Post on 25-Dec-2015
transcript
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Plate Tectonics• Earth’s crust is cracked and
fragmented– Fragments called plates
• The Earth’s mantle is very hot and fluid, so the plates move atop the mantle
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Earth’s Crust• Think of the Earth as
completely covered with a layer of thin, dense basalt rock with chunks of thicker, less dense granite here and there–The granite chunks are the
continents riding on the basalt like wood floats on water
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Divergent Boundaries
• Where plates are moving apart–Cracks in the crust are filled by
upwelling molten rock
Give one example of a divergent boundary:
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Divergent Boundaries• Divergent boundaries on continents
are called rifts–Example: the African Rift Valley
• Splitting Africa in two
• Divergent boundaries under oceans form mid-ocean ridges
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Divergent Boundaries• Several plates are pulling apart
beneath the Atlantic ocean forming the Mid-Atlantic Ridge–Diverging ocean plates cause sea
floor spreading• Where new sea floor is constantly being
added
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Mid-ocean ridges (rifts) normally form where tectonic plates are(1) converging (3) stationary(2) diverging (4) sliding past each other
The motion of the convection currents in the mantle beneath the Atlantic Ocean appears to be mainly making this ocean basin(1) deeper (3) wider(2) shallower (4) narrower
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Convergent Boundaries• Where plates are coming together
Here for example
What is the name of this boundary?
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• Where mountains form
• Where earthquakes occur (and sometimes volcanoes)–Several plates are colliding with the
Pacific Plate creating the Pacific Ring of Fire• An area that experiences lots of
earthquake and volcanic activity
Convergent Boundaries
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Convergent Boundaries
CONVERGENT BOUNDARIES Oceanic crust - Oceanic Crust
older, denser crust subducts forming ocean trench Oceanic Crust – Continental Crust
denser oceanic crust subducts forming ocean trench Continental Crust – Continental Crust
resists subduction - folding, faulting, and mountain building
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Ocean-Ocean Convergence
• Forms ocean trenches– Deepest places on Earth
Name one ocean-ocean boundary
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Oceanic Crust – Oceanic Crust Older, denser oceanic crust is SUBDUCTED
VOLCANIC ISLAND ARC FORMED – ALEUTIAN ISLANDS
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Ocean-Continental Convergence
Site of subduction zones• Denser ocean plate slides beneath the less
dense continental plate–Example: the Pacific Northwestern U.S.
• Creates many of the Earth’s volcanic mountain chains as the ocean plate dives down, melts and is forced back to the surface
Name one ocean-continental boundary
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Continental-Continental Convergence
• How non-volcanic mountains are formed– Example: the Appalachian chain and the
Himalayas
– Rising of land due to plate collisions is called uplift
Name one continental-continental boundary
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Transform Fault Boundaries
TRANSFORM PLATE BOUNDARIES
At a transform fault boundary, plates grind past each other without creating or destroying the lithosphere.
SHALLOW EARTHQUAKES
Transform faults
• Most join two segments of a mid-ocean ridge.
• At the time of formation, they roughly parallel the direction of plate movement.
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So, what causes plates to move?
• Convection currents: drag and move the lithospheric plates above the asthenosphere
(three sources of heat produce the convection currents):
(1)Leftover heat from earth’s formation
(2)Decay of Radioactive elements
(3)Plate friction
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Mid-Atlantic Ridge
• As the plates pull apart new ocean floor is added
What 2 continents are moving away from each other as a result of the mid-Atlantic Ridge?
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Convection Currents• It is theorized
convection currents within the Mantle cause plates to move around
• There are other theories about what causes plates to move!
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Evidence for Plate Tectonics
Ocean Drilling• The data on the ages of seafloor sediment
confirmed what the seafloor spreading hypothesis predicted.
• The youngest oceanic crust is at the ridge crest, and the oldest oceanic crust is at the continental margins.
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More Evidence for Plate Tectonics
Earthquake Patterns• Scientists found a close link between
deep-focus earthquakes and ocean trenches.
• The absence of deep-focus earthquakes along the oceanic ridge system was shown to be consistent with the new theory.
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Convergent plate (subduction) boundaries have deeper earthquakes
Divergent plate boundaries and collision zones have shallow earthquakes
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SUMMARY 3 PLATE BOUNDARIES
DIVERGING CONVERGING (SUBDUCTION ZONE)
Oceanic Crust – Continental Crust
Oceanic Crust - Oceanic Crust CONVERGING (COLLISION ZONE)
Continental Crust – Continental Crust TRANSFORM