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5.4 Concentrically zoned plugs

These four models show the magnetic anomaly patterns that may develop in a igneous intrusion due either to the production of an alteration halo, or from a change in the orientation of the thermo-remanent component of the natural remanent magnetisation as the body cools.
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	Block Diagram LOAD JPEG IMAGE Concentric half-spheres with variable magnetic properties.

Link	Magnetics	Magnetics	Magnetics at Pole	Magnetics at Pole 1VD
Alteration halo (magnetic susceptibility greater than igneous body)	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	Outer zone of plug defined by alteration zone enriched in high susceptibility minerals.
Remanent zone (magnetisation vector same as current field)	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	Outer zone of plug defined by remanently magnetised minerals, perhaps due to change in grain size of magnetic minerals as body cooled. The remanent component has same orientation as current external field.
Alteration halo (magentic susceptibility less than igneous body)	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	Outer zone of plug defined by alteration zone enriched in high susceptibility minerals, but has lower susceptibility than igneous body itself.
Remanent zone (magnetisation vector opposite to current field)	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
	Outer zone of plug defined by remanently magnetised minerals, perhaps due to change in grain size of magnetic minerals as body cooled. The remanent component has opposite orientation to current external field.

Key	Survey Parameters	Scales
plug k = 10-2 background m.s. = 0 image width 10,000 m	Inclination -50° Intensity 50,000 gamma Flight height 80 m	max min max min

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

WWW conversion by Ian Brayshaw