Warm Up 11/3 1. 1. What hypothesis states that the continents were once joined to form a single supercontinent? a. continental driftc. plate tectonics.

Warm Up 11/3Warm Up 11/31. What hypothesis states that the continents were

once joined to form a single supercontinent?a. continental drift c. plate tectonicsb. seafloor spreading d. paleomagnetism

2. What kind of plate boundary occurs where two plates grind past each other without destroying or producing lithosphere?a. convergent boundary c. divergent boundaryb. transitional boundary d. transform fault boundary

3. The lithospheric plates move an average of ____.a. 50 inches per year c. 5 centimeters per yearb. 5 inches per year d. 50 centimeters per year

Answers: 1) a. 2) d. 3) c.

Actions at Plate Actions at Plate BoundariesBoundaries

Chapter 9, Section 3Chapter 9, Section 3

Divergent BoundariesDivergent Boundaries

Most divergent boundaries are Most divergent boundaries are located along the crests of located along the crests of oceanic ridgesoceanic ridges

These plate boundaries can be These plate boundaries can be thought of as thought of as constructive plate constructive plate boundariesboundaries, because it is where , because it is where new oceanic lithosphere is new oceanic lithosphere is createdcreated

Location of Most Location of Most Divergent BoundariesDivergent Boundaries

Oceanic Ridges and Seafloor Oceanic Ridges and Seafloor SpreadingSpreading

Oceanic Ridge – Oceanic Ridge – along well-developed divergent along well-developed divergent plate boundaries, area where seafloor is elevatedplate boundaries, area where seafloor is elevated

The system of ridges is the longest physical The system of ridges is the longest physical feature on Earth’s surface (70,000 km long)feature on Earth’s surface (70,000 km long)

These features are 1000 to 4000 km wide, not These features are 1000 to 4000 km wide, not narrow at allnarrow at all

Rift Valley – Rift Valley – Deep faulted structures found Deep faulted structures found along the ridge systemalong the ridge system

Seafloor Spreading –Seafloor Spreading – process by which plate process by which plate tectonics produces new lithospheretectonics produces new lithosphere

Typically the rates of spreading average about 5 Typically the rates of spreading average about 5 cm/year, fast enough that all of the current cm/year, fast enough that all of the current oceans have been produced in the last 200 oceans have been produced in the last 200 million yearsmillion years

Seafloor SpreadingSeafloor Spreading

Continental RiftsContinental Rifts When spreading centers develop within When spreading centers develop within

a continent, the landmass may split into a continent, the landmass may split into two or more smaller segmentstwo or more smaller segments

The most widely accepted view is that The most widely accepted view is that areas where plumes of hot rock rise from areas where plumes of hot rock rise from the mantle are weaker then other areas, the mantle are weaker then other areas, stretching the areas above it causing stretching the areas above it causing faulting and volcanismfaulting and volcanism

In the East African rift valley, the In the East African rift valley, the beginning stages of continental breakup beginning stages of continental breakup may be occurring creating the Red Seamay be occurring creating the Red Sea

East African Rift East African Rift ValleysValleys

Concept CheckConcept Check

How do rifts begin to form?How do rifts begin to form? The lithosphere is stretched and a The lithosphere is stretched and a

plume of hot rock from the plume of hot rock from the mantle weakens and then splits mantle weakens and then splits the lithospherethe lithosphere

Convergent Convergent BoundariesBoundaries

Because lithosphere is being “destroyed” Because lithosphere is being “destroyed” at convergent boundaries, they are also at convergent boundaries, they are also called called destructive plate marginsdestructive plate margins

Subduction Zones –Subduction Zones – destructive plate destructive plate margins where oceanic crust is being margins where oceanic crust is being pushed down into the mantlepushed down into the mantle

Trench – Trench – Surface feature produced by Surface feature produced by descending slab, some of the deepest descending slab, some of the deepest spots on Earthspots on Earth

Convergent boundaries are controlled by Convergent boundaries are controlled by the type of crust involved in the the type of crust involved in the convergenceconvergence

Oceanic-Continental Oceanic-Continental ConvergenceConvergence

When a continental plate meets an oceanic When a continental plate meets an oceanic plate, the less dense continental plate plate, the less dense continental plate remains floating as the oceanic plate is remains floating as the oceanic plate is pushed underneathpushed underneath

When the descending plate reaches a depth When the descending plate reaches a depth of ~100-150 km, some of the surrounding of ~100-150 km, some of the surrounding material will begin to melt, forming magmamaterial will begin to melt, forming magma

Some of this magma may reach the surface Some of this magma may reach the surface and cause volcanic eruptionsand cause volcanic eruptions

Continental Volcanic Arc – Continental Volcanic Arc – mountains mountains produced by the volcanic activity that is produced by the volcanic activity that is caused by the subduction of oceanic caused by the subduction of oceanic lithosphere under continental (Andes lithosphere under continental (Andes Mountains)Mountains)

Oceanic-Continental Oceanic-Continental ConvergenceConvergence

Oceanic-Oceanic Oceanic-Oceanic ConvergenceConvergence

When two oceanic slabs converge, one When two oceanic slabs converge, one descends below the otherdescends below the other

This causes volcanic activity similar to the This causes volcanic activity similar to the oceanic-continental boundary, with the oceanic-continental boundary, with the volcanoes forming on the ocean floor volcanoes forming on the ocean floor insteadinstead

It will eventually form a chain of volcanic It will eventually form a chain of volcanic structures that will become islandsstructures that will become islands

Volcanic Island Arc – Volcanic Island Arc – newly formed land newly formed land consisting of an arc-shaped chain of small consisting of an arc-shaped chain of small volcanic islands (Aleutian Islands, Alaska)volcanic islands (Aleutian Islands, Alaska)

Oceanic-Oceanic Oceanic-Oceanic ConvergenceConvergence

Continental-Continental-Continental Continental

ConvergenceConvergence Eventually, subduction may bring two continents Eventually, subduction may bring two continents together and a collision occurstogether and a collision occurs

The result of this collision is usually seen in the The result of this collision is usually seen in the form of complex mountains such as the form of complex mountains such as the Himalayas in South AsiaHimalayas in South Asia

When the continents collide, after all of an ocean When the continents collide, after all of an ocean basin between them has been subducted, the basin between them has been subducted, the collision folds and deforms the sediments along collision folds and deforms the sediments along the marginthe margin

A mountain chain forms that is composed of A mountain chain forms that is composed of deformed and metamorphosed sedimentary rocksdeformed and metamorphosed sedimentary rocks

The Himalayas, Alps, Appalachians, and Urals The Himalayas, Alps, Appalachians, and Urals were all formed by this processwere all formed by this process

Continental-Continental-Continental Continental ConvergenceConvergence

Collision of India and Collision of India and AsiaAsia

Concept CheckConcept Check

What happens when continents What happens when continents collide?collide?

Mountains form as the lithosphere Mountains form as the lithosphere is forced upwardis forced upward

Transform Fault Transform Fault BoundariesBoundaries

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

Most transform faults join two segments of mid-Most transform faults join two segments of mid-ocean ridges, present about every 100 km ocean ridges, present about every 100 km along the ridge axesalong the ridge axes

The seafloor produced at one ridge axis moves The seafloor produced at one ridge axis moves in the opposite direction as the seafloor in the opposite direction as the seafloor produced at an opposing ridge segment, and produced at an opposing ridge segment, and these segments grind past each other on their these segments grind past each other on their waysways

Most transform faults are found within the Most transform faults are found within the ocean basins, a few cut through the continental ocean basins, a few cut through the continental crust (San Andreas Fault)crust (San Andreas Fault)

Transform FaultsTransform Faults

The Role of Transform The Role of Transform FaultsFaults

The World’s Oceanic Trenches, The World’s Oceanic Trenches, Ridge System, and Transform Ridge System, and Transform FaultsFaults

AssignmentAssignment

Read Chapter 9, Section 3 (pg. 258-Read Chapter 9, Section 3 (pg. 258-264)264)

Do Chapter 9 Assessment #1-30 (pg. Do Chapter 9 Assessment #1-30 (pg. 275-276)275-276)

For Section 3: Do #’s 5, 7, 14, 17, 22, For Section 3: Do #’s 5, 7, 14, 17, 22, 23, 25, 27, & 3123, 25, 27, & 31