Extension of Hellenic forearc shear zones in SW Turkey: the Pliocene–Quaternary deformation of the Eşen Çay Basin

Abstract

The Pliocene–Quaternary Eşen Çay Basin in southwestern Turkey has a key position in the southern Aegean to gain insight into both lateral and temporal changes in stresses exerted by plate convergence at the Hellenic–Cyprus arc junction. A tectonosedimentary study of the basin development in combination with a structural analysis helped to reveal internal basin deformation and adjacent basement kinematics in order to delineate 3D strain through time. In the Pliocene the basin originated as a fluviolacustrine basin situated in a depression related to a ramp-fold geometry in the Lycian nappe stack. During the late Pliocene, E–W extension caused the development of N–S normal faults, displacement along which caused the differentiation of the relief and deposition of local alluvial fan systems. The Pleistocene is also marked by widespread alluvial-fluvial sedimentation that is triggered by activity at 020° faults. This fault system resulted from WNW–ESE extension and caused disruption of the former basin floor by uplift and tilting of intrabasinal areas, which initiated development of new source areas for the fan sedimentation. The Holocene–Recent period is characterized by a complex combination of faults of which 070° sinistral strike-slip faults are the most important. Fault-slip analysis reveals that deformation occurred in transtension, explained by the addition of a sinistral shear component. This implies that stresses evolved from simple tensional to transtensional over the Pliocene–Quaternary period. The initial extension phase is explained by the kinematic effects of outward growth of the Hellenic forearc, comparable with observations from the island of Rhodes and the eastern Anaximander Mountains. The time-transgressive addition of a sinistral shear component was likely produced by the northeastward propagating transcurrent motions of forearc slivers sheared from the expanding forearc as has been previously inferred for Crete and Rhodes. The latter process is related to the incipient continental collision of an African promontory south of Crete. This implies a kinematic linkage between the studied domain in southwestern Turkey and the eastern Hellenic Arc.