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

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Presentation on theme: "Plate Tectonics Evolution of Continents, Ocean Basins, Mountains Continental Margins."— Presentation transcript:

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

2 Plate Margins - Where Stuff Happens….. Divergent Convergent Transform

3 Relative Movements of Plates a) Divergent, (b) Convergent-continent/ocean basin, © transform, (d) convergent-continent/continent

4 Plate Boundaries Seismic activity Volcanic activity Mountain building

5 Ocean-Ocean Divergent Margin Mid Ocean Ridges - long, sinuous ridge system, central rift valley New ocean crust Active volcanism Shallow earthquakes < 100 km Rounded “Pillow” basalts Ridge offset by transform faults

6 Lava fountains (10 m high) spouting from eruptive fissures during the October 1980 eruption of Krafla Volcano. Ocean-Ocean Divergent Margin

7 MOR cools by: Conduction Convection - cold sea water circulates Hydro-thermal springs - >350°C Circulating waters rich in H2S, SiO2, Mn, CO2, H2, CH4, K, Ca, etc. Precipitate - form black / white smokers Adaptations to Vents Hydrogen-sulfide- (H2S) oxidizing bacteria - base of food chain View of the first seen by scientists - deep-sea submersible Alvin on the East Pacific Rise in 1979.

8 Pillow Basalts Hot magma cools quickly in cold ocean water

9 ACTIVE - Red Sea began ~10 Ma INACTIVE - East African Rift Zone; parts up to 20 Ma Example of stable triple junction - 3 breaks. One arm fails Continent- Continent Divergent Margin

10 Rio Grande Trough (USA) and African Rift Valley - < 100 km deep Volcanism - basaltic and rhyolitic Oldoinyo Lengai, active volcano in the East African Rift Zone

11 Seafloor Spreading at Mid-Ocean Ridges Sediment accumulation increases away from ridge - “pelagic rain” Depth of crust increases away from ridge Age of crust increases away from ridge

12 Sea Floor Age (less than 200 Ma)

13 DOMING High heat flow, thermal expansion of crust - few km high / 1000’s km across. High, dry climate RIFTING Normal faults accommodate stretch NO ocean crust Possible formation of triple junction High, dry climate: non-marine sandstones, conglomerates in basin East African Rift Zone DRIFTING Crust thins and 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) How Do Divergent Margins Develop?

14 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

15 Types of Convergence Ocean-Ocean, Ocean-Continent, and Continent-Continent

16 Seismic Activity Along Descending Plate

17 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 / 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

18 Components: Oceanic plate Trench Fore-arc ridge (melange) Fore-arc basin Continental plate with volcanic mountain range (e.g. Andes)

19 The Ring of Fire- Volcanics associated with Pacific plate boundaries

20 Mountain Building-e.g. the Andes

21 Ocean to Ocean Collision Two plates of same thickness (? Age/temperature) Which one wins? Deep trench on “ocean” side Arcuate line of islands ~100 Km land ward from trench - Island Arc Zone is long and narrow (1000’s Km x Km) High volcanic activity- Andesitic High seismic activity; earthquake foci 0 to 700 km deep Aleutian Trench Marianas Trench (10,860 m deep) Tonga Trench (10,800 m deep) Lesser Antilles

22 Skinner and Porter, 2000 Components: Oceanic plate Trench Fore-arc ridge (melange) Fore-arc basin, Island arc Back-arc basin (down-going plate melts / accom. of spreading) Oceanic Plate

23 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)

24

25 Building Continental Material Precambrian Shields


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