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Extensional Fault Kinematics and Basin Segmentation in Highly-Extending Terrains: A Case Study From Western Turkey


The Alasehir supradetachment basin, western Turkey is a unique example of extensional basin evolution and basin segmentation in highly-extending terrains. The basin occurs in the footwall of the ~E-W-striking, low-angle Alasehir detachment fault that developed during the late Cenozoic exhumation of the Menderes core complex. The overall geometry, size, and accommodation of the basin and internal structure–stratigraphy were strongly controlled by the four different fault generations throughout its early Miocene-Pleistocene evolution. The Alasehir detachment fault separates the high-grade crystalline rocks of the core complex from the Neogene deposits of the basin in the hanging wall. The basin-parallel, synthetic and antithetic high-angle normal faults represent a block-faulting stage of the continued horizontal extension High-angle faults are responsible for the formation of horst-graben structures in and across the basin; and control facies changes vertically and laterally. These faults caused back-tilting and rotation of the basinal strata and the previously formed faults around a horizontal axis. The mutually crosscutting relationships between the intra-basinal low-angle and basement-involved high-angle normal faults indicate contemporaneous development and operation of fault generations. The NNE-striking, basin-perpendicular oblique–slip hinge faults divided the supradetachment basin into a series of fault blocks with their own internal structure and stratigraphy. The hinge faults, reminiscent of transfer faults, accommodate differential extension and uplift rates throughout the basin. The structural analysis indicates that rotational deformation due to hinge faulting leads to the formation of local unconformities in the supradetachment basin. The varied displacement and slip rates along and across the hinge faults causes differential extension and block-uplift, and limit propagation of alluvial facies within uplifted fault blocks. Hinge faulting can also result in significant changes in the dip directions and strike orientations of the sedimentary beds and deviations from the inferred direction of maximum extension in the adjacent fault blocks. Fault segmentation of the Alasehir basin as a result of extension-parallel hinge-faulting is a characteristic feature of supradetachment basin evolution. This study provides a better understanding of intrabasinal deformation in highly-extending terrains such as Basin and Range, Aegean Extensional Province.