Download Rocks: Materials of the Solid Earth

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Rocks: Materials of
the Solid Earth
Presentation modified from: Instructor Resource Center on CDCD-ROM,
Foundations of Earth Science,
Science, 4th Edition, Lutgens/Tarbuck,
Lutgens/Tarbuck,
Today
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Rock Cycle
Igneous Rocks
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Rock Cycle
Shows the interrelationships among the three
rock types
Earth as a system: The rock cycle
• Magma
Crystallization
• Igneous rock
Weathering,
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
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
Figure 2.2
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Rock Cycle Questions
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What do the colored
arrows in Figure 2.2
represent?
Where does the rock cycle
“start”
start” and “end”
end”?
What is the source of
energy for each arrow in
Figure 2.2? Choices are
Earth’
Earth’s Internal Heat
Gravity
Sun’
Sun’s Heat
Figure 2.2
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Basic Rock Types
Igneous Rocks
Crystallize from Magma
(molten Earth material)
Sedimentary Rocks
From pieces of other
rocks, or
Chemical breakbreak-down of
other rocks or organisms
Metamorphic Rocks
Alternation of other rocks
by high temperature and
pressure
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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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Form from “magma”
magma”
Molten earth material
Mineral crystals form
as magma cools
Like ice from water
Magma on Earth’
Earth’s
surface is “Lava”
Lava”
Cools rapidly
“Extruded”
Extruded”
Photograph by C.Heliker on October 3, 2003
“Extrusive”
Extrusive”
http://hvo.wr.usgs.gov/archive/spotlight_images/20031003-ch-0050.html
igneous rocks
Magma below the Earth’
Earth’s surface is magma
Cools slowly
“Intruded”
Intruded” into the crust
“Intrusive”
Intrusive” 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 rock's texture and
mineral constituents
Texture
Size and arrangement of crystals
Types
FineFine-grained—
grained—fast rate of cooling
CoarseCoarse-grained—
grained—slow rate of cooling
Porphyritic (two crystal sizes)—
sizes)— two rates of cooling
Glassy—
Glassy—very fast rate of cooling
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Lava & Volcanic Rocks
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Volcanic Rocks –
Devil’
Devil’s Tower
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Igneous Rocks - Granite
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FineFine-Grained
Igneous Texture
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Fig 2.4 A
CoarseCoarse-Grained
Igneous Texture
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Fig 2.4 B
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Porphyritic Igneous Texture
Fig 2.6
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Obsidian Exhibits
a Glassy Texture
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Fig 2.7 A
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Igneous Compositions
Composed mainly of silicate minerals
Two major groups
Dark silicates = rich in iron and/or magnesium
Light silicates = greater amounts of potassium,
sodium, and calcium
Igneous Compositions
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Granitic rocks
Composed almost entirely of lightlight-colored
silicates—quartz and feldspar
Also referred to as felsic: feldspar
feldspar and silica
silica (quartz)
High silica content (about 70 percent)
Common rock is granite
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Igneous Compositions
Basaltic rocks
Contain substantial dark silicate minerals and calciumcalciumrich plagioclase feldspar
Also referred to as mafic: magnesium
magnesium and ferrum
ferrum (iron)
Common rock is basalt
Basalt
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Igneous Compositions
Other compositional groups
Andesitic (or intermediate)
Common volcanic rock is andesite
Ultramafic
Peridotite
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Classification of
Igneous Rocks
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Figure 2.8
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How Different Igneous Rocks Form
Bowen’
Bowen’s reaction series
Magma crystallizes over a temperature range of
several hundred degrees
Therefore, minerals crystallize in a predictable
order
Last minerals to crystallize are very different in
composition from the earlier formed minerals
Bowen’s Reaction Series
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Figure 2.9
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How Different Igneous Rocks Form
Magmatic differentiation
Differentiation refers to the formation of one or
more secondary magmas from a single parent
magma
One example of this is crystal settling
EarlierEarlier-formed minerals are denser than the liquid portion
and sink to the bottom of the magma chamber
These 2 rocks have the same chemical
and mineralogical composition
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They are classified as different rock types
How do they differ in appearance?
Figure 2.4
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These two rocks have the same texture
They are classified as different rocks
How do they differ in appearance?
Figure 2.4a
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What criteria are used to classify
igneous rocks?
“Texture”
Texture”
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Coarse grained or fine grained
Mineral
composition
Light colored (lots of quartz and feldspar)
• “Felsic”
Felsic”
Dark colored (lots of Magnesium and
Iron minerals)
• “Mafic”
Mafic”
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A Demonstration
I need a volunteer…
volunteer…
Texture: CoarseCoarse-grained
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Individual mineral crystals are visible
Cooled slowly (underground)
Intrusive (or plutonic after Pluto – Greek
god of the underworld)
Figure 2.4B
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Texture: FineFine-grained
Cannot see individual crystals with naked eye
Cooled rapidly
Extrusive (or volcanic)
Figure 2.4A
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Texture: Glassy
Did this rock cool slowly or rapidly?
In what environment might this rock have formed?
Figure 2.7A
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Texture: Vesicular
GasGas-escape bubbles
(vesicles)
Did this rock cool
rapidly or slowly?
Is this an intrusive
(plutonic) or
extrusive (volcanic)
rock?
Figure 2.5
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Tell me about the origin of this rock
It is glassy
It contains vesicles
It is called “pumice”
pumice”
Figure 2.7B
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Tell me about the origin of this rock
It
has some wellwelldeveloped crystals, but
It is mostly fine
grained
(It is called porphyry)
Figure 2.6
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Instant Recall Challenge
Close your notes and books.
What are some igneous textures are what do they
indicate about the origin of the igneous rock?
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What criteria are used to classify igneous rocks?40
Appearance or “Texture”
Texture”
Coarse grained
Fine grained
Glassy
Vesicular
Porphyritic
Mineral
composition
Light colored (lots of quartz and feldspar)
• “Felsic”
Felsic”
Dark colored (lots of Magnesium and Iron
minerals)
• “Mafic”
Mafic”
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Two Compositions to worry about
Rhyolite (or Granite) Composition
Basalt (or Gabbro)
Gabbro) Composition
Hand Samples
What are these rocks?
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Basalt
Gabbro
Granite
Rhyolite
Figure 2.4
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Rocks to be able to identify
these igneous rocks
Gabbro
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Basalt
Coarse grained,
Dark Colored
Granite
Fine grained
Dark Colored
Rhyolite
Coarse Grained
Light Colored
Fine Grained
Light Colored
How and where did these rocks form?
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Oceanic
Crust
Continental
Crust
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Oceanic Versus Continental Igneous Rocks
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Recall from plate tectonics
At what type of tectonic boundaries is new
crust formed?
Divergent Boundaries
Is new crust usually
(A) Oceanic (B) Continental (C) Either ?
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A good question:
If
new crust is formed at divergent
boundaries, and
If new crust has the composition of ocean
crust – Basalt –
Where
does granite come from?
(Or, how come continental crust is made of granite?)
Can I get granite (or rhyolite)
rhyolite) by
rere-crystallizing basalt?
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I
have a piece of basalt
I melt it to make magma (basaltic magma)
Now I let it cool (rapidly)
What kind of rock will I end up with?
Think about this individually, then compare
your answer with your neighbor’
neighbor’s.
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To make a rock with a granite
composition (granite or rhyolite)
rhyolite) from a
basaltic magma, I need to change the
chemistry of the magma!
Gabbro &
Basalt
Granite &
Rhyolite
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A thought experiment
Silica
Granite (rhyolite
(rhyolite)) has
more silica than basalt
(and gabbro)
gabbro)
Basalt (and gabbro)
gabbro) has
more iron, calcium, and
magnesium than granite
(and rhyolite)
rhyolite)
Iron and
Magnesium
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I have a jar of jellybeans.
Half of the jellybeans are white, half are colored.
In case you are wondering, the white jellybeans represent
silica, the colored jellybeans represent other elements
(iron, magnesium, aluminum, etc.)
I periodically remove a handful of jellybeans from
the jar.
With each handful I remove a few more colored
jellybeans than white ones.
How will the proportion of white jellybeans change
over time?
Graph the proportion of white jellybeans with time.
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A jellybean graph
Proportion of White JB’s
A
B
50%
C
Time (Handfuls removed)
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Bowen’
Bowen’s Reaction Series and Crystal
Removal
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Olivine
SilicaSilica-Rich
Magma
Pyroxene
Amphibole
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How Different Igneous Rocks Form
Bowen’
Bowen’s reaction series
Magma crystallizes over a temperature range of
several hundred degrees
Therefore, minerals crystallize in a predictable
order
Last minerals to crystallize are very different in
composition from the earlier formed minerals
Bowen’
Bowen’s Reaction Series
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Figure 2.9
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Bowen’
Bowen’s Reaction Series & Jellybeans
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From an Earlier Question About Quartz
In groups: Speculate about how minerals
might get separated from magma in
nature?
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Separation of Minerals By Crystal Settling
Figure 2.9
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Crystal Settling
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