Earth Materials. The Crust and its Composition. Igneous Rocks. Sediments and Sedimentary Rocks. Metamorphic Rocks. The Cycle of Rock Change

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2 Earth Materials The Crust and its Composition Igneous Rocks Sediments and Sedimentary Rocks Metamorphic Rocks The Cycle of Rock Change

3 The Crust and its Composition oxygen and silicon account for about 75% of the earth's crust metallic elements iron, aluminum and the base elements account for most of the rest Figure11.1, p. 399

4 The Crust and its Composition the elements of the crust are combined in inorganic chemical compounds called minerals these minerals are mixed together in various proportions to form different rock classes rocks of the Earth's crust are grouped into three major classes: igneous, sedimentary and metamorphic rocks

5 Mineral The Nature of Minerals A naturally occurring inorganic solid that has an exact (or clearly defined range) chemical composition with an orderly internal arrangement of atoms generally formed by inorganic processes.

6 Minerals Internal structure Repetitive geometric pattern of atoms Expressed in physical properties Interfacial angles Cleavage Revealed in X-ray diffraction

7 Ionic Bonding

8 Periodic Table of the Elements

9 8.3

10 Polymorphs of Carbon Minerals

11 Physical Properties Cleavage/Fracture Optical Properties: Luster, Color, Streak Hardness Density Magnetism

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16 Rock-Forming Minerals About 20 common minerals make up most rocks Silicates dominate Quartz, Feldspars, Mica, Amphiboles, Pyroxenes Carbonates are common; limestones Evaporite minerals, salt mines, gypsum Secondary minerals formed during weathering, e.g. Aluminum and Iron oxides

17 Silicate Minerals Most common minerals on Earth Comprise 95% of the volume of the crust Approximately 75% of the Earth s mass is made up of silicon and oxygen All silicate minerals are based on the silica tetrahedron SiO 4-4

18 Silica Tetrahedron

19 Silicate Structures Isolated Single chain Double chain Sheet Solid

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23 Clay Minerals Sheet silicates similar to mica Products of chemical weathering near the Earth s surface Usually microscopic crystals Kaolinite

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25 SEM photograph of clay minerals: authigenic chlorite flake from the Watahomigi Formation in Andrus Canyon, Supai Group, Grand Canyon; x 20,900. Figure 05-D, U.S. Geological Survey Professional Paper 1173.

26 Nonsilicate Minerals Usually form at low temperatures (reactions that occur at the surface of the E arth ) Carbonates (biologic) Calcite - Ca CO 3 Dolomite - CaMg(CO 3 ) 2 Evaporite Minerals (seawater evaporation) Gypsum - CaSO 4-2H 2 O Halite - NaCl Oxides (rust and weathering) Hematite

27 Igneous Rocks and the Rock Cycle

28 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

29 Imagine the first rock and the cycles that it has been through.

30 Igneous Rocks Form from Magma Hot, partially molten mixture of solid liquid and gas Mineral crystals form in the magma making a crystal slush Gases - H 2 O, CO 2, etc. - are dissolved in the magma

31 Magma vs. Lava Igneous Rocks Magma is molten rock beneath the surface Lava is molten rock that has reached the surface Magma solidifies to form intrusive igneous rocks Lava solidifies to form extrusive igneous rocks

32 Figure 4.2. Distribution of igneous rocks in North America

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35 Igneous Textures Texture - the size, shape and relationship of mineral crystals in the rock Reflects cooling history of the magma or lava Slow cooling rate >> Big crystals Fast cooling rate >> Small crystals Very fast cooling rate >> glass

36 Figure 4.3C. Phaneritic texture in granite

37 Figure 4.3B. Aphanitic texture in rhyolite

38 Figure 4.3A. Glassy texture in obsidian

39 Porphyritic Texture Well formed crystals (phenocrysts) Fine grained matrix (groundmass) Complex cooling history Initial stage of slow cooling Large, well formed crystals form Later stage of rapid cooling Remaining magma crystallizes more rapidly

40 Porphyritic igneous rock: Big xtals in a fine grain matrix

41 Pyroclastic Texture Produced by explosive volcanic eruptions May appear porphyritic with visible crystals Crystals show breakage or distortion Matrix may be dominated by glassy fragments Fragments also show distortion Hot fragments may weld together

42 Figure 4.3D. Pyroclastic texture

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44 Extrusive Rock Bodies Volcanic Form of extrusive bodies influenced by magma properties Composition Silica content Viscosity Volatile content Temperature

45 Aa flow Pahoehoe flow Figures 4.6 A & B

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48 movies F ountain.mov Stromboli.proj.mpg Lava4.mov PyroclasticFlow.mov MainC rater.mpg O ldfaith.av i Redflow.mpg JuandeFucaSmok er.av i Smoker.mov Tube3.mov

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50 Devil s Tower; a volcanic neck, a feeder pipe

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52 Shiprock, New Mexico; a volcanic neck

53 Rhumski, Cameroon; a volcanic neck

54 Sill; parallels layers in the country rock

55 Dike; cuts across layers in the country rock

56 Half Dome; part of the Sierra Nevada batholith

57 Beginnings of a spatter cone Large cinder cone

58 Flood basalts with several thick and thin layers. Each layer represents a separate eruption.

59 pillow lavas

60 Formation of Volcanic Domes

61 Mt Fuji: Stratovolcano

62 Mt. St. Helen's prior to 1980 eruption, a classic stratovolcano

63 Process of formation of ash flow caldera - e.g., Crater Lake, Oregon or the super Caldera of Yellowstone

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65 Size comparison of various volcanic features

66 Intrusive Rock Bodies Plutonic Less dense magmas rise through the crust Rising magmas slowly cool Viscosity increases Density increases Intrusions form as magma solidifies beneath the surface

67 Figure Types of magmatic intrusions

68 Metamorphosis

69 One of the oldest rocks in the world. A gneiss produced by metamorphosis of an even older shale.

70 Metamorphism The transformation of rock by temperature and pressure Metamorphic rocks are produced by transformation of: Igneous, sedimentary and even other metamorphic rocks

71 What causes metamorphism? Heat Most important agent Heat drives recrystallization - creates new, stable minerals Pressure (stress) Increases with depth Pressure can be applied equally in all directions or differentially, i.e. directed

72 Main factor affecting metamorphism Parent rock Metamorphic rocks typically have the same chemical composition as the rock they were formed from Different minerals, but made of the same stuff.

73 Metamorphism Three types of metamorphic settings: Contact metamorphism from a rise in temperature within host rock Hydrothermal metamorphism chemical alterations from hot, ion-rich water Regional metamorphism -- Occurs in the cores of mountain belts and makes great volumes of metamorphic rock

74 Contact metamorphism Produced mostly by local heat source

75 Hydrothermal Metamorphism Circulation of hot fluids through cracks and porous rock Important source of ores

76 Regional Metamorphism: Subduction zones..

77 and/or deep burial

78 Metamorphic textures Foliation Foliation can form in various ways: Rotation of platy or elongated minerals Recrystallization of minerals in a preferred orientation Changing the shape of equidimensional grains into elongated and aligned shapes

79 Development of foliation due to directed pressure

80 Foliated vs. Nonfoliated textures under the microscope

81 Flattened Pebble Conglomerate = flattening

82 Progressive metamorphism of a shale Shale

83 Slate

84 Phyllite (left) and Slate (right) lack visible mineral grains Phyllite

85 Schist

86 Schist

87 A mica garnet schist

88 Gneiss

89 Gneiss displays bands of light and dark minerals

90 Gneiss

91 Change in metamorphic grade with depth

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93 Metamorphic rocks exposed at Mt. Everest. Deformation occurs at various scales

94 Outcrop of foliated gneiss

95 Common metamorphic rocks Nonfoliated rocks Quartzite Formed from a parent rock of quartz-rich sandstone Quartz grains are fused together Forms in intermediate T, P conditions

96 Sample of quartzite Thin section of quartzite

97 Common metamorphic rocks Nonfoliated rocks Marble Coarse, crystalline Parent rock usually limestone Composed of calcite crystals Fabric can be random or oriented

98 Marble (Random fabric = annealing; nonfoliated)

99 Marble

100 Question: Where do we see metamorphic rocks in outcrops?

101 North American Craton Shield Western North American Mobile Belt Eastern Nor American Mobile Be Platform

102 Answer: In continental shields and uplifted basement rocks