We present a detailed structural and stratigraphic record of a Neogene-Quaternary supradetachment sedimentary succession in the Aegean extensional province of western Anatolia, and we compare its tectonic features and evolution to those of other well-documented supradetachment basins around the world. The sedimentary fill of the Alasehir basin records the uplift and exhumation of a core complex in the footwall of a detachment fault within the Central Menderes Massif. Accumulation of footwall-derived clastic sediments in this basin started ca. 20 Ma, shortly after the initiation of the approximately E-W-trending Alasehir detachment and its shear zone, and continued until ca. 2 Ma. Major sedimentary facies types include fl uvial and alluvial-fan deposits, debris-fl ow and mass-fl ow deposits, and locally developed lacustrine rocks. These sedimentary units were accumulated largely in distal depocenters within the extending basin, as the low-angle (15°-28°) detachment faulting created little accommodation space near the basin margins while producing high back-shed topography in the uplifted Menderes core complex. The drainage system was dominated mainly by extension-parallel transverse streams during the main phases of basin evolution. Extension-parallel, scissor (hinge) faulting produced differential uplift and subsidence in the adjacent fault blocks, changed the direction of sediment transport and drainage patterns over short distances, and resulted in the local uplift of the older basin strata. These processes led to the development of subbasins with lateral variations in basement topography, strata thickness, and sedimentary facies distribution, and generated a segmented basin archi tec ture. High-angle synthetic and antithetic faults that formed extensively after 3 Ma caused back-tilting of the sedimentary strata, formation of half grabens with their own axial drainage systems, and development of angular unconformities. With the onset of this crustal-scale block faulting, the detachment fault ceased to operate, and the Quaternary Gediz graben started to develop at the northern end of the Alasehir supra detachment 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 0.1-0.2 mm yr -1 (uncorrected for compaction) in supra detachment basins in general. The rates and amounts of extension, the geom etry of detachment faulting, the rates of footwall uplift, and the kinematics and interplay of different fault systems are the most important factors controlling threedimensional structural architecture and evolution of supradetachment basins.For permission to copy, contact editing@geosociety.org

The Miocene granitoid plutons exposed in the footwalls of major detachment faults in the Menderes core complex in western Anatolia represent syn-extensional intrusions, providing important geochronological and geochemical constraints on the nature of the late Cenozoic magmatism associated with crustal extension in the Aegean province. Ranging in composition from granite, granodiorite to monzonite, these plutons crosscut the extensional deformation fabrics in their metamorphic host rocks but are foliated, mylonitized and cataclastically deformed in shear zones along the detachment faults structurally upward near the surface. Crystallization and cooling ages of the granitoid rocks are nearly coeval with the documented ages of metamorphism and deformation dating back to the latest Oligocene–early Miocene that record tectonic extension and exhumation in the Menderes massif. The Menderes granitoids (MEG) are represented by mainly metaluminous-slightly peraluminous, high-K calc-alkaline and partly shoshonitic rocks with their silica contents ranging from 62.5 to 78.2 wt%. They display similar major and trace element characteristics and overlapping inter-element ratios (Zr/Nb, La/Nb, Rb/Nb, Ce/Y) suggesting common melt sources. Their enrichment in LILE, strong negative anomalies in Ba, Ta, Nb, Sr and Ti and high incompatible element abundances are consistent with derivation of their magmas from a subduction-metasomatized, heterogeneous sub-continental lithospheric mantle source. Fractional crystalization processes and lower to middle crustal contamination also affected the evolution of the MEG magmas. These geochemical characteristics of the MEG are similar to those of the granitoids in the Cyclades to the west and the Rhodope massif to the north. Partial melting of the subduction-metasomatized lithospheric mantle and the overlying lower-middle crust produced the MEG magmas starting in the late Oligocene–early Miocene. The heat and the basaltic material to induce this partial melting were provided by asthenospheric upwelling caused by lithospheric delamination. Rapid slab rollback of the post-Eocene Hellenic subduction zone may have peeled off the base of the subcontinental lithosphere, triggering the inferred lithospheric delamination. Both slab retreat-generated upper plate deformation and magmatically induced crustal weakening led to the onset of the Aegean extension, which has migrated southward through time.

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