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Intrusive Activity
Chapter 18.2
• Molten Magma is less dense than
surrounding rocks.
• This forces magma to move upward
intrude into, the overlying crust.
Intrusive Activity
A. Magma can force the overlying rock apart and
enter the newly formed fissures.
B. Magma can also cause
blocks of rock to
break off and sink
into the magma, where
the rocks may
eventually melt.
C. Magma can melt the
rock into which it
intrudes.
Plutons
• Plutons are
intrusive igneous
rock bodies that can
be exposed at
Earth’s surface as a
result of uplift and
erosion and are
classified based on
their size, shape,
and relationship to
surrounding rocks.
Plutons
Batholiths
– Batholiths, the largest plutons, are irregularly
shaped masses of coarse-grained igneous
rocks covering at least 100 km2 and take
millions of years to form.
Batholiths
The Sierra Nevada and San Gabriel
mountains are large Batholiths
Stocks
– Stocks are irregularly
shaped plutons that are
similar to batholiths but
smaller in size.
Laccoliths
– A laccolith is a mushroomshaped pluton with a round
top and flat bottom
resulting from a Magma
intrusion into parallel rock
layers close to Earth’s
surface.
Laccoliths
Sills
– A sill is a pluton,
ranging from only a
few centimeters to
hundreds of meters in
thickness, that forms
when magma intrudes
parallel to layers of
rock.
Sills
• Glacier Park in PreCambrian rocks
Dikes
– A dike is a pluton, ranging
from a few centimeters to
several meters wide and
up to tens of kilometers
long, that cuts across
preexisting rocks.
Dikes
Dikes
• Sierra Nevada
Dike Near Shiprock NM
Dike Near Shiprock NM
Dike Near Shiprock NM