Intrusive Landforms

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  • Created on: 30-03-13 12:52
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http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/communities/Geography/AS%20Geography/AS%2
0Revision/Earth%20Systems%20Revision/Characteristics%20and%20formation%20of%20Intrusive
%20landforms
http://www.tulane.edu/~sanelson/geol212/intro&textures.htm
Dikes
Dikes are small (<20 m wide) shallow
intrusions that show a discordant relationship
to the rocks in which they intrude. Discordant
means that they cut across pre-existing
structures. They may occur as isolated
bodies or may occur as swarms of dikes
emanating from a large intrusive body at
depth
Type of Intrusion: Discordant (Vertical)
Intrusion - cut across the sedimentary rock
layers they intrude into.
Characteristics: These are vertical intrusions which have horizontal cracks / joints which have formed
parallel to the surface as the magma has cooled, contracted and solidified.
Formation: These usually form by forcing open existing fractures as well as opening up channels
through cracks created by magmatic injection.
Where found in large numbers radiating from a batholith, they form a dyke swarm
Sill
Sills are also small (<50 m thick) shallow
intrusions that show a concordant
relationship with the rocks that they
intrude. Sills usually are fed by dikes, but
these may not be exposed in the field.
Type of Intrusion: Concordant (Horizontal)
Intrusion - formed parallel to the bedding
planes
Characteristics: boundaries of the intrusion
are parallel to the existing layers and as
the magma cools it forms vertical cooling cracks as it contracts
Formation: created by magma being intruded along bedding planes which provide a weakness for
the flow of magma to exploit / flow along.
Not always formed as horizontal features and earth movements can also change the angle of sills

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Batholiths
Batholiths are very large intrusive bodies,
usually so large that there bottoms are
rarely exposed. Sometimes they are
composed of several smaller intrusions.
Type of Intrusion: Discordant (Vertical)
Intrusion - cut across the sedimentary rock
layers they intrude into.
Characteristics: large, igneous dome
shaped features (deep-seated); coarse
grained (due to slow cooling). These are of
a significant size and usually cover at least 100km2.…read more

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