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Lecture 5: Igneous Rocks
1. Big Island Field Trip. Sign-up by Friday Sept. 11
2. Extra credit
001 Abreu 003 Agena 004 Albert 006 Araki 091 Atiburcio 008 Buck 010 Byce 011 Clements 012 Colle
067 Peahu 068 Santiago 069 Shigemitsu 070 Soares 084 Teramura 086 Tomaszek 073 Wu 074 Yamamoto 075 Yanagi 077 Yokota 079 Zoller
013 Comilla 014 Cuadrado 015 Dang 016 Duncan 080 Fujihara 018 Ganther 021 Guerrero 022 Haupt 025 Hedden
027 Higa 028 Hipolito 090 Inserra 031 Jadu 030 Johnasen 034 Kaaihue 036 Keanini-White 037 Kipi 089 Lee
039 Lockett 040 Manion 041 McTigue 042 Meyers 043 Mitamura 044 Morikawa 047 Nassiri 048 Ota 088 Pavao
iClicker assignments – pick yours up
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1. What we’ll learn today:"
2. 1. Describe igneous rock"3. 2. Identify the information revealed by igneous texture"4. 3. Identify how igneous rock color relates to chemical "5. composition"6. 4. Describe the process of igneous evolution and the role of "7. plate tectonics in it"8. 5. Describe the environments where basalt accumulates "
Learning Objectives (LO)
1. Lecture 5: Igneous Rocks"
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Kilauea lava flow, Aug 7, 2013
• Earth’s crust is 4/5 igneous rock
• Every igneous rock begins life as magma
• As magma migrates toward the surface, some of it chills & hardens underground into various types of igneous rocks
• Magma that makes it to the surface erupts in either flowing or explosive volcanoes, generating lava or pyroclastic debris
Quick Facts
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Igneous rock is formed when molten, or partially molten,
rock solidifies.
Igneous rock is formed when molten, or partially molten,
rock solidifies
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Fundamental Rock Types Igneous Rocks: form when magma solidifies
Sedimentary Rocks: form when sediment becomes cemented into solid
rock!
Metamorphic rocks: form when heat, pressure, or hot water alter any preexisting rock
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The Rock! Cycle
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The Rock Cycle Def.: All rocks change slowly from 1 of 3 rock types to another
Rocks are created, changed, and recycled
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Igneous rocks are the foundation of the
Rock Cycle
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Igneous Rocks = Magma Magma: solid rock that is melted (high temperatures) to form molten liquid
Magma rises toward Earth’s surface & cools, solidifies
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Igneous Rock-Forming Environments
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Types of Igneous Rocks
Extrusive (volcanic) - forms when magma erupts & solidifies on the surface
Intrusive (plutonic) - forms when magma solidifies within the crust
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lava splatter
lava flow
pluton (deep)
magma chamber
oceanic lithosphere
Cooling is VERY SLOW for large magma bodies
intr
usiv
e ex
trus
ive
Cooling of Magma
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Extrusive Igneous Rocks
Lava: fluid magma that flows from a crack or volcano onto Earth’s surface
Magma cools quickly = less time for crystals to form
Ex.: Basalt - common volcanic rock, ocean crust, few crystals
Porphyric rock
Obsidian
Basalt
Lava
Rhyolite
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Intrusive Igneous Rocks
Magma cools slowly, more time for crystals to form
Ex. Granite: most abundant rock in continental crust medium- to coarse-grained crystals
Granite Gabbro
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Igneous intrusions occur in a variety of shapes and sizes
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dike
Sill
volcanic pipe
laccolith
Igneous intrusions occur in a variety of shapes and sizes
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Basalt forms at spreading centers & hotspots
Spreading centers
hotspots
Pillow basalts
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Pillow lavas form where erupting lava interacts with water
http://www.youtube.com/watch v=DdIUuUY0L9c
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Lava erupting beneath ice forms volcanoes with flat tops and steep sides
Called a “Tuva”
Herðubreið, Iceland
Subglacial Volcanos: Eruption Beneath ice
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https://www.youtube.com/watch?v=yvSmPqqZB3Q
What Happens When Lava Meets Ice?
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Composition: assemblage of minerals (Si vs. Mg)
Texture: size and arrangement of cyrstals (cooling history)
Igneous rocks are classified based on their composition and texture
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The Major 7 Types of Igneous Rocks
+ Peridotite
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Composition Types
Felsic: Feldspar & Silica Granite (large grains), Rhyolite (small)
Mafic: Magnesium & Iron (Fe) Gabbro (large), Basalt (small)
Ultramafic: High Mg & Fe Peridotite (mantle material, rare)
Intermediate: Andesite
Felsic Mafic
Ultramafic
Andesite
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Felsic Intermediate Mafic
+ Peridotite Ultramafic
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Bowen’s Reaction Series Describes the Crystallization of Magma !
As magma crystallizes, a network of interlocking minerals forms
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Minerals at the BOTTOM of the series: • Light in color
• Felsic
• Na & K
Minerals at the TOP of the series: • Dark in color • Mafic to ultramafic • Fe & Mg
Mafic minerals crystallize early and Felsic minerals crystallize late in magma
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Composition vs. Color Igneous color (gray scale) is used to estimate chemical composition
Felsic Intermediate Mafic
Mg/Fe content Si/O content
more less less more
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Using visual color to estimate composition can be misleading.
Obsidian is Felsic!
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Composition: The assemblage of minerals (Si vs. Mg)
Texture: the size and arrangement of minerals (cooling history)
Igneous rocks are classified based on their composition and texture
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Texture is a Record of the Crystallization History
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Texture Styles
Phaneritic: • Slow cooling, larger crystals • Coarse texture • Intrusive or plutonic
Aphanitic: • Rapid cooling, smaller crystals • Finer texture • Extrusive or volcanic
Other textures are glassy, pyroclastic, vesicular, and porphyritic Volcanic bomb - aphanitic
phaneritic
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Phaneritic large minerals
Large crystals had a long time to crystallize.
Texture
Example: Granite
Therefore, this is an intrusive rock
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Texture
Aphanitic mineral grains too
small to see with the unaided eye
Small crystals had a short time
to crystallize.
Example: Basalt
Therefore, this is an extrusive rock
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Texture
Vesicular many pits from gas
escape
Extrusive rock
Example: Basalt
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Texture
Glassy no obvious
minerals
Example: Obsidian
No crystals.
This is an extrusive rock that cooled
VERY quickly
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https://www.youtube.com/watch?v=eVk5Gbn1ePU
Glass Formation
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Extrusive rock (made during an
eruption)
Example: Tuff
Pyroclastic Fused rock
fragments & ash from an explosive
eruption
Texture
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Texture
Porphyritic 2 distinct grain sizes,
large & small
Example: Andesite
Two phases of cooling:
Intrusive phase: large crystals Extrusive phase: fine crystals
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Composition
Text
ure
The Major 7 Types of Igneous Rocks
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Igneous rocks are named based on their texture & composition
Seven major types of igneous rocks
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Green Sand Beach, Big Island is made of Olivine.
True or false? Olivine is also the most common mineral in the upper mantle.
iClicker Question
A. True B. False
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Many Uses of Igneous Rocks
pumice stone arrowheads countertops
building materials
walls of lava rock
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The Rock! Cycle
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Igneous rock is a ubiquitous component of Earth’s crust because it evolves as a product of tectonic processes.
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Action Items for Thursday, Sept. 10
1. Read Chapter 5 2. Complete homework assignment #5
1. What you should know from today:"
2. 1. Describe igneous rock"3. 2. Identify the information revealed by igneous texture"4. 3. Identify how igneous rock color relates to chemical "5. composition"6. 4. Describe the process of igneous evolution and the role of "7. plate tectonics in it"8. 5. Describe the environments where basalt accumulates "