GEOMETRY AND TECTONIC SIGNIFICANCE OF THE BASCAYIR DETACHMENT, BUYUK MENDERES GRABEN, WESTERN TURKEY

The central Menderes Massif Metamorphic core complex is bounded by two east-trending grabens, the Alasehir (Gediz) graben to the north and the Buyuk Menderes Graben to the south. Field-oriented geological studies in the central Menderes Massif metamorphic core complex suggest the presence of two low-angle detachment surfaces: 1) a north dipping detachment along the southern margin of the Alasehir (Gediz) Graben, termed the Alasehir Detachment and 2) a south-dipping detachment surface along the northern margin of the Buyuk Menderes Graben, named the Bascayir Detachment. Although the Alasehir Detachment has been studied in detail in recent years, the Bascayir Detachment remained relatively unstudied.

In this study, we mapped the footwall and hanging wall rocks of the Bascayir Detachment in the vicinity of the village of Bascayir on a 1/10 000 scale topographic map. We also examined characteristics of cataclastic and mylonitic features in the footwall of the detachment surface. The footwall is made up of quartzite and marble intercalated micaschists. The hangingwall contains the gneissic metamorphic rocks and the Early-Miocene sedimentary rocks, usually referred in the area as the Haskoy Formation. A disconformity is also observed in the hanging wall between the gneissic metamorphic rocks and the sedimentary rocks. The footwall rocks contain well developed shear-sense indicators. Our preliminary examination of these shear sense indicators along the footwall of the Bascayir Detachment suggest that the detachment contains both top to the North and top to the South shear sense indicators. This, in turn suggests that the Bascayir Detachment may have developed in two stages.