Transcript Plate Tectonics

Plate Tectonics

…or the bump and
grind of the planet
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Joe Cocker –
Woodstock…. It
seems oddly related,
but I don’t know how
Alfred Wegner, 1912
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Looked at a map of
the world and saw it
as a puzzle
Continental Drift
Alfred Wegner came up with the idea of
Pangea
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Continents seem to fit together like pieces of a puzzle
Continental Drift
Fossils
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Similar distribution of fossils such as the Mesosaurus
Continental Drift
Mountains
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Mountain ranges match across oceans
Continental Drift
Glaciation
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Glacial ages and climate evidence
Continental Drift Model
Problems
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Alfred Wegener
– Presented research to
professionals
– Did not provide a
plausible mechanism to
explain how continents
drifted
In the 1960’s a discovery - MidAtlantic Ridge - Series of ridges and
volcanic activity in the center of the
Atlantic Ocean
Seafloor Spreading
Continental drift reexamined in 1960’s with new
information
• New theory developed – Seafloor spreading
• Supporting evidence for seafloor spreading
– World seismicity (like your map)
– Volcanism
– Age of seafloor
– Paleomagnetism
– Heat flow
• Theory combining continental drift and seafloor spreading
termed “Plate Tectonics”
Spreading at the Mid-Ocean ridges
Evidence:
 Mud depth gets
deeper as you move
away
 Rocks get older
 Magnetic reversals Paleomagnetism
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Evidence for Seafloor Spreading
World Seismicity
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Earthquake distribution matches plate boundaries
Evidence for Seafloor Spreading
Volcanism
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Volcanoes match some plate boundaries; some are
hot spots
Seafloor Spreading
Heat Flow
Seafloor Spreading
Convection Currents
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In 1960, proposed as driving force to move continents
Theory of Plate Tectonics
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John Tuzo Wilson combined ideas of continental
drift and seafloor spreading into “Plate Tectonics”
Rifts at Mid-Ocean ridges
So - Magma comes up
because the sea floor
is spreading
 Creates rifts – parallel
ridges
 This was all called,
oddly enough… Sea
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Floor Spreading
Divergent Plate Boundaries
Examples
East African Rift
Mid-Atlantic Ocean Ridge
If it can spread…..
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It can CRUNCH
Subduction
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Happens when
Oceanic Crust
(denser) dives
beneath Continental
Crust (not as dense)
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You also get Deep
Ocean Trenches
Crunches
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When 2 continental
plates collide – rocks
bend and fold,
mountains are made
Sooo… the continents slide around
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Called Continental Drift
The continents are really on Giant
Plates
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So the whole thing is called Plate Tectonics and
it depends on 2 ideas: CONTINENTAL DRIFT
AND SEAFLOOR SPREADING
Hot Spots…Hawaii
Plate Boundaries Cartoons – 4
frames per cartoon
1) Divergent Boudary
 2) Transform Boundary
 3) Convergent Boundary –
Continental-Continental
 4) Convergent Boundary –
Continental-Oceanic
 5) Convergent Boundary –
Oceanic-Oceanic
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