Akademik Veri Yönetim Sistemi
TECTONOPHYSICS, cilt.374, sa.1-2, ss.1-18, 2003 (SCI-Expanded)
Western Turkey has experienced extensional deformation since the Tertiary. An early phase of extensional deformation resulted in the formation of detachment faults in the northern part of the Menderes massif, the Alasehir and Simav detachment faults. The footwalls of these two detachment faults are mid-crustal level rocks. The Alasehir detachment fault developed in metamorphic rocks and in a syn-extensional intrusion, the Salihli granodiorite. The Salihli granodiorite shows a gradual change from undeformed isotropic granodiorite to protomylonite, mylonite and ultramylonite towards its upper structural levels. The deformed granodiorite, in turn, grades into a cataclastic zone whose uppermost part is the Alasehir detachment surface. This gradual upward change from the undeformed granodiorite to a brittlely deformed detachment surface suggests that Tertiary extension resulted in a ductile deformation at depth and the ductilely deformed granitoids were brought to shallower depths where they were brittlely deformed. The metamorphic wall rocks of the intrusion are also mylonitized structurally upward. A similar transition has also been found in the footwall of the Simav detachment fault. The upper part of which is also a cataclastic zone leading to the Simav detachment fault separating the low-grade metamorphic rocks and/or non-metamorphic rocks in its hanging wall from mainly high-grade metamorphic rocks and syn-tectonic granitoids in its footwall. During ductile extension, greenschist facies-grade mylonitic deformation developed in the metamorphic rocks and the granitoids. Shear sense indicators along the two shear zones show top to N-NE sense shear, consistent With the regional Cenozoic extension direction in western Turkey. Available radiometric age data from the granitoids in the footwall of the two detachment faults suggest that the Cenozoic extension in western Turkey was initiated in Oligocene to Early Miocene and the Simav detachment fault is older than the Alasehir detachment fault. Extensional features of these detachment faults suggest that the Simav detachment fault characterise the earlier stage of the Tertiary extensional tectonics of the Menderes massif, and later stage of this deformation resulted in the development of the Alasehir detachment fault. (C) 2003 Elsevier B.V. All rights reserved.