Title: Types of Plate Boundaries Brown 24-25
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# Types of Plate Boundaries Plates Interact with each other in 3 possible ways
1) Converge: - - -> |<- - -2) Diverge: <- - -|- - -> - - - - -> 3) Transform: _____
< - - - - -So how do the plates move?
Convection currents in the asthenosphere: warm material rises, cool material sinks Creates a circular motion of material due to heating and cooling Convection Currents in the Asthenosphere 3 Types of Plate Boundaries
Blue = divergent Green = transform Red = convergent Divergent Plate Boundaries
At divergent plate boundaries, the plates are moving apart Place where new crust is created at rift valleys or mid-ocean ridges Examples: Great Rift Valley in E. Africa, Lake Baikal in Russia, and Mid-Atlantic Ridge (MAR) volcanism and earthquakes No subduction Lets draw a divergent boundary: Stage 1: Upwarping of the lithosphere
caused by convection currents in the asthenosphere. Beginning of the formation of the divergent plate boundary.
Stage 2: Formation of a rift valley that leads to a series of valleys and ridges .
Great Rift Valley are at this stage.
Stage 3: Formation of a narrow sea.
Red Sea & Gulf of Aden are at this stage.
Stage 4: Formation of ocean. Awell-developed mid-oceanic ridge. Active crust formation. All 4 major oceans are at this stage.
Process of Rifting The Great Rift Valley of Africa
African Great Lakes make up ~25% of the planet's unfrozen surface fresh water The Great Rift Valley of Africa
Rifting started 35 million years ago Created some of the deepest lakes in the world (Victoria and Tanganyika) Is 4,300 miles long Continent will split in half in tens of millions of years Graben (valley)
a block of crust between faults that has shifted downward in relation to the blocks on either side
Horst (ridge)
higher blocks/ridges (either shifted upward or remaining stationary) on either side of grabens Basin and Range Province
Series of horst and graben features in western U.S. and Mexico Basin and Range Province Lake Baikal of Russia
Part of a rift valley (widens 2 cm/year) Largest lake by volume on Earth (contains 19% of all our fresh water) Deepest lake on Earth (~1 mile deep) Oldest lake on Earth (25-30 million years old) The Red Sea & Gulf of Aden Mid-Atlantic Ridge: Iceland Transform Plate Boundaries
At transform plate boundaries, tectonic plates move horizontally past each other No up or down motion of plates
> Sketch this in your notes
What happens at a transform boundary?
No volcanism, but there are earthquakes No subduction A great example of a transform boundary: The San Andreas Fault
> Transform motion of North American and Pacific plates
The San Andreas Fault
In ~20 million years, the cities of San Francisco and Los Angeles will be neighbors Convergent Boundaries : when plates move together
Two types of crust means three possible scenarios: (O = Oceanic / C = Continental) O-C O-O C-C What happens at each boundary depends on the density of the crusts: Subduction
The sinking of lithosphere into the asthenosphere, where plates converge, is called subduction
Crust that is more dense will be pushed under less dense crust at convergent boundaries. Continental crust (2.7 g/cm 3 ) is less dense than oceanic crust (3.0 g/cm 3 ) Oceanic crust is more dense = slides under ( subducts ), pushing continental crust upward Formation of mountain ranges on the continental crust side =
continental volcanic arcs
Formation of trench in the ocean floor where subduction begins Volcanism and earthquakes
What happens at Convergent O-C boundaries?
> Sketch this in your notes
> 2.7 g/cm 3
> 3.0 g/cm 3
A great example of an O-C convergent boundary: The Andes Mountains
> Nazca plate subducted under South American plate
The Andes Mountains What happens at convergent O-O boundaries?
Subduction of whichever oceanic crust is more dense ( usually whichever plate is older ) Formation of a volcanic island arc
Formation of trench in the ocean floor where subduction begins Volcanism and earthquakes
> Sketch this in your notes
A great example of an O-O convergent boundary: Mariana Trench
> Subduction of Pacific plate under the Philippine plate
The Pacific Ocean is full of trenches and volcanic island arcs! What happens at a convergent C-C boundary?
Overriding of one continental plate over another Formation of collisional mountain ranges
No volcanism, but there are earthquakes No subduction of continental crust here
> Sketch this in your notes
A great example of a C-C convergent boundary: The Himalayan Mountains
> Collision of Indian Plate and Eurasian Plate
Himalayan Mountains (and Mount Everest) What drives plate motions? (Honors only)
Slab pull and ridge push Which is the driving force out of the two? homework - take notes on What Drives Plate Motions?