Transcript Class5-RxCycle

Quiz Question
• Do you expect that the earthquake in
Hawaii was:
– Tensionsal (pull-apart movement)
– Compressional (push-together movement)
– Shear (moving-past movement)
• Given the geologic setting of Hawaii, why
do you expect this?
Where does continental crust
come from?
Continental Crust
What defines a specific mineral?
Crystal structure and Chemical Composition
Mineral Name
Chemical Composition
Crystal structure
Quartz
SiO2
Al2O3
C
C
Framework Silicate
Corundum
Diamond
Graphite
3-D framework
Sheets
The Silicate Minerals
Basic Building Block
Silicate ion: SiO4-4
One Si surrounded by 4 O in
a tetrahedron. Can be
combined in different ways:
•Isolated tetrahedra
•Chains
•Sheets
•3-D Framework
Isolated
Chains
Tetrahedra
Sheets
Framework
Silicates
In framework silicates, every
O is shared with two Si
tetrahedra:
Quartz: SiO2
Rocks, some context
• What is a rock?
– A coherent, natural, aggregate of minerals (or
glass)
• Types of rocks
– Igneous - formed from melt
– Sedimentary - formed by surface processes
– Metamorphic - formed by transforming other
rocks
Let there be… magma
• Where is magma formed? In the
lithosphere
Plate
Boundaries
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At subduction zones (addition of water)
At midocean ridges (decompression)
At rifts (decompression)
At hot spots (decompression)
In next to other magma (contact)
Solid material rises
Pressure decreases
Decompression melting
Surface
Hot Spot Vulcanism
Addition of volatiles
(water and CO2)
Contact Melting
Where are Igneous Rocks
Formed?
Intrusive (Plutonic) vs. Extrusive
(Volcanic) Rocks
What is a Metamorphic Rock
• Metamorphic rocks are formed by
metamorphism of other rocks
– Changes in physical, chemical, and
mineralogical characteristics
– In Solid State
Metamorphism
• What causes rocks to metamorphose?
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Heat (different mineral stability, faster reactions)
Hot water (addition/removal of elements)
Confining Pressure (different mineral stability)
Directional forces due to deformation
Kinds of Metamorphism
• Contact Metamorphism with hot rocks
Kinds of Metamorphism
• Burial Metamorphism of Sediments
(think isostacy! And then think geotherm!)
Kinds of Metamorphism
• Regional Metamorphism from mountain building
Where do Metamorphic Rocks
Form?
Weathering
• The conversion of solid rock to smaller
pieces or other (non-rock-forming) minerals
• Physical v. Chemical weathering (they work
together!)
Physical weathering
• … the process whereby large rocks are
broken into smaller rocks.
• Many different processes
Chemical Weathering
• Dissolution = dissolving salt in water
• Hydrolysis
2 KAlSi3O8 + 2 H2CO3 + H2O 
Al2Si2O5(OH)4 + 4SiO2 + 2K+ + 2HCO3• Oxidation (where does the Fe+2 come from?)
4 Fe+2 + 3 O2  2 (Fe+3)2O3
• The role of organisms
Transport (erosion)
• What transports sediments?
– Water, primarily
– Wind
• Why?
– Ultimately, for water: gravity
Sedimentary Rocks
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Sediments: layers of loose particles that originate from the weathering of the
continents (solid debris or dissolved substances)
Sedimentary Rocks: Rocks formed from sediments by the process of
lithification.
Two types
– Clastic Sediments
– Chemical and Biochemical Sediments
Requirements
– Weathering
– Erosion
– Deposition
– Lithification
Sedimentary Environments
Principal of Original Horizontality
and the
The Law of Superposition
Sediments (and sedimentary rocks) record conditions on the
(local) earth’s surface at the time they were formed.
1000 mya
600 mya
600-240 mya
420 mya
370 mya
270 mya
180 mya