Download Plate Tectonics

10/9/2008
Understanding Earth
Fifth Edition
Grotzinger • Jordan • Press • Siever
Chapter 2:
PLATE TECTONICS
Lecturer: H Mohammadzadeh
Assistant professors,
Department of Geology, FUM
Copyright © 2007 by W. H. Freeman and Company
Chapter 2
Plate
Tectonics
1
10/9/2008
About Plate Tectonics
• It is the movement of plates and the
forces acting between them.
• It explains the distribution of volcanoes,
earthquakes, folded mountain chains, rock
assemblages, and seafloor structures.
• The forces that drive plate motions arise
from the mantle convection system.
Lecture Outline
1. Evolution of the theory of plate tectonics
2. Mosaic of the Earth’s crustal plates
3. Rates and history of plate motion
4. Mantle convection: the engine of plate
tectonics
2
10/9/2008
1. Evolution of the theory
Continental
drift
• fit of continents “jigsaw puzzle”
• similarity of rock assemblages
and ages across oceans
1. Evolution of the theory
Continental
drift
distribution of
certain fossils
3
10/9/2008
1. Evolution of the theory
Seafloor
spreading
geological
activity in midmidocean ridges
1. Evolution of the theory
Seafloor
spreading
new crust
formed there
4
10/9/2008
2. The mosaic of Earth’s crustal plates
• mosaic of rigid plates
• three types of boundaries
(divergent,, convergent, transform)
(divergent
2. The mosaic of Earth’s crustal plates
● next: a detailed look at the above
5
10/9/2008
1. Divergent Boundaries
(a) Oceanic plate separation
rifting, volcanoes, and earthquakes
MidMidAtlantic
Ridge
1. Divergent Boundaries
(b) Continental plate separation
rift valleys, volcanoes, and earthquakes
East African
Rift Valley
6
10/9/2008
2. Convergent Boundaries
(a) OceanOcean-ocean convergence
oceanic trench, volcanic island arc, and deep earthquakes
Mariana Islands
Marianas Trench
2. Convergent Boundaries
(b) OceanOcean-continent convergence
volcanic mountain chain, folded mountains, and
deep earthquakes
Andes
Mountains
Peru--Chile Trench
Peru
South
American
Plate
7
10/9/2008
2. Convergent Boundaries
(c) ContinentContinent-continent convergence
crustal thickening, folded
mountains, and earthquakes
Himalayan
Mountains
Tibetan
Plateau
subduction
Eurasian
Plate
3. TransformTransform-Fault Boundaries
(a) MidMid-ocean ridge transform fault
lateral (transform) faults and earthquakes
8
10/9/2008
3. TransformTransform-Fault Boundaries
(b) Continental transform fault
lateral (transform) fault and earthquakes
3. Rates and history of plate motion
Magnetic
anomalies
seafloor areas
of high and
low magnetic
values
9
10/9/2008
3. Rates and history of plate motion
● sea floor as a magnetic tape recorder
3. Rates and history of plate motion
5.0 Ma
4.0
Gilbert
reversed chron
3.0
Gauss
normal chron
2.0
1.0
Matuyama
reversed chron
Present
Brunhes
normal chron
● magnetic time scale developed
10
10/9/2008
3. Rates and history of plate motion
● magnetic isochrons on the sea floor
3. Rates and history of plate motion
● velocity of seafloor spreading = d / t
11
10/9/2008
3. Rates and history of plate motion
● example area: midmid-ocean ridge,
south of Iceland
Velocity = 60 km / 3.3 mil. yr. =
18 km / mil. yr. (or 18 mm / yr)
3. Rates and history of plate motion
Example relative plate velocities:
East Pacific Rise (Pacific and Nazca plates) –
138 to 150 mm/yr
South Atlantic (Mid(Mid-Atlantic Ridge) –
34 to 35 mm/yr
Southern Ocean, south of Australia –
70 to 75 mm/yr
Southern Ocean, south of Africa –
14 mm/yr
12
10/9/2008
3. Rates and history of plate motion
Reconstructing the history of plate motions:
1. Assembly and breakup of the
supercontinent Rodinia
2. Assembly and breakup of the
supercontinent Pangaea
3. Rates and history of plate motion
The Earth’s geography one billion years
ago. Let’s see continental motion!
13
10/9/2008
ASSEMBLY OF RODINIA
Late Proterozoic
Formed about 1.1 billion years
ago; began to break up about 750
million years ago
ASSEMBLY OF PANGAEA
Late Proterozoic
The distribution of
continents and
oceans between
Rodinia and the
assembly of
Pangaea
Middle Ordovician
The distribution
of continents
and oceans
about 458
million years
ago
14
10/9/2008
ASSEMBLY OF PANGAEA
Early Devonian
The distribution
of continents and
oceans about 390
million years ago
Early Triassic
The distribution of
continents and
oceans about 237
million years ago;
Pangaea is formed
BREAKUP OF PANGAEA
Early Jurassic
The breakup of the
supercontinent
about 195 million
years ago;
Pangaea is being
rifted
Late Jurassic
The distribution
of continents
and oceans
about 152
million years
ago
15
10/9/2008
BREAKUP OF PANGAEA
Late CretaceousEarly Tertiary
The distribution of
continents and
oceans about 65
million years ago;
much like today in
some ways
PRESENT DAY
The distribution
of continents
and oceans as
we know them
today
4. Mantle convection: the engine of
plate tectonics
Upper
mantle
● theory 1:
whole mantle
convection
700 km
Lower
mantle
2900 km
Outer core
16
10/9/2008
4. Mantle convection: the engine of
plate tectonics
● theory 2:
stratified
convection
Boundary near
700 km separates
the two different
convection
systems
4. Mantle convection: the engine of
plate tectonics
spreading
centers
and hot
spots
17
10/9/2008
Thought questions for this chapter
1. What is the theory of plate tectonics?
2. What are some of the geologic characteristics of plate
boundaries?
3. How can the age of the seafloor be determined?
4. What is the engine that drives plate tectonics?
Key terms and concepts
Continental drift
Geodesy
Island arc
Isochron
Magnetic anomaly
Magnetic time scale
Pangaea
Plate tectonics
Relative plate velocity
Rodinia
Seafloor spreading
Spreading center
Subduction
Transform fault
18