10.2 Intrusive Igneous ActivityTextbook 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 pre-

existing 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.