Kinematics of rock flow in a crustal-scale shear zone: implication for theorogenic evolution of the southwestern Hellenides

Combined shear-sense criteria, finite-strain data and vorticity analyses we re used to study the deformation path in a curved crustal-scale shear zone (Phyllite-Quartzite Series) of the southwestern Hellenides. The results are combined with data on the structural evolution of a cover nappe (Pindos th rust belt) to provide new insights into the orogenic evolution of this regi on. Ductile deformation within the Phyllite-Quartzite Series was associated wit h a top-to-the-west-southwest shearing and was partitioned into two structu ral domains: a root zone and a frontal domain. The root zone is characteriz ed by vertical coaxial stretching, high strain and upward movement of the m aterial, while the frontal domain comprises simple-shear deformation at the base and pure shear at the top. This pattern suggests superposition of pur e shear on simple-shear deformation, and implies tectonic extrusion of the material from the root zone. The initiation of brittle deformation in the Pindos thrust belt was associa ted with westward translation above the sub-horizontal Pindos Thrust. Later , as the mountain range elevated, normal faulting at high altitudes and mig ration of thrusting to the west occurred, while east-directed folding and t hrusting in the belt started to the east. According to the proposed model, crustal thickening was taking place throug hout the Oligocene and early Miocene, including the subduction of the Apuli an beneath the Pelagonian microcontinent and the intracontinental subductio n of the Phyllite-Quartzite Series. During the lower Miocene, vertical buoy ancy forces led to the successive steepening of the shear zone and the simu ltaneous duplexing of its basement, facilitating tectonic extrusion of the material from its root zone. Finally, an indentation process caused vertica l expulsion of the orogenic wedge and gravity collapse in the brittle crust .