Varto ve Muş Havzalarındaki (Doğu Anadolu, Türkiye) Jeotermal Sistemlerin Yapısal Kontrolleri

Abstract

Varto and Muş basins are transpressional ramp basins which are affected by the compressive tectonic regime resulting from the collision of the African and Anatolian plates in the East Anatolian Contractional Province. Muş Fault Zone, Bitlis Zagros Suture Zone, Varto Fault Zone and the Yorgançayır-Kaynarca Fault Zone are responsible for the deformation of the region. The main structural elements in the effect area of these fault zones are the NW-SE trending dextral strike-slip fault segments, NE-SW trending sinistral strike-slip fault segments, N-S trending extension zones. Pliocene Solhan volcanism and Quaternary Nemrut volcanism are the most important factors that morphologically shape the region. With the tectonic and volcanic processes, the region has gained a geologically very active character and a suitable environment has been formed for geothermal systems around the study area. In areas around the volcanic centers where the Nemrut volcanism is effective, fault-tips, stepping-over and bending areas of segments of the Varto Fault Zone, intersecting areas of segments with intense fracture systems and opening zones, important geothermal fields (e.g., Alagöz, Kaynarca, Güzelkent, Güroymak and Nemrut) have been formed.

In the study area, Karstic limestones of Bitlis Metamorphics and fracture-crack controlled Pliocene volcano-sedimentary sequence are the reservoir rocks of geothermal systems. The crack and fracture systems observed in the volcanic units containing andesite and basalt and the faults that control the formation of the basin have deformed in the basement rocks which are suitable for the fluid circulation due to secondary permeability. In these areas, hot, cold and mineral water waters can reach the surface. While the average surface discharge temperature of the hot water was 42.9°C, the highest temperature was measured from Nemrut geothermal field with approximately 60°C. It was observed that hot waters and mineral waters were mostly in the type of Na-Mg-HCO3 while cold waters were Ca-HCO3 type. The cold waters in the Varto basin are of Ca-HCO3 type and the hot waters and mineral waters are of Na-Mg-HCO3 and mixed water type.

According to Oxygen-18 (18O) and Deuterium (2H) isotope analyzes, Varto, Muş basin, mineral waters and other waters formed three groups. Water resources in Varto have the lowest δ18O and δD values. The feeding area of the waters in Varto is topographically higher and waters fed by air masses with higher moisture with lower contents and isotope differentiation. The waters in the Muş basin are fed from lower elevations. The water resources in this area show that the waters are in origin meteoric because they are located on or near the local meteoric lines and the global meteoric water line. In this study, which is also supported by tritium analysis, it is possible to comment that the meteoric region waters in Varto basin are relatively older than in Muş plain while the waters of the Muş plain can be interpreted as younger and shallow circulating waters.