Plate TectonicsPlate Tectonics

What is Plate Tectonics?What is Plate Tectonics?

According to the plate tectonics theory, the uppermost mantle, along with the overlying crust, behaves as a strong, rigid layer.

This layer is known as the lithosphere

A plate is one of numerous rigid sections of the lithosphere that move as a unit over the material of the asthenosphere

Types of Plate BoundariesTypes of Plate Boundaries

Divergent boundaries (also called spreading centers) are the place where two plates move apart.

Convergent boundaries form where two plates move together.

Transform fault boundaries are margins where two plates grind past each other without the production or destruction of the lithosphere.

Plate BoundariesPlate Boundaries

Divergent BoundariesDivergent Boundaries

Oceanic Ridges and Seafloor Spreading• Oceanic ridges are continuous elevated zones

on the floor of all major ocean basins. The rifts at the crest of ridges represent divergent plate boundaries.

• Rift valleys are deep faulted structures found along the axes of divergent plate boundaries. They can develop on the seafloor or on land.

• Seafloor spreading produces new oceanic lithosphere.

Spreading CenterSpreading Center

Actions at Divergent BoundariesActions at Divergent Boundaries

CONTINENTAL RIFTSCONTINENTAL RIFTS• When spreading centers develop within a

continent, the landmass may split into two or more smaller segments, forming a rift.

East African Rift ValleyEast African Rift Valley

Actions at Convergent BoundariesActions at Convergent Boundaries

A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.

Oceanic-Continental - Denser oceanic slab sinks into the asthenosphere. - Pockets of magma develop and rise. - Continental volcanic arcs form in part by volcanic

activity caused by the subduction of oceanic lithosphere beneath a continent

• Examples include the Andes, Cascades, and the Sierra Nevadas.

Oceanic-continental Plate Oceanic-continental Plate BoundaryBoundary

Actions at Convergent Plate Actions at Convergent Plate BoundariesBoundaries

OCEANIC – OCEANICOCEANIC – OCEANIC

Two oceanic slabs converge and one descends beneath the other.

- This kind of boundary often forms volcanoes on the ocean floor.

- Volcanic island arcs form as volcanoes emerge from the sea.

- Examples include the Aleutian, Mariana, and Tonga islands.

Oceanic-Oceanic ConvergenceOceanic-Oceanic Convergence

Actions at Convergent BoundariesActions at Convergent Boundaries

CONTINENTAL-CONTINENTALCONTINENTAL-CONTINENTAL• When subducting plates contain

continental material, two continents collide.

• This kind of boundary can produce new mountain ranges, such as the Himalayas.

Continental-Continental Continental-Continental ConvergenceConvergence

Collision of India and AsiaCollision of India and Asia

Actions at Transform BoundariesActions at Transform Boundaries

At a transform fault boundary, plates grind past each other without destroying the lithosphere.

TRANSFORM FAULTSTRANSFORM FAULTS

• Most join two segments of a mid-ocean ridge.• At the time of formation, they roughly parallel the

direction of plate movement. • They aid the movement of oceanic crustal

material.

Transform Fault BoundaryTransform Fault Boundary

Evidence for Plate TectonicsEvidence for Plate Tectonics

Magnetic Pole ReversalsMagnetic Pole ReversalsThe The mid-ocean ridgemid-ocean ridge is a mountain range at is a mountain range at the bottom of the ocean that is composed mainly the bottom of the ocean that is composed mainly of volcanoes and lava flows. See map p. 5 of volcanoes and lava flows. See map p. 5 ESRTESRTThe rocks created at the mid-ocean ridge have The rocks created at the mid-ocean ridge have magnetic minerals that are aligned with Earth’s magnetic minerals that are aligned with Earth’s magnetic field.magnetic field.Earth’s magnetic field reverses polarity on a Earth’s magnetic field reverses polarity on a cycle of thousands of years.cycle of thousands of years.

Evidence of Plate TectonicsEvidence of Plate Tectonics

The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges, is among the strongest evidence of seafloor spreading.

Polarity of Ocean CrustPolarity of Ocean Crust

Evidence of Plate MotionEvidence of Plate Motion

Seafloor SpreadingSeafloor Spreading• The data on the ages of seafloor sediment

confirmed what the seafloor spreading hypothesis predicted.

• The youngest oceanic crust is at the ridge, and the oldest oceanic crust is at the continental margins (away from the ridge).

Evidence of Plate TectonicsEvidence of Plate Tectonics

HOT SPOTSHOT SPOTS• A hot spot is a concentration of heat in

the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands.

• Hot spot evidence supports that the plates move over the Earth’s surface.

Ring of FireRing of Fire

Passive Continental MarginPassive Continental Margin

5 main features5 main features1.1.Coast – edge of continentCoast – edge of continent

2.2.Continental Shelf – wide shallow extension of Continental Shelf – wide shallow extension of continentcontinent

3.3.Continental Slope – steepest gradient drop toward Continental Slope – steepest gradient drop toward ocean floorocean floor

4.4.Continental Rise – collection of sediment from Continental Rise – collection of sediment from turbidity currentsturbidity currents

5.5.Abyssal plain – ocean floor, flattest places on Abyssal plain – ocean floor, flattest places on EarthEarth

Passive Continental Margin – Passive Continental Margin – simplesimple

Trailing Edge of ContinentTrailing Edge of Continent

Active Continental MarginActive Continental MarginSubduction ZoneSubduction Zone

SubductionSubduction is the sinking of the is the sinking of the denserdenser crust out of the two plates that are crust out of the two plates that are colliding. See map p. 5 ESRTcolliding. See map p. 5 ESRT

Ocean trenchesOcean trenches are the deepest parts of are the deepest parts of the oceans.the oceans. created at subduction boundaries by bending created at subduction boundaries by bending

down of the subducting plate and warping of down of the subducting plate and warping of the crustthe crust

Active Continental MarginActive Continental MarginSubduction ZoneSubduction Zone

Continental Volcanic ArcsContinental Volcanic Arcs form on the form on the edge of the continental plate due a edge of the continental plate due a combination of factors:combination of factors:

1.1.Friction between platesFriction between platesSubducting slabSubducting slab

Overriding slabOverriding slab

2.2.Increased temperature at depthIncreased temperature at depth

3.3.Lower density magma rises through denser solid Lower density magma rises through denser solid rockrock

Active Continental MarginActive Continental Margin

Hot SpotsHot Spots

are areas where intraplateare areas where intraplate volcanism volcanism occurs.occurs. where a mass of hotter than normal mantle where a mass of hotter than normal mantle

material called a mantle plume rises toward material called a mantle plume rises toward the surfacethe surface

Examples: Hawaiian Islands, Yellowstone, Examples: Hawaiian Islands, Yellowstone, Iceland, Canary IslandsIceland, Canary Islands

See Tectonic Plates p. 5 ESRTSee Tectonic Plates p. 5 ESRT

Hot SpotHot Spot

Causes of Plate MotionCauses of Plate Motion

CONVECTION CURRENTS WITHIN THE CONVECTION CURRENTS WITHIN THE EARTHEARTH

Scientists generally agree that convection occurring in the mantle is the basic driving force for plate movement.

Convective flow is the motion of matter resulting from changes in temperature

Mantle ConvectionMantle Convection

• Mantle plumes are masses of hotter-than-normal mantle material that ascend toward the surface, where they may lead to igneous activity.

The unequal distribution of heat within Earth causes the thermal convection in the mantle that ultimately drives plate motion

Mantle ConvectionMantle Convection

Mantle ConvectionMantle Convection