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Transcript
Rocks: Materials of
the Solid Earth
Chapter 2
Earth Science, 6e
Modified by Dr. Kane
What is a Rock?
How would you define a rock and a
mineral?
What types of Rocks are there?
Igneous Rocks: from magma or lava
Origin: igneous activity
• Example: granite or basalt
Sedimentary rocks: from sediments
Origin: weathering and erosion
Example: sandstone or clay
Metamorphic rocks: from stress
Origin: mountain building
Example: gneiss or marble
The rock cycle (page 45)
PART – I: IGNEOUS ROCKS
FEEDBACK:
From what process igneous rocks from?
Origin of Magma (page 228)
Magma forms at three major geological
settings:
• Divergent (mid ocean ridge)
• Convergent (subduction zone)
• Intra plate (hotspot)
Origin of Magma (page 148)
Mid Ocean Ridge (divergent)
Subduction Zone (Convergent)
Causes of Magma Formation
Decompression Melting (opening a bottle of soda)
Factors influencing magma formation:
1. Heat Increase
2. Reduction of confining Pressure
3. Increase in volatiles (gases)
Types of Igneous rocks
 Magma cools and crystallizes
Inside the crust → Plutonic or Intrusive rocks
Lava cools and crystallizes
Outside the crust → volcanic or extrusive rocks
Classification of Igneous rocks
 When identifying Igneous rocks look
for:
1. Grain Size (TEXTURE)
and
2. Rock color (CHEMICAL COMPOSITION)
Rate of Cooling and Crystal Size
• Texture is size and arrangement of crystals
• Crystal size is determined by the rate and
depth of cooling of magma/lava
• Slow rate forms large crystals
• Fast rate forms microscopic crystals
• Very fast rate forms glass
Feedback:
The slower the rate
of cooling, the
smaller / larger the
crystals?
Types of Textures
Phaneritic: Coarse grain/slow cooling rate
Example: Granite or Diorite
Aphanitic: Fine grain/fast cooling rate
Example: basalt or rhyolite
Glassy: glasslike/very fast cooling rate
Example: Obsidian (volcanic rock)
Types of Textures
Porphyritic: Slow then rapid cooling
Example: porphyry basalt, porphyry granite
Vesicular: Full of holes due to gases
Example: Vesicular basalt, scoria, and pumice
Pyroclastic: Angular volcanic fragments
cemented by ash from violent eruptions
Example: tuff
Photomicrograph
Photomicrograph
What’s the texture?
What’s the texture?
What’s the texture?
What’s the texture?
What’s the texture?
Chemical Classification of Igneous
rocks
• Bowen's reaction series (page 53):
• Minerals form in a systematic order
through
Discontinuous series (Olivine to Quartz) and
Continuous series (Feldspars series)
• Magmatic Differentiation
First to form settle at the bottom
Feedback
• Which mineral crystallizes
first?
• Which mineral crystallizes last?
Question
• Can Olivine and Quartz be
found together in the same
rock?
• Why? …
Naming Igneous rocks
Granitic or Felsic rocks
• Light-colored rocks
• Rich in silica/poor in Fe and Mg
• Form from melting of continental crust
• Common rock is Granite (intrusive) or Rhyolite
(volcanic)
Naming Igneous rocks
Basaltic or Mafic/ultramafic Rocks
• Dark Rocks
• Rich in Fe and Mg/poor in silica
• Originate mostly from the oceanic crust at midocean ridge, and the upper mantle
• Common rock is Basalt (volcanic) or Gabbro
(plutonic)
Texture? Mafic or Felsic?
Texture? Mafic or
Felsic?
Naming Igneous rocks
Intermediate or Andesitic Rocks
• Mineral and chemical composition are average of felsic and
mafic rocks
• Has dark minerals (pyroxene, amphibole, and mica) and light
minerals (feldspar and quartz)
• Silica content: 50%<SiO2 <60%
• Common rock is Andesite (volcanic) or Diorite (intrusive)
• Found mostly at Suduction Zone
Naming Igneous Rocks
 Ultramafic Rocks
• Dark rocks
• Very poor in silica: SiO2 <45%
• Originates from lower mantle and is found in oceanic floor at
mid-ocean ridge along mafic rocks
• Typical rock is peridotite (intrusive) or Komatiite (volcanic)
Classification of igneous rocks
PART – II: Sedimentary rocks
FEEDBACK
From what geological process sedimentary
rocks form?
Weathering
Two kinds of weathering
1. Mechanical weathering
• Breaking of rocks into smaller pieces
• Processes of mechanical weathering
• Frost wedging (freezing and thawing/exfoliation)
• Unloading (exposure to surface)
• Biological activity (burrow animals)
Frost wedging (page 55)
Joint-controlled weathering
in igneous rocks
Unloading and exfoliation
of igneous rocks
Weathering
Two kinds of weathering
2. Chemical weathering
• Alters the internal structures of minerals by
removing or adding elements
• Most important agent is water
• Oxygen dissolved in water oxidizes materials
• Carbon dioxide (CO2) dissolved in water forms
carbonic acid and alters the material
Factors of weathering
Important factors
• Climate (heat and moisture)
• Chemical weathering is most effective in areas of
warm temperatures and abundant moisture
Chemical Weathering
Weathering of granite minerals
• Weathering of potassium feldspar produces clay
Sedimentary Rocks
Lithification:
1.Compaction of loose sediment through
confining pressure of overlying rocks
2.Cementation of loose sediment by
• Calcite
• Silica
• Iron Oxide
Classifying sedimentary rocks
•
Two groups based on the source of the
material
1. Detrital rocks (Residual solid material)
• Common rocks include
• Shale (fine grained)
• Sandstone (medium grained)
• Conglomerate (Coarse grained)
Classification of
sedimentary rocks (page 59)
Shale with plant fossils
Sandstone
Conglomerate
Classifying sedimentary Rocks
2. Chemical Sedimentary rocks
• Derived from material that was
once in solution and
precipitates to form sediment.
Two groups:
A – Chemical Organic Rocks
 From biochemical processes; the
most common sedimentary rocks:
Example: Limestone is the most
abundant chemical rock .
• Coal: from plants-peat-bituminous
coal-lignite-anthracite
Fossiliferous limestone
B - Chemical Inorganic rocks
Chemical Sedimentary Rocks
From precipitating solutions
• Evaporites: Salt or gypsum rocks,
• Through increase in concentration:
Hematite, chert, flint, jasper, or agate
Rock salt
Features of Sedimentary rocks
Features of sedimentary rocks
• Strata, or beds (most characteristic)
• Bedding planes separate stratas
• Fossils
•
•
•
•
•
Are traces or remains of prehistoric life
Are the most important inclusions
Help determine past environments
Are used to determine age of sedimentary rocks
Are used for rock correlation
PART – III: Metamorphic Rocks
FEEDBACK:
• What process forms metamorphic rocks?
• Where would you expect to find
metamorphic rocks?
• Florida or Georgia? Why?
Metamorphic rocks
Are changed from other rocks, including
other metamorphic rocks
• “Every metamorphic rock has a parent rock “
Metamorphism occurs between 200C – 800C at
several kms depth
Causes and Types of
metamorphism?
Heat from magma → Contact metamorphism
 Pressure (stress) → Regional metamorphism
• Confining pressure: from burial
• Differential stress: during mountain building
• Chemically active fluids
• Water and other volatiles (Hydrothermal fluids)
Types of pressure (stress) in
metamorphism
Metamorphic Grades
Degrees of metamorphism
• Low-grade (where shale becomes slate)
• Medium-grade (where granite becomes gneiss)
• High-grade (rock partially melts → migmatite)
Metamorphic Textures
 Nonfoliated from contact metamorphism
Typical rocks: Marble and Quartzite
Resembles a coarse-grained igneous rock
Is localized around intrusion
Marble – a Nonfoliated
metamorphic rock
Development of foliation due
to directed pressure
Gneiss typically displays
a banded appearance
Classification of
metamorphic rocks
Resources from rocks
and minerals
Nonmetallic mineral resources
• Make use of the material’s
• Nonmetallic elements
• Physical or chemical properties
• Two broad groups
• Building materials (e.g., limestone, gypsum)
• Industrial minerals (e.g., fluorite, corundum, sylvite)
End of Chapter 3
1 - The Texture of an igneous
rock is
a.
b.
c.
d.
e.
Shape of the crystals
Size and arrangement of crystals
How hard of soft the rock feels
All of the above
I have no idea
2 – Texture of igneous rocks is
determined by
a.
b.
c.
d.
e.
Pressure and temperature
Amount of sulfur in the magma
Rate of cooling of magma
Depth of cooling of magma
c and d only
3 - The slower the rate of
cooling,
the …
a. Smaller the crystals of the rock
formed
b. Larger the crystals
c. No relation whatsoever
4 - Which terms characterize a
basalt?
a.
b.
c.
d.
Felsic/Light colored/silica rich
Mafic/dark colored/silica poor
Felsic/dark colored/silica rich
Mafic/light colored/silica poor
5 - Name the volcanic rock (s)
a. Granite
b. Basalt
c. Rhyolite
d. Gabbro
e. b and c
6 - Is this rock:
a: Plutonic? Or b: Volcanic?
7 – Porphyritic-aphanitic is
what type of rock?
a. Plutonic with two rates of
cooling
b. Volcanic with two rates of
cooling
c. None of these
8 – Where to find a basaltic
magma?
a.
b.
c.
d.
e.
On the continental crust mainly
On the Oceanic crust
At the mid-ocean ridge
At subduction zone
b and c
9 –Which texture indicates a
magma rich in gases?
a.
b.
c.
d.
e.
Phaneritic
Aphanitic
Porphyritic
Pyroclastic
None of these
10 –Which texture indicates two
rates of cooling?
a.
b.
c.
d.
e.
Phaneritic
Aphanitic
Vesicular
Pyroclastic
None of these
11 – Where to find a felsic
magma?
a.
b.
c.
d.
At mid ocean ridge
On the ocean floor
On the continental crust
At subduction zone
12 –Which term means finegrained texture?
a.
b.
c.
d.
e.
Aphanitic
Phaneritic
Porphyritic
Vesicular
None of these
13 - Texture?
a: Glassy Or b: Pophyritic
14 - Which texture means all
coarse-grained rock?
a.
b.
c.
d.
e.
Aphanitic
Porphyritic
Phaneritic
Glassy
Vesicular
16 - Quartzite is what type of
metamorphic rock?
a. Regional metamorphism
b. Contact metamorphism
c. Not a metamorphic rock
81
17 – In what type of metamorphism
do pressure and temperature work
together?
a.
b.
c.
d.
Contact metamorphism
Regional metamorphism
All of the above
None of the above
82
18 - What is the parent rock of
limestone?
a.
b.
c.
d.
e.
Quartzite
Granite
Marble
Basalt
This does not make sense
83
19 – Which one of these is a foliated
metamorphic rock?
a.
b.
c.
d.
e.
Marble
Granite
Mica-schist
Basalt
Shale
84
20 -What type of weathering is
frost wedging?
a. Chemical weathering
b. Mechanical weathering
c. Soil sampling
d. a and b
e. None of the above
21- What type of weathering is oxydation?
a. Chemical weathering
b. Mechanical weathering
c. Soil sampling
d. a and b
e. None of the above
22 - Exfoliation results from
a. Frost wedging
b. Oxidation
c. Unloading
d. Thermal expansion
e. None of the above
23 - Which one is the metamorphic
rock?
Do not take
a. SANDSTONE for
b. GRANITE (granted)!
Have a
c. GNEISS (nice) day!
88
THE END
THAT’S ALL FOLKS!
THANK YOU!!!