Tectonic evolution of the Söke Basin: Extension-dominated transtensional basin formation in western part of the Büyük Menderes Graben, Western Anatolia, Turkey

Integrated study on the stratigraphic and structural features of the Söke Basin on the western end of the Büyük Menderes Graben, Western Anatolia, has indicated that the tectonic evolution of Söke Basin includes extension-dominated transtension. At its western end, the EW-trending Büyük Menderes Graben tends to follow a zig-zag path influenced by zones of NE–SW-trending weakness in pre-rift crystalline rocks. The pre-existing fabric trends lie at angles up to 45–70° to the regional extension direction and are followed by extensional faults. The basin fill can be grouped into four major sequences separated by angular unconformities: (1) normal- to strike-slip-faulted Early–Middle Miocene alluvial fan–lacustrine sediments with economic coal beds, (2) folded and normal- to strike-slip-faulted Middle–Late Miocene lacustrine deposits intruded by volcanic rocks, (3) tilted Late Pliocene–Pleistocene alluvial fan–lacustrine carbonate deposits and shallow marine fan–delta deposits, and (4) undeformed Holocene alluvial, fluvial, and coastal sediments.The earliest sediments are interpreted, for the first time, to have been deposited in a supradetachment basin governed by the activity of an extensional detachment that separated metamorphic rocks in the footwall from ophiolitic nappes in the hangingwall. During the Middle–Late Miocene, high-angle faults cross-cut the low-angle detachment, and alluvial fans from lacustrine sediments were deposited under the control of an E–W-trending dip-slip normal fault and NE–SW-trending oblique-slip normal faults that formed an extensional basin. This activity was followed by normal to strike-slip-dominated deformation, leading to a highly complex mosaic of faults and fault-blocks, and fragmentation of the oldest basin-fill rock units. Finally, from Pleistocene until modern times, extensional forces have been in operation and have led to the reactivation of the Priene–Sazli fault, in front of which the Quaternary Söke–Milet Basin developed under the control of oblique extension. These results support an extension-dominated transtension that has existed since the Early Miocene in the western end of the Büyük Menderes Graben.