Author:

Keywords:

Science & Technology, Physical Sciences, Geosciences, Multidisciplinary, Geology, En echelon vein arrays, Sigmoidal veins, Riedel shear systems, Pennant veins, Slickenfibre shear veins, Kinking, ARDENNE SLATE BELT, KINK BANDS, UPPER CRUST, GEOMETRY, ZONES, FAULTS, EVOLUTION, EXAMPLES, GROWTH, KINEMATICS, 0403 Geology, Geochemistry & Geophysics, 3705 Geology

Abstract:

This paper presents the geometric analysis of sigmoidal en echelon vein system that formed by non-coaxial deformation within conjugate Riedel-shear zones. Both sinistral S-type and dextral Z-type vein arrays, which have a subparallel enveloping surface, are observed. Individual asymmetric quartz veins consist of (1) a central, thin slickenfibre shear vein that is separating (2) pennant-shaped extensional vein tips characterised by strong dilation. Our observations closely resemble the results from published analogue experiments, which suggest that dilation occurs along R and R′ Riedel shear fractures during progressive rotation and slip within brittle-ductile shear zones. The shear vein formed by incremental pull-apart in the extensional step of overlapping R′ shear fractures, as marked by the presence of solid inclusion trails and bands. The pennant veins opened in the obtuse angle between intersecting R’ and R shears. The close association with a kinked pre-existing tectonic foliation, which acted as a passive marker of non-coaxial deformation, allows a kinematic restoration of the initial conjugate shear zone geometry that formed under approximate NE-SW compression. This model could warrant the reassessment of the classic interpretation of sigmoidal en echelon vein systems that are associated with kink bands.