Episodic, two-stage Neogene extension and short-term intervening compression in Western Turkey: field evidence from the Kiraz Basin and Bozdağ Horst

Abstract

Western Anatolia (Turkey) is a region of widespread active N-S continental extension that forms the eastern part of the Aegean extensional province. The extension in the region is expressed by two distinct/different structural styles, separated by a short-term gap: (1) rapid exhumation of metamorphic core complexes along presently low-angle ductile-brittle normal faults commenced by the latest Oligocene-Early Miocene period, and; (2) late stretching of crust and, consequent graben evolution along Plio-Quaternary high-angle normal faults, cross-cutting the pre-existing low-angle normal faults. However, current understanding of the processes (tectonic quiescence vs N-S continental compression) operating during the short-time interval is incomplete. This paper therefore reports the results of recent field mapping and structural analysis from the NE of Küçük Menderes Graben—Kiraz Basin—that shed lights on the processes operating during this short-time interval. The data includes the thrusting of metamorphic rocks of the Menderes Massif over the Mio-Pliocene sediments along WNW-ESE-trending high-angle reverse fault and the development of compressional fabrics in the metamorphic rocks of the Menderes Massif. There, the metamorphic rocks display evidence for four distinct phases of deformation: (1) southfacing top-N ductile fabrics developed at relatively high-grade metamorphic conditions, possibly during the Eocene main Menderes metamorphism (amphibolite facies) associated with top-N thrust tectonics (D1); (2) top-S and top-N ductile gentle-moderatley south-dipping extensional fabrics formed at relatively lower-grade metamorphic (possibly greenschist facies) conditions associated with the exhumation of Menderes Massif along presently low-angle normal fault plane that accompanied the first phase of extension (D2); (3) moderately north-dipping top-S ductile-brittle fabrics, present configuration of which suggest a thrust-related compression (D3); and (4) south-facing approximately E-W-trending brittle high-angle normal faults (D4) that form the youngest structures in the region. It is interpreted that D4 faults are time equivalent of graben-bounding major high-angle normal faults and they correspond to the second phase of extension in western Anatolia. The presence of thrust-related D3 compressional fabrics suggests N-S compression during the time interval between the two phases of extension (D2 and D4). The results of the present study therefore support the episodic, two-stage extension model in western Anatolia and confirm that a short-time, intervening N-S compression separated the two distinct phases.