Late-Stage Extensional Tectonics of the Menderes Metamorphic Core Complex, Western Anatolia (Turkey), as Observed in Its Supra-Detachment Basin

The Menderes metamorphic massif (MM) in western Turkey is the largest core complex in the Aegean extensional province and includes a series of nappe structures composed of high-grade crustal rocks of Gondwana origin. It is intruded by metaluminous to peraluminous granitoid plutons and overlain by syn-extensional sedimentary rocks. Late-stage structural grabens (Alasehir, Buyuk Menderes) within the MM are bounded by high-angle and seismically active faults and are filled with Quaternary sediments. On the southern flank of the Alasehir graben metamorphic rocks of the MM are overlain by the Miocene and younger sedimentary rocks above a N-dipping detachment surface. The nearly 100-m-thick cataclastic shear zone beneath this surface contain S-C fabrics, microfaults, Riedel shears, and shear bands, all consistently indicating top-to-the North shearing. The Miocene granitoid plutons crosscutting the MM and the detachment surface are also deformed, displaying mylonitic textures and extensional ductile-brittle structures. The oldest sedimentary rocks overlying the Alasehir detachment surface are the middle Miocene lacustrine shale-limestone units. The upper Miocene fluvial and alluvial fan deposits unconformably overlying these units represent a surge of clastic deposition along the northern edge of the core complex associated with the onset of range-front faulting in the MM by the late Miocene. The continued uplift of the MM provided the necessary relief and detrital material for the Plio-Pleistocene fluvial systems in the Alasehir supradetachment basin (ASDB). A combination of rotational normal and scissor faulting in the extending ASDB affected the depositional patterns and produced local unconformities within the basinal strata. High-angle, oblique-slip scissor faults crosscutting the MM, the detachment surface and the basinal rocks caused differential uplift, producing fault blocks with different structural architecture and metamorphic grades. This fault kinematics and the distribution of range-parallel and range-perpendicular faults strongly controlled the shape and depth of the accommodation space within the ASDB.