Igneous Processes and Products

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Minor intrusion
cool at hypabyssal depth below the surface and include sills and dykes
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Major intrusions
plutonic and cool deep below the surface and include batholiths
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Country Rock
any rock that the igneous rock intrudes into
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Sills
Made of Dolerite (mostly), intrude along bedding planes (concordant), can become a transgressive sills
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Transgressive Sill
When a sill cuts across the beds in steps from one bed to another
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Dykes
discordant, often vertical, range in size from a few centimetres to metres and metres, intruded along zones of weakness in the country rock such as faults and joints
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how do sills intrude
when the fluid pressure is so great that the underlying magma actually lifts the overlying rocks. this means sills usually form at shallow depths
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Batholiths
discordant, cool very slowly as plutonic rocks, the outcrop is usually circular in shape with steep sides, normally granitic although can be composed of diorite or granodiorite
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Formation of Granite magmas
Most batholiths are intruded at convergent plate margins where fold mountains are formed. high temperature mafic magmas will rise up through the crust and the heat from which will partially melt continental crust, partial melting produces silicic
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Stoping
Stoping is where magma moves up along joints, faults and bedding planes, separating masses of country rock. The rocks that detach and fall into magma are called XENOLITHS.
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Assimilation
As the Xenoliths fall into the magma most will be assimilated as they gradually melt to become more magma
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Chilled Margin
where the igneous rock has cooled rapidly. This margin has fine grained crystals as it cooled rapidly
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Baked Margin
adjacent to a minor intrusion. The country rock where it was heated and altered by the intrusion. The rock has been contact metamorphosed and has become harder and lighter in colour
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Metamorphic Aureole
A large area around a batholith where the rocks have been metamorphosed. The rocks in the aureole are altered b contact metamorphism to produce new metamorphic rock.
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The width of a mentamorphic aureole depends on....
the size and temperature of the intrusion, the dip of the sides of the intrusion and the composition of the surrounding rocks
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Other cards in this set

Card 2

Front

plutonic and cool deep below the surface and include batholiths

Back

Major intrusions

Card 3

Front

any rock that the igneous rock intrudes into

Back

Preview of the back of card 3

Card 4

Front

Made of Dolerite (mostly), intrude along bedding planes (concordant), can become a transgressive sills

Back

Preview of the back of card 4

Card 5

Front

When a sill cuts across the beds in steps from one bed to another

Back

Preview of the back of card 5
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