1. The 3 Types of Rocks Rock: A geologic material composed of 2 or more different minerals (rarely just 1 mineral). Rocks are mixtures. (remember that minerals are chemical elements or compounds.) _______________________________ Igneous- Formed when minerals solidify (crystallize) from liquid rock (magma or lava). Sedimentary- Formed when minerals precipitate from water or when mineral fragments get cemented by water. Metamorphic- Formed when igneous or sedimentary rocks get “baked” at higher temperature and pressure due to contact with magma or due to tectonic plate collisions.

2. Rock vs. Mineral Granite is a rock made of 3 main minerals: alkali feldspar, quartz, and micas (biotite and muscovite)

3. Igneous rocks are rocks that crystallize from liquid rock. Magma- Molten rock below Earth’s surface in the crust or mantle. It is composed mostly of Si and O (silica, SiO 2 ) and dissolved gases. Where is the image of magma? Igneous Rocks – Chapter 5

4. Lava- Molten rock material at Earth’s surface. Magmas can become lavas when they extrude at the surface through fissures (cracks) in the surface of the earth or through volcanoes.

5. Igneous rock- A silicate-rich rock that forms when molten rock (magma or lava) solidifies and crystallizes. (liquid  solid, so freezing).

6. Two main types of igneous rocks: 1) Intrusive/Plutonic- Formed when magma solidifies deep underground. Includes granite (the main rock of the continental crust). Never directly witnessed!

7. 2) Extrusive/Volcanic- Formed when lava solidifies at the Earth’s surface. Includes basalt (the main rock of oceanic crust).

8. Where does the heat inside the Earth come from? Original heat still left over from earth’s original formation 4.6 billion years ago. Earth is still cooling. Heat produced from the decay of radioactive elements inside the earth’s mantle and crust. (radioactive elements like. uranium and thorium release heat) Frictional heat caused by the gravitational pull of the moon on the earth.

9. Heat moves outward towards the surface of the earth As heat moves upward, it causes the mantle to convect (hot material rises, cold material sinks) like wax in a lava lamp. Convection moves heat that causes melting. Mantle convection also cause the tectonic plates to move!

10. What Favors Melting of Rock? 1) Increase the Temperature! The temperature of the Earth increases from crust to core at approximately 25 C/km (the geothermal gradient). The core temperature is > 5000 C, so heat moves upward and melts the upper mantle and crust.

11. What Favors Melting or Rock? 2) Decrease the pressure! Pressure favors solids and less pressure favors liquids. Decompression melting occurs when hot mantle rock moves upward by convection. Liquid

12. What Favors Melting of Rock? 3) Add water! Water reduces the melting point of rock. Minerals with water in them help melting of rock to occur. Dry granite melting temperature: 900°C. Wet granite melting temperature: 700°C.

13. What Favors Melting of Rock? 4) Mineral Content! Rocks are mixtures of minerals and different minerals have different melting points. Rocks with minerals that have more iron and magnesium and less silicon and oxygen (mafic rocks) generally melt at higher temperatures that rocks that contain more silicon and oxygen (felsic rocks). Granite melts at a lower temperature than basalt.

14. Rocks do not melt at one specific melting point. They melt over a range of temperatures. Rocks are chemical mixtures so the different minerals in them retain their own unique properties like melting point. Each mineral in a rock melts at its own melting point. This leads to partial melting of rocks when heated. The minerals with the lowest melting points melt first, followed by those with higher melting points. The entire rock may not melt!

15. A household example of partial melting…..

16. Rock-Forming Minerals in Igneous Rocks MineralChemical CompositionMelting Temperature Quartz SiO 2 Lowest (600  C) Alkali Feldspar(K,Na)AlSi 3 O 8 Low (700  C) Muscovite MicaKAl 2 (AlSi 3 O 10 )(F,OH) 2 Low (750  C) Biotite MicaK(Mg,Fe) 3 AlSi 3 O 10 (F,OH) 2 Medium (800  C) AmphiboleCa 2 (Mg,Fe,Al) 5 (Al,Si) 8 O 22 (OH) 2 Med-High (850  C) PlagioclaseNaAlSi 3 O 8 – CaAl 2 Si 2 O 8 Med-High (800-1000) Pyroxene(Ca,Mg,Fe) 2 Si 2 O 6 High (1000  C) Olivine(Mg,Fe) 2 SiO 4 Highest (1100  C)

17. Partial melting of source rock will produce magma with a different chemical composition. Minerals richer in silicon and oxygen (like quartz and feldspars) melt at lower temperatures, leaving minerals richer in iron and magnesium (like amphibole, pyroxene, or olivine) behind. So, the magma produced (the partial melt) will be felsic, richer in silica (SiO 2 ) and the residue will be more mafic, poorer in silica (SiO 2 ). Source Rock

18. Partial melting produces magmas of different compositions which form the different types of igneous rocks found on the earth. Deeper melting in the Earth (say in the mantle) leads to more mafic magmas richer in magneisum (Mg) and iron (Fe) and poorer in silica (Si and O), since the source rocks are richer in these elements. Shallower melting in the earth (say in the crust) leads to more felsic magmas richer in silica (Si and O) and in sodium and potassium, since the source rocks are richer in these elements. Partial melting is the norm on Earth! Partial melting created the crust from the mantle. Basalt Granite

19. Quartz (SiO 2 )

20. Alkali Feldspar ( (K,Na)AlSi 3 O 8 )

21. Muscovite Mica ( KAl 2 (AlSi 3 O 10 )(F,OH) 2 )

22. Biotite Mica ( K(Mg,Fe) 3 AlSi 3 O 10 (F,OH) 2 )

23. Amphibole ( Ca 2 (Mg,Fe,Al) 5 (Al,Si) 8 O 22 (OH) 2 )

24. Plagioclase Feldspar ( NaAlSi 3 O 8 – CaAl 2 Si 2 O 8 )

25. Pyroxene ( (Ca,Mg,Fe) 2 Si 2 O 6 )

26. Olivine ( (Mg,Fe) 2 SiO 4 )

27. What happens to a partial melt or magma once it forms?? It can travel up and away from the source rocks because it is less dense and will rise. It can melt other rocks into itself as it moves up towards the surface. The farther it moves from the source rock, the more chemically different it becomes compared to the source rock. It will eventually crystallize back to solid rock, but it will be chemically different than the source rock that partially melted to produce it.

28. Bowen’s Reaction Series: Tells you the sequence of crystallization of minerals from a magma or lava (including a partial melt). Minerals crystallize in a predictable order as the magma or lava cools. Minerals crystallize in an order that is the opposite of the order they melted when partial melting occurred. So, last melted = first to crystallize.

29. Bowen’s Reaction Series

30. Bowen’s Reaction Series: Two Paths The left side is the discontinuous series. As the magma cools and crystallizes, earlier formed, iron-magnesium rich minerals react with the remaining magma to form new minerals. The right side is the continuous series. The right side represents the continuous crystallization of plagioclase feldspar, which starts out calcium-rich and ends up more sodium-rich. Alkali

31. Mineral Textures of Igneous Rocks show Bowen’s Reaction Series in Action A zoned crystal of plagioclase in an igneous rock. The center (core) is Ca- rich and the edge (rim) is Na-rich. An olivine crystal surrounded by pyroxene in an extrusive (volcanic) igneous rock.

32. Alkali feldspar, muscovite mica, and quartz crystallize last Plagioclase feldspar Quartz Amphibole Alkali feldspar

33. Lessons from Bowen’s Reaction Series 1) The chemical composition of a magma controls the types of minerals and kind of igneous rock that can form from it. 2) The first minerals to solidify at high temperature are olivine, pyroxene, Ca-rich plagioclase. This produces a mafic rock (rich in Fe, Mg, Ca) like basalt or gabbro. 3) At lower temperatures, minerals like quartz and alkali feldspar solidify. This produces a felsic rock (rich in Si and Al) like granite or rhyolite. 4) At intermediate temperatures, minerals like amphibole, biotite, and plagioclase crystallize together. This produces an intermediate rock like diorite or andesite.

34. Fractional Crystallization Fractional crystallization is the separation of previously-formed minerals from the rest of a magma during cooling and crystallization. This often occurs as dense, iron-magnesium rich minerals like olivine and pyroxene settle out under the influence of gravity. Fractional crystallization is important because if these iron- magnesium rich minerals are removed, they can no longer react with the magma along the discontinous side of Bowen’s reaction series. Once their elements are removed, the magma becomes more highly concentrated in silicon and aluminum and so is now more felsic than before.

35. Fractional Crystallization and Crystal Settling in the Palisades Sill in the Hudson River Valley of New York

36. Quartz “Veins” Represent the most felsic (SiO 2 – rich) bit of magma left at the end of fractional crystallization. Quartz veins often cut across other igneous rocks because they solidify last. Quartz veins often contain rare elements (like gold) that don’t fit into any other crystal structures. They are often mined.

37. Summary Questions: 1) How are partial melting and fractional crytallization similar? 2) How are partial melting and fractional crystallization different? 3) How do partial melting and fractional crystallization both lead to the formation of igneous rocks?

38. Partial Melting vs. Fractional Crystallization

39. Classification of Igneous Rocks – Ch. 5.2 The most useful system for classifying igneous rocks utilizes texture and composition (color). Type of Igneous Rock Felsic (light) Intermediate (medium) Mafic (dark) Ultramafic Intrusive / Plutonic (coarse- grained) Extrusive / Volcanic (fine- grained) It is a binary classification system!

40. What is Texture? The size, shape and arrangement of crystal grains within a rock. Igneous rocks have an interlocking texture formed by growth of minerals from a melt. Crystal size is controlled by cooling-rate.

41. Intrusive or Plutonic Textures Intrusive/plutonic rocks cooled slowly, deep within the Earth. These are coarse-grained or phaneritic (most crystals >1 to 10 mm across) because crystals have time to grow large.

42. Extrusive or Volcanic Textures Extrusive/volcanic rocks cooled quickly at the Earth’s surface (so less time for crystal growth). These are fine- grained or aphanitic (most crystals <1 mm across).

43. Extrusive Textures Cont. An extreme case occurs when rocks are glassy (no crystals formed due to extremely rapid cooling). An example is volcanic glass or obsidian. Volcanic rocks with a frothy or foamy appearance are glassy too! The magma just had a lot of gases dissolved in it, and the gases came out when the lava erupted at Earth’s surface. Examples are pumice and scoria.

44. Rock Sort Part I Using Texture-Grain Size to Infer Origin Sort your rocks into 3 piles now: - Intrusive / Plutonic (coarse-grained) -Extrusive / Volcanic (fine-grained) -Extrusive / Volcanic (glassy or frothy)

45. Igneous Rocks are also Classified by Composition! 4 compositional categories: A rock's color tells us about the minerals present and overall composition. Felsic (Granitic) Rich in silicon (Si) and Oxygen (O) and Aluminum (Al) Mafic (Basaltic) Rich in magnesium (Mg) and iron (Fe); less Si and O than granitic Intermediate (Andesitic) In-between felsic and mafic Ultramafic (Ultrabasic) Extremely rich in magnesium and iron compared to mafic

46. Mineral Composition vs. Color Minerals With Light Elements (Si, O, Al, Na, K)… Tend to be __________ colored. Minerals With Heavier Elements (Ca, Mg, Fe)… Tend to be __________ colored. Felsic Mafic

47. Felsic (Granitic) Rocks Are: Rich in light-colored minerals (quartz, alkali feldspar, micas, and some plagioclase feldspar). Compositionally rich in Si, Na, Al, and K (and poor in Fe and Mg). The dark-colored minerals like biotite and amphibole are present, but only in small amounts). No olivine or pyroxene.

48. Mafic (Basaltic) Rocks Are: Rich in dark-colored minerals (plagioclase feldspar, olivine, and pyroxene with rare to no amphibole and biotite). Compositionally rich in Ca, Fe, and Mg (lower in Si, Na, Al, and K). There is no alkali feldspar, muscovite mica, or quartz!

49. Intermediate Rocks Are: Composed of roughly equal amounts of dark- and light- colored minerals so they tend to have a “salt and pepper” color. Little to no quartz, no olivine, little pyroxene present. Amphibole, plagioclase feldspar, and biotite are common. Quartz and some alkali feldspar may be present too, in lesser amounts.

50. Ultramafic Rocks Are: Composed almost exclusively of Fe and Mg-rich minerals from the mantle (olivine and pyroxene, but no feldspar or quartz). They are called peridotite. Compositionally rich in Fe, Mg, and Ca, but poorer in Si compared to mafic rocks.

51. Rock Sort Part II – Using Color to Infer Composition Sort your rocks into 3 piles now: - Felsic (Granitic) - light colored -Intermediate (Andesitic) – medium colored (salt and pepper) -Mafic (Basaltic) – dark colored

52. Classification of Igneous Rocks The binary system for classifying igneous rocks utilizes texture and composition (color). Type of Igneous Rock Felsic (light) Intermediate (medium) Mafic (dark) Ultramafic Intrusive / Plutonic (coarse- grained) Extrusive / Volcanic (fine- grained)

53. Classification of Igneous Rocks The most useful system for classifying igneous rocks utilizes texture and composition (color). Type of Igneous Rock Felsic (light) Intermediate (medium) Mafic (dark) Ultramafic Intrusive / Plutonic (coarse- grained) GraniteDioriteGabbroPeridotite Extrusive / Volcanic (fine- grained) RhyoliteAndesiteBasaltKomatiite

54. Bowen’s Reaction Series: Tells you the sequence of crystallization of minerals from a magma or lava (including a partial melt). Minerals crystallize in a predictable order as the magma or lava cools. Minerals crystallize in an order that is the opposite of the order they melted when partial melting occurred. So, last melted = first to crystallize.

55. Classification of Igneous Rocks

56. Special Igneous Textures Xenolith: A fragment of rock within an igneous rock that differs compositionally from the host rock. The host rock and zenolith inclusions formed from different magmas. Vesicules: A bubble or hole formed by escaping gas (common in basalts). Igneous rocks with vesicles in them are called vesicular.

57. Special Igneous Textures Porphyry: Igneous rock with large crystals (called phenocrysts) in a fine-grained matrix. Rhyolite and andesite are often porphyritic. Porphyritic rocks represent a two-state cooling history: 1) slow cooling at depth followed by... 2) rapid ascent and fast cooling of magma or lave near or at Earth's surface.

58. Pegmatite: A very coarse grained igneous rock (crystal sizes > 10 cm) in which crystal growth was enhanced by the presence of fluids. Igneous rocks with very coarse- grained crystals are called pegmatitic. Special Igneous Textures

59. Intrusive Rock Bodies Intrusive rocks exist in intrusions that penetrate or cut through pre- existing country rock. The names of intrusive bodies are based on 1) size, 2) shape and 3) geometric relationship to the country rock. The two basic types of intrusions are: A. Shallow intrusions (formed < 2 km beneath Earth’s surface). These cool and solidify fairly quickly resulting in relatively fine-grained rocks (but coarser than extrusive rocks). B. Deep intrusions (formed > 2 km beneath Earth's surface). These cool and solidify slowly resulting in coarse-grained rocks.

60. Intrusive Rock Bodies Types of shallow intrusions: Dike: Tabular structure that cuts across the layering in the country rock.

61. Intrusive Rock Bodies Types of shallow intrusions: Sill: Tabular structure that parallels layering in the country rock.

62. Intrusive Rock Bodies Types of shallow intrusions: Volcanic Neck: Shallow intrusion formed when magma solidifies in the throat of a volcano (Ship Rock, New Mexico).

63. Types of deep intrusions. Plutons are large, blob-shaped intrusive bodies formed when rising blobs of magma (diapirs) get trapped within the crust.

64. Stock: A small plutons (exposed over <100 km 2 ). Batholith: A large pluton (exposed over >100 km 2 ). The interfaces between instrusions and country rock are called contacts. Rapid cooling of igneous rock near the contact (called a chill zone) often results in a smaller crystal size near the contact.

65. Where Does Most Igneous Activity Occur? Mainly at or near tectonic plate boundaries.

66. Types of Igneous Rocks relate to where they are formed Igneous rocks usually form at tectonic plate margins where plates are converging (moving together) or diverging (moving apart). Different types of igneous rocks form at different types of plate margins.

67. Mafic Rocks are common at divergent boundaries. The magma comes from the upper mantle (asthenosphere) and rises through thin crust. Little opportunity to differentiated  mafic.

68. Felsic Rocks are Common on Continents. Possibly form above subduction zones by “magmatic underplating”. Lots of magma differentiation  felsic.

69. Intermediate Rocks. Common at convergent boundaries. Partial melting of subducted ocean crust (mafic) produces basaltic magma; this evolves into more felsic magma by the assimilation of felsic crust.

70. Intermediate igneous rocks commonly form at convergent boundaries. Here, partial melting of subducted asthenosphere produces basaltic magma which evolves into more felsic magma by the assimilation of felsic crust.

71. Some igneous rocks form within plates (not at a plate boundary). Rising mantle plumes (of controversial origin) can produce localized hotspots and volcanoes as they rise through continental or oceanic crust.

72. End of Chapter 5

74. The Rock Cycle A rock is a naturally formed, consolidated material usually composed of grains of one or more minerals The rock cycle shows how one type of rocky material gets transformed into another –Representation of how rocks are formed, broken down, and processed in response to changing conditions –Processes may involve interactions of geosphere with hydrosphere, atmosphere and/or biosphere –Arrows indicate possible process paths within the cycle

75. The Rock Cycle and Plate Tectonics Magma is created by melting of rock above a subduction zone Less dense magma rises and cools to form igneous rock Igneous rock exposed at surface gets weathered into sediment Sediments transported to low areas, buried and hardened into sedimentary rock Sedimentary rock heated and squeezed at depth to form metamorphic rock Metamorphic rock may heat up and melt at depth to form magma Convergent plate boundary