A Quantitative Method for Relating Structural Map Patterns, Strains, and Fault Offsets in Strike-Slip Zones
Bob W. Krantz
Exploration targets in strike-slip-dominated systems include complex three-dimensional structures. These structures develop through distinctly non-plane strain, so that traditional cross section balancing techniques do not apply. Classic models of strike-slip geometries relate oblique or en echelon folds and faults to horizontal shear, but not in a constrained or predictive way.
New models quantitatively describe the 3-D transpressional or transtensional shear strains within convergent to divergent strike-slip zones. The models relate horizontal and vertical strains within a volume of distributed shear to shear magnitude and to degree of convergence or divergence. The models apply to regions adjacent to major strike-slip faults, where trap-scale structures accommodate additional deformation, and to systems lacking a through-going surface fault, where small structures account for all of the strain.
The models can be used to calculate 3-D strain parameters, derived from structural patterns. As developed here, the model focuses on relating structural orientations in map view to the shear magnitude, the degree of convergence or divergence, and the magnitudes of horizontal and vertical strains. Applications of the model to both field examples and laboratory analogs show how determining one or more parameters constrains the others. The model provides explorationists with a rigorous way of evaluating and predicting structural orientations, testing map and cross section interpretations, and even balancing strain in three dimensions.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California