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
How?
Magmatic Stoping
Forceful Injection
Plutons
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
Batholiths
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
Xenoliths are foreign inclusions of pre-existing rocks.
• Xenolith Example 1
• Xenolith Example 2
• Xenolith Example 3
• Xenolith Example 4
Monadnocks
Erosional remnants of a larger body surrounded by a peneplain (large flat erosional surface)
Can develop in any rock type - common in eroded plutons