Plate Tectonics Continental Drift Theory Theory of Plate Tectonics Plate Boundaries.
Topic 4 Plate Tectonics—Plate Theory
description
Transcript of Topic 4 Plate Tectonics—Plate Theory
![Page 1: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/1.jpg)
Topic 4Plate Tectonics—Plate Theory
GEOL 2503Introduction to Oceanography
![Page 2: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/2.jpg)
Two Parts
• Topic 4. The Birth of a Theory• Topic 5. Plate Dynamics• See videos on Learner.org under the
Earth Revealed series• See the U. S. Geological Survey on-line
publication This Dynamic Earth athttp://pubs.usgs.gov/gip/dynamic/dynamic.html
![Page 3: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/3.jpg)
Evolution of plate tectonic thinking• 1620 Francis Bacon: Continents on either side of Atlantic
Ocean fit together--continents once were joined?• 1750 Georges Buffon: Life forms similar in Europe and
N. America--continents once were joined?• 1883 Edward Suess: Southern hemisphere continents
once were joined as super-continent Gondwana• 1908-1912 Alfred Wegener: Proposes hypothesis of
“continental drift”• 1950s-1960s: Mapping of ocean floor (and many other
discoveries) leads to theory of plate tectonics
![Page 4: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/4.jpg)
In 1858, geographer Antonio Snider-Pellegrini made these two maps showing his version of how the American and African continents may once have fit together, then later separated. Left: The formerly joined continents before their separation. Right: The continents after the separation. From USGS, This Dynamic Earth.
![Page 5: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/5.jpg)
Interior of the Earth• Four main layers
Inner coreOuter coreMantleCrust
• Other layersLithosphereAsthenosphere
![Page 6: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/6.jpg)
![Page 7: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/7.jpg)
Inner Core
• Mostly iron• Magnetized and very hot (4000-5500 C)• Radius of 1222 km. (759 mi.)—about the
same size as the moon• Solid due to intense pressure and heat
![Page 8: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/8.jpg)
Outer Core
• Mostly iron • 3200 C, slightly cooler than Inner Core• Radius of 2258 km. (1402 mi.)• Has fluid or liquid characteristics
![Page 9: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/9.jpg)
Mantle
• Largest layer• 2866 km. (1780 mi.) thick• Cooler than core (1100-3200 C)• Composed of magnesium/iron
![Page 10: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/10.jpg)
Crust• Cold and rigid• Oceanic crust
– Thin 10 km (6 mi)– Basalt– Denser
• Continental crust– Thick 100 km (60 mi)– Granite– Less dense
![Page 11: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/11.jpg)
Lithosphere• Crust and very upper mantle• Cold and rigid• Brittle—can crack and break• Floats on asthenosphere• Forms the “plates” in plate
tectonics
![Page 12: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/12.jpg)
Asthenosphere
• Upper part of mantle below lithosphere• Weaker than lithosphere, behaves
plastically
![Page 13: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/13.jpg)
Lithosphere (crust and mantle; rigid)
Asthenosphere (mantle; plastic)
Mesosphere (mantle; rigid)
![Page 14: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/14.jpg)
Evidence for Internal Structure
• From seismic waves• P-waves (primary waves) are fast and can
penetrate all states of matter• S-waves (secondary waves) are slow and
cannot pass through liquid outer core• Patterns of seismic wave travel give
information on earth internal structure• Earthquakes and nuclear bomb testing
![Page 15: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/15.jpg)
Don’t worry about the details, just know that this is how we have learned of Earth’s internal structure.
![Page 16: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/16.jpg)
Density
• Measure of mass per unit volume (m/v)• Mass versus weight• Units: grams per cubic centimeter (g/cm3)
or kilograms per cubic meter (kg/m3)• Average density of Earth 5.51 (g/cm3)• Pure water has a density of 1 g/cm3 which is
equal to 1,000 kg/m3
![Page 17: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/17.jpg)
Note especially the thicknesses and densities.
![Page 18: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/18.jpg)
Theory of Continental Drift
• Continents move about on the surface of the Earth• Proposed by Alfred Wegener in Early 1900’s• Evidence
– Fit of continents– Rock and mountain formations– Fossils– Climatic evidence in fossils and rocks
![Page 19: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/19.jpg)
![Page 20: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/20.jpg)
Where is Central America? ?
![Page 21: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/21.jpg)
Indications of glaciers found around several continents
![Page 22: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/22.jpg)
Glacial striations—formed by gravel and rocks in the ice scratch the rock surface
![Page 23: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/23.jpg)
Large and small rocks, many angular and broken, mixed with very fine silt and clay. Indicative of being dumped from a melted glacier.
Diamictite
![Page 24: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/24.jpg)
Diamictite
• poorly sorted sediment• glacial origin• deposited by rapidly melting glaciers
![Page 25: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/25.jpg)
http://geomaps.wr.usgs.gov/parks/pltec/pangea.html
The Glossopteris fauna
![Page 26: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/26.jpg)
![Page 27: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/27.jpg)
![Page 28: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/28.jpg)
Sea Floor Spreading
• Proposed by Harry Hess in 1960• Proposed convection cells in the mantle as
the mechanism for continental drift• Oceanographic observations during the
years after World War II provided evidence
![Page 29: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/29.jpg)
Sea floor spreading• Harry Hess (1962)• Mid-ocean ridge site of new ocean crust• Oceanic trench site of crust destruction
(subduction) Fig. 2.10
![Page 30: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/30.jpg)
![Page 31: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/31.jpg)
Evidence of Sea Floor Spreading
• Earthquakes along spreading and subducting areas
• Radiometric dating of rocks(youngest at ridge oldest, farther from ridge)
• Magnetism of rocks/polar reversals
![Page 32: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/32.jpg)
Not randomly distributed, but mostly restricted to narrow belts
![Page 33: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/33.jpg)
![Page 34: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/34.jpg)
Ocean crust is young (Y) at spreading centers—and older (O) in both directions away from spreading centers
Y
O
O
YO O
spreading centers
![Page 35: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/35.jpg)
Iceland is one place where the spreading center comes up on land.
![Page 36: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/36.jpg)
Paleomagnetism
• New oceanic crust is formed as sea floor spreading continues
• Earth’s magnetic field reverses often as the ocean crust is formed
• Earth’s magnetism is recorded in the new crust• The result is magnetic stripes in the sea floor
parallel to ridges recording the magnetic reversals
![Page 37: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/37.jpg)
![Page 38: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/38.jpg)
Magnetic polarity reversals
Fig. 2.9
![Page 39: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/39.jpg)
Fig. 2.11
![Page 40: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/40.jpg)
Magnetic anomalies
Fig. 2.12
![Page 41: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/41.jpg)
![Page 42: Topic 4 Plate Tectonics—Plate Theory](https://reader036.fdocuments.in/reader036/viewer/2022081505/568165f9550346895dd924ec/html5/thumbnails/42.jpg)