Titolo della tesi: Tephrochronological study on Ulukışla Caldera pyroclastic deposits (Hasandağ Volcanic Complex, Central Anatolia, Turkey) to reconstruct its explosive volcanic history
The Ulukışla Caldera is located within the Hasandağ Volcanic Complex (Ulusoy et al., 2021; Diker et al., 2024). It has an elongated morphology, measuring ~4 km in length and ~2.5 km in width. As a newly defined volcanic collapse structure, the Ulukışla Caldera has not been the subject of detailed volcano geological studies yet. The region surrounding the Ulukışla Caldera is characterised by several pyroclastic deposits (Aydar and Gourgaud, 1998; Kuzucuoğlu et al., 2020). However, the primary challenge is the limited study of these outcrops, which are crucial for constructing a more comprehensive and detailed record of explosive volcanism within the Ulukışla Caldera.
This study aims to reconstruct the explosive volcanic history of the Ulukışla Caldera to better understand the volcanic evolution of the Hasandağ Volcanic Complex. To achieve this, the research employed a multidisciplinary approach, incorporating detailed field observations, stratigraphic logging, geochemical and geochronological analyses, and physical volcanology studies. This study addresses a gap in volcano-geological research by characterising and identifying pyroclastic deposits, which will contribute to a better understanding of the volcanic activity in this region. As part of this study, I elaborated a new geological map detailing the recently differentiated pyroclastic deposits of Ulukışla Caldera. This map will provide a comprehensive view of the pyroclastic deposits and their distribution. In addition to distinguishing between different pyroclastic deposits, the geochemistry and geochronological data obtained will also support future tephrochronology studies, including archaeological and paleoenvironmental research. Moreover, the interpretation of the eruption dynamics of the Belbaşhanı Pumice and the estimation of fundamental physical volcanology parameters have enhanced the volcanic hazard assessment for the region. These parameters will be crucial for evaluating the potential risks of future eruptions.
The first part of this PhD thesis focused on the Belbaşhanı Pumice eruption, which are relatively well-preserved and widely distributed pumice fall deposits in the region. This physical volcanology study is the first to be conducted for this region. The Belbaşhanı Pumice fallout deposit has been investigated by field observations, tephrostratigraphic correlations, U–(Th)–Pb and 40Ar/39Ar geochronology, glass geochemistry, pumice morphology, and isopach and isopleth maps. Moreover, related eruption source parameters (e.g., volume and column height) have been estimated along with the associated uncertainties. The parameters obtained from this study will help to improve our knowledge of the volcanic history of Ulukışla Caldera (in Hasandağ Volcanic Complex), also supporting future studies on volcanic hazard assessment in Central Anatolia and surrounding regions.
A more comprehensive study focuses on Ulukışla Caldera volcanic history, was carried out during the second part of my PhD thesis to distinguish the pyroclastic deposits present in the region. Several pyroclastic sequences outcropping around the Ulukışla Caldera and the Belbaşhanı area have been characterised. These deposits separated by paleosols, unconformities, and tectonic relationships, indicate a hiatus of time between eruptions. By applying similar fieldwork and laboratory methodologies used in the first part of this thesis, pyroclastic deposits have been differentiated in the region. The Belbaşhanı Pumice has been used as a horizon marker to distinguish the pyroclastic deposits. I have established tephrostratigraphic correlations among pyroclastic deposits from several outcrops based on volcano-stratigraphy, major and trace element glass geochemistry, and geochronological data. The results of this study will enhance our understanding of the evolutionary phases of the Ulukışla Caldera and the complex volcanic history of the region.