STRUCTURAL EVOLUTION OF THE BUYUK MENDERES GRABEN: IMPLICATIONS FOR CENOZOIC EXTENSIONAL TECTONICS IN WESTERN TURKEY

The Menderes Metamorphic Core Complex (MMCC) covers over 40.000 km²in Western Turkey. The Alaşehir and Büyük Menderes Grabens are two major E-W trending grabens that border the central part of the 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 north-dipping Alaşehir detachment to the north and the south-dipping Büyük Menderes detachment to the south, which were initially formed as high angle normal faults and rotated to low angle detachment faults. Detailed field mapping and structural interpretation of seismic reflection profiles by previous geological researches in the Alaşehir Graben suggest the presence of a well-developed roll over structure associated with the fault-bend geometry of the north dipping Alaşehir detachment surface.

During this study, eight N-S and six E-W trending seismic reflection profiles in the Büyük Menderes Graben were interpreted to determine subsurface structural geometry of the graben. Eight N-S trending structural cross-sections were restored to determine the original geometry of the normal faults during their initiation in early Miocene. The balanced and restored cross-sections reveal that a roll over geometry did not develop on the hanging wall of the south dipping normal fault due to its planar geometry. 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 both margins. Therefore, this study suggests the Büyük Menderes Graben differs from the Alaşehir Graben in terms of extensional origin and may have been formed as rift basin during the early Miocene.