Similar to the western Great Basin in North America, western Turkey contains complex systems of active, kinematically related strike-slip and normal fault zones and abundant geothermal activity. In both regions, geothermal activity is focused in a transtensional setting and is largely amagmatic. In western Turkey, the right-lateral North Anatolian fault splits into several branches, and the tectonic regime changes from translation to transtension toward the southwest. Heat flow is higher in the transtensional region south of the Marmara Sea. In the western USA, geothermal activity is greatest in the transtensional setting of the western Great Basin. Here, a system of right-lateral strike-slip faults known as the Walker Lane accommodates ~20% of the Pacific – North American plate motion. As the Walker Lane terminates northward, dextral shear is transferred into extension in the northwestern Great Basin. This strain transfer enhances extension in the western Great Basin, thereby favoring dilation, deep circulation of fluids, and ultimately geothermal activity along fault zones.
Faults are known to be the primary control on geothermal activity in amagmatic transtensional regions, but questions remain concerning the favorable types and parts of faults for geothermal activity. Better characterization of the structural controls in such regions is needed to develop and enhance exploration strategies, particularly the selection of drilling sites in fields without surficial expressions (i.e., blind or hidden fields). Developing better methods of discovering blind geothermal fields is critical for future development, because these systems can represent the bulk of the resource in arid regions and their development minimizes impact on thermal springs in culturally sensitive areas (e.g. Turkey).
Due to the need to develop alternative sources of clean energy worldwide, we have recently initiated a comparative analysis of geothermal activity in western Turkey and the western Great Basin, USA, through integrated geologic and geophysical investigations. The major goal of this study is to better characterize structural controls on geothermal systems in transtensional amagmatic regions. This project involves 1) detailed geologic mapping and reconnaissance of ~6 geothermal fields in western Turkey; 2) structural analysis of related fault zones in these fields; 3) GIS compilation of geologic, geochemical and geophysical data; and 4) comparative analysis of fields in western Turkey and the Great Basin (USA). Our recent studies have defined several structural settings common to geothermal fields in the western Great Basin, including 1) discrete steps in normal fault zones, 2) belts of intersecting, overlapping, and/or terminating normal faults, and 3) small pull-aparts at the intersection of strike-slip and normal faults. Our initial assessment suggests that similar settings characterize geothermal fields in western Turkey. If certain structural features are common to geothermal systems in both western Turkey and the Great Basin, our findings may serve as a guide to exploration, including targeting of drill sites, in amagmatic transtensional settings throughout the world.