Structural investigations in the central part of the Menderes Massif (Ödemiº-Kiraz submas-sif) reveal the presence of a large-scale, low-angle extensional shear zone with a top-to-the-N-NE shear sense. Regional ductile deformation was accompanied by the intrusion of two syntectonic granodiorites that have been dated with the
40
Ar/
39
Ar method. One hornblende isochron age of 19.5 ± 1.4 Ma and two biotite plateau ages of 13.1 ± 0.2 and 12.2 ± 0.4 Ma, respectively, constrain that extension was already active in the early Miocene. Successive tectonic denudation of the Ödemiº-Kiraz submassif resulted in the formation of a N-dipping detachment fault, in which ductile fabrics were severely reworked by cataclasis under decreasing temperature. Syntectonic Neogene sediments, currently exposed along the southern margin of the Gediz Graben, were deposited in the hanging wall of the extensional fault system and were tectonically emplaced onto the cataclasites during progressive exhumation. Minor rotation (< 15°) of the detachment fault to its present gentle dip of
c
. 15° caused southward tilting of the sediments. Ongoing NNE-directed extension created a steep normal fault that truncates the detachment fault and constitutes the southern boundary fault of the Gediz Graben.
Exhumation of rocks in extensional tectonic settings results from a combination of normal faulting and erosion but the relative contribution of these processes has rarely been quantified. Here we present new low-temperature thermochronological data and the first
10
Be-based catchment-wide erosion rates from the Boz Dağ region in the central Menderes Massif, which has experienced NNE–SSW extension since the Miocene. The slip rate of the shallow-dipping Gediz detachment fault, which defines the northern flank of the Boz Dağ block, is 4.3 (+3.0/−1.2) mm a
−1
, as constrained by zircon (U–Th)/He ages of
c
. 4–2 Ma in the footwall. Apatite and zircon (U–Th)/He and fission-track ages from the northern flank of the Boz Dağ block yield exhumation rates of 0.6–2 km Ma
−1
beneath the Gediz detachment, whereas those on the southern flank are only 0.2–0.6 km Ma
−1
. Erosion of catchments on the northern and southern flanks proceeds at rates of 80–180 and 330–460 mm ka
−1
, respectively. This marked contrast is a combined effect of the topographic asymmetry of the Boz Dağ block and differences in rock erodibility. If these erosion rates persisted in the past, rock exhumation on the northern flank occurred predominantly by tectonic denudation, whereas rocks on the southern flank were mainly exhumed by erosion.
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