Microstructures of shear zones from selected domains of the Western Tatra Mountains

Maciej Kania

doi:10.7306/gq.1243

Abstract

The paper is focused on the meso- and microstructural characteristics of selected shearing zones in the Western Tatra Mts. The domains of crystalline rocks studied (Długi Upłaz Ridge, Rakoń Mt., Zabraty Ridge and Zabrať Pass, Wołowiec Mt., Trzydniowiański Mt., Czubik Mt. and Jarząbczy Mt.) show evidences of heterogeneous shearing with development of shear zones. Four types of shear zones were distinguished: (1) ductile shear zones in gneisses, (2) brittle-ductile complex shear zones, (3) gneisses with clear later brittle deformation; (4) leucogranites, produced by anatexis with later brittle deformation. The development of these shear zones is characterised by occurrences of various types of fault rocks: cataclasites, S-C cataclasites and mylonites. The different shearing-related rocks and structures are interpreted as an effect of protolith diversity and strain partitioning. Shape-preferred orientation is an important structural feature of all the shearing-related rocks. Kinematic analyses revealed generally a southward sense of shearing documented by structures related to brittle conditions and northwards sense of shearing recognised in ductily sheared crystalline rocks. The time relationships between different shear zone types are discussed, leading to the conclusions that the 1 st type of shear zone is pure Variscan, the 2 nd type is Variscan with Alpine brittle deformation, and the 3 rd and 4 th types are mainly Alpine brittle deformations of Variscan syntectonic anatectic leucogranites.

Highlights

Non-coaxial shearing leads to forming shear zones which are localized areas of intense deformation (Ramsay, 1980)
Taking into account the type of structures correlated with the protolith rock, the following four structural types of shear zones can be distinguished in the discussed area (Fig. 16):
The shear zones take a key role in the Western Tatra crystalline massif structure

Summary

Introduction

Non-coaxial shearing leads to forming shear zones which are localized areas of intense deformation (Ramsay, 1980). Shear zone-related research is an fast-developing branch of the structural geology, especially with a multi-scale approach to the structures (Passchier and Trouw, 2005; Trouw et al, 2010; Jiang, 2014), analyses of grains shapes and orientation (e.g., Stahr and Law, 2014) and micromechanical modelling of the structures (e.g., a new point of view on the micafish formation by Chen et al, 2014) This paper is another approach to the meso- and microstructural features of some shear zones observed in selected areas from the Western Tatra Mts. crystalline core. The shape-preferred orientation measurements published in this paper form a link between a morphometric approach presented earlier and structure descriptions presented

Methods

Findings

Discussion

Conclusion