rocks: materials of the solid earth chapter 2 earth science, 6e modified by dr. kane
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 lavaOrigin: igneous activity
• Example: granite or basalt
Sedimentary rocks: from sedimentsOrigin: weathering and erosionExample: sandstone or clay
Metamorphic rocks: from stressOrigin: mountain buildingExample: gneiss or marble
The rock cycle (page 45)
PART – I: IGNEOUS ROCKS
FEEDBACK:
From what process igneous rocks from?
Plate Margins
• Divergent: Plates pull apart
Example: Mid ocean ridge; Rift
• Convergent: Plate come together– Ocean – Continent; Ex: Cascades, Andes– Ocean – Ocean; Ex: Japan, Caribbean– Continent – Continent; Himalaya
• Transform Fault: Plates slide
Origin of Magma (page 228)
Magma forms at three major geological settings:
• Divergent (Ex: Mid ocean ridge)
• Convergent (Ex: Cascades volcanoes)
• Intra plate Not a plate margin (Ex: Hawaii, Hot spot)
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 Increase2. Reduction of confining Pressure
Role of 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 DioriteAphanitic: Fine grain/fast cooling rate
Example: basalt or rhyoliteGlassy: glasslike/very fast cooling rate
Example: Obsidian (volcanic rock)
Types of Textures
Porphyritic: Slow then rapid coolingExample: 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?
Obsidian Aztec
Temple Mayor, Mexico
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 mid-
ocean 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 (round coarse grained)
• or Breccia (sharp coarse grain)
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 RocksFrom 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. Shape of the crystals
b. Size and arrangement of crystals
c. How hard of soft the rock feels
d. All of the above
e. I have no idea
2 – Texture of igneous rocks is determined by
a. Pressure and temperature
b. Amount of sulfur in the magma
c. Rate of cooling of magma
d. Depth of cooling of magma
e. 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. Felsic/Light colored/silica rich
b. Mafic/dark colored/silica poor
c. Felsic/dark colored/silica rich
d. Mafic/light colored/silica poor
5 - Name the volcanic rock (s)
a. Graniteb. Basaltc. Rhyolited. Gabbroe. 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. On the continental crust mainly
b. On the Oceanic crust
c. At the mid-ocean ridge
d. At subduction zone
e. b and c
9 –Which texture indicates a magma rich in gases?
a. Phaneritic
b. Aphanitic
c. Porphyritic
d. Pyroclastic
e. None of these
10 –Which texture indicates two rates of cooling?
a. Phaneritic
b. Aphanitic
c. Vesicular
d. Pyroclastic
e. None of these
11 – Where to find a felsic magma?
a. At mid ocean ridge
b. On the ocean floor
c. On the continental crust
d. At subduction zone
12 –Which term means fine-grained texture?
a. Aphanitic
b. Phaneritic
c. Porphyritic
d. Vesicular
e. None of these
13 - Texture?a: Glassy Or b: Pophyritic
14 - Which texture means all coarse-grained rock?
a. Aphanitic
b. Porphyritic
c. Phaneritic
d. Glassy
e. Vesicular
84
16 - Quartzite is what type of metamorphic rock?
a. Regional metamorphism
b. Contact metamorphism
c. Not a metamorphic rock
85
17 – In what type of metamorphism do pressure and temperature work
together?
a. Contact metamorphism
b. Regional metamorphism
c. All of the above
d. None of the above
86
18 - What is the parent rock of limestone?
a. Quartzite
b. Granite
c. Marble
d. Basalt
e. This does not make sense
87
19 – Which one of these is a foliated metamorphic rock?
a. Marble
b. Granite
c. Mica-schist
d. Basalt
e. Shale
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
a. Chemical weathering
b. Mechanical weathering
c. Soil sampling
d. a and b
e. None of the above
What type of weathering is oxidation?
22 - Exfoliation results from
a. Frost wedging
b. Oxidation
c. Unloading
d. Thermal expansion
e. None of the above
91
23 - Which one is the metamorphic rock?
Do not take
a. SANDSTONE for
b. GRANITE (granted)!
Have a
c. GNEISS (nice) day!
THE END
THAT’S ALL FOLKS!
THANK YOU!!!