Download Theory of Plate Tectonics

Theory of Plate Tectonics
Tectonic Plates
Plates Meet at Boundaries
Hot, mantle moves the plates.
Continental Drift
 Wagener’s first theory
 Continents are on
crustal plates
 Continents are moving
 Did not explain “how”
 Did not include ocean
crust
Evidence for Continental Drift
1. The
shapes fit together!
Alfred Wegener: 1915
2. Rocks Match
3. Glaciers left scratches
4. Fossils match: land plants &
animals
5. Climates have changed:
(Shows the continent
Was closer to the equator.)
New Mexico Climate through Time
NEW THEORY: Plate Tectonics
Ocean Floor Evidence
Evidence Continues
6. Mid-Ocean Ridges
7. Paleomagnetism
(Magnetic field
changed!)
8. Sea-Floor Spreading
Three Boundary Types:
1.Divergent
2. Convergent
3. Transform
Divergent Boundary:
1.Plates move apart.
2.New Crust from Mantle
RED SEA:
Young divergent boundary
Divergent Boundaries
Continued
3. Most are underwater
4. Look for Mid-ocean
ridge
Evidence 1. Sea Floor Spreading
2. Volcanic Ridge Under the
Ocean
3. Magnetic Pole Reversal
•Lava Flows Harden
•New Rock Records the Magnetic Field
•Each side is a mirror image of the other
Divergent Boundary & Sea
Floor Spreading
Sea-floor spreading is the process in which the
ocean floor is extended when two plates move
apart. As the plates move apart, the rocks
break and form a crack between the plates.
Earthquakes occur along the plate boundary.
Magma rises through the cracks and seeps out
onto the ocean floor like a long, thin, undersea
volcano.
Mid Ocean Ridge
As magma meets the
water, it cools and
solidifies, adding to
the edges of the
sideways-moving
plates. As magma
piles up along the
crack, a long chain of
mountains forms
gradually on the
ocean floor. This
chain is called a
Mid-ocean ridge.
Black Smokers
The new rock at the edge
has no sediments like the
sand or mud, since it is
formed only recently.
Farther away from the
ridge, sand and mud
gradually settle on it, in an
ever-thickening blanket.
The oldest rocks may have
14,000 feet of sand and
other sediments resting on
top of it.
Africa’s Rift Valley
Formation of Divergent Boundary
1.
2.
3.
4.
Continents spread
Plates sink
Volcanic Activity
New sea forms
Divergent
Boundary
Mid-ocean Ridge
Volcanoes
Magma
Lithosphere: Crust &
Moho (Stone-sphere)
Asthenosphere: Upper
Mantle with plasticity
(weak sphere)
Mid-Ocean Ridge: A
mountain range underwater
Convergent Boundary:Plates collide
Causes:
1. Heat Energy travels in Convection Currents
2. Less Dense Material goes up
Plates Crash Together
Trench
Ocean Plate
Continental
Plate
Ocean Plate with Continental Plate
2. Ocean crust is denser
3. Ocean crust sinks under the
continent.
Convergent: 2 Ocean Plates
Island Chain Forms
3. Volcanic Mountains form as magma
melts its way up.
Subduction Zone

Ocean plate collides with
continental plate to form
a Subduction Zone.
Signs of the zone are:
1. Deep Trenches in the Ocean
2.Mountain Range on the Continent
3. Volcanoes and Earthquakes
 Places where plates crash or crunch together are
called convergent boundaries. Plates only move a
few centimeters each year, so collisions are very
slow and last millions of years. Even though plate
collisions take a long time, lots of interesting things
happen. Two continental plates collided to form the
Himalaya Mountains.
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
 The edge of the continental plate can fold into a huge
mountain range while the edge of the oceanic plate
bends downward and digs deep into the Earth. A
trench forms at the bend. All that folding and bending
makes rock in both plates break and slip, causing
earthquakes. As the edge of the oceanic plate digs
into Earth's hot interior, some of the rock in it melts.
The melted rock rises up through the continental
plate, causing more earthquakes on its way up, and
forming volcanic eruptions when it finally reaches the
surface.
Mt. St. Helen
Devil’s Punchbowl
Transform Fault Boundary




Plates slide past.
No spectacular features
Long valleys
Displacement of rivers & mountains
San Andreas Fault: Most studied
Displacement Pictures