Author:

Keywords:

cataclasis, shear zone, Science & Technology, Physical Sciences, Geology, Armorica, immature shear zone, palaeostress analysis, Queffleuth cataclastic zone, slip sense indicators, South Iceland seismic zone, COMPRESSIONAL TECTONIC INVERSION, STRESS, DEFORMATION, BELT, ARC, 0403 Geology, 0914 Resources Engineering and Extractive Metallurgy, Paleontology, 3705 Geology

Abstract:

The Palaeozoic North-Armorican shear zone (NASZ) (Brittany, France) is described as an E-W trending dextral, intracontinental shear zone. In the valley of the Queffleuth river, we outline a well-exposed zone of protocataclasite to cataclasite as the Queffleuth cataclastic zone (QCZ). Four morphological fault classes are defined in the QCZ based on the petrographic characteristics of the fault planes. The first fault class is clearly related to cataclasis, as the matrix/clast ratio increases and the clast size decreases towards the individual fault planes. The other three morphological classes cross-cut the cataclasite and are therefore considered to postdate cataclasis. A palaeostress analysis allowed to distinguish five distinct stress states, which are dominated by oblique to pure strike-slip N-S trending faults, that are oriented antithetic with respect to the overall trend of the NASZ. Both dextral and sinistral E-W kinematics are inferred for the QCZ. Because all morphological fault classes are identified in each of the stress states, dextral and sinistral kinematics must have occurred during and after cataclasis. Based on the kinematic similarities with the active South Iceland seismic zone, it is suggested that the defined stress states reflect local stress permutations during the early, immature stage of the NASZ.