Plate TectonicsPlate Tectonics

Wegener’s Continental DriftWegener’s Continental Drift

The proposition first published in The proposition first published in 1912.1912.

Continents can shift positions around the Continents can shift positions around the globe.globe.

Continents were once joined together to Continents were once joined together to form one landmass.form one landmass.

Supercontinent PANGAEASupercontinent PANGAEA

Breakup of PangaeaBreakup of Pangaea

Breakup of PangaeaBreakup of Pangaea

Evidence for Wegener’s Continental Evidence for Wegener’s Continental DriftDrift

Jigsaw PuzzleJigsaw PuzzleEdges of Continents fit together like puzzleEdges of Continents fit together like puzzle

Rock LayersRock LayersSimilarities of rock layers and structures on opposing Similarities of rock layers and structures on opposing

shores of Atlanticshores of Atlantic

Fossil CorrelationFossil CorrelationGlossopterisGlossopteris plant leaf fossils found in Southern plant leaf fossils found in Southern

Africa, Australia, South America, India, and AntarcticaAfrica, Australia, South America, India, and Antarctica

MesosaurusMesosaurus dinosaur fossils found in both South dinosaur fossils found in both South America and Southern AfricaAmerica and Southern Africa

Evidence for Wegener’s Continental DriftEvidence for Wegener’s Continental DriftJigsaw PuzzleJigsaw Puzzle

Evidence for Wegener’s Continental Evidence for Wegener’s Continental DriftDrift

Matching Mountain Ranges and Matching Mountain Ranges and GlaciersGlaciers

Evidence for Wegener’s Continental Evidence for Wegener’s Continental DriftDrift

Fossil CorrelationFossil Correlation

Plate Tectonics TheoryPlate Tectonics TheoryWidely accepted theory for plate Widely accepted theory for plate

movement in scientific community.movement in scientific community.Earth’s lithosphere is broken up into rigid Earth’s lithosphere is broken up into rigid

sections called sections called platesplates..The movement and interaction of these plates The movement and interaction of these plates

cause major changes in Earth’s surface.cause major changes in Earth’s surface.Plates can move horizontally and vertically.Plates can move horizontally and vertically.Plates move due to Plates move due to floatingfloating on the on the

asthenosphere.asthenosphere.Continents move as the plates they are Continents move as the plates they are

attached to move.attached to move.

Mantle ConvectionMantle Convection

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

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

Plate tectonics is a density driven process. The molten rock is less dense than the surrounding rock.

Mantle ConvectionMantle Convection

Mantle ConvectionMantle Convection

Mantle Convection ModelsMantle Convection Models

Convection and TectonicsConvection and Tectonics

Continents and the Plates to Continents and the Plates to which they are attachedwhich they are attached

Tectonic Plates and Boundaries Tectonic Plates and Boundaries ESRT p. 5ESRT p. 5

Types of Plate Boundaries

Plate TectonicsPlate Tectonics

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.

Three Types of Three Types of Plate BoundariesPlate Boundaries

Divergent Plate Boundaries – Divergent Plate Boundaries – Spreading CentersSpreading Centers

plates move apartplates move apartmagma rises from below to fill gap and magma rises from below to fill gap and

push plates away from each otherpush plates away from each otheroccurs at the occurs at the mid-ocean ridgesmid-ocean ridges and and

at at continental riftscontinental riftscreates new basaltic ocean crust creates new basaltic ocean crust

(dense) at the ridge(dense) at the ridgethe oldest basaltic ocean crust is at the the oldest basaltic ocean crust is at the

edge of the continents – see diagram edge of the continents – see diagram

Spreading CenterSpreading CenterDivergent BoundaryDivergent Boundary

Oldest Oceanic Crust

Youngest Oceanic Crust

Mid-Ocean RidgesMid-Ocean Ridges

The The mid-ocean ridgemid-ocean ridge is a mountain is a mountain range at the bottom of the ocean that is range at the bottom of the ocean that is composed mainly of volcanoes and lava composed mainly of volcanoes and lava flows. See map p. 5 ESRTflows. See map p. 5 ESRT

The rocks created at the mid-ocean The rocks created at the mid-ocean ridge have magnetic minerals that are ridge have magnetic minerals that are aligned with Earth’s magnetic field.aligned with Earth’s magnetic field.

Earth’s magnetic field reverses polarity Earth’s magnetic field reverses polarity on a cycle of thousands of years.on a cycle of thousands of years.

Evidence for Plate Tectonics

Testing Plate TectonicsTesting 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 the Ocean CrustPolarity of the Ocean Crust

Magnetic Striping of the Ocean Magnetic Striping of the Ocean FloorFloor

Transform Fault Boundaries

Actions at Plate BoundariesActions at Plate Boundaries

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

Transform faults • Most join two segments of a mid-ocean ridge.

• At the time of formation, they are roughly parallel to the direction of plate movement.

• They aid the movement of oceanic crustal material.

Transform Fault BoundaryTransform Fault Boundary

Convergent Boundaries

Actions at Plate BoundariesActions at Plate Boundaries

• Two oceanic slabs converge and one descends beneath the other.

Oceanic-Oceanic

• 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 Oceanic-Oceanic Convergent BoundaryConvergent Boundary

Convergent Boundaries

Actions at Plate BoundariesActions at Plate Boundaries

• When subducting plates contain continental material, two continents collide.

Continental-Continental

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

Continental-Continental Continental-Continental Convergent BoundaryConvergent Boundary

Collision of India and AsiaCollision of India and Asia

Convergent Boundaries

Actions at Plate BoundariesActions at Plate Boundaries

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

• Denser oceanic slab sinks into the asthenosphere. Oceanic-Continental

• 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 Oceanic-Continental Convergent BoundaryConvergent Boundary

Tectonic Settings and Volcanic ActivityTectonic Settings and Volcanic Activity

The Ring of FireThe Ring 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 Continental Slope – steepest gradient drop toward ocean floortoward ocean 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

Passive Continental Margin – Passive Continental Margin – detaileddetailed

Trailing Edge of Continent Trailing 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 crust out of the two plates that are colliding. See map p. 5 that are colliding. See map p. 5 ESRTESRT

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

bending down of the subducting plate bending down of the subducting plate and warping of the crustand warping of the crust

Active Continental MarginActive Continental MarginSubduction ZoneSubduction Zone

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

1.1. Friction between platesFriction between plates Subducting slabSubducting slab Overriding slabOverriding slab

2.2. Increased temperature at depthIncreased temperature at depth

3.3. Lower density magma rises through denser Lower density magma rises through denser solid rocksolid rock

Active Continental MarginActive Continental Margin

Continental Margins of the USContinental Margins of the US

VolcanoesVolcanoes created at subduction boundaries due to the created at subduction boundaries due to the

melting of the subducting plate at great melting of the subducting plate at great depthdepth the rock becomes magma and rises because it is the rock becomes magma and rises because it is

now less dense than the surrounding rocknow less dense than the surrounding rock

continental volcanic arcscontinental volcanic arcs form on the edge of form on the edge of a continent that the plate is subducting beneatha continent that the plate is subducting beneath

Examples: Andes in South America, Cascades in United Examples: Andes in South America, Cascades in United StatesStates

volcanic island arcsvolcanic island arcs form on a plate boundary form on a plate boundary where an oceanic plate is colliding with another where an oceanic plate is colliding with another oceanic plate and the denser (older) plate is oceanic plate and the denser (older) plate is subducting below the less dense (younger) platesubducting below the less dense (younger) plate

Example: Mariana, Aleutian, and Tonga IslandsExample: Mariana, Aleutian, and Tonga Islands

Anatomy of a “Typical” Anatomy of a “Typical” VolcanoVolcano

Hot SpotsHot Spots

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

mantle material called a mantle plume mantle material called a mantle plume rises toward the surfacerises toward the surfaceExamples: Hawaiian Islands, Yellowstone, Examples: Hawaiian Islands, Yellowstone,

Iceland, Canary IslandsIceland, Canary IslandsSee Tectonic Plates p. 5 ESRTSee Tectonic Plates p. 5 ESRT

Hawaiian Hot SpotHawaiian Hot Spot

Hot Spot Volcano TracksHot Spot Volcano Tracks