A quantitative study of the influence of pre-existing compositional and fabric heterogeneities upon fracture-zone development during basement reactivation
Published:January 01, 2001
L. E. Beacom, R. E. Holdsworth, K. J. W. McCaffrey, T. B. Anderson, 2001. "A quantitative study of the influence of pre-existing compositional and fabric heterogeneities upon fracture-zone development during basement reactivation", The Nature and Tectonic Significance of Fault Zone Weakening, R. E. Holdsworth, R. A. Strachan, J. F. Magloughlin, R. J. Knipe
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In common with many other regions of exposed continental basement, the Late Archaean to Palaeoproterozoic Lewisian Complex, NW Scotland, preserves numerous examples of faults that appear to reactivate pre-existing compositional and structural heterogeneities in the host gneisses. A regionally recognized set of late Laxfordian sinistral strike-slip faults and fractures are spatially associated with pre-existing NW–SE-trending ductile shear zones of Inverian and Laxfordian age. Field observations suggest that most of the sinistral displacements have been accommodated along laterally persistent faults (here termed principal displacement zones (PDZ)) that lie sub-parallel to the pre-existing foliation in the shear zones. Geometric and orientation data collected during structural logging of the PDZ faults have been used to quantitatively test the influence of lithology and pre-existing structural geometry on the spatial patterns of fault development. Stereographic analysis shows a strong geometrical correspondence between the intensity and form of the pre-existing anisotropy and the alignment of the PDZ brittle faults. Spatial clustering of PDZ faults varies depending on lithology (amphibolite v. acid gneiss v. Quartz–mica schist). A close correlation exists between the geometry and intensity of the pre-existing foliation and fault spatial clustering. The results demonstrate that reactivation of pre-existing anisotropies in typical continental basement gneisses exert a significant control on brittle fault development and growth in the upper crust.
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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.