Kate A. Cooper1, Rob L. Gawthorpe1, Stuart Hardy1
(1) University of Manchester, Manchester, United Kingdom
ABSTRACT: Three-Dimensional Thrust Fault-Related Folding and Growth Strata Architectures: Insights from Numerical Modelling
Emphasis has recently been placed on the use of synorogenic stratal geometries to decipher the structural evolution of fault-related folds. Although work has extensively covered this subject in two dimensions, a basic lack of understanding of the processes involved in 3D still exists. This is addressed by the development of a three-dimensional trishear fault-propagation fold numerical model, in which the fault-tip can propagate perpendicular and parallel to the shortening direction. The model is used to investigate the effects of variations in lateral and forward slip rates on the development of associated syntectonic strata. Syntectonic sedimentation is modelled as background deposition below a base level. By varying the mode of displacement on the fault between slippage due to creep and seismic events, the influence of these variables on the geometries of growth strata can be investigated.
Results indicate key factors to consider when examining three-dimensional growth strata geometries: (1) Unless fold growth is self-similar, fault-centre geometries will be markedly different from those towards fault tips; (2) Unless lateral fault propagation is extremely rapid, time-equivalent stratigraphic units typically display a transition from true 'growth' geometries at the fault centre to 'pre-growth' geometries towards the fault tips; (3) Characteristic growth strata geometries result from lateral fault-tip propagation, where early pre-growth strata (laterally) are incorporated and folded during propagation, resulting in characteristic unconformities and pinch outs towards fold noses.
Comparison of model results with natural fault-related fold examples highlight the importance of along strike variability in growth strata associated with these structures.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado