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Plate Tectonics and Earthquakes
Natural Disasters, 5th edition, Chapter 3
Plate Tectonics
I.
II.
III.
IV.
The Discovery of Plate Tectonics
The Mosaic of Plates
Rates and History of Motion
Mantle Convection
I. Discovery of Plate
Tectonics
A. Continental Drift
B. Seafloor Spreading
A. Continental Drift
1. Continental drift:
large-scale
movements of
continents
A. Continental Drift
(continued)
2. Support
a. Puzzle fit
1. Suess (1900)Gondwana
2. Wegner (1915)Pangea
A. Continental Drift
(continued)
b. Similar rock ages
c. Similar geologic
structures
d. Fossil Evidence
e. Climate Evidence
B. Seafloor Spreading
1. Convection currents
move plates around
2. Mantle source
3. Post-WWII: MidAtlantic Ridge
4. Hess & Dietz
(1960’s) propose
new and recycled
seafloor
II. The Mosaic of Plates
A. Lithospheric Plates
B. Divergent
Boundaries
C. Convergent
Boundaries
D. Transform-Fault
Boundaries
A. Lithospheric Plates
1. Mosaic of large
moving plates
2. Geologic activities
occur at plate
boundaries
a.
b.
c.
d.
e.
Earthquakes
Volcanoes
Rifts
Folding
Faulting
B. Divergent Boundaries
1. Narrow rifts
2. Continental plate
separation
3. Oceanic plate
separationspreading centers
Divergent Boundaries
Oceanic Plate Separation
MidAtlantic
Ridge
Divergent Boundaries
Oceanic Plate Separation
Volcanoes and earthquakes concentrate.
MidAtlantic
Ridge
Divergent Boundaries
Continental Plate Separation
East African
Rift Valley
Divergent Boundaries
Continental Plate Separation
Parallel valleys; volcanoes and earthquakes.
East African
Rift Valley
C. Convergent Boundaries
1. Conservation of
Earth’s surface area
2. Ocean-ocean
convergence
3. Ocean-continent
convergence
4. Continent-continent
convergence
Convergent Boundaries
Ocean-Ocean Convergence
Mariana Islands
Marianas Trench
Convergent Boundaries
Ocean-Ocean Convergence
Deep-sea trench; volcanic island arc.
Mariana Islands
Marianas Trench
Convergent Boundaries
Ocean-Continent Convergence
Andes
Mountains
Peru-Chile Trench
South
American
Plate
Convergent Boundaries
Ocean-Continent Convergence
A volcanic belt of
mountains forms.
Andes
Mountains
Peru-Chile Trench
South
American
Plate
Convergent Boundaries
Continent-Continent Convergence
Himalaya
Tibetan
Plateau
Main
thrust
fault
Eurasian
Plate
Convergent Boundaries
Continent-Continent Convergence
Crust crumbles, creating high
mountains and a wide plateau.
Himalaya
Tibetan
Plateau
Main
thrust
fault
Eurasian
Plate
D. Transform-Fault
Boundaries
1. Plates slide past one
another
2. Fracture with relative
displacement
Transform-Fault Boundaries
Mid-Ocean Ridge Transform Fault
Transform-Fault Boundaries
Mid-Ocean Ridge Transform Fault
Spreading centers offset.
Transform-Fault Boundaries
Continental Transform Fault
Transform-Fault Boundaries
Continental Transform Fault
Offset continental crust.
As plates
move past
each other...
As plates
move past
each other...
…creek beds
are offset
As plates
move past
each other...
…creek beds
are offset
San
Francisco
Los Angeles
III. Rates and History of
Motion
A. Seafloor Magnetic
Tape Recorder
B. Geodesy
A. Seafloor Magnetic Tape Recorder
1. Magnetic reversals
a. Switching strength to
the south
b. Preserved in lava
c. Age can be dated
d. Magnetic chrons- ½
million years
e. Magnetic subchrons
– 200 000 years
Magnetic anomalies also in volcanic lava.
Magnetic anomalies also in volcanic lava.
Normal
Reversed
Magnetic anomalies also in volcanic lava.
Earth’s magnetic field
reverses direction.
Normal
Reversed
Layers “remember”.
Older layers preserve
their direction.
Scientists constructed
a magnetic time scale.
Subchrons
5.0 Ma
4.0
Gilbert
reversed chron
3.0
Gauss
normal chron
2.0
1.0
Matuyama
reversed chron
Present
Brunhes
normal chron
Mid-ocean ridge
Million years ago (Ma)
4.0
3.0
2.0
Ocean
crust today
A. Seafloor Magnetic Tape Recorder (continued)
2. Magnetic anomaly
a. Normal-positive
anomaly
b. Reverse-negative
anomaly
3. Seafloor ages
a. Speed = distance /
time
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic
Ridge southwest of Iceland, showed an oscillating pattern of
magnetic field strength. This figure illustrates how scientists worked
out the explanation of this pattern.
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic
Ridge southwest of Iceland, showed an oscillating pattern of
magnetic field strength. This figure illustrates how scientists worked
out the explanation of this pattern.
A sensitive magnetometer
records magnetic anomalies,…
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic
Ridge southwest of Iceland, showed an oscillating pattern of
magnetic field strength. This figure illustrates how scientists worked
out the explanation of this pattern.
A sensitive magnetometer
records magnetic anomalies,…
Iceland
MidAtlantic
Ridge
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic
Ridge southwest of Iceland, showed an oscillating pattern of
magnetic field strength. This figure illustrates how scientists worked
out the explanation of this pattern.
A sensitive magnetometer
records magnetic anomalies,…
…alternating bands of high
and low magnetism.
Iceland
MidAtlantic
Ridge
Symmetrical bands on both sides.
Why?
B. Geodesy
1. Astronomical
Positioning
a. Position with respect
to fixed stars
b. 100 m error
2. Global Positioning
a. 24 Earth-orbiting
satellites
b. Measure plate
movement
IV. Mantle Convection
A. Driving Forces
B. Plate Recycling
C. Convection Currents
A. Driving Forces
1. Mantle convection
2. Gravitational pull
B. Plate Recyling
1. New lithosphereridges
2. Old lithospheresubduction
3. Recycling within
upper and lower
mantle-seismic
waves
Whole-mantle convection
Mantle
Outer core
Inner core
Upper
mantle
700 km
Lower
mantle
2900 km
Outer core
Whole-mantle convection
Upper
mantle
700 km
Lower
mantle
2900 km
Outer core
Stratified convection
Boundary near
700 km separates
the two convection
systems.
C. Convection Currents
1. Movement of
lithospheric plates
2. Mantle plumes
a. Hot spots
b. Deep mantle
Plate Tectonics
I.
II.
III.
IV.
The Discovery of Plate Tectonics
The Mosaic of Plates
Rates and History of Motion
Mantle Convection