Water-rock interaction in the geothermal systems related to post-collision zone volcanism: A case study based on multivariate statistical analysis from the Kavak geothermal field (Konya, Turkey)

Water-rock interaction is the focus of geothermal energy studies and can be documented by traditional geochemical methods such as ion ratio method and hydrogeochemical modelling etc. Statistical approaches are also vital for the quantitative models, and mainly combined with the traditional methods. In this study, we re-evaluate the published data, including water chemistry and volcanic and metamorphic whole-rock geochemistry fromthe Kavak geothermal field (Konya, Turkey) by using multivariate statistical analysis (e.g. factor analysis and clustering analysis) to research possible interaction between the thermal waters and surrounding rocks. The Kavak geothermal field (KGF) overlies a metamorphic basement composed of the Paleozoic metacarbonates and metaclastic rocks, yet is located near the Erenlerda.g-Alacada.g volcanic complex (ErAVC). An example of unimodal orogenic volcanism in an extensional geodynamic setting, the Neogene ErAVC is composed of widespread high-K calcalkaline andesite to rhyodacite lavas with enclaves and their pyroclastic counterparts. The Kavak geothermal field covers a small area (similar to 7.5 km(2)) and lies along the Seydisehir fault zone in the southeast of the ErAVC. The Kavak thermal waters are meteoric in origin and peripheral waters (Ca-Na-HCO3) in the geothermal system related to the orogenic volcanism. The Kavak thermal waters are characterised by high K+ and Na+ cations, and low pH (between 6.4-6.9 pH) values relative to the cold waters around the KGF. Two types of thermal waters were identified in the KGF based on the slight difference in their hydrochemistry and discharge temperature. The first type thermal water (similar to 22 degrees C) has higher TDS and Cl/Br ratio and lower dissolved silica and Br content relative to the second type of water (up to 45 degrees C). The chemical relationship between the KGF and high-K ErAVC is clearly seen in the cation-based diagrams. Multivariate statistical analysis confirms that first type and second type thermal waters identified based on their hydrochemistry formed two separate statistical groups, and suggests that the chemistry of the KGF waters was mainly controlled by the composition of the ErAVC rather than those of the basementmetamorphic rocks as a result of water-rock interaction.