Plate Tectonics Evolution of Continents, Ocean Basins, Mountains Continental Margins

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Plate Tectonics Evolution of Continents,
Ocean Basins, Mountains Continental Margins
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Plate Margins - Where Stuff Happens..
Divergent Convergent Transform
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Relative Movements of Platesa) Divergent, (b)
Convergent-continent/ocean basin, transform,
(d) convergent-continent/continent
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Plate Boundaries
Seismic activity Volcanic activity Mountain bui
lding
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Ocean-Ocean Divergent Margin
Mid Ocean Ridges - long, sinuous ridge system,
central rift valley New ocean crust Activ
e volcanism Shallow earthquakes Rounded Pillow basalts Ridge offset by trans
form faults
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Ocean-Ocean Divergent Margin
Lava fountains (10 m high) spouting from eruptive
fissures during the October 1980 eruption of
Krafla Volcano.
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MOR cools by Conduction Convection - cold sea
water circulates Hydro-thermal springs - 350C
Circulating waters rich in H2S, SiO2, Mn, CO2,
H2, CH4, K, Ca, etc. Precipitate - form black / w
hite smokers
Adaptations to Vents Hydrogen-sulfide- (H2S) oxi
dizing bacteria - base of food chain
View of the first seen by scientists - deep-sea
submersible Alvin on the East Pacific Rise in
1979.
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Pillow Basalts Hot magma cools quickly in cold oc
ean water

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Continent-Continent Divergent Margin
ACTIVE - Red Sea began 10 Ma
INACTIVE - East African Rift Zone parts up to
20 Ma Example of stable triple junction - 3 break
s. One arm fails
http//earthview.sdsu.edu/trees/tecqest.html
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Continent-Continent Divergent Margin
Rio Grande Trough (USA) and African Rift Valley
- tic

Oldoinyo Lengai, active volcano in the East
African Rift Zone
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Seafloor Spreading at Mid-Ocean Ridges
Sediment accumulation increases away from ridge
- pelagic rain Depth of crust increases awa
y from ridge Age of crust increases away from
ridge
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Sea Floor Age (less than 200 Ma)
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How Do Divergent Margins Develop?
DOMING High heat flow, thermal expansion of crust
- few km high / 1000s km across.
High, dry climate RIFTING Normal faults accom
modate stretch NO ocean crust Possible formation
of triple junction High, dry climate non-marin
e sandstones, conglomerates in basin
East African Rift Zone DRIFTING Crust thins an
d initial intrusion of basalts as new seafloor
Shallow ocean high evaporation
Later normal marine sediment
Drainage reverses in to the sea.
Gulf of California (5 Ma) Red Sea (10 Ma)
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Convergent Boundaries

• Plate Boundaries where plates are moving together
  .. or converging
  
• High seismicity to depths of 700 km
• Volcanism and/or metamorphism
• Areas of continental accretion / growth
• Subduction of crust / mountain building
• Types
• Ocean to ocean and ocean to continent
• Continent to continent

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Types of ConvergenceOcean-Ocean,
Ocean-Continent, andContinent-Continent
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Seismic Activity Along Descending Plate
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Ocean - Continent Collision

• Oceanic crust more dense than continental crust
• Continental margin / Volcanic Arc
• Deep trench on ocean side Fore arc attached to
  continental crust
  
• Volcanoes - mountain range parallel to / 300-400
  km from trench
  
• High volcanic activity- Andesitic
• High seismic activity earthquake foci 0 to 700
  km deep
  
• W margin of North / South America
• Andes and Cascades

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Components Oceanic plate Trench Fore-arc ridg
e (melange) Fore-arc basin Continental plate wit
h volcanic mountain range (e.g. Andes)

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The Ring of Fire- Volcanics associated with
Pacific plate boundaries
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Mountain Building-e.g. the Andes
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Ocean to Ocean Collision
Two plates of same thickness (? Age/temperature)
Which one wins? Deep trench on ocean side A
rcuate line of islands 100 Km land ward from
trench - Island Arc Zone is long and narrow (1000
s Km x 200-300 Km) High volcanic activity- And
esitic High seismic activity earthquake foci 0 t
o 700 km deep Aleutian Trench Marianas Trenc
h (10,860 m deep) Tonga Trench (10,800 m deep) L
esser Antilles
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Components Oceanic plate Trench Fore-arc ridg
e (melange) Fore-arc basin, Island arcBack-arc b
asin (down-going plate melts / accom. of
spreading) Oceanic Plate
Skinner and Porter, 2000
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Continent to Continent Collision

• Two pieces of continental crust of equal - light
  - density
  
• Neither subducts mountain building, continental
  accretion
  
• Australia/India and Eurasia - Himalayas
• Africa and Europe - Alps (early Mesozoic)
• Africa and North America -
• Appalachians (Paleozoic)

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Building Continental Material Precambrian Shields