Plate tectonics:

The Key to understanding mountain formation

Plate boundaries

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Volcanoes, earthquakes

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World’s tectonic plates

Earth’s Topographic Regions

Clue #1:Mountain ranges found only in certain areas (edges of continents)

Marine fossils on top of Everest

N side, view from Rongbuk Monastery, Tibet

•Granite core•sedimentaryrock layer•Limestone(top)

Clue #2: Material composition of mountains

Clue #3: Continental Shields

in interior of continents

GEOLOGY OF THE USACraton (kratos; Greek for strength)

• old and stable part of thecontinental crust that has survived the merging and splitting of continents

•interiors of continents

•formed of a crust oflightweight rock, e.g. granite,attached to a section of the upper mantle.

Clue #4:Ocean crust oldest near continents and youngest towards middle of oceans

youngest

oldest

Plate motion

• Plates move away from, toward, or slide past each other.

• There are 3 types of plate boundaries: - divergent

- convergent- transform.

Three types of plate boundary

A. DIVERGENT PLATE BOUNDARY

• occur along spreading centers where plates are moving apart

• new crust is created by magma pushing up from the mantle

Example: Mid-Atlantic Ridge

•a topographically high area near the middle of the Atlantic Ocean

•splits nearly the entire Atlantic Ocean north to south,

Divergent: Atlantic Ridge

LAVA FOUNTAINSKRAFLA VOLCANOICELAND

B. CONVERGENT PLATE BOUNDARY

• Plates are moving toward each other

• destruction (recycling) of crust takes place along convergent boundaries

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Sometimes, pne plate sinks (is subducted) -SUBDUCTION ZONE

Convergent plate boundaries

3 types depending on type of plate involved:• Oceanic-continental convergence• Oceanic-oceanic convergence• Continental-continental convergence

1. Oceanic-Continental Collision•oceanic Nazca Plate is pushing into and being subducted

under the continental part of the South American Plate

•South American Plate is being lifted up, creating the Andes

•Strong, destructive earthquakes

•rapid uplift of mountain ranges are common in this region.

Oceanic-continental: Pacific RING OF FIRE

Example: Andes MtnsWest margin of the South American continent

•oceanic Nazca Plate is pushed toward and beneath the continental portion of the South American Plate

•typical example of a convergent plate boundary

ALPAMAYO, CORDILLERA BLANCA

2. Oceanic-oceanic Collision

Subduction processes in oceanic-oceanic

plate convergence result in the

formation of volcanic arc islands

Examples of volcanic arc islands

• Aleutians• the Kuriles• Japan • the Ryukyus, • the Philippines• Indonesia

3. Continental-continental Collision• neither plate subducted because

the continental rocks are relatively light • like two colliding icebergs, plates resist

downward motion

HIMALAYAScollision between the Indian and Eurasian plates has pushed up the Himalayas and the Tibetan Plateau

C. TRANSFORM BOUNDARY

• At a transform plate boundary, plates slide past each other.

• Crust neither produced nor destroyed

Example:San Andreas fault in California

Pacific Plate slides past the North American Plate.

Special case: HOTSPOTS

“Plume” = huge column of upwelling lava

HOTSPOTS

HAWAII VIDEOhttp://www.teachersdomain.org/resource/ess05.sci.ess.earthsys.hawaii/

How fast are plates moving?

• The Arctic Ridge – slowest rate (less than 2.5 cm/yr)

• East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile– fastest rate (more than 15 cm/yr).

Plate Motion Summary

Mountain Maker, Earth shaker

• Interactive media