An intrusion is a body of igneous rock formed by the injection of magma into the Crust.
As an underground feature originally, an intrusion now seen at the surface has been revealed by erosion of overlying
rock over quite a long period of time.
Intrusions may be divided into:
Major intrusions
- massive intrusion
- large volume of igneous rock compared with the area of its surface
- batholith; stock; pluton; laccolith; lopolith
Minor intrusions
- sheet-like intrusion, following a fracture or bedding plane
- large surface area compared with the thickness of the sheet
- sill; dyke; ring dyke; cone sheet
Concordant intrusion
- the igneous body is parallel to the bedding planes
- the term applies to major and minor intrusions
Discordant intrusion
- the igneous body cuts through or across the bedding planes
- the term applies to major and minor intrusions
Geopix Study Topic "Intrusions"
- gives full images of the examples shown below, and others, to illustrate the main types of intrusions
- explains the classification of intrusions
- describes the formation of intrusions
- distinguishes between lavas and sills
- includes metamorphic effects and variations in grain size
- suggests how to answer exam questions on this topic
Batholith
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Batholith
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Pluton
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Gabbro pluton
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Granite pluton
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Laccolith
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The Intrusion Study Guide contains the following pages:
'Intrusions' is part of the Igneous Processes Study Guide CD.
To order this CD go to the Geopix Online Store
