Pangaea Colliding Plates Objectives –Explain how plate tectonics accounts for the movement of continents –Compare and contrast divergent, convergent.

PangaeaPangaea

Colliding PlatesColliding Plates• Objectives

– Explain how plate tectonics accounts for the movement of continents

– Compare and contrast divergent, convergent and transform plate boundaries.

– Explain how convection currents inside Earth might be the cause of plate tectonics

• Key Terms– plate tectonics, lithosphere, divergent

boundary– Convergent boundary, transform fault boundary

Plate TectonicsPlate Tectonics• Tectonic plates

– Think of the hypotheses of continental drift and sea-floor spreading as clues to a mystery.

– How can the two hypotheses be explained?• In the 1960’s, geologists developed a new theory to

explain the apparent movement of the continents.• The theory of plate tectonics suggests that Earth’s

crust and upper mantle are broken into sections called plates (that move).

• But, what are they made of and how do they move??

• We already know that the Earth’s crust is a layer of solid rock.

• The uppermost portion of the mantle is also solid– Together, these two areas are known as the

lithosphere

• We also know that there is an area in the mantle that is less solid. Here, the material acts more like a putty; it’s a solid that can flow.– This putty-like layer is called the

asthenosphere

PlatesPlates

• Divergent Boundaries– The boundary between two tectonic plates

that are moving away from each other• Magma is forced upward between the two plates,

creating a new crust, thus making….• Mid-ocean ridges are divergent boundaries

Divergent BoundaryDivergent Boundary

Learning CheckLearning Check• The theory that suggests that Earth’s crust and

upper mantle are broken into sections called plates (that move) is known as…– plate tectonics

• Together, the Earth’s crust is a layer of solid rock and the uppermost portion of the mantle is also solid are known as – Lithosphere

• The boundary between two tectonic plates that are moving away from each other is known as…– Divergent boundary

• Convergent Boundaries– Crustal material can be

destroyed where 2 plates meet head on.– This type of boundary is called a convergent

boundary– What do you think happens when two plates

containing continental crust collide?• The two plates crumple forming mountain ranges!

• The Himalaya Mountains formed when the Indian Plate collided with the southern part of the Eurasia plate.

HimalayasHimalayas

• There are three styles of convergent plate boundaries– Continent-continent collision– Continent-oceanic crust collision– Ocean-ocean collision

Convergent BoundariesConvergent Boundaries

Convergent BoundaryConvergent Boundary

• Transform Fault Boundaries

– A third type of boundary that is formed when two plates slide past one another in opposite directions.

• Think about the San Andreas Fault in California – This is where the North America and the Pacific plate slide past one another!

• Along this boundary, the Pacific plate moves NW relative to the North American plate at an average rate of 2 cm per year.

Transform Fault BoundaryTransform Fault Boundary

Transform Fault Bound. Cause Transform Fault Bound. Cause Earthquakes!Earthquakes!

• Causes of Plate Tectonics– How does the theory of plate tectonics explain

the cause of plate movements?• The driving force behind this movement is

HEAT!• A material that is hot is less dense than the

same material that is cold• This is because the same mass takes up

more volume (space) when the material is heated.

• This helps us explain the process of convection currents…

Convection Currents in the Earth

• Convection Currents– C.C.’s within the Mantle

cause the various plates in Earth’s lithosphere to move around.

– As the plates bump into each other, boundaries form!

– Plates move in different directions because there are many conv. cells within the Mantle!

Learning Check!Learning Check!

• A type of boundary that is formed when two plates slide past one another in opposite directions is known as– Transform Fault Boundary

• Boundary where crustal material can be destroyed where 2 plates meet head on is– Convergent Boundary

• Mountain Ranges– Convergent

• Earthquakes– Transform Fault

Convergent BoundariesConvergent Boundaries

• Forms mountains, e.g. European Alps, Himalayas

Continent-Continent CollisionContinent-Continent Collision

• Called SUBDUCTION

Continent-Oceanic Crust CollisionContinent-Oceanic Crust Collision

• Oceanic lithosphere subducts underneath the continental lithosphere

• Oceanic lithosphere heats and dehydrates as it subsides

• The melt rises forming volcanism

• E.g. The Andes

SubductionSubduction

• When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.

• The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.

• The worlds deepest parts of the ocean are found along trenches. – E.g. The Mariana Trench is 11 km deep!

Ocean-Ocean Plate CollisionOcean-Ocean Plate Collision

Convergent BoundaryConvergent Boundary