Turkey)

Master Thesis SUMMARY PETROLOGY OF LATE CRETACEOUS VOLCANITS IN ARTVIN AND BORCKA REGION (NE-TURKEY) Rasim BAŞER Karadeniz Technical University The Graduate School of Natural and Applied Sciences Geological Engineering Graduate Program Supervisor: Prof. Dr. Faruk AYDIN 2016, 110 Pages, 9 Appendix In this study, the major and trace element contents, U-Pb zircon ages and Sr-Nd-Pb isotopic data of Late Cretaceous volcanic rocks which are located in Artvin and Borçka (NE Turkey) have been presented, and also tried to determine development processes and origin of these rocks. These rocks are observed as alternating mafic and felsic extrusives within the Çatak, Kızılkaya, Çağlayan, Tirebolu and Cankurtaran formations which were deposited in submarine enviroments during the Late Mesozoic-Early Tertiary. While mafic rocks (basaltic-andesitic) consist of Pl±Cpx±Fe-Ti oxides, felsic rocks (dacitic-rhyolitic) consist of Q±Pl±Fe-Ti oxides. U-Pb zircon seperates from the Çatak and Kızılkaya samples yielded U-Pb ages of 86.5±1 and 83.5±1.2 Ma respectively. The studied mafic and felsic volcanic rocks have mostly transitional geochemical character from tholeiitic to calcalkaline which is typical of those from arc settings. Normal-mid ocean ridge basalt normalised multi element and chondrite normalised lanthanum group element (LGE) patterns show that all rocks are enriched in large ion lithophile elements and light LGEs, but depleted in Nb and Ti. The felsic samples in particular show distinct negative Eu anomalies pointing to the Pl-fractionation. Sr-Nd-Pb isotopic compositions of the studied mafic and felsic volcanic rocks are different from those of subduction related I-type calcalkaline granitoids with same age in the region. Formerly depleted and then metasomatized mantle which was enriched by fluids and/or sediments is suggested to be the source of the mafic volcanics. However, mantle- and/or lower crust-derived differentiated basalticandesitic melts which experienced considerable fractional crystallization and low degree of crustal assimilation are suggested to be the parent melt of the felsic rocks. Key Words: NE Turkey, Late Cretaceous, Volcanism, U-Pb Zircon dating, Geochemistry