Erciyes Stratovolkanı Holosen Volkanizmasının Petrolojik İncelenmesi

Abstract

Erciyes Stratovolcano is located in the Central Anatolian Region, with an altitude of 3917 m, and considered active due to its activities in the last 10000 years. It’s composition varies from rhyolite to basalt. On the northern and southern slopes, there are dacitic Yılanlı Dağ dome and rhyolitic Perikartın, Karagüllü and Dikkartın domes and widely distributed pyroclastic products. These are the Holocene products of the stratovolcano. Field research was conducted to investigate the origin of the Holocene volcanological evolution of the volcano. A new stratigraphic section was taken and samples were collected in these studies. Petrographic observations with a polarized microscope were performed on the samples, and mineralogical and chemical analyzes such as major element, mineral point and linear analyzes with SEM-EDS and EMP-WDS were conducted on the glass and minerals. Additionally, whole rock major and trace elementiv analyzes and glass trace element analyzes were carried out. Yılanlı Dağ dome mineralogically contains clinopyroxene minerals that are not found in other products. For the first time, a typology study on zircons separated from Dikkartın, Perikartın and Karagüllü pyroclastics was performed. This study shows hybrid origin (crust and mantle). Furthermore, temperature ranges were determined using zircon typology and zircon saturation calculations, which yielded results that were consistent with each other (700- 800 °C). Thermobarometric calculations were performed using data obtained from mineral analyzes. These results were interpreted and compared, and the magma chamber depths were similar for the three units (8-19 km), indicating shallow crustal origin. According to the whole-rock trace element data, it was determined that the Karagüllü pumice sample differed from other pumices (Sr 206-210 ppm, Co 19-25 ppm) with high Sr (241 ppm) and low Co (16 ppm) ratios. Karagüllü samples have approximately 60-90 ppm Zr and 430-57 ppm Ba contents in the glass trace element analyzes, whereas Dikkartın samples include higher Zr (115-150 ppm) and Ba (474-597 ppm) contents. Ta element in lavas are high (1.6 ppm), indicating crustal contamination. The findings are generally consistent with fractional crystallization processes. Although the similarities in mineral analyzes, zircon types, and thermobarometer calculations indicate the same origin, differences in glass analyzes raise concerns. As a result of these studies and interpretations, magma reservoir models were made. Experimental studies were also carried out on the samples. It has been tested whether the phenocryst ratios obtained by the point counting method for modal analyze from rocks can be represented by the ratios calculated on the thin section photograph. The phenocrystal ratios were generally high (3-23%) in the point counting method, indicating that the second method could not represent them. Another experimental study is the comparison of wavelength and energy dispersion X-ray spectrometric techniques on some samples. In the results, both techniques gave the same results. However, it was observed that, on smaller scale, the SiO2 values of glass and minerals were lower for EMP-WDS analyzes, while SEM-EDS analyzes present lower values for the total alkaline ratios.