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Structural Geology. Strike-slip fault System 010021-38 He Qi. Simple Shear --Reidel model. Fractures Generated During Strike-Slip Faulting. FIVE SETS OF Fractures. R shear Fractures R ’ shear Fractures P shear Fractures T tensional Fractures
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Structural Geology Strike-slip fault System 010021-38 He Qi
Simple Shear --Reidel model Fractures Generated During Strike-Slip Faulting
FIVE SETS OFFractures • R shear Fractures • R’ shear Fractures • P shear Fractures • T tensional Fractures • Shear Fractures Parallel to main fault zone Ideal Model
Arrangement of folds and faults in an ideal right-lateral strick-slip fault
GEOMTRY OF STRIKE-SLIP FAULT ZONES Strick-slip faults often consist of a series of subparallel shear faults. There are two types: pinnate and en-echelon. Within large strick-slip fault zones ,subparallel faults are often arranged in a pinnate pattern, the en-echelon pattern being rare. In the pinnate arrangement the angle between the whole fault zone and that of the individual sub-parallelfault is less than 25˚,and the subparallel faults are shear or shear-plus-tensile fractures. In the en-echelon arrangement the so-called en-echelon angle is usually greater than 25˚,and the subparallel faults are tensional fractures.
Overlappingbetween two subparallel faults is a common feature in both the pinnate and en-echelon arrangements. The pattern of overlapping consist of right steps and left steps. Theoretical analysis and model experiments would show that right steps occur in left-lateral fault zones and left steps in right-lateral fault zones, but some-times reverse overlapping. A ‘rock bridge’—the block between two overlapping subparallel faults—is an important unit within the fault zone that create compression or extension zones. Such as pull-apart area.
Pull-apart basins Pull-apart basins formed in local extensional zones as a result of overlapping process.
The deformation patterns in pull-apart areas are of four types. D is depth ,S is separtion, O is overlapping. (a). Single center, D>>O, S/O>=1. (b).Double center,D>>O,S and S/O<1. (c). Terminal extension type, D<O,S. (d). Combination.
Two different kinds of evolution of strick-slip fault zones Basins are controlled by subparallel faults with large dip-slip componts. Normal faults developed at both ends of the basins. The thickness of sediments within the basins reaches750m. In the later stage of the basin’s history a series of shear faults with normal dip-slip components was generated in the interior of the basin. For a strick-slip fault zone with a compressional component normal to its general trend, the subparallel faults that bound the pull-apart basins will be linked through the formation of internal tensile shear faults, and the pull-apart basin will decrease in size until it disappears. For a strick-slip fault zone with a tensional component normal to its general trend, the adjacent rock bridges are enlarged and linked gradually ,so as to form a large pull-apart basin with more than one subsidence centers.
Negative flower Positive flower Strike-slip faults are arranged in segment or sections that may jog or bend where they link together. Pull-apart basins form where strike-slip fault sections overlap at jogs. Flower structures form where there are bends in strike-slip faults.
FLOWER STRUCTURE IN STRIKE-SLIP FAULTS Positive flower structure for uplift blocks Negative flower structure for depressed blocks
