10.2 Intrusive Igneous Activity
Textbook p 289-291
Plutons
• The structures that result from the cooling
and hardening of magma are called plutons.
• Intrusive igneous
bodies, or plutons, are
generally classified
according to their
shape, size, and
relationship to the
surrounding rock
layers.
Sills and Laccoliths
• Sills and laccoliths are plutons that form
when magma is intruded close to the surface.
Sill
Laccolith
• A sill forms when magma is injected between
rock layers that are already present.
Sill in Antarctica
Laccoliths
• Laccoliths are formed in a way similar to sills,
but the magma is thicker and more dense.
Dikes
• Dikes form when magma is injected into preexisting fractures, cutting across rock layers.
Batholiths
• The largest intrusive
igneous bodies are
batholiths.
• An intrusive igneous
body must have a
surface exposure
greater than 100 square
kilometers to be
considered a batholith.
Mount Rushmore was
carved from a granite
batholith in North Dakota.