1. Rock Cycle & Igneous Rocks

2. The Rock Cycle

3. Differences between rocks and minerals
Pure (made of same substance)
More than one mineral
Some have crystals
Not single crystals
No fossils
Some have fossils
Usually have shape
No definite shape

4. The Rock Cycle-Types of Rocks
Rocks are any solid mass of mineral or mineral-like matter occurring naturally as part of our planet.
Types of Rocks
1. Igneous rock is formed by the crystallization of molten magma.

5. Rock Cycle-Types of Rocks
2. Sedimentary rock is formed from the weathered products of preexisting rocks that have been transported, deposited, compacted, and cemented.
3. Metamorphic rock is formed by the alteration of pre-existing rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids.

6. The Rock Cycle
Rock Cycle: shows the interrelationships among the three rock types (igneous, sedimentary, and metamorphic)
Magma is molten material that forms deep beneath the Earth’s surface.
Lava is magma that reaches the surface.
Weathering is a process in which rocks are broken down by water, air, and living things.
Sediment is weathered pieces of Earth elements.

7. The Rock Cycle

8. Energy that drives the Rock Cycle
 Earth’s Interior (Internal Processes): Igneous & Metamorphic Rocks
 Sun (External processes): Sedimentary rocks.
 Weathering and the movement of weathered materials are external processes powered by energy from the sun.

9. Igneous Rocks & Magma

10. Igneous Rocks Named for the Latin ‘Ignis’=Fire Occurrence
Found globally
Found in discrete geologic locations
Convergent plate boundaries
Divergent plate boundaries
Mantle plumes
Formed by the crystallization of magma or lava

11. The Nature of Igneous Rocks
Form from Magma [Greek=“paste”]
Hot, partially molten mixture of solid, liquid, and gas
Gases: H2O, CO2, etc.
less dense than solid rock
solidifies upon
cooling

12. Magma vs. Lava Magma Vs. Lava (again)
Magma: molten rock beneath the surface
Lava: molten rock that has reached the surface
Magma: form intrusive igneous rocks
Lava: form extrusive igneous rocks

13. Igneous Rocks in NM- Cornudas Peak

14. Composition varies widely
Magma Composition
Composition varies widely
Oxygen plus major elements
Generally a silica (SiO2) melt
Silica and water content control viscosity
Silica content used in classification

15. Mafic Magmas Silica content ~ 50%
High Fe, Mg and Ca (Iron, Magnesium, and Calcium)
High temperature molten magma
1000o to 1200oC ( oF)
Major minerals:
Olivine - Ca Plagioclase
Pyroxene

16. Rocks formed from Mafic Magmas

17. Felsic Magma Silica content: 65-77%
High Al, Na and K (Aluminum, Sodium, Potassium)
Lower temperature magmas
Less than 850oC (1575 oF)
Major minerals:
Feldspars - Micas
Quartz

19. Magma Viscosity Viscosity: resistance to flow
High Viscosity= HIGH resistance, SLOWER flow
Low Viscosity=LOW resistance=FASTER flow

20. Magma Viscosity
Controlled by silica and water content, and temperature
As magma cools-silica tetrahedron form links
Linkages control viscosity

21. Magma Viscosity High Silica=high viscosity (slow)
Low Silica=low viscosity (fast)
Cooler Temperatures=higher viscosity
Higher Temperatures=lower viscosity
More Links=higher viscosity
Fewer Links=lower viscosity
Water=lower viscosity

22. Plate Tectonic Setting of Igneous Rocks
Divergent Plate Boundaries
Partial melting of mantle produces basaltic magma (MAFIC)
Convergent Plate Boundaries
Subduction produces partial melting of basalt, sediments, parts of mantle
Andesitic and rhyolitic magma (INTERMEDIATE & FELSIC)
Ascending magma assimilates lower crustal material

23. Plate Tectonic Setting of Igneous Rocks
Mantle Plumes
Partial melting of plumes of mantle material
Basaltic magma is produced (MAFIC)
Rising magma produce
Intraplate island chains
Flood basalt [Columbia River Basalts]

25. Igneous Rocks-Classification
Igneous Rocks are classified by 3 main factors:
Formation (by magma or lava)
Texture
Composition

26. Igneous Rocks: Classification
Formation
Intrusive Igneous Rocks:
formed when magma hardens beneath Earth’s surface.
See these after erosion occurs
Ex: Granite
Extrusive Igneous Rocks:
Formed when lava hardens above Earth’s surface
Ex: Rhyolite

27. Granite

28. Rhyolite

29. Igneous Rocks: Classification
Texture
the size, shape and relationship of minerals in the rock
Cooling history of the magma or lava
Crystal size increases as rate of cooling slows
There are 5 main textures: coarse, fine, glassy, porphyritic, pyroclastic

30. Igneous Rocks: Classification
Coarse (Phaneritic)Texture
Slow cooling rate
Large Crystals
Equigranular, interlocking crystals
Ex. Granite

31. Igneous Rocks: Classification
Fine (Aphanitic)Texture
Fast cooling rate
Smaller, interconnected crystals
Few crystals visible in hand specimen
Ex. Rhyolite

32. Igneous Rocks: Classification
Glassy Texture
Very fast cooling rate
No visible crystals
Volcanic Glass
Ex. Obsidian

33. Igneous Rocks: Classification
Porphyritic Texture
Complex cooling history
Different cooling rates throughout the rock
Different sized crystals
Ex. Andesite

34. Igneous Rocks: Classification
Pyroclastic Texture
forms as an explosive volcanic eruption mixes fragments of the volcano with hot ash in the atmosphere
As this hot combination of tiny ash particles and larger, angular fragments settles to the ground, they blanket the Earth's surface and weld together
Appear porphyritic with visible crystals
A generic term for all these rocks is “tuff”

36. Igneous Rocks: Classification
Composition
Which types of minerals make up the rock
Composition determined by Bowen’s reaction series (later)
Range from light colored (felsic) to very dark colored (ultramafic)

37. Igneous Rocks: Classification
Felsic Composition
Also called silicic or granitic composition
Light colored rocks
White to pink in color
Mostly composed of quartz and potassium feldspar
Very High amounts of: Si, Na, K
Very Low amounts of: Fe, Mg, Ca
Examples: Granite (I) Rhyolite (E)

38. Felsic Rocks

39. Igneous Rocks: Classification
Intermediate Composition
Also called andesitic composition
Combination of light and dark colored minerals
Salt and Pepper OR gray coloration
Mostly composed of amphibole, plagioclase feldspar, quartz, pyroxene
High amounts of: Si, Na, K
Low amounts of: Fe, Mg, Ca
Examples: Diorite (I) Andesite (E)

40. Intermediate Rocks

41. Igneous Rocks: Classification
Mafic Composition
Also called basaltic composition
Dark colored minerals
Mostly composed of pyroxene, plagioclase feldspar, olivine
Low amounts of: Si, Na, K
High amounts of: Fe, Mg, Ca
Examples: Gabbro (I) Basalt (E)

42. Mafic Rocks

43. Igneous Rocks: Classification
Ultramafic Composition
Very Dark colored minerals (usually has dark greens)
Mostly composed of pyroxene and olivine
Very Low amounts of: Si, Na, K
Very High amounts of: Fe, Mg, Ca
Examples: Peridotite (I) Komatiite (E)

44. Ultramafic Rocks

45. Classification of Igneous Rocks

46. Classification of Igneous Rocks

48. Bowen’s Reaction Series
Chemical Evolution of Igneous Rocks proposed by Norman Bowen in the early 1900s.
Proposed mafic magmas may evolve by cooling and crystallization to produce more silica-rich magmas
Found the following through experiment:
There is a regular sequence of silicate mineral crystallization
Minerals common to mafic rocks crystallize at the highest temperatures
Minerals common to felsic rocks crystallize at the lowest temperatures

49. Bowen’s Reaction Series
Once a mineral forms, it will undergo a chemical reaction with the surrounding melt to produce the next  lower temperature mineral in the sequence
Example: Olivine undergoes a reaction with the surrounding melt to form pyroxene. Pyroxene reacts with the surrounding melt to form amphibole, etc.

50. Bowen’s Reaction Series
There are two important parts of the reaction series:
The discontinuous series - includes minerals with differing arrangement of Si-O tetrahedra; (olivine, pyroxene, amphibole, biotite)
The continuous series - includes plagioclase feldspar minerals, all of which are framework silicates; (Ca-rich plagioclase (anorthite), Na-rich plagioclase (albite))

51. Bowen’s Reaction Series

52. Importance of Bowen’s Reaction Series
Explains how a variety of igneous rock types can come from a single (mafic) magma composition
Fractional Crystallization
Crystal Settling
Volcanic Eruption
Allows interpretation of crystallization temperature based on mineralogical composition.
Ultramafic=highest temps
Felsic=lowest temps