The imaging of the tectonic structure of Isparta Angle by 3D inversion of Magnetotelluric Data

Abstract

Anatolia has been the center of civilizations throughout history, as well as a laboratory for geoscientists in terms of its geological history. The eastern Mediterranean region and Anatolia are located at the intersection of different tectonic plates controlled by the African-Eurasian convergence, which continues along the Cyprus and Aegean (Hellenic) arcs in the southwest and resulted in collision in the east. The interrelation between Cyprus and Aegean arcs remains a topic of discussion among scientists. It is thought that the intersection area of ​​the Aegean and Cyprus arcs, located beneath the Western Anatolia and Isparta Angle (IA), is a slab tear that causes asthenospheric upwelling in SW Anatolia and IA. The reflection of this tear on the surface occurs as a STEP fault type and is represented by the Fethiye - Burdur Fault Zone (FBFZ) forming the western border of IA and Akşehir Fault Zone (AFZ) forming the eastern border of the region. Isparta Angle, influenced by the aforementioned tectonic systems, is located between the FBFZ and AFZ as a reverse triangle shape. Therefore, besides the main border fault zones, there are various normal and reverse faults and related graben-horst structures in the region.     IA is located at where opening and closing of various oceans took place. The main geological basement consists of autochthonous and allocton units. Autochthonous units are called as Beydağları and Anamas - Akseki carbonate platforms. Allocton units were transported and obducted over these carbonate platforms in different geological times and they can be ordered as Lycia nappes, Antalya nappes and Beyşehir-Hoyran-Hadim nappes, respectively. There are various basin formations observed throughout the region, related to nappe emplacements and Cyprus subduction zone back-arc tensional forces before Miocene, and extensional tectonism which became effective after Miocene. The magnetotelluric (MT) method involves the measurement of the time variations of the orthogonal components of natural electric and magnetic fields, which contain information about the electrical resistivity structure from crustal to upper mantle depths. The superiority of the MT method in determining conductivity differences makes it possible to detect aqueous fluids and magma (partial melting). In active tectonic regions such as IA, where various tectonic systems intersect and an asthenospheric upwelling is proposed where aqueous fluids, partial melting or both could be the reason for high conductivity, magnetotellurics is well suited method to study fault-related structures and tectonic processes.In this study, magnetotelluric data were collected in 4 profiles at 47 stations and inverted by using ModEM software to reveal 3D subsurface conductivity structure of the area. The most striking feature is a lower crust conductor located mostly in western part of the region and an upper crustal conductive structure which is related to the lower one imaged in the region. This upper-crust conductor structure reaches up to the surface beneath the main fault zones. The basement structures which consist of nappes, carbonate platforms are imaged as resistive zones and their depths are clearly imaged in the recovered resistivity models.