The nature and origin of asymmetric arrays of shear surfaces in fault zones
Published:January 01, 2001
Steven F. Wojtal, 2001. "The nature and origin of asymmetric arrays of shear surfaces in fault zones", The Nature and Tectonic Significance of Fault Zone Weakening, R. E. Holdsworth, R. A. Strachan, J. F. Magloughlin, R. J. Knipe
Download citation file:
Mid- to upper-crustal fault zones often possess arrays of shear surfaces whose traces on sections perpendicular to the fault surface and parallel to the ac-plane conform with one or more of the ‘Riedel shear’ orientations. These shear surfaces often are oblique to the transport plane, however, so arrays exhibit monoclinic rather than orthorhombic symmetry. In a mudstone-dominated mélange in Humber Arm Supergroup strata in the Bay of Islands, Newfoundland, and in serpentinites from the base of the Bay of Islands complex, shear surfaces have orientations inclined to major fault-zone boundaries and an inferred ac-plane for macroscopic fault-related deformation. Deformation in these zones exhibits an overall monoclinic symmetry. The 3D, asymmetric character of shear surface fabrics suggests that a factor other than stress or the symmetric strain rate tensor controlled their formation. The velocity gradient tensor in a steady, non-coaxial shearing flow possesses a symmetry consistent with monoclinic fabrics. Shear surfaces in asymmetric arrays may initiate with predictable orientations relative to the velocity gradient tensor and then rotate toward flow apophyses, which identify stable positions in steady, 3D flows.
Figures & Tables
The Nature and Tectonic Significance of Fault Zone Weakening
Many faults appears to form persistent zones of weakness that fundamentally influence the distribution, arichitecture and movement patterns of crustal-scale deformation and associated processes in both continental and oceanic regions. They act as conduits for the focused migration of economically important fluids and, as most seismicity is associated with active faults, they also constitute one of the most important global geological hazards.
This book brings together papers by an international group of Earth Scientists to discuss a broad range of topics centred upon the controls of fault weakening and the role of such faults during lithosphere deformation.
The book will be of interests to both academic and industrial Earth Scientists with an interest in geodynamics, structure at all scales, tectonics and the migration of petroleum and water.