1. 10.2 Intrusive Igneous Activity

2. Pluton
• An intrusive igneous structure that
results from the cooling and hardening of
magma beneath the surface of Earth.

3. Sill
• A tabular igneous body formed when
magma is injected along sedimentary
bedding surfaces.

4. Laccolith
• A massive igneous body intruded
between preexisting strata.

5. Dike
• A tabular-shaped intrusive igneous feature
that occurs when magma is injected into
fractures in the surrounding rock, cutting
across preexisting rock layers.

6. Batholith
• A large mass of igneous rock that formed
when magma intruded at depth, became
crystallized, and subsequently was
exposed by erosion; Batholiths have a
surface exposure greater than 100
square kilometers.

7. Geothermal Gradient
• The gradual increase in temperature with
depth in the crust; The average is 30 degrees
Celsius per kilometer in the upper crust.

8. Decompression Melting
• Melting due to a drop in confining pressure
that occurs as rock rises.

9. Key Concept
• How are intrusive igneous features
classified?
–Intrusive igneous bodies, or plutons,
are generally classified according to
their shape, size, and relationship to
the surrounding rock layers.

10. Key Concept
• What is the origin of magma?
–Geologists conclude that magma
originates when essentially solid rock,
located in the crust and upper mantle,
partially melts. The most obvious way
to generate magma from solid rock is
to raise the temperature above the
level at which the rock begins to melt.