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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.

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Link
Block
Gravity
Magnetics
Magnetics
Magnetics at Pole
Magnetics at Pole 1VD
Oblique Slip Translational fault

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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

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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

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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

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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

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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 = 1k = 10-2
background
r = 0k = 0
image width
10,000 m
Inclination
50° or 90°
Intensity
50,000 or 70,000 gamma
Flight height
80 m

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min

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min

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Copyright © 1998-2002 AGCRC & Mark Jessell

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