Plate TectonicsPlate Tectonics

I. Continental Drift

A.A. Alfred WegenerAlfred Wegener1. First proposed the hypothesis, 1. First proposed the hypothesis,

(1915)(1915)2. German Meteorologist & 2. German Meteorologist &

GeophysicistGeophysicist

3. 3. Published Published The Origin ofThe Origin of Continents and OceansContinents and Oceans

B.B. Continental Drift HypothesisContinental Drift Hypothesis1.1. Super continent called Pangaea Super continent called Pangaea

began breaking apart about 200 began breaking apart about 200 million years ago.million years ago.

2.2. Continents “drifted” to present Continents “drifted” to present positionspositions

3.3. Continents “broke” through Continents “broke” through oceanic crustoceanic crust

C.C. Evidence for Continental DriftEvidence for Continental Drift

1.1. Map Fit- some of the Map Fit- some of the continents continents seem to fit seem to fit

together like a together like a jigsaw jigsaw puzzle. puzzle.

Ex: S. America & AfricaEx: S. America & Africa

2.2. Fossils- Fossils-

Fossils of certain species of Fossils of certain species of ancient organisms were found ancient organisms were found on separate continents on separate continents throughout the world. throughout the world. MesosaurusMesosaurus

The continents must have been The continents must have been as ONE in order for these as ONE in order for these species to be found on species to be found on different, widespread different, widespread landmasses. landmasses.

Organisms were either too large Organisms were either too large or small to swim or fly to other or small to swim or fly to other continents without them being continents without them being linked.linked.

Land bridges could not have Land bridges could not have been the solution, because the been the solution, because the remnants are nowhere to be remnants are nowhere to be found.found.

3.3. Rock StructuresRock Structures

Mountain chains of Mountain chains of comparable age that appear to comparable age that appear to be severed by the oceans be severed by the oceans (Appalachians)(Appalachians)

When these landmasses are When these landmasses are reassembled they form a reassembled they form a continuous mountain belt.continuous mountain belt.

N. America & EuropeN. America & Europe

S. America & AfricaS. America & Africa

S. America & AntarcticaS. America & Antarctica

4.4. Ancient ClimatesAncient Climates

Glacial deposits show that Glacial deposits show that most of the Southern most of the Southern Hemisphere was covered by Hemisphere was covered by ice sheets.ice sheets.

Rock deposits left behind by Rock deposits left behind by moving glaciers were found in moving glaciers were found in all southern continents & India.all southern continents & India.

Coal fields produced by Coal fields produced by ancient tropical plant fossils ancient tropical plant fossils indicate that the Northern indicate that the Northern Hemisphere was once a Hemisphere was once a tropical environment.tropical environment.

Main objection to Wegener’s Main objection to Wegener’s hypothesis was its inability to hypothesis was its inability to provide a mechanism for the provide a mechanism for the movement of the continents.movement of the continents.

II. Plate TectonicsA.A. What is the Theory?What is the Theory?

The crust is broken into The crust is broken into large large moving sections called moving sections called plates plates Lithosphere:Lithosphere: rigid layer made rigid layer made of the crust & upper mantleof the crust & upper mantle Asthenosphere:Asthenosphere: weaker upper weaker upper part of the mantlepart of the mantle

Explains the formation, Explains the formation, movements, collisions, & movements, collisions, & destruction of the Earth’s crust.destruction of the Earth’s crust.

Seven major plates:Seven major plates:Pacific (largest) Pacific (largest) N. American N. American S. American S. American AfricanAfricanEurasianEurasian Australian Australian AntarcticAntarctic

Plates include a continent & Plates include a continent & mostly ocean floor.mostly ocean floor.

Plates are slowly moving Plates are slowly moving continuously.continuously.

B.B. Plate BoundariesPlate Boundaries

1.1. What occurs at plate What occurs at plate boundaries?boundaries?

a.a. Seismic activitySeismic activity

b.b. VolcanismVolcanism

c.c. Mountain buildingMountain building

2.2. Types of Plate BoundariesTypes of Plate Boundaries

a.a. Divergent Boundaries Divergent Boundaries

1. Where plates move 1. Where plates move apartapart

(Constructive)(Constructive)Rift Valley Midocean Ridge

2.2. Seafloor Spreading Seafloor Spreading ** As divergent plates As divergent plates

spread spread apart creating a apart creating a fissure, fissure, magma flows magma flows through the through the fissure (rift fissure (rift valley.)valley.)

*The lava then cools & crystallizes *The lava then cools & crystallizes to form new seafloor mountains to form new seafloor mountains

(midocean ridges.)(midocean ridges.)

*Younger rock is at the midocean *Younger rock is at the midocean ridges & the older rock is at the ridges & the older rock is at the continental margins.continental margins.

b.b. Convergent Convergent BoundariesBoundaries

1.1. Where plates move Where plates move together, resulting together, resulting

in in the subduction of the subduction of oceanic oceanic

lithosphere lithosphere into into the mantlethe mantle.

2. Types of Convergent Boundaries2. Types of Convergent Boundaries

a.a. Oceanic-ContinentalOceanic-Continental

*Forms a subduction zone *Forms a subduction zone producing a deep-ocean producing a deep-ocean trench. trench.

* Continental volcanic arcs are * Continental volcanic arcs are mountains formed by igneous activity mountains formed by igneous activity associated with the subduction of associated with the subduction of oceanic lithosphere oceanic lithosphere beneath a continent. beneath a continent.

Ex: Andes, Cascades, Sierra NevadaEx: Andes, Cascades, Sierra Nevada

b.) Oceanic-Oceanicb.) Oceanic-Oceanic

** Occurs when two oceanic Occurs when two oceanic plates converge, one plate plates converge, one plate

subducts below another.subducts below another.

** Volcanic island arc forms as Volcanic island arc forms as volcanoes emerge from volcanoes emerge from underwater.underwater.

Ex:Ex: Mariana Islands Mariana Islands Aleutian IslandsAleutian Islands

c.c. Continental-ContinentalContinental-Continental

* Neither plate will subduct* Neither plate will subduct

* Causes the continents to fold & * Causes the continents to fold & buckle upwards forming buckle upwards forming mountains.mountains.

Ex:Ex: Himalayas, Alps, Himalayas, Alps, Appalachians,UralsAppalachians,Urals

c. Transform Fault Boundaryc. Transform Fault Boundary

1.1. Where plates grind past Where plates grind past one another without one another without

the the

production or destruction production or destruction of lithosphereof lithosphere

2. Most transform faults are 2. Most transform faults are located within located within

the the ocean basins, a ocean basins, a few cut few cut

through through continental crustcontinental crust

San Andreas FaultSan Andreas Fault

C.C. EvidenceEvidence

1.1. PaleomagnetismPaleomagnetism

*Study of ancient *Study of ancient magnetism preserved in magnetism preserved in rocks rocks

*Shows the location of the *Shows the location of the magnetic poles at the time magnetic poles at the time of the rock’s formation. of the rock’s formation.

a. Polar Wanderinga. Polar Wandering

* Study showing that the * Study showing that the magnetism of older rocks point magnetism of older rocks point

in different directions.in different directions.

* Showed that the magnetic * Showed that the magnetic poles either moved or the poles either moved or the continents moved.continents moved.

* The Earth’s magnetic poles * The Earth’s magnetic poles should remain close to the should remain close to the geographic polesgeographic poles

* If the magnetic poles don’t * If the magnetic poles don’t move, the apparent movement move, the apparent movement

must have been produced by must have been produced by the continents moving.the continents moving.

b.b. Magnetic ReversalsMagnetic Reversals

*Earth’s magnetic field reverses *Earth’s magnetic field reverses its polarity periodically.its polarity periodically.

*These reversals have been *These reversals have been shown in the crust of the shown in the crust of the

ocean floorocean floor

*Proves seafloor spreading*Proves seafloor spreading.

2.2. Earthquake PatternsEarthquake Patterns

* If earthquake epicenters are * If earthquake epicenters are plotted on the globe, it shows plotted on the globe, it shows

the outline of the plates. the outline of the plates.

3. Ocean Drilling3. Ocean Drilling

*Drilling showed that the youngest *Drilling showed that the youngest rock is near the ridges & the rock is near the ridges & the oldest is further from the ridgeoldest is further from the ridge

*Proves seafloor spreading*Proves seafloor spreading

4. Hot Spots4. Hot Spots* Rising plumes of magma* Rising plumes of magma

* As the plate moves above a hot * As the plate moves above a hot spot, it will create volcanoes that spot, it will create volcanoes that produce underwater mountains produce underwater mountains and volcanic islands and volcanic islands

Hawaiian & Midway IslandsHawaiian & Midway Islands

* Used to track the direction a * Used to track the direction a plate is moving.plate is moving.

Hawaiian Islands

D.D. Breakup of PangaeaBreakup of Pangaea

1.1. Fragmented landmasses Fragmented landmasses collided 500 to 225 million collided 500 to 225 million years ago to form Pangaeayears ago to form Pangaea

2.2. Pangaea began to break Pangaea began to break apart 200 million years ago apart 200 million years ago during the Jurassic Periodduring the Jurassic Period

3.3. Break up formed two Break up formed two subcontinents : subcontinents :

Laurasia Laurasia & & GondwanalandGondwanaland

4.4. Those subcontinents Those subcontinents began dividing about began dividing about

165 165 & 100 mya& 100 mya

E.E. Mechanisms & MethodsMechanisms & Methods

1.Convection Current Hypothesis1.Convection Current Hypothesis

**Hotter magma rises in the mantleHotter magma rises in the mantle

*The magma cools and spreads*The magma cools and spreads

*The spreading magma moves *The spreading magma moves the the plates laterallyplates laterally

*The cooled magma then sinks *The cooled magma then sinks back into the mantle & reheatsback into the mantle & reheats

2. Slab-Pull & Slab-Push Hypotheses

*Colder oceanic plate will sink/subduct, pulling the rest of the plate with it.

*As new crust is formed at a rift valley, it pushes the plate

forward.

3. Hot Plumes Hypothesis

* Plumes of hot magma rise through the mantle, striking and pushing the plates in different directions