Ph.D. Tezi Görüntüleme
Petrographical, Mineralogical, Mineral Chemistry andGeochemical Characteristics of Büyük Yaylâ Obsidians (İkizdere/Rize)
In this study, petrographical, mineralogical and geochemical characteristics of Büyük Yaylâ Obsidians (BYO) (İkizdere/Rize) as well as their neighbour rocks have been investigated.Büyük Yaylâ Obsidians are represented by the latest product of the mgmatic units in the study area. The unit is given an age between 1,7 ± 0,28 ma and 2,00 ± 0,24 ma on the basis of 40Ar/39Ar age determinations. Late Cretaceous aged basalt, andesite and their pyroclastics, cut by İkizdere Granitoides, form the basement of the investigate area. Granitoides are unconformably overlain by basanite, trachyandesite, felsite (rhyolite), and obsidians.
Büyük Yaylâ Obsidians are massive black, brownish red, red with black bands and black with red bands in colour. These obsidians are found to be interesting due to their colours as well as columnar and brecciated texture. They show glassy, glassy porphyry and flow banded structure and contain feldspar, biotite, pyroxene, Fe-Ti oxide, as well as apatite, zircon, quartz as accessory minerals and very rare chalcopyrite, pyrite and anhydrite. They are calcalkalen, peralumine and high-K rhyolite in composition. Clinopyroxene, olivine, Fe-Ti oxide and apatite in basanites, and clinopyroxene, biotite, plagioclase and Fe-Ti oxides in trachyandesite, obsidians and felsites, are the minerals played an important role in fractionation. Negative correlations in major and trace elements bivariation diagrams imply that fractional crystallization was responsible for the formation of these rocks. Similar trend and negative-positive anomalies in chondrite- normalized REE and trace elements patterns of obsidians and felsites may have the same source as the granitoidic rocks outcropped in the investigated area. The crystallization temperature of feldspar in the felsites and granitoidic rocks is found to be below 1000 0C. H2O and CO2 are the gas types, obtained on the basis of gas transition temperatures in obsidian, and are accompanied by sulfur compounds of SO2, SO ve H2S.
Key Words: Büyük Yaylâ, Obsidian, Felsite, Granitoide, Peralumine, Crystallisationtemperature, Gas transition temperature