An oligocene ductile strike-slip shear zone: The Uludag Massif, northwest Turkey - Implications for the westward translation of Anatolia


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Okay A. , SATIR M., ZATTIN M., CAVAZZA W., Topuz G.

GEOLOGICAL SOCIETY OF AMERICA BULLETIN, vol.120, pp.893-911, 2008 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 120
  • Publication Date: 2008
  • Doi Number: 10.1130/b26229.1
  • Title of Journal : GEOLOGICAL SOCIETY OF AMERICA BULLETIN
  • Page Numbers: pp.893-911
  • Keywords: ductile shear zone, strike-slip faulting, Rb/Sr ages, apatite fission tracks, amphibolite-facies metamorphism, Turkey, Aegean Sea, METAMORPHIC CORE COMPLEX, GARNET AMPHIBOLITES, TECTONIC EVOLUTION, FAULT ZONE, WESTERN, MIOCENE, GEOCHRONOLOGY, CALIBRATION, EXTENSION, SYSTEM

Abstract

The Uludag Massif in northwest Turkey represents an exhumed segment of an Oligocene ductile strike-slip shear zone that is over 225 kin long and has similar to 100 km of right-lateral strike-slip displacement. It forms a fault-bounded mountain of amphibolite-facies gneiss and intrusive Oligocene granites. A shear-zone origin for the Uludag Massif is indicated by: (1) its location at the tip of the active Eskisehir oblique-slip fault, (2) pervasive subhorizontal mineral lineation in the gneisses with a right-lateral sense of slip, (3) foliation with a consistent strike, (4) the presence of a subvertical synkinematic intrusion, and (5) the alignment of the Eskisehir fault, synkinematic metagranite, and the strike of the foliation and mineral lineation. The shear zone nucleated in amphibolite-facies gneisses at peak pressure-temperature (P-T) conditions of 7.0 kbar and 670 degrees C, and it preserves Eocene (49 Ma) and Oligocene (36-30 Ma) Rb/Sr muscovite and biotite cooling ages. The shear zone was active during the latest Eocene and Oligocene (38-27 Ma), as shown by the crystallization and cooling ages from synkinematic granite. A 27 Ma postkinematic granite marks the termination of shear-zone activity. The 20-21 Ma apatite fission-track (AFT) ages indicate rapid exhumation during the early Miocene. A 14 Ma AFT age from an Uludag gneiss clast deposited in a neighboring Neogene basin shows that the shear zone was on the surface by the late Miocene. Results of this study indicate that during the Oligocene, crustal-scale right-lateral strike-slip faults were transporting crustal fragments from Anatolia into the north-south-extending Aegean; this implies that the westward translation of Turkey, related to the Hellenic slab suction, started earlier than the Miocene Arabia-Eurasia collision.