Abstract:
The Alaşehir and Büyük Menderes Grabens are two major E-W trending grabens that border the central part of the Menderes Metamorphic Core Complex (MMCC) to the north and south, respectively. These two grabens were previously considered to be developed symmetrically under the control of two detachment surfaces; the Alaşehir detachment to the north and the Büyük Menderes detachment to the south, which were initially formed as high angle normal faults and rotated to low angle detachment faults (Gessner et. al., 2001; Seyitoglu et al., 2002 and 2004; Çemen et al., 2006; Çiftci et al., 2009 and 2010; Gessner et al., 2013). Detailed field mapping and structural interpretation of seismic reflection profiles by previous geological researchers in the Alaşehir Graben suggest the presence of a well-developed rollover structure associated with the fault-bend geometry of the Alaşehir detachment surface (Seyitoglu et al., 2000 and 2002; Çiftci et al., 2009 and 2010). During this study, eight N-S and six E-W trending seismic reflection profiles in the Büyük Menderes Graben were interpreted to determine the subsurface structural geometry of the graben. Eight N-S cross-sections were restored to determine the original geometry of the normal faults during their initiation in the early Miocene. The cross-section restoration based on seismic reflection profiles reveals that a roll over geometry did not develop on the hanging wall of the south dipping normal fault. Furthermore, the kinematic modeling created by backstripped cross sections and tectonic subsidence rates suggest that the evolution of the Büyük Menderes Graben was controlled by two active boundary faults on its northern and southern margins. Therefore, this study suggests that the Büyük Menderes Graben differs from the Alaşehir Graben in terms of its structural evolution and may have formed as a rift basin during the early Miocene. This in return indicates that the central part of MMCC has experienced asymmetrical extensional tectonics.
