Title: Plate Tectonics Evolution of Continents, Ocean Basins, Mountains Continental Margins
1Plate Tectonics Evolution of Continents,
Ocean Basins, Mountains Continental Margins
2Plate Margins - Where Stuff Happens..
Divergent Convergent Transform
3Relative Movements of Platesa) Divergent, (b)
Convergent-continent/ocean basin, transform,
(d) convergent-continent/continent
4Plate Boundaries
Seismic activity Volcanic activity Mountain bui
lding
5Ocean-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
6Ocean-Ocean Divergent Margin
Lava fountains (10 m high) spouting from eruptive
fissures during the October 1980 eruption of
Krafla Volcano.
7MOR 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.
8Pillow Basalts Hot magma cools quickly in cold oc
ean water
9Continent-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
10Continent-Continent Divergent Margin
Rio Grande Trough (USA) and African Rift Valley
- tic
Oldoinyo Lengai, active volcano in the East
African Rift Zone
11Seafloor 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
12Sea Floor Age (less than 200 Ma)
13How 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)
14Convergent 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
15Types of ConvergenceOcean-Ocean,
Ocean-Continent, andContinent-Continent
16Seismic Activity Along Descending Plate
17Ocean - 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
18Components Oceanic plate Trench Fore-arc ridg
e (melange) Fore-arc basin Continental plate wit
h volcanic mountain range (e.g. Andes)
19The Ring of Fire- Volcanics associated with
Pacific plate boundaries
20Mountain Building-e.g. the Andes
21Ocean 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
22Components 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
23Continent 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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25Building Continental Material Precambrian Shields