Volcanoes and Igneous Activity Earth - Chapter 4

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Earth Science Tarbuck/Lutgens
2
Earth Science

• Rocks
• Earths
• Materials
• Chapter 3

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Chapter-3 Rocks Pretest

• Describe the strength of bonds between atoms in a
  solid.
• What is a mineral?
• True or False Only eight elements make up the
  bulk of the minerals found in Earths crust.
• What is the most common mineral group?
• What are rock-forming minerals?
• What are some common properties of minerals?

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Rocks

• A rock is any solid mass of mineral or
  mineral-like matter that occurs naturally as part
  of our planet.
• Some rocks are composed of one mineral, however
  most rocks are a solid mixture of many minerals.
• The three major types of rocks are igneous rocks,
  sedimentary rocks, and metamorphic rocks.

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Rock cycle

• Shows the interrelationships among the three rock
  types.
• It shows that interactions among Earths water,
  air, and land can cause rocks to change from one
  type to another.
• Earth as a system the rock cycle
• Magma
• Crystallization of magma or lava
• Igneous rock
• Weathering, transportation, and deposition

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Rock cycle

• Earth as a system the rock cycle
• Sediment
• Lithification
• Sedimentary rock
• Metamorphism
• Metamorphic rock
• Melting
• Magma

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Rock cycle

• Earth as a system the rock cycle
• Full cycle does not always take place due to
  shortcuts or interruptions (alternate paths)
• e.g., Sedimentary rock melts
• e.g., Igneous rock is metamorphosed
• e.g., Sedimentary rock is weathered
• e.g., Metamorphic rock weathers

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The Rock Cycle
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Igneous rocks

• Form as magma cools and crystallizes
• Rocks formed inside Earth are called plutonic or
  intrusive rocks
• Rocks formed on the surface
• Formed from lava (a material similar to magma,
  but without gas)
• Called volcanic or extrusive rocks

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Igneous Rocks
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Igneous rocks

• Crystallization of magma
• Ions are arranged into orderly patterns
• Crystal size is determined by the rate of cooling
  
• Slow rate forms large crystals
• Fast rate forms microscopic crystals
• Very fast rate forms glass

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Igneous rocks

• Classification is based on the rocks texture and
  mineral constituents
• Texture
• Size and arrangement of crystals
• Types
• Fine-grained fast rate of cooling
• Coarse-grained slow rate of cooling
• Porphyritic (two crystal sizes) two rates of
  cooling
• Glassy very fast rate of cooling

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Fine-grained igneous texture
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Coarse-grained igneous texture
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Porphyritic igneous texture
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Obsidian exhibits a glassy texture
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Composition of Magma

• Silica (SiO2) is the most abundant compound found
  in magma and has the greatest effect on magma
  characteristics.
• Silica content affects
• Melting temperature
• Speed at which magma flows

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Origins of Magma

• Most rocks melt between 800oC and 1200oC
• Sources of Earths heat comes from
• Earths formation
• Radioactive elements
• Gravitational pull
• Factors affecting magma formation
• Temperature
• Temperature increases with depth

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Origins of Magma

• Factors affecting magma formation (continued)
• Pressure
• Pressure increases with depth
• As pressure increases, its melting point also
  increases
• Water Content
• As water content increases, the melting point
  decreases
• Mineral Content
• Different minerals have different melting points

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Origins of Magma

• How Rocks Melt
• Partial Melting
• Process whereby some minerals melt at low
  temperatures while others remain solid
• Magma chemistry can change if it partially melted

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Origins of Magma

• How Rocks Melt
• Fractional Crystallization
• Process wherein different minerals form at
  different temperatures

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Igneous rocks

• Classification is based on the rocks texture and
  mineral constituents
• Mineral composition
• Explained by Bowens reaction series which shows
  the order of mineral crystallization
• Influenced by crystal settling in the magma

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Bowens reaction series
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Origins of Magma

• Crystal Separation
• Occurs when crystals settle to the bottom of the
  magma body, or when liquid magma is separated
  from the magma body
• Layered Intrusions
• In some magma bodies, the minerals form into
  distinct bands in the order shown in Bowens
  Reaction Series

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Classification of igneous rocks
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Classification of igneous rocks
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Igneous rocks

• Naming igneous rocks
• Granitic rocks
• Composed almost entirely of light-colored
  silicates quartz and feldspar
• Also referred to as felsic feldspar and silica
  (quartz)
• High silica content (about 70 percent)
• Common rock is granite

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Granite
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Igneous rocks

• Naming igneous rocks
• Basaltic rocks
• Contain substantial dark silicate minerals and
  calcium-rich plagioclase feldspar
• Also referred to as mafic magnesium and ferrum
  (iron)
• Common rock is basalt

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Basalt
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Igneous rocks

• Naming igneous rocks
• Other compositional groups
• Andesitic (or intermediate)
• Ultramafic

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End of Chapter 3Sections 1 2