Download Chapter 10.2

CHAPTER 10.2
Intrusive Igneous Activity
Plutons
•
Most magma cools deep in the Earth
and form the bottom of mountain
ranges.
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Plutons are structures that are made
from the cooling and hardening of
magma deep in the Earth.
•
Plutons can be studied after they
reach the surface – plutons are
classified by their shape, size, and
relationship to surrounding rock.
Sills and Laccoliths
•
These are plutons that are formed
when magma is cooled close to the
surface.
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A sill is formed when magma is
injected into sedimentary rock.
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Laccoliths are similar but they push
the rock up.
Dikes
•
This occurs when magma is injected
into fractures, and cuts across
preexisting rock layers. They are
sheetlike structures. Dikes will usually
come out from an eroded volcanic
neck.
Batholiths
•
This is an intrusive (from under
ground) igneous body that has a
surface exposure of more than 100
square km.
Origin of Magma
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Magma occurs when solid rock, from the
crust and upper mantle, partially melts
from high temperatures.
•
The geothermal gradient is how the
temperature increases the deeper into
the Earth you go.
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At 100 km deep it is estimated that the
temperature is between 1400 and
1600˚C. This is still not quite hot enough
to melt rock.
•
There are a couple different ways more
heat is generated – at subduction zones a
lot of friction creates more heat. The
second way is crustal rocks are heated as
they move in the mantle by subduction.
Role of Pressure
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Pressure increases with depth. Therefore melting occurs at a higher temperature
because of pressure.
•
When pressure decreases you can have decompression melting – this can make
magma.
Role of Water
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Water causes rock to melt at lower temperatures.
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That makes 3 ways magma can be formed – adding heat, a decrease in pressure,
and lastly water lowering the melting point.