Geochemical and isotopic characteristics of thermal and mineral waters in the Sakarya (Adapazarı) Pull-Apart Basin

Abstract

Abstract This study based on the project titled "Examination of the Economic Potentials of the developed Basins Along the North Anatolian Fault System (NAFS) and East Anatolian Fault System (EAFS) with Remote Sensing and Geographic Information Systems (GIS) Methods" carried out by the General Directorate of Mineral Research and Exploration (MTA). The Sakarya (Adapazarı) Basin is controlled by the right lateral strike-slip North Anatolian Fault Zone (NAFS) which is one of the most active structures in Turkey. The Basin showing a different evolution mechanism from the pull-apart basins along the NAFS is represented by the sedimentation by the Sakarya River in the northern site towards the Black Sea. Moreover, the southern margin of the basin is shaped by the active faults. On the accounts of these factors, the geological significance of the basin for both geothermal and deformation features entirely focuses around the southern margin of the basin. In the study area, the Paleocene and Eocene aged limestones have abundantly broken, cracked and karstic cavity. The clayey-silty levels of the Plio-Quaternary sediments on the limestones showing the reservoir character are also cover rock.Chemical and isotopic compositions were determined by sampling from hot fluids produced from wells drilled in the Sakarya Basin and various cold-water sources. The electrical conductivity of cold and thermal waters varies between 199 and 7250 µS/cm. Temperatures of fluids taken from wells and springs are between 24 and 80° C. According to the classification of International Association of Hydrogeologists (IAH), Sakarya thermal waters are classified as boron-containing sodium, chlorinated, bicarbonate thermal and mineral waters and are deeply circulating fluids.The maturation index of Sapanca-Uzunkum and Akyazı waters is greater than 2. The cation geothermometers have been applied to these waters as well as silica geothermometers. The reservoir temperatures of these waters calculated by silica and cation geothermometers are 44-109oC and 34-99oC, respectively. These results can be attributed to the enrichment of oxygen isotopes in Akyazı and Sapanca-Uzunkum waters, their deep circulation and longer interaction with reservoir rocks.