The concept of ‘Global Plate Tectonics’courseweb.glendale.edu/ppal/ppt/plate tectonics.pdf ·...
Transcript of The concept of ‘Global Plate Tectonics’courseweb.glendale.edu/ppal/ppt/plate tectonics.pdf ·...
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The concept of ‘Global Plate Tectonics’
is a unifying theme in modern geology that integrates the earlier ideas of
continental drift,sea-floor spread, andmountain building
To explain why the present ocean floor, which covers only ~71% of earth’s surface area, has <200 Ma old rocks, compared to up to ~4.2 Ga old rocks on land, while there is no evidence of any change in earth’s surface area during this period.
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To Alfred Wegener, theevidence of 250-300 Ma glaciation in today’s far flung continents pointed to their having once been joined together and located at the south pole.
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This is a USGS animation of Wegner’s reconstruction of continents made to explain the paleoclimatic evidence.
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This is a USGS animation of Wegner’s reconstruction of continents made to explain the paleoclimatic evidence.
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Sea floor spread by intermittant volcanism at the mid-ocean ridge (top left) results in the recording by subsequent lavas of the geo-magnetic polarity reversals (left bottom) and the resulting marine magnetic anomalies can be mapped by the magnetometers towed by ships (bottom right).
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How deep sea trenches form
Convergence of the continental edges of plates
Convergence of continental edge of one plate and the oceanic edge of the other.
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How folded mountain belts form
Convergence of the continental edges of plates
Convergence of continental edge of one plate and the oceanic edge of the other.
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http://pao.cnmoc.navy.mil/PAO/Educate/OceanTalk2/indexnew.htm
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This is the relief map of the world. If you go to the URL below, you will be able to click on any of the 45°×45° grids here to view enlarged versions of them.
http://www.ngdc.noaa.gov/mgg/image/2minrelief.html
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The sea floor is not a flat surface
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Earthquake epicenters display a typically nonrandom distribution
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Seismicity defines the plate boundaries
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Some major plates
Pacific Pacific plateplate
NazcaNazcaplateplateAustralian Australian
plateplate
South South American American plateplate
North North American American plateplate
African African plateplate
GordaGordaplateplate
CocosCocosplateplate
Antarctic plateAntarctic plate
Philippine Philippine plateplate
Indi
an p
late
Indi
an p
late
Eurasian platesEurasian platesEurasian Eurasian platesplates
Caribbean Caribbean plateplate
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The older the sea floor the farther it is from the ridge axis
0.0
9.6
20.2
33.0
40.2
47.9
56.0
68.7
83.0
118.
012
6.5
131.
7
141.
914
9.9
156.
6
180.
0
Age of the sea floor (Ma B.P.)
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http://www.ngdc.noaa.gov/mgg/image/relief_slides2.html
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http://www.ngdc.noaa.gov/mgg/image/relief_slides2.html
The Pacific Ring of
Fire
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North American Plate Boundarieshttp://www.ngdc.noaa.gov/mgg/image/relief_slides2.html
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Inner core
Outer core
Mantle
2250 km63
71 k
m2900 km
Man
tle Lith
osph
ere
Continental crustOceanic crust
0 km
200 km
100 km
Earth is amulti-layered
body. This is based on the following evidences:
1. seismic2. gravity and
3. geomagnetic.
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A convergent plate boundary, e.g., the convergence of Nazca
and South American plates
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Juan de Fuca ridge and the associated plates and plate boundaries off the Pacific North-
east and Canada. Note that the Cascadia
subduction zone is also called the “Filled
Trench”, as this trench got filled by sediments
carried by the huge runoff from land that
has characterized this region particularly
since the Last Ice Age.
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Seismicity at the Filled Trench offers the most likely scenario of the western U.S. facing the kind of disaster that the Dec 2004 Asian tsunami, caused by the magnitude 9+ Sumatra earthquake of Dec 26, 2004, wrecked on the Indian Ocean coasts.
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The Dec 2004 Indian Ocean tsunami was produced by perhaps the strongest earthquake of the past 100 years. It occurred in the Java trench, off Bandar Aceh in north-western Sunatra.This image is a work of the National Oceanic and Atmospheric Administration
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East African Rift valleys and the Red Sea Rift
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Models of mantle convection
A. Whole-MantleB. Two-Layer (Ridge)C. Two-Layer (Trench)
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Nin
tyea
stR
idge
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The Hawaii-Emperor seamounts have evolved over the past ~65 Ma as the Pacific plate traversed a fixed mantle plume.(http://www.colorado.edu/geography/cartpro/cartography2/spring2001/campbell/final/anime_pg.html)
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