1. Igneous Processes, Igneous Intrusions
I. Processes that change the composition of the magma
A. Fractional crystallization (crystal settling)
B. Assimilation
C. Magma mixing
Online rocks and mineral table.
Viscosity & melts
Partial melt
Bowen’s reaction series

2. 1. What three factors control the melting of rocks?
Question of the Day
1. What three factors control the melting of rocks?
Use 8 1/2” x 11” paper. Put your name and class on the top of your paper.

3. Plate tectonics and Igneous Rocks
Basics
Basalt and Gabbro—
Low viscosity, so often reach the surface (most common rock)
1. Oceanic Basalts
Mid ocean ridge basalts (MORBs)
65% of Earth’s surface
Divergent boundaries
b. Ocean Island Basalts (OIBs)
Over hot spots

4. Plate tectonics and Igneous Rocks
Basalts and Gabbros
Oceanic Basalts
2. Continental Basalts (rare)
a. continental rifting
b. continental hot spots
c. over subduction zones
rare because often undergo fractional crystallization  more felsic rocks

5. Plate tectonics and Igneous Rocks
B. Andesite and Diorite
Forms over subduction zones
Basalt forms from partial melting of ultramafic mantle
Fractional crystallization and assimilation of crust  intermediate magmas
Also, melting of sediment on top of slab  more intermediate magmas

6. Plate tectonics and Igneous Rocks
C. Rhyolites and Granites
Continental hot spots
Over subduction zones
So the melts are very viscous, so they rarely reach the surface, usually plutonic/intrusive.
Rhyolite and granite form by:
Melting of crust
Heat source from intermediate and mafic magmas.
Fractional crystallization and assimilation are important

7. Plate tectonics and Igneous Rocks
III. Intrusive Igneous Rocks (plutonic rocks)
Plutons—formations created by emplacement of magma at depth
Tabular
1. Dike—discordant, cuts cross pre-existing layers
Look lie sheets and generally dip steeply or vertical
Dikes are magma injected into fractures - pressure of magma may open up small fractures
Range in size from < centimeter to hundreds of kilometers
Often more resistant to erosion than surrounding rock, so remains like a wall
Spanish Peaks, southern Colorado, Shiprock Peak, NM, all over SW US

8. 06_10.jpg

12. Plate tectonics and Igneous Rocks
III. Intrusive Igneous Rocks (plutonic rocks).
Plutons—formations created by emplacement of magma at depth
Tabular
2. Sill: a concordant tabular pluton
Lies parallel to layers of preexisting rock.
Intrudes between layers and pushed overlying rock up, so shallow where overlying pressure is low.
Generally basalt (low viscosity), form uniform thickness layers/large extent

13. 06_11e.jpg

14. 06_11f.jpg

15. Plate tectonics and Igneous Rocks

17. 06_11b.jpg

18. 06_11c.jpg

19. 06_11d.jpg

20. Plate tectonics and Igneous Rocks
III. Intrusive Igneous Rocks (plutonic rocks).
Plutons—formations created by emplacement of magma at depth
Tabular
3. Laccolith: concordant, similar to sill, but mushroom shaped/domed
Formed by more viscous magma: intermediate - felsic
Shallow depth = low pressure
Henry Mountains of SE Utah (draw erosion of overlying rock to form mts)

21. Plate tectonics and Igneous Rocks
III. Intrusive Igneous Rocks (plutonic rocks).
Plutons—formations created by emplacement of magma at depth
A. Massive plutons—several km thick and 10’s-100’s km across
Batholiths—massive discordant plutons
When exposed, surface areas of >hundred km2
Intermediate-felsic (too viscous to reach surface)
Form ~25 km below the surface
Examples: Sierra Nevada Mts., Yosemite, White Mts in NH, Pikes Peak CO, Idaho Batholith

22. Plate tectonics and Igneous Rocks
III. Intrusive Igneous Rocks (plutonic rocks).
Plutons—formations created by emplacement of magma at depth
A. Massive plutons—several km thick and 10’s-100’s km across
Batholiths: massive discordant plutons
When exposed, surface areas of >hundred km2
Intermediate-felsic (too viscous to reach surface)
Form ~25 km below the surface
Examples: Sierra Nevada Mts., Yosemite, White Mts in NH, Pikes Peak CO, Idaho Batholith

23. 06_12.jpg

24. 06_13a.jpg

25. 06_13b.jpg

26. 06_14ab.jpg

28. 06_17a.jpg

29. 06_17b.jpg

31. Plate tectonic setting and igneous rock types
06_19.jpg

32. Summary Intrusive rocks Cool slowly Phaneritic texture
Extrusive rocks (volanic rx)
Cool rapidly
Aphanitic texture
Types of igneous rocks and tectonic settings
Divergent boundary
Convergent boundary
Concepts
Partial melting
Fractional crystallization & Crystal settling
Assimilation
Magma Mixing
Igneous rocks on and in the Earth
Dikes, sills, batholiths