Journal of Geodynamics 65 (2013) 148–175 Contents lists available at SciVerse ScienceDirect Journal of Geodynamics jo u r n al hom epage : http://www.elsevier.com/locate/jog Tectonic evolution of the Söke Basin: Extension-dominated transtensional basin formation in western part of the Büyük Menderes Graben, Western Anatolia, Turkey Ökmen Sümer a,b,∗ , U˘ gur ˙ Inci a , Hasan Sözbilir a a Dokuz Eylül University, Faculty of Engineering, Department of Geological Engineering, Tınaztepe Campus, 35160 Buca, ˙ Izmir, Turkey b Dokuz Eylül University, The Graduate School of Natural and Applied Science, Tınaztepe Campus, 35160 Buca, ˙ Izmir, Turkey a r t i c l e i n f o Article history: Received 15 December 2011 Received in revised form 31 May 2012 Accepted 1 June 2012 Available online 23 June 2012 Keywords: Söke Basin Supradetachment basin Transtensional basin Oblique extension Büyük Menderes Graben Western Anatolia Late Cenozoic a b s t r a c t 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 direc- tion 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 allu- vial 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. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction The Söke Basin is located in the West Anatolian Extensional Province (WAEP), where contractional deformation was over- printed by post-orogenic extension that began 35–20 Ma ago in the backarc region of the retreating Hellenic subduction zone (Jolivet and Brun, 2010) (Fig. 1 ). This post-orogenic extension led to the formation of sev- eral types of Late Cenozoic basins characterised by basin-bounding ∗ Corresponding author at: Dokuz Eylül University, Faculty of Engineering, Department of Geological Engineering, Tınaztepe Campus, 35160 Buca, ˙ Izmir, Turkey. E-mail address: okmen.sumer@deu.edu.tr (Ö. Sümer). faults and basin infills (Sözbilir, 2005; ten Veen et al., 2009; van Hinsbergen, 2010; Alc ¸ ic ¸ ek, 2010). In the central part of the WAEP, the post-orogenic extension can be separated into two main styles of faulting: a core complex mode of faulting followed by a rift mode of faulting (Sözbilir and Emre, 1996; Koc ¸ yi˘ git et al., 1999a; Bozkurt, 2000; Sözbilir, 2001; Bozkurt and Sözbilir, 2004). The former led to the formation of the Menderes metamorphic core complex, detachment faults, and associated E–W-trending Miocene suprade- tachment basins such as Gediz (Alas ¸ ehir) and Büyük Menderes. The Early–Middle Miocene core complex mode of structures is overprinted by the younger rift mode structures characterised by high-angle normal faults. However, Seyito˘ glu et al. (2002) and C ¸ iftc ¸ i and Bozkurt (2010) suggest that the detachment faulting in the Gediz Graben was initiated as a rolling-hinge mechanism by the Early Miocene and underwent continuous evolution since 0264-3707/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jog.2012.06.005