Geothermal investigations in western Anatolia using equilibrium temperatures from shallow boreholes

K Erkan

doi:10.5194/se-6-103-2015

Abstract

Abstract. Determination of the conductive heat flow in western Anatolia has broad implications in many areas, including studies on the present-day extensional tectonic activity and assessments of the geothermal resources in the region. In this study, high-resolution equilibrium temperatures from 113 boreholes with depths of ~100 m were analyzed for determination of the conductive heat flow. Thermal conductivities were either determined by measurements on outcrops or estimated using lithologic records. By a detailed analysis of temperature–depth curves, a total of 55 sites were selected as being useful for further conductive gradient/heat flow calculations, while the remaining 58 sites were abandoned due to hydrological effects on temperatures. Heat flow values with formal errors were calculated for 24 sites where rock thermal conductivity information is available. Due to the shallow depths of the investigated boreholes and uncertainties in thermal conductivity information, the results include a large accumulated error. A preliminary heat flow map is generated using the results of this study and a previous study in the southern Marmara region. Elevated heat flow values of 85–95 mW m-2 are observed in the coastal areas, including peninsular parts of Çanakkale and Izmir. The central part of the Menderes Massif also shows elevated heat flow values, the highest values (>100 mW m-2) being in the northeastern part of the Gediz Graben near the Kula volcanic center. Moderate heat flow values of 55–70 mW m-2 are observed in the eastern part of Çanakkale, central part of Balıkesir, northwest of Manisa, and northeast end of Bursa including Yalova. Some of the observed moderate values may be related to unconstrained near surface phenomena due to shallow depth of measurements. Towards the south of the study region, moderate heat flow values are also observed in Muğla. Previously reported regional heat flow values exceeding ~120 mW m-2 is not observed in the region. The heat flow values reported in this study are comparable to the previously reported values in the Aegean Sea, as the two regions form the back-arc section of the Hellenic subduction zone.

Highlights

Determination of the conductive heat flow near the surface of the earth has many important applications, such as understanding the recent history of plate tectonic activity (Erkan and Blackwell, 2008, 2009), determining the depth of brittle/ductile transition in the crust (Bonner et al, 2003), and estimating the geothermal energy potential of a region (Tester et al, 2006; Serpen et al, 2009).Western Anatolia is a unique region with intense presentday plate tectonic activity (Dilek and Altunkaynak, 2009)
The Menderes Massif is divided into three units: the northern Menderes Massif (NMM), the central Menderes Massif (CMM), and the southern Menderes Massif (SMM), separated by two major graben units, the Gediz Graben (GG), which are and the Büyük Menderes Graben (BMG)
A total of 113 borehole sites were investigated in western Anatolia, and 55 of them were found to be useful for conductive gradients and/or heat flow analysis. 24 data points fall into class A/B/C quality, and can be used for heat flow mapping

Summary

Introduction

Determination of the conductive heat flow near the surface of the earth has many important applications, such as understanding the recent history of plate tectonic activity (Erkan and Blackwell, 2008, 2009), determining the depth of brittle/ductile transition in the crust (Bonner et al, 2003), and estimating the geothermal energy potential of a region (Tester et al, 2006; Serpen et al, 2009).Western Anatolia is a unique region with intense presentday plate tectonic activity (Dilek and Altunkaynak, 2009). The region has been characterized by crustal extension and subduction-related andesitic volcanism since the Oligocene (Fytikas et al, 1984). The crustal extension in the region is considered to have two major phases: an early phase of nearly E– W directed extension from the Miocene to the early Pliocene, and a second phase of N–S extension during the Pliocene and the Quaternary. The latter resulted in the formation of modern horst/graben structures observed in the Menderes Massif (Koçyigit et al, 1999)

Results

Discussion

Conclusion