Transcript PLATE BOUNDARIES Geologically active regions Three classes of

Plate Boundaries
Boundaries-Geologically Active Regions
Three Main Classes of Plate Boundaries
1. Convergent
2. Divergent
3. Transform
1.
Convergent Plate Boundaries
Converging - Ocean to Ocean plate

Subduction, volcanic island arc (andesite
- conversion of oceanic crust), deep
ocean trench

Unstable geologically

Examples - West Indies, Japan, Aleutian
Islands, Philippine Islands, Indonesia,
Central America
Volcanic Island Arc-Aleutians, Japan, Indonesia

Converging plate boundary composite volcanoes, Fuego and Acatenango, as seen
from
the flanks of the Volcan de Agua, near Antigua Guatemala
August, 2000, Nikon FE2, 200 mm Nikon AIS f4 lens.
First stage in conversion of oceanic crust to
continental crust
2. Convergent Plate Boundary - Continent
to Ocean
Volcanic alpine chain, subduction,
deep ocean trench
Examples - Andes Mtns., West coast
of Mexico, Cascades - Pacific
Northwest of United States
Andes Mountains
South America
3.
Convergent - Continent to Continent

Shallow focus earthquakes, granitic mountain
range

Himalayan Mtns. - India/Australian plate
collides with Asian plate - creates Himalayan
Mtns.

Destructive earthquakes in China - 2,000 miles
from plate boundary
Nepal/China/India
Himalayas
Divergent (Rifting) Plates

1. Continent-Continent Rifting (Diverging)

Rift Valley, block faulted mountain ranges,
basaltic volcanic activity, shallow focus
earthquakes

East African Rift Valley
Lake Region
Extends to Jordan River Valley
Sinai Peninsula - Asia and Africa Rift apart
Dead Sea - between Israel/Jordan - 300 m
below sea level
Lowest point on continental crust
Djibouti - Red Sea trickles into Africa
*First stage in the development of an ocean
basin
Great Rift Valley
Kenya

2. Ocean - Ocean Divergent

Sea floor spreading, pillow basalts, shallow
focus earthquakes, oceanic ridge

Growth of an ocean basin

Red Sea - early stage
Atlantic Ocean - advanced
Iceland
Mid-Ocean Ridge present in all ocean basins
East Pacific Rise
Mid Atlantic Ridge
MAR in Iceland
Transform Boundary

Sliding plates
One plate grinds past another - friction

Shallow focus earthquakes
Only contact without volcanic activity

San Andreas Fault, Anatolian Fault, Motagua
Fault
San Andreas
Fault
North Anatolian Fault, Turkey
Convection - Heat Flow
Heat (convection) cells in
mantle/asthenosphere
Lithosphere rests on asthenosphere
Rising heat cells - plates separate
Sinking heat cells - plates pushed down into
mantle
Convection Currents
Convection Currents
Convection Currents
Measured heat flow
Highest at ridge
Lowest at trench
Deep heat - from convection, highest
under ocean crust
Thermal Plume-Mantle Hot Spots
Area of concentrated heat flow from deep mantle
Hawaii - not on plate boundary
Pacific plate passing over thermal plume
New Hawaiian Island Loihi
Other thermal plumes
Afar Triangle - numerous thermal
plumes intra African plate
Yellowstone
Pacific Plate contains numerous
thermal plumes
Reunion Islands - similar to Hawaii
Afar Triangle
Africa
Rate of Plate Movement

San Andreas Fault - 5.5 cm/yr

Mid-Atlantic Ridge
Iceland - 1.8 cm/yr; South Atlantic
(Ascension Island) - 3.9 cm/yr

East Pacific Rise - off South America
Most rapid movement - 17.1 cm/yr

Lost Continents

Micro-continent
Seychelles Bank in Indian Ocean
Granitic crust "floating" over oceanic crust
Broke away from Africa, has not subducted
Beaches of Seychelles Is. - pink sand - indicative of
granite Seychelles