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6.1 Depletion alteration halo around a dyke


This model shows the results of emplacing a dyke in an area of refolded folds. The refolded fold patterns are similar to those seen in the type D model of section 3.7. The density and susceptibility values are modelled as depletion haloes where the rock properties are varied as a function of distance from the dyke, before returning to normal as the distance away increases.

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Block diagram of unaltered geology

Block diagram showing the geology of the model with dyke intrusion but no alteration halo. The top layer has been removed to show the internal structure of the model. Colours are used simply to highlight the structures.

 
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Block diagram showing density variations in altered geology

Block diagram showing the geology of the model with dyke intrusion and alteration halo. The top layer has been removed to show the internal structure of the model. Colours are used to demonstrate density variations, using a rainbow look up table.

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Block diagram showing magnetic susceptibility variations in altered geology

Block diagram showing the geology of the model with dyke intrusion but no alteration halo. The top layer has been removed to show the internal structure of the model. Colours are used to demonstrate magnetic susceptibility variations, using a rainbow look up table.

Link
Gravity
Magnetics
Magnetics
Magnetics at Pole
Magnetics at Pole 1VD
No alteration

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Open magnetics with Noddy

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Open magnetics with Noddy

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Open magnetics at pole with Noddy

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Open magnetics at pole 1VD with Noddy

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Note the constructive interference between the dyke and the background layers that produces a local high where the dyke cuts the layers.       Note the appearance of a variation in intensities along the dyke.
Alteration

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Open magnetics with Noddy

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Open magnetics with Noddy

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Open magnetics at pole with Noddy

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Open magnetics at pole 1VD with Noddy

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Note the destructive nature of the alteration halo. Note the destructive nature of the alteration halo. Note the destructive nature of the alteration halo. Note the destructive nature of the alteration halo. Note the appearance of a variation in intensities along the dyke.

Key
Survey Specifications
Scales
yellow
k = 10-2r = 3.5
blue
k = 10-2r = 2.5
dyke
k = 10-2r = 3.5
image width
10,000 m
inclination
50° or 90°
intensities
50,000 or 70,000 gamma
flying height
80 m

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min

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min

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Copyright © 1998-2002 AGCRC & Mark Jessell

WWW conversion by Ian Brayshaw