PLATE TECTONICS

Plate Tectonics

Earth is a dynamic planet: its land masses and oceans are in constant motion. Continental blocks split to form new oceans

Plate Tectonics

while oceans subduct to recycle material to Earth’s interior…. Continents rift; oceans subduct

Plate Tectonics

Plate tectonics are responsible for:EarthquakesVolcanoesAnd creates our landforms through

mountain building

Plate Tectonics Plate tectonics is the unifying theory that describes

our earth’s dynamics.

Plate Tectonics Plate tectonics: outer rigid layer of earth consists

of about 7 or 8 major plates and many minor plates: some are mostly oceanic crust, but most contain both continents and ocean

basins

Plate Tectonics

Lithosphere:Earth’s outer rigid shell formed of the platesIt is about 100 km thick, and overlies zone of weaker,

hotter material called the asthenosphere. It is thick over continents, thin over oceansThe weak rock of

asthenosphere allows lithosphere to move

Plate Tectonics Plates move as rigid blocks, with all major

interactions at margins. Most of earth’s earthquakes, volcanism and mountain building occur at plate boundaries: divergent, convergent, transform

Plate Tectonics

Divergent boundaries: The plates move apart, creating new sea floor as

mantle material pushes up from the pressure below. These are most commonly the oceanic ridges, which

may begin with continental rifting. Upwelling magma cools to create new slivers of ocean

floor, at about 5 cm/year

Plate Tectonics

Convergent boundaries: plates collide at

convergent boundaries,

destroying older crust.

Plate Tectonics When oceanic plates converge, one subducts

beneath the other, descending into the asthenosphere and producing an oceanic trench.

Plate Tectonics When continental and oceanic plates collide, the

denser oceanic plate is subducted Water forced out of subducting slab lowers melting

point in overlying mantle, causing magmatism. This is why volcanoes are associated with subduction zones

Plate Tectonics

When 2 continental plates collide, no subduction can occur, and mountain building occurs instead.

Plate Tectonics

Transform fault boundaries: Often connect 2 oceanic ridge crests. May

also connect divergent to convergent boundaries. Most are offshore, but some like San Andreas cross land

Plate Tectonics

Haiti The January 12, 2010, Haiti

earthquake occurred in the boundary region separating the Caribbean plate and the North America plate. This plate boundary is dominated by left-lateral strike slip motion and compression, and accommodates about 20 mm/y slip, with the Caribbean plate moving eastward with respect to the North America plate.

Plate Tectonics

Plate tectonics and earthquakes: subduction explains the distribution of deep

focus earthquakes (up to 700 km), at depths much greater than earth’s brittle zone, and their correlation with ocean trenches.

Plate Tectonics

Driving mechanisms of plate tectonics: generation and dissipation of heat within the earth. This can drive plate tectonics through convection

Plate Tectonics Other mechanisms also contribute:

Ridge push, slab pull, slab suction

Earth’s Future Over the next 50 million

years, Baja peninsula and parts of So. Calif. west of San Andreas will slide past North American plate, such that Los Angeles will pass San Francisco.

Earth’s Future

A new sea will emerge in east Africa, where rifting is currently taking place

Earth’s Future

Africa will collide with Europe to form new mountains.

Australia and New Guinea will capture the Philippines, then collide with Asia

Homework

P. 447 #1 P. 454 #1, 2 P. 459 #1, 2, 3, 4 P. 463 #3