SUPRADETACHMENT BASIN EVOLUTION IN CONTINENTAL EXTENSION: THE AEGEAN PROVINCE OF WESTERN ANATOLIA, TURKEY

We report on the structure-stratigraphy of a Neogene-Quaternary supradetachment basin in the Aegean extensional province (Turkey), and compare its evolution to those of other supradetachment basins around the world. The sedimentary fill of the Alasehir basin records the uplift-exhumation of a core complex in the footwall of a detachment fault within the Central Menderes Massif. Accumulation of footwall-derived sediments in this basin started ~20 Ma, shortly after the initiation of the ~E-W-trending Alasehir detachment, and continued until ~2 Ma. Major sedimentary facies types include fluvial-alluvial fan deposits, debris flow/mass-flow deposits & locally developed lacustrine rocks, which were accumulated in distal depocenters within the extending basin, as the low-angle detachment faulting created little accommodation space near the basin margins. The drainage system was dominated by extension-parallel transverse streams during the main phases of basin evolution. Extension-parallel, hinge faulting produced differential uplift & subsidence in the adjacent fault blocks, changed the direction of sediment transport & drainage patterns in short distances & resulted in the local uplift of the older basin strata. These processes developed sub-basins with lateral variations in basement topography, strata thickness & sedimentary facies distribution, and generated a segmented basin architecture. High-angle synthetic & antithetic faults that formed extensively <3 Ma caused back-tilting of the sedimentary strata, formation of half grabens with their own axial drainage systems & development of angular unconformities. With the onset of this crustal-scale block faulting, the detachment fault ceased to operate & the modern Gediz graben started to develop at the northern end of the supradetachment basin. Our comparative evaluation of select basins shows a maximum sediment thickness of 3 km, average extension rates of 6 to 8-9 mm.yr^-1, and accumulation rates of 0.1 to 0.2 mm.yr^-1 (uncorrected for compaction) in supradetachment basins in general. The rates & amounts of extension, the geometry of detachment faulting, the rates of footwall uplift & the kinematics & interplay of different fault systems are the most important factors controlling 3-D structural architecture & evolution of supradetachment basins.