Download Plate Tectonics

FI-6121 System Fisis Bumi
Lecturer: Dr. M.Edisar, MT
2011/10/21
Plate Tectonics
@ By Dr.Muhammad Edisar, MT
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Plate Tectonics
Without question, the theory of “plate tectonics” is the most important
advancement in earth sciences in the 20th century. It provides the
framework for earth processes that previously were known to exist, but
it was unknown why these activities occurred.
Because the portions of the earth's interior and differences between
continental and oceanic crust are an essential part of plate tectonics, it
is worth our while to review these concepts briefly:
Earth's crust (lithosphere) is composed of several elements crucial to our existence.
In order of their abundance, these eight (8) elements are:
1. Oxygen
2. Silicon
3. Aluminum
4. Iron
5. Calcium
6. Sodium
7. Potassium
8. Magnesium
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The Upper Mantle and Crust
• Crust (5 mi for ocean,
25 mi for continents)
• Dense iron-rich basalts
(mafic) make up ocean
floor  Fe, Silica,
magnesium
• Silica- rich rock makes
up the continents (felsic)
 Silica, aluminum
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The Earth’s Interior
• General trends: temperature, density
• Horizon composition, behavior
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Distance: 6730 km (3963 miles)
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What is ‘tectonics’?
• From Greek ‘tektonikus’
meaning building or construction
• Plate tectonics refers to the process of plate
formation, movement, and destruction.
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What is a ‘Plate?’
• Lithospheric plate: crust + upper mantle
• Asthenosphere: plastic mantle
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Lithosphere and the solid earth: the solid earth lies beneath the atmosphere and
the oceans and composes 29% of the earth's surface. It is divided into
several distinct units or layers:
a.
Lithosphere or crust: two (2) types of crust: oceanic and continental with
basic differences
*Oceanic crust is thinner and denser and usually darker in color
*Continental crust is lighter in weight, less dense, light in color, and tends to float
over oceanic crust
b. Mantle: beneath the crust; houses molten rock material called magma
c.
Outer core: composed of liquid iron and nickel; very dense material
d.
Inner core: composed of solid iron and nickel; extremely dense material
The upper mantle and lower crust (lithosphere) are referred to as the
asthenosphere.
*There is a distinct seismic discontinuity where seismic waves slow down
considerably due to the composition of molten rock. This is located in the
asthenosphere and is referred to as the Mohorovicic Discontinuity, after the
Russian scientist who discovered it. We refer to it as the "Moho".
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History of Events Leading up to the Formulation of the
Theory of Plate Tectonics
*Note that plate tectonics is a theory. It is not something that we can directly
sample or touch, or for that matter prove. That is why we will refer to it as
a theory.
*In 1915, a Bavarian scientist named Alfred Wegener (later referred to as the
"Father of Plate Tectonics") noticed, while working near the North Pole,
that his compass needle did not point to where north "should" have been. In
other words, true north and magnetic north were in two separate localities.
Wegener theorized that the poles (both North and South) were
"wandering" with time. He called this "Polar Wandering".
*Subsequent to his theory, he began to also notice how continents fit together
like a jigsaw puzzle…most notably the western coast of Africa and the
eastern coast of South America. In addition, rocks from these localities
were the same rock type, same age, and contained the same age and type of
fossils. His revised theory became known as "Continental Drift", because he
realized that it was not the poles that shifted, but the continents
themselves.
*Wegener died of a heart attack on a voyage studying glaciers near the North
Pole in early 1930 and his work was virtually forgotten for several decades.
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History of Plate Tectonics
• ‘Fit’ of coastlines recognized early
– Sir Francis Bacon (1600s)
• No mechanism for motion
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• 1915 Alfred Wegener
proposes theory of
continental drift.
• Supercontinent Pangaea (‘all-earth’) [225mya].
• Fragmentation and drift to current positions.
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Correlation of Africa and South America by Wegener
Evidence used by Wegener:
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1.
Shape of continents fit like a jigsaw puzzle.
2.
Similar fossils on both continents
3.
Mountain belts line up
4.
@ By
Dr.Muhammad
Mineral
belts
line up Edisar, MT
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Further evidence used by Wegener
to support continental drift
hypothesis:
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1.
Mountains line up in Northern
Hemisphere
2.
North America, Europe, South
America, and Africa all fit
together.
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Explanation by
Wegener that
present-day Africa,
South America, India,
and Australia were all
once glaciated.
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Plate
Movement
History
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• Wegner’s evidence
– Fit of continents
– Fossil plants, animals, rock types / geology
• match on opposite shores
• deposits inconsistent with current geography
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Striking Match of Biological Regions
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Striking Match of Geologic
Regions
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*It was not until the advent of World War II that a technology (Echo
Sounding) developed to a degree that a stunning discovery was made by a
geologist and seaboat commander, Harry Hess. He noticed that rocks on
either side of a prominent geologic feature in the middle of the Atlantic
Ocean (called the mid-oceanic rift zone) were a perfect mirror image of
each other on either side of the rift zone. He theorized that the rift zone
was oozing out magma material from submarine volcanoes and that the
material spread laterally across either sides of the rift. As time
progressed, Hess took more and more samples to back up his findings, as
part of a series of drill voyages aboard the research vessel, Glomar
Challenger.
*Later in the 1960’s, Frederick Vine and Drummond Matthews, a Cambridge
University professor/student team, discovered the principles of magnetic
patterns on the ocean floor and went on the road to present their
discoveries. They published first in a rather obscure journal and then on
the lecture circuit at Scripps Oceanographic Institute. Further findings
revealed that not only did the stripes have the same age of rocks, but a
magnetic polarity image resulted as well, showing that during earth history
there have been several "magnetic reversals" (A time when the compass
needle would have pointed south instead of north).
*In the late 1960's and early 1970's, two scientists, revisited Wegener's
findings and combined them with Hess' discoveries to formulate a new
package called "Plate Tectonics". Robert Palmer and Donald Mackenzie are
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@ synthesizing
By Dr.Muhammad
Edisar,
MT of “plate tectonics”.
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credited with naming and
the
theory
History of Plate Tectonics
• Problem with continental drift?
– No sound mechanism for the ‘drift’!
– Wegner hypothesizes spin of earth or tides…..
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History of Plate Tectonics
• New theory for motion: Arthur Holmes (1930s)
– thermal convective cells in the upper mantle
(aesthenosphere)
– theory is largely ignored
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History of Plate Tectonics
• In the 1960s, Harry Hess and Robert Deitz
(geophysicists) propose sea floor spreading
along mid-oceanic ridges for plate motion.
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Echo Sounding Device Used By Hess
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Sea Floor Spreading
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The theory of plate tectonics is that rigid lithospheric plates move across the
surface of the earth. There are approximately 12 major and 8 minor plates
that move in concert with each other. Some pull apart, some push together
and some move horizontally against each other.
The plate motion is driven by one or more of the following mechanisms:
1. Convection -- heat transferred by movement of a fluid (magma)
2. Conduction -- heat transfer by touching plates
3. Push-Pull Slab -- heavy slabs pull plates downward and magma forced upward
pushes plates to the surface (upwelling)
*There are several geological processes that occur where plates meet (called
plate boundaries or margins):
1.
Volcanoes tend to erupt at plate margins as a result of a process called
subduction
2. Earthquakes occur where plates grind against or over one other
3. Mountain building occurs as one plate is pushed over another
4. Seafloor spreading occurs where two oceanic plates pull apart
There are three (3) major types of plate boundaries (margins):
1.
Convergent -- plates move towards each other (compression)
2. Divergent -- plates move away from each other (tension)
3. Transform -- plates horizontally grind against one another (strike-slip
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motion)
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Plate Tectonics Theory
• Continental Drift + Sea Floor Spreading
+ new data  Theory of Plate Tectonics
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Plate Tectonics Theory
• Plate boundaries: main location for
Earth’s
volcanic and earthquake activity. This is main
place where mountains are created.
• Type of plate boundary determines activity.
• 3 types
– diverging (spreading)
– converging (colliding)
– transform (sliding past each other)
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• Crustal Processes
– Destruction (subduction)
– Creation (volcanism )
– Alteration / deformation (folding and
faulting)
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Types of Plate Boundaries:
Divergent
Convergent
Transform
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Oceanic spreading center with convection of
magma occurring in the mantle.
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Convection Cell Development in Mantle
A. Volcanic Arc
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B. Oceanic Rift Zone
C. Transform Fault Zone
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Volcanic Zones Depicting Plate Boundaries
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Earthquake Zones in Relation to Plate Boundaries
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Subducting Plate
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“Hot Spot” Volcanism
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Geography of the Plates
• 7 major plates; several minor plates
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• Small plates / boundaries still unknown
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Plate Margins: how do we know?
• Marked by volcanic and tectonic activity
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*Plate boundaries can occur on landmasses (continents) or in marine settings (oceans) or
both at the same time.
Convergent plate movement is associated with the following:
a. Compression
b. Reverse faulting
c. Creation of a subduction zone
d. Mountain building processes
e. Collisions of plates:
–
–
–
1.
2.
3.
Continent vs. continent
Continent vs. oceanic
Oceanic vs. oceanic
Divergent plate boundaries are associated with the following:
•
a.
Tension or extension (pulling apart)
•
b.
Normal faulting
•
c.
Rifting (as in the mid-oceanic rift zone)
•
d.
Creation of magma material inside the rift zone
Transform boundaries are associated with the following:
•
a.
Horizontal grinding motion
•
b. Strike-slip faulting
•
c.
Lateral offset of rock units
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Divergent Plate Boundaries
• Landscape features:
– land: rift valleys,
volcanic mountains,
thinning crust
– ocean/sea: rift valleys,
mountain ranges
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Divergent Plate Boundaries
• Examples:
– Atlantic Mid-Oceanic
Ridge
– Red Sea
– Rift valleys of eastern
Africa
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Convergent Plate Boundaries
• Activity:
– subduction; shallow to deep earthquakes; volcanism
(continental)
• Features:
– ocean trench; explosive volcanic mtns on continental
margin
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Collision Zones:
Continent vs. Oceanic
Oceanic vs. Oceanic
Continental vs. Continental
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Continent vs. Oceanic Collision Zone
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Example of Continent vs. Continent Collision Zone: India vs. Asia
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Volcanic Zones (both continental and oceanic in origin) associated with Plate Tectonics
are located:
1.
a.
Subduction zones
Continent vs. ocean collision (ex.: Andes Mts., Pacific NW of U.S
Ocean vs. ocean collision (ex.: Japan, Philippines); Basaltic rocks
2. Rift Zones (Spreading centers) are located:
a.
Ocean - ocean divergent zones (ex.: mid-oceanic rift); Basaltic rocks
b.
Continental rift zone (ex.: East African Rift Zone); Granitic rocks
3. "Hot Spot" Volcanism is located:
a.
Oceanic; (ex.: Hawaiian Islands chain); Basaltic rocks
b.
Continental; (ex.: Yellowstone Nat. Park); Granitic/Andesitic rocks
Seismic (Earthquake) Zones associated with Plate Tectonics:
1.
Subducting oceanic plate; shallow focus as plate subducts
2.
Intermediate focus earthquakes; partial melting and rising of magma; in the
"Benioff Zone"
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3.
Deep focus as slab of crust is pulled by sheer gravity
East African Rift Zone
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1.
2.
Features/Landforms Associated with Plate Tectonics
1. Continent vs. Oceanic collision zone: subduction zone, deep sea
trench associated, volcanic arc, andesitic volcanic rock.
2. Continent vs. Continent collision zone: Granitic rocks, mountain
building processes, no volcanism, no magmatic activities.
3. Oceanic vs. Oceanic collision zone: deep sea trench associated,
volcanic island arc, basaltic volcanic rock.
4. Divergent zone: Oceanic, basaltic magma, spreading center (MidOcean Ridge). Also, Continental: granitic, (East African Rift Zone)
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Plate Tectonics Summary
Continental vs. Oceanic crust
Continental crust = lighter, thicker, less dense (Al, K, Si), Granitic
Oceanic crust = darker, thinner, denser (Fe, Mg, Ca) Basaltic
Layers of the Earth
Lithosphere/crust = outermost
Mantle houses magma (molten rock)
Outer core is liquid iron and nickel
Inner core is solid iron and nickel
Evolutionary history of Plate Tectonics Development
Alfred Wegener - polar wandering and continental drift (1912-1930)
Harry Hess - seafloor spreading (late 1950's and early 1960's)
Frederick Vine and Drummond Matthews - magnetic polarities, subduction (1960's)
Robert Palmer and Donald McKenzie - synthesizers of previous ideas, named "plate
tectonics"
Plate Dynamics
12-15 major lithospheric plates; includes both oceanic and continental crust
Three types of plate boundaries or margins:
Convergent: compression
Divergent: tension/extension
Transform: strike-slip horizontal motion
Occurrences/activities at plate boundaries
Earthquakes
Volcanoes
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Mountain building
Seafloor spreading
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Convergent Plate Boundaries
Continental vs. Oceanic crust: Cascade Mts. (Pacific NW) and Andes Mts. (Western S. America)
Subduction zone with deep sea trench
Volcanic arc with Andesitic volcanoes
Oceanic vs., Oceanic crust
Volcanic island arc with basaltic volcanoes
Deep sea trench with NO subduction zone
Continental vs. Continental crust
Granitic mountains but NO volcanoes
Strong earthquakes as in India vs. Asia collision
Divergent plate boundaries
Mid-oceanic ridge (rift zone) with basaltic pillow lava volcanoes
East African rift zone with granitic rock
Transform boundaries
Ridge-ridge faults - in oceanic setting
Strike-slip faults - continental setting (San Andreas Fault in California)
Earthquakes in convergent zones
Shallow focus near deep sea trench
Intermediate focus where oceanic plate melts (Benioff Zone)
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Deep focus - never deeper than 500 miles (700 km) plate completely melted
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Volcanoes
Andesitic - in subduction zones
Basaltic - ocean vs. ocean collision zones and mid-oceanic ridge
"Hot Spot" - Hawaiian Islands chain in ocean setting; Yellowstone National Park
in continental setting
Causes for Plate Movement
Convection -cells of magma (lava lamp type movement) - most probable cause
Conduction - transference of heat from one plate to another
Push-pull slab - especially at leading edge of subduction zones and mid-oceanic
ridges
Miscellaneous
Gondwanaland - S. America, Africa, Antarctica, and Australia bunched at S.
Pole 300+ million years ago
Pangaea: "Super continent" that split apart 200 million years ago;
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next "Pangaea" in 250 million years from now
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Key Terminology
Oceanic crust
Lithosphere
Mantle
Inner Core
Mohorovicic Discontinuity (Moho)
Continental Drift
Harry Hess
Echo Sounding
Glomar Challenger
Frederick Vine
Robert Palmer
Plate Tectonics
Conduction
Convergent
Transform
Subduction Zone
Volcanic Arc
“Hot Spot” Volcanism
Benioff Zone
Gondwanaland
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Continental crust
Asthenosphere
Magma
Outer Core
Polar Wandering
Alfred Wegener
Seafloor Spreading
Mid-Oceanic Ridge (Rift) Zone
Magnetic Reversal
Drummond Matthews
Donald MacKenzie
Convection
Push-Pull Slab
Divergent
Plate Boundary (Margin)
Deep Sea Trench
Volcanic Island Arc
Collision Zones
East African Rift Zone
Pangaea
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Pertinent Web Sites
Active Tectonics Web Server
The Active Tectonics Web Server was established to effectively disseminate ideas resulting from the Active Tectonics initiative.
American Geophysical Union (AGU)
For over 75 years, American Geophysical Union (AGU) researchers, teachers, and science administrators have dedicated themselves to
advancing the understanding of the Earth and its environment in space and making the results available to the public.
Ask a Geologist (USGS)
Have a geological question? Here is your chance to ask it.
Dynamic Earth Tutorial (USGS)
An excellent online, interactive plate tectonics tutorial from the United States Geological Survey.
Global Earth History
The Global Earth history site uses a series of plate-tectonic reconstructions to show the broad patterns of Phanerozoic Earth history.
Hawaii Undersea Geo-Observatory (HUGO)
The Hawaii Undersea Geo-Observatory (HUGO) is an automated submarine volcano observatory installed on the summit of the undersea
Loihi seamount and connected to the shore via fiber optic cable.
Hot Spot Activity (Geosphere)
An excellent interactive activity on hot spots from the University of Montana's Geosphere. With this activity learners study mantle convection
and utilize image processing techniques to determine sizes of geologic formations of Hawaii and Yellowstone National Park from
remote sensing data. (The site may be slow to connect, but its usually there.)
JOIDES Resolution Page
The JOIDES Resolution is the drillship of the Ocean Drilling Program.
Map of Plate Boundaries (NEIS)
Map of plate boundaries from the National Earthquake Information Center.
Marine Geology & Geophysics (NGDC)
The Marine Geology & Geophysics Division of the NOAA National Geophysical Data Center (NGDC) and the collocated World Data Center A
for Marine Geology and Geophysics (WDC-A for MGG) compiles and maintains extensive databases in both coastal and open ocean
areas.
Moving Plates Activity (Geosphere)
An excellent interactive activity on calculating plate motion from the University of Montana's Geosphere. With this activity learners use
numeric representations to identify the positions and perform absolute/relative plate motion calculations using Internet resources.
Nordic Volcanological Institute
This site contains the geology and tectonics of Iceland.
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Ocean Drilling Program
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The Ocean Drilling Program home page with links to related agencies and institutions.
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Ocean Floor Ages Map
A great global map illustrating ocean floor ages from NOAA.
Ocean Floor Animations
A good visualization of the Pacific hemisphere plate tectonic history.
Ocean Floor Datasets
Ocean floor data and images from Columbia University.
Paleomap
This Web site illustrates plate tectonics development of the ocean basins and continents, including projections for the future.
Plate Motion Calculator
An interactive plate motion calculator from the University of Tokyo.
Plate Motion Calculator (UNAVCO)
This program is designed for the calculation of plate motion at any location on Earth. You can specify the tectonic plate or, with the AUTO
option, let the program determine which plate the point is on. Program returns with the plate model velocity components (Evel, the east
velocity, and Nvel, the north velocity) in mm/yr.
Plate Tectonics Activity (Geosphere)
An excellent interactive activity on plate tectonics from the University of Montana's Geosphere. With this activity learners use current satellite
images to determine sea floor spreading rates, identify relationships between earthquake epicenters and sites of active volcanism, and
create a scale model of the Earth's layered structure. (The site may be slow to connect, but its usually there.)
Plate Tectonics Animations
Excellent animations of faults, plate subduction, earthquake wave propagation, and other processes from PBS' Savage Earth program.
Plate Tectonics Animations (USGS)
Great plate tectonics animations from the United States Geological Survey—a must see!
Plate Tectonics Information (NEIS)
National Earthquake Information Center (NEIS) plate tectonics information.
Plate Tectonics Information (USGS)
United States Geologic Survey (USGS) information on plate tectonics and sea-floor spreading.
Plate Tectonics Links
This Central Michigan University site maintained by Dr. Mark Francek lists several good links to Web sites containing information relative to
topics discussed in the chapter.
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Plate Tectonics Links (Houghton Mifflin)
Links to several plate tectonics sites, including class lecture notes, arranged by topic.
Plate Tectonics (NASA's Observatorium)
A good tutorial on plate tectonics.
Plate Tectonics Tutorial (1 of 2)
Plate tectonics tutorial from Texas A & M University.
Plate Tectonics Tutorial (2 of 2)
Plate tectonics tutorial from Texas A & M University.
Plate Tectonics Tutorial (VolcanoWorld)
An in-depth review of plate tectonics from VolcanoWorld.
Plate Tectonics (University of California, Berkeley)
This University of California, Berkeley, Web site explains the history and science of tectonics and also contains animations showing the
movement of plates.
Related Topics Index
Information on several topics related to plate tectonics from the University of North Dakota's VolcanoWorld site.
San Andreas Fault and the Bay Area
A virtual field trip along the San Andreas fault.
Scripps Institution of Oceanography
The Scripps Institution of Oceanography home page features numerous links to related oceanography Web sites.
Seafloor Spreading Calculator
This "Seafloor Spreading Rates Calculator" calculates the spreading rate at any point on mid-ocean ridges. The system is developed and
maintained by K. Okino and K. Tamaki of Ocean Research Institute, University of Tokyo.
Tectonic Plate Motion (Space Geodesy)
An excellent site that explains how NASA monitors plate motions.
Woods Hole Oceanographic Institution (WHOI)
Scientists at the Woods Hole Oceanographic Institution (WHOI), a world leader in the field of oceanography, have been probing the
mysteries of the oceans for more than 65 years.
World Data Center for Marine Geology & Geophysics
The World Data Center for Marine Geology & Geophysics promotes excellence in archiving, managing, and exchanging data obtained from
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measurements of the seafloor.
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