Assessment of the deformation in the subparallel shear zone set: A case study from the Veporic Unit, Western Carpathians

Abstract

: During the Alpine convergence of the Central Western Carpathians, a set of subparallel NW–SE shear zones formed in the eastern part of the Veporic Unit, near the tectonic contact with the Gemeric Unit. Deformation in low-grade metamorphic conditions was typical of the Alpine movements in the shear zones. Mylonitic rocks of the crystalline complex and their cover formations were studied on a macro and micro scale to characterise the evolution of deformation structures in the shear zones. The differential stress of dynamically-recrystallized quartz, which aggregates in mylonitic rocks, was determined using quartz paleopiezometry. Several types of foliation structures, but mainly penetrative subhorizontal stretching lineation in all observed mylonites, provide evidence of stretching and oriented ductile flow in a NW–SE direction. Shear sense indicators show the subhorizontal movement of the shear zone hanging walls to the SE. Dynamically-recrystallized quartz aggregates in the mylonitic rocks show different values of grain sizes and differential stresses, depending on the structure in which they occur. The lowest differential stresses were found in the quartz aggregates parallel to the S planes of the mylonites. Higher values are related to the C shear bands. The character of the structural setting indicates the formation of the shear zones in the orogen-parallel extension conditions.