1. Chapter 5 : Rocks from molten liquids
Including adaptions from Dupre and Copeland (2004)

2. Concepts you should know for the exam
Texture – grain size of intrusive (e.g., granite) and extrusive rocks (e.g., basalt)
Relative cooling rates of intrusive and extrusive igneous rocks
Rocks from lavas vs. pyroclastic rocks
Mafic, intermediate and felsic rocks
Know table! (Temperature, Silica, Na, K, Fe, Mg, Ca content)
Melting point as a function of pressure, water content and composition
Partial melting of magma-generating rocks
Fractional crystallization
Shapes of magmatic bodies – sills, dykes, batholiths
Hot spots and volcanoes (mafic composition)
Volcanoes at convergent margins ( mafic to felsic composition)
Volcanoes at divergent margins (mafic composition)
Lavas, welded tuff, vesicular basalt, volcanic bombs, pyroclastic flows, volcanic cloud
Relation between the shape of volcano, chemistry, viscosity of lavas (shield volcano, cinder cone volcano,composite volcano)
Dangerous pyroclastic flows cause almost 30% fatalities natural disasters vs. tsunamis (~20%)

3. Lecture Outline Where do magmas form?
How do igneous rocks differ from one another?
3. How do magmas form?
4. Magmatic differentiation
5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics

4. Lecture Outline Where do magmas form?
How do igneous rocks differ from one another?
3. How do magmas form?
4. Magmatic differentiation
5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics

5. Divergent Plate Boundary
Usually start within continents—
grows to become ocean basin

10. 2. How do igneous rocks differ
from one another?
Texture – size of crystals
Coarse-grained rocks
Fine-grained rocks
Mixed texture rocks

11. How do igneous rocks differ
from one another?
Texture is related to rate of cooling.
Intrusive igneous rocks
Extrusive igneous rocks

15. Andesite - granite near the surface
Hand sample-Santiago de Chile
Microscope slide

16. Giant’s Causeway, Ireland

18. At which plate boundary does water-aided melting help generate magma?
Divergent?
Transform
Convergent?

20. Genetic Classification of Igneous Rocks
Intrusive: crystallized from slowly cooling magma intruded within the Earth’s crust; e.g. granite, gabbro

21. Genetic Classification of Igneous Rocks
Extrusive: crystallized from rapidly cooling magma extruded on the surface of the Earth as lava or erupted as pyroclastic material.

22. Extrusive Igneous Rocks Include:
rocks formed from the cooling of lavas
rocks formed by the cooling of pyroclastic material, i.e. fragmented pieces of magma and material erupted into the air

24. Last Days of Pompeii-Karl Briullov--Copyright © 1999. George Mitrevski
Last Days of Pompeii-Karl Briullov--Copyright © George Mitrevski. Auburn University

25. Mt St Helens crater 08-7-80, 60 mph, 800 deg F-pyroclastic flow- USGS

26. Composition and Classification of Igneous Rocks
Chemistry: e.g. % SiO2
Mineralogy: e.g.
Felsic (Feldspar and Silica)
Intermediate
Mafic (Magnesium and Ferric)
Ultramafic

27. Two basic compositional groups:
Felsic igneous rocks
Mafic igneous rocks

29. Why last figure is so important
The color and mineral distribution indicate an increasing density and melting temperature. Darker igneous rocks generally weigh more and are formed at higher temperatures and pressures. This reflects the density-stratification of the whole Earth!

30. Felsic Igneous Rocks: -Igneous rocks rich in minerals high in silica
Felsic Igneous Rocks: -Igneous rocks rich in minerals high in silica. They include:
Granite
Rhyolite

31. Intermediate Igneous Rocks: -Igneous rocks in between in composition between felsic and mafic igneous rocks. They include:
Diorite
Andesite

32. Mafic Igneous rocks -very low silica content, and consist primarily of mafic minerals. The most common ultramafic rock is:
Peridotite

33. What controls the melting temperatures of minerals?
*External pressure
*and Water content
*Internal composition (including internal water content)

35. Factors Affecting Melting of Minerals (and Rocks)
Pressure: Increased Pressures raises melting points
Water Content (internal and external to the mineral): Increased Water Content lowers melting points
Composition: Felsic minerals melt at lower temperatures than mafic minerals

36. Lecture Outline Where do magmas form?
How do igneous rocks differ from one another?
3. How do magmas form?
4. Magmatic differentiation
5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics

37. When rocks melt (or partially melt).
4. How do magmas form?
When rocks melt (or partially melt).
Why do rocks melt?
When the temperature exceeds the melting point of the rock or some minerals within the rock.

38. Partial Melting
--Occurs when some of the minerals forming a rock melt at lower temperatures than other minerals within the same rock

39. If different minerals melt at different pressures that means that different minerals become solid at different temperatures too. What does this imply about the internal composition of a magma body as it cools???

40. Which rocks are hardest to melt?
Granite countertop
Hawaiian beach sands?
marble

41. Fractional Crystallization!

44. Lecture Outline Where do magmas form?
How do igneous rocks differ from one another?
3. How do magmas form?
4. Magmatic differentiation
5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics

45. What is Magmatic Differentiation ?
If, during fractional crystallization, the remaining magma were to erupt it would be
(a) more felsic or
(b) more mafic than the original magma????

46. Lecture Outline Where do magmas form?
How do igneous rocks differ from one another?
3. How do magmas form?
4. Magmatic differentiation
5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics

47. What do we know about the shape of magmatic bodies. Are they sheets
What do we know about the shape of magmatic bodies? Are they sheets? Blobs? Spheres?

49. “Magmatic Pipes -101” Dykes are near-vertical
Sills are horizontal and squeeze in between other layers of rock
Plutons are deep (km) bodies of solidified magma. An example of a plutonic rock is granite or gabbro.

55. www.jemmoore.com/flying/ shiprock.html
Shiprock, NM. It's hard to tell, mainly because I was flying at about 12,000ft when I took this picture, but this massive piece of rock sticks up over 2,000ft from the surrounding plain, and is as big as a small city. It is on Navajo land, and is a significant spiritual site for the Navajo. The hard, volcanic spines radiating out from the main spire are really amazing. From this high up, you couldn't even see an eighteen-wheeler on the ground next to Shiprock, it would be just a speck.

56. Shiprock, NM www.jemmoore.com/flying/ shiprock.html
“Shiprock, NM. It's hard to tell, mainly because I was flying at about 12,000ft when I took this picture, but this massive piece of rock sticks up over 2,000ft from the surrounding plain, and is as big as a small city. It is on Navajo land, and is a significant spiritual site for the Navajo. The hard, volcanic spines radiating out from the main spire are really amazing. From this high up, you couldn't even see an eighteen-wheeler on the ground next to Shiprock, it would be just a speck.”

57. 6. Igneous activity and plate tectonics
Magmatic geosystems:
Island arc plate subduction
Plate divergence
Hot-spot volcanism
Continental plate subduction

58. Geomagmatic systems of Earth

59. Geomagmatic systems of Earth

60. Island arc plate subduction
Mafic to intermediate
intrusives (plutonism)
Mafic to intermediate extrusives (volcanism)
Island arc
volcano
Subduction zone
Oceanic
lithosphere

61. Plate divergent boundary
DIVERGENCE
Basaltic extrusives
Basaltic intrusives
Mid-ocean ridge
Partial melting
Of upper mantle
Rising magma

62. Hot-spot volcanism HOT-SPOT VOLCANISM Basaltic extrusives
Basaltic intrusives
Hot-spot volcano
Mantle plume
(hot spot)
Mantle

63. Mafic to felsic intrusives Mafic to felsic extrusives
Continental plate subduction
CONTINENTAL
PLATE SUBDUCTION
Mafic to felsic intrusives
Mafic to felsic extrusives
Continental
margin volcano
Subduction
zone
Oceanic
crust
Continental crust
Continental mantle
lithosphere
Oceanic lithosphere

66. Summary of Volcanoes
Subduction volcanoes in continental crustal and oceanic crust at convergent plate margins
Hot spot volcanoes (anywhere)
decompression volcanoes at divergent plate margins

67. IGNEOUS ROCKS-rocks from liquid melts
END of CHAPTER 5
IGNEOUS ROCKS-rocks from liquid melts