Theory of Plate TectonicsTheory of Plate Tectonics
Plates Meet at BoundariesPlates Meet at Boundaries
Hot, mantle moves the plates.
Tectonic Plates
Continental DriftContinental Drift
Wagener’s first theory
Continents are on crustal plates
Continents are moving
Did not explain “how”
Did not include ocean crust
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
Evidence for Continental Drift
1. The shapes fit together!
Alfred Wegener: 1915
2. Rocks Match2. Rocks Match
3. Glaciers left scratches3. Glaciers left scratches
4. Fossils match: land plants & animals
4. Fossils match: land plants & animals
5. Climates have changed:
5. Climates have changed:
New Mexico Climate through Time
(Shows the continentWas closer to the equator.)
NEW THEORY: Plate Tectonics
NEW THEORY: Plate Tectonics
Ocean Floor Evidence
Evidence ContinuesEvidence Continues
6. Mid-Ocean Ridges
7. Paleomagnetism (Magnetic field changed!)
8. Sea-Floor Spreading
6. Mid-Ocean Ridges
7. Paleomagnetism (Magnetic field changed!)
8. Sea-Floor Spreading
Three Boundary Types:1.Divergent 2. Convergent 3. Transform
Three Boundary Types:1.Divergent 2. Convergent 3. Transform
Divergent Boundary: 1.Plates move apart.
2.New Crust from Mantle
Divergent Boundary: 1.Plates move apart.
2.New Crust from Mantle
RED SEA:Young divergent boundary
Divergent Boundaries Continued
Divergent Boundaries Continued
3. Most are underwater4. Look for Mid-ocean
ridge
1. Sea Floor Spreading2. Volcanic Ridge Under the Ocean
1. Sea Floor Spreading2. Volcanic Ridge Under the Ocean
Evidence
•Lava Flows Harden•New Rock Records the Magnetic Field•Each side is a mirror image of the other
3. Magnetic Pole Reversal
Divergent Boundary & Sea Floor Spreading
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.
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.
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.
Mid Ocean Ridge
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.
Black Smokers
Africa’s Rift ValleyAfrica’s Rift Valley
Formation of Divergent BoundaryFormation of Divergent Boundary
1. Continents spread2. Plates sink3. Volcanic Activity4. New sea forms
Divergent Boundary
Divergent Boundary
Lithosphere: Crust & Moho (Stone-sphere)Asthenosphere: Upper Mantle with plasticity (weak sphere)Mid-Ocean Ridge: A mountain range underwater
Magma
Volcanoes
Mid-ocean Ridge
Causes: 1. Heat Energy travels in Convection Currents2. Less Dense Material goes up
Causes: 1. Heat Energy travels in Convection Currents2. Less Dense Material goes up
Convergent Boundary:Plates collide
Plates Crash Together
Plates Crash Together
Ocean Plate
ContinentalPlate
Trench
Ocean Plate with Continental Plate
2. Ocean crust is denser3. Ocean crust sinks under the continent.
2. Ocean crust is denser3. Ocean crust sinks under the continent.
Convergent: 2 Ocean Plates
Island Chain Forms
Convergent: 2 Ocean Plates
Island Chain Forms
3. Volcanic Mountains form as magma melts its way up.
3. Volcanic Mountains form as magma melts its way up.
Subduction ZoneSubduction Zone
Ocean plate collides with continental plate to form a Subduction Zone. Signs of the zone are:
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.
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.
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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.
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 BoundaryTransform Fault Boundary
Plates slide past. No spectacular features Long valleys Displacement of rivers & mountains
Plates slide past. No spectacular features Long valleys Displacement of rivers & mountains
San Andreas Fault: Most studied
San Andreas Fault: Most studied
Displacement PicturesDisplacement Pictures