Plate tectonics: The Key to understanding mountain formation

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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 sedimentary rock layer Limestone (top) Clue #2: Material composition of mountains

Clue #3: Continental Shields in interior of continents

GEOLOGY OF THE USA Craton (kratos; Greek for strength) old and stable part of the continental crustcontinental crust that has survived the merging and splitting of continentscontinents interiors of continents formed of a crust of lightweight rock, e.g. granite, attached to a section of the upper mantle.mantle

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

Summary: Clues to mountain formation Mountains only in certain areas Fossils on top of mountains Shields in interior of continents Ocean crust oldest near continents and youngest towards middle of oceans

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 FOUNTAINS KRAFLA VOLCANO ICELAND

B. CONVERGENT PLATE BOUNDARY Plates are moving toward each other destruction (recycling) of crust takes place along convergent boundaries 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 Mtns West 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

Island Arc formation Oceanic- oceanic convergence: one plate subducted under the other a trench is formed, ex. Mariana trench (nearly 11,000 m) erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form an island volcano

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

HIMALAYAS collision 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 VIDEO org/resource/ess05.sci.ess.ea rthsys.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