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3.2 Faulted Fold

These models demonstrate another aspect of the ambiguities that may arise when interpreting folds. In each model a single fault cuts through the nose of a plunging anticline, producing offset on one side of the fold but not on the other. A number of different fault geometries are shown which all result in similar outcrop geometries. It is likely that only mapping at the outcrop scale (of slickenside lineations of fault trace for example) would enable one to distinguish between these models.

All block diagrams viewed from SW.
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Link	Block	Gravity	Magnetics	Magnetics	Magnetics at Pole	Magnetics at Pole 1VD
Oblique Slip Translational fault	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	In this model we have a simple translational fault in which the slip vector is approximately parallel to the dip of the west limb of the fold, so that the offset is only apparent in the east limb.
Scissor fault	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	In this model the north block is rotated clockwise around a point at the surface near where the fault cuts the west limb, so again the west limb appears to be un-displaced.
Variable displacement fault	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	Here the fault displacement decays towards the west, so that by the time the fault plane reaches the west limb, the amount of displacement is minimal.
Curved fault	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	Here the fault starts off cutting through the east limb of the fold and then swings around parallel to the layering as it reaches the west limb, so no offest occurs.
Alteration zone around a fracture	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	In this case we have a fracture with no displacement, and instead an alteration zone around the fracture causes the disruption in the east limb (which could be misinterpreted as a fault offset).

Key	Survey Parameters	Scales
plug r = 1 k = 10-2 background r = 0 k = 0 image width 10,000 m	Inclination 50° or 90° Intensity 50,000 or 70,000 gamma Flight height 80 m	max min max min

All models created using Noddy
Copyright © 1998-2002 AGCRC & Mark Jessell

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