Physical Geology 101
Plutonic Rocks

Plutonic Rocks

Igneous rocks which cool beneath the surface
Slow cooling - results in a phaneritic texture

Magma Emplacement

Magma is produced beneath surface
Magma then rises through crust

Magmatic Stoping

Forceful Injection


Once solidified, these bodies of magma are called plutons.
Magma may be produced in large bodies - large scale melting.
Magma may be produced in small quantities, then will collect together to form large bodies - magma mixing.

Plutonic Bodies

Plutons are classified based on the shape and size of body, and by its relation to surrounding rock.
Exposure of a pluton occurs due to erosion of overlying rock or uplift of pluton.

Types of Plutons

Concordant Plutons
- intrude into layered rocks
- boundaries are parallel to the layers

Discordant Plutons
- intrude into layered rocks
- boundaries cut across the layers

Tabular Plutons
Plutonic bodies that are relatively thin compared to other dimensions

Sills - tabular concordant plutons
Sill Example 1
Sill Example 2
Sill Example 3
Dikes - tabular discordant plutons
Dike Example 1
Dike Example 2
Dike Example 3
Dike Example 4
Dike Example 5
Laccoliths - tabular, plano-convex plutons
Laccolith Example 1

Massive Plutons
The term pluton is used to describe any intrusive igneous body.
The term pluton is also used for large, massive, intrusive igneous bodies produced by a single batch of magma.
Massive Pluton Example 1


Two definitions:
1) Large (>100 km2 surface area) discordant plutons that increase in size with depth with no known base.
2) Large discordant bodies composed of multiple plutons.
Composed dominantly of granite or granodiorite - may contain plutons of diorite, gabbro or other mafic and ultramafic rocks.
Irregular, dome-shaped roofs - stoping.
Batholith Example 1
Batholith Example 2
Batholith Example 3
Batholith Example 4


Xenoliths are foreign inclusions of pre-existing rocks.
Xenolith Example 1
Xenolith Example 2
Xenolith Example 3
Xenolith Example 4


Erosional remnants of a larger body surrounded by a peneplain (large flat erosional surface)
Can develop in any rock type - common in eroded plutons