Neogene–Quaternary evolution of the Manisa Basin: Evidence for variation in the stress pattern of the İzmir-Balıkesir Transfer Zone, western Anatolia

In this paper, we aim to identify the Neogene–Quaternary evolution of the Manisa Basin located in the İzmir-Balıkesir Transfer Zone (İBTZ) which lies between the normal-fault-dominated West Anatolian Extensional Province (WAEP) and the strike-slip-dominated North Aegean Region (NAR). The Manisa Basin, which forms a connection with the Gediz Graben, underwent two-stage basin evolution, distinguished by an ancient and modern graben-fill. The ancient basin-fill is made up of a folded and normal-to-reverse faulted and strike-slip-faulted Miocene volcano-sedimentary sequence. The younger modern basin-fill is represented by the Quaternary Bahadır Formation comprising fluvial terrace deposits, early–middle Pleistocene continental clastics of the Turgutlu Formation, alluvial/colluvial sediments of late Pleistocene–early Holocene Emlakdere Formation, and Holocene alluvium.Structural and stratigraphical data reveal that the basin was initially formed as a lacustrine basin bounded by a volcanic ridge from the west; it was subsequently uplifted and deformed probably as a result of Pliocene wrench-dominated strike-slip tectonics, which is characterised by NNW–SSE horizontal σ3 and vertical σ2. Post-Miocene strike-slip faulting along the İBTZ occurred along a right-lateral shear zone in the Manisa Basin. This suggests that some branches of the right-lateral movement of the North Anatolian Fault Zone may continue into the WAEP. The youngest stage shows an extension-dominated transtension with a NE–SW trending σ3 and a vertical σ1. These results are consistent with progressive deformation developed during late Pliocene and onwards wherein the axis of minimum horizontal stress remained in the horizontal plane but the intermediate and maximum horizontal stress axes switched position in the vertical plane. In addition, available palaeostress data for the Gediz Graben are consistent with the pure extension in the eastern and middle part of the graben and with the wrench-to-extension-dominated transtension in the western part, where the Manisa Basin is located. This indicates a NE–SW trending segment boundary zone forming the western end of the E–W trending Gediz Graben.