PLATE
TECTONICS
A LITTLE BACKGROUND INFO:
EARTH: A UNIQUE PLANET
Earth is covered by 71 percent
water and about 97 percent of
that water is in the salty oceans.
We have learned about Earth’s
interior by studying seismic waves,
which are vibrations that travel
through the earth. These can be
caused by earthquakes or
explosions near the surface.
Zones of the Earth:
• Crust (1% of mass)
• Thin, solid outermost covering
• Both oceanic and continental
crust
• Mantle (2/3 of mass)
• Upper part is solid, lower part is
plastic-like
Zones of the Earth:
• Core (1/3 of mass)
• Outer core is liquid and inner is
solid
• Made mostly of iron
http://scienceblogs.com/startswithabang/upload/2011/03/why_physics_gives_us_earthquak/Layers%20of%20Earth.jpg
Another way to look at it:
• Lithosphere
• Rigid layer
• Crust and solid portion of the mantle
• Asthenosphere:
• Just below lithosphere
• Due to extreme heat & pressure, the solid
rock has the ability to flow, known as
plasticity.
http://mediatheek.thinkquest.nl/~ll125/images/struct.jpg
DISCOVERING
EARTH’S LAYERS
In 1909, a Croatian seismologist,
Andrija Mohorovicic, used the
information from seismic waves to
determine that all layers of Earth
weren’t the same. He is credited
with finding the Moho, which is a
boundary between the crust and
the mantle.
PLATE
TECTONICS
The idea that the continents have
changed locations throughout history is
known as continental drift.
• Pangaea - Single landmass, means
“all lands”
• Panthalassa – One huge ocean,
means “all seas”
Evidence of Continental Drift:
Alfred Wegener proposed the theory
continental drift.
In addition to the puzzle piece fit, Wegener
soon found other evidence to support his
hypothesis.
http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/Images_specific/sa_af.gif
Evidence of Continental Drift:
1.
Fossil Evidence:
• Mesosaurus, a small, extinct land reptile
was found on both South America and
Africa.
• There was no evidence of land bridges
and the animal could not have swam
across the ocean.
Evidence of Continental Drift
2. Geologic Evidence
• The age and types of rock in
coastal regions of widely
separated areas and Africa
and S. America matched
closely.
• Mountain chains (ex. The
Appalachains) that ended
on one coastline seemed to
continue on the coastline of
other landmasses.
Evidence of Continental Drift
3. Climatic Changes
• Layers of debris
from glaciers were
found in southern
Africa and South
America.
• Coal deposits
were found in
eastern US,
Europe, and
Siberia.
Many scientists rejected
Wegener’s ideas because it
lacked an explanation of the
force that caused continental
drift.
Seafloor Spreading:
•The Mid-Atlantic Ridge is an undersea mountain
range, with a steep, narrow valley running down its
center.
•Scientists in the 1950s discovered that the ocean
floor was younger than the continental rocks. (!!!)
•Harry Hess and Robert Dietz explained this
movement, known as seafloor spreading.
Paleomagnetism:
• When magma cools and solidifies,
iron-bearing minerals become
magnetized.
• The magnetic orientation of these
minerals becomes permanent and
points towards the north.
• The validity of this idea grew when
scientists discovered the difference of
the magnetism of the ocean floor.
Paleomagnetism:
• In 1965 scientists discovered a
reversal in the earth’s magnetic
orientation.
• This was the evidence that Wegener
was looking for to support his theory of
continental drift.
PLATE TECTONIC THEORY
• The theory of plate tectonics not
only describes continental
movement, but also presents a
possible explanation of why and how
the continents move.
• Two types of crust: oceanic and
continental. To date 30 plates have
been identified.
• Oceanic and
continental crust AND
the rigid upper mantle
make up the
lithosphere.
• Under this lies the
asthenosphere,
which is solid rock
that flows like melted
silly putty due to
extreme heat and
pressure.
3 TYPES OF LITHOSPHERIC
PLATE BOUNDARIES
1.) Divergent Boundary
•Two plates moving away from each other
•Forms a rift valley
• A narrow valley that forms as two plates
separate. (ex: at center of a mid-ocean
ridge)
•Ex. Mid-ocean ridge
http://cmspugliano.wikispaces.com/file/view/divergent4.jpg/100083335/divergent4.jpg
3 TYPES OF LITHOSPEHERIC
PLATE BOUNDARIES
2.) Convergent boundary
(warning: there are three variations of this one,
based on the types of crust involved)
•Two plates colliding with each other
• Subduction zone - area where one
plate slides under another plate
•Ocean trench - this is the feature that
you see at a subduction zone
THREE TYPES OF
CONVERGENT BOUNDARIES
A.Continental-continental:
•2 plates push together
•fold upward to form folded
mountains
•Ex. Himalayas and Appalachains
THREE TYPES OF
CONVERGENT BOUNDARIES
B. Oceanic-oceanic:
•2 plates push together
•the older oceanic plate is pushed
down (subducts)
•forms volcanic island arc (chain of
volcanic islands)
•ex. Aleutian Islands and Japanese
Islands
THREE TYPES OF
CONVERGENT BOUNDARIES
C.Continental-oceanic:
•2 plates push together
•the oceanic plate subducts
•volcanic mountains are formed on
the continent’s edge
•ex. Andes Mountains and
Cascade Mountains
http://www.daukas.com/Geoscience/MAtour/images/convergent.jpg
http://rst.gsfc.nasa.gov/Sect2/boundaries.jpg
TYPES OF PLATE
BOUNDARIES
3. Transform Boundary
• neither destructive nor constructive
• 2 plates are grinding past each other
• usually move in a series of sudden
movement separated by periods of no
motion
• Ex. San Andreas fault
http://www.gweaver.net/techhigh/projects/period1_2/Yellowstone/Images/transform.jpeg
http://conceptactivityresearchvault.files.wordpress.com/2011/03/usn-research-laboratory-plate-boundary-depiction.gif
CAUSES OF PLATE MOTION
Convection currents - the transfer of
heat thru the movement of heated
material, it is a cycle of warm rising
currents and cold currents sinking
Scientists have measured the amount of
heat leaving rocks at various points in the
lithosphere. Hot convection currents
are rising along these boundaries, thus
explaining the temperature difference.
CAUSES OF PLATE MOTION
SUSPECT TERRANES
Theory of Suspect Terranes - theory that
continents are patches of land that have
different distinct geologic histories
Blocks of terranes are carried along the
ocean floor by the action of seafloor
spreading. When they meet a plate
boundary, subduction occurs.
Geologists have found evidence to support
this theory in Northern California.
ROCK DEFORMATION
• Deformation - the bending, breaking, and
tilting of the earth’s crust.
• Isostatic Adjustments - the up-and-down
movements of the crust in an attempt to
reach
isostasy – which is the balance of the
upward and downward forces that act on the
earth’s crust
Isostatic adjustment and plate movement
cause stress in the rocks that make up the
earth’s crust. Stress is a force that causes
pressure in the rocks of the crust.
This stress causes strain in crustal rocks.
Strain is a change in the shape or volume
of rocks that results from being squeezed,
twisted or pulled apart.
ROCK DEFORMATION
• Three types of
Stress:
1. Tensional
• 
2. Compressional
• 
3. Shear
• 
http://www.eas.purdue.edu/mesozoic/Lab_12/Stress_Types.jpg
Stress – 3 Types
1. Compression - when crustal
rocks are squeezed together
2. Tension - when crustal rocks
are pulled apart
3. Shearing - when crustal rocks
are pushed in opposite
horizontal directions
FOLDING - flat layers of rock are
under severe compression and are
squeezed from the sides. The
layers moved into folded positions
without breaking (although some
cracks may appear).
Three types of Folds:
1. Anticlines - upward folds
2. Synclines – downward folds
3. Monoclines – gently
dipping bends in horizontal
rock layers
http://www.cr.nps.gov/history/online_books/geology/publications/bul/1508/images/fig27.jpg
A break in the rock layers
along which there is no
movement is called a
fracture.
Once movement occurs, the
fracture is known as a fault.
The type of fault is determined by how
the blocks of rock on either side of the
fault move.
Hanging Wall – the block of rock above
the fault
Foot Wall – the block of rock below the
fault
Foot
Wall
Hanging
Wall
Three Main Types of Faults:
1. Normal Fault
• occurs along divergent boundaries
(tension force present)
• The hanging wall drops down below
the foot wall.
2. Reverse Fault
•occurs along convergent boundaries
(compression force)
•The hanging wall moves up above the foot
wall
•Thrust Fault
ospecial type of reverse fault where the
hanging wall is pushed at such a low
angle (not steep) that it moves UP AND
OVER the foot wall
3. Strike-Slip Fault
•occurs at transform boundaries
(shearing force)
• The rocks along either side of the fault
slide horizontally
Ex. San Andreas Fault
JUST FOR
REVIEW
Four major types of faults:
1. Normal
•
•
Tension
Hanging wall goes down
2. Reverse
•
•
Compression
Hanging wall goes up
 Thrust (special type of reverse)
•
•
Compression
Hanging wall goes up and over
3. Strike-slip
•
•
Shearing
Side-to-side
http://www.geol.umd.edu/~jmerck/geol100/images/20/faults.gif
Mountain Hierarchy
Single Mountain
(ex. Mt. Mitchell)
Mountain Range
(ex. Smoky Mts.)
Mountain Belt
(Ex. Eurasian Melanesian)
Mountain System
(Ex. Appalachian Mts.)
Mountain Belts:
1.) Eurasian-Melanesian Belt
2.) circum-Pacific Belt (aka Ring of Fire)
FOUR TYPES OF
MOUNTAINS
1. Folded Mountains - Found where continents have
collided. Ex. Appalachian Mts., Himalayan Mts.
• Plateaus - areas of flat-topped land high above
sea level. Ex. Tibetan Plateau (part of
Himalayas)
2. Fault-Block Mountains - Formed by faults, where
part of the earth’s crust have been broken into large
blocks and then were lifted above the surrounding
crust.
Ex. Sierra Nevada Mts. in California
• Graben - long, narrow valleys formed when blocks
of rock slipped downward Ex. Death Valley in CA
http://upload.wikimedia.org/wikipedia/commons/d/d8/Fault_block_mountain.JPG
http://martianchronicles.files.wordpress.com/2010/04/horstgraben.gif
3. Volcanic Mountains - Form when
molten rock erupts onto earth’s surface.
Ex. Cascade Mts. in Pacific NW and
the mid-Ocean ridges
4. Dome Mountains - An unusual type
that is formed when molten rock rises but
does not break through the surface.
Ex. Adirondacks, Black Hills of SD