Plate Tectonics (Wrong kind of plateand wheres my salad fork?)
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Transcript of Plate Tectonics (Wrong kind of plateand wheres my salad fork?)
Plate Tectonics
(Wrong kind of plate…and where’s my salad fork?)
The crust is broken!
The crust is broken!
We measure plate motion with GPS
Continental Drift Whiplash
Plate Boundary TypesPlate Boundary Types
Divergent plate boundaryDivergent plate boundary
Divergent plate boundaryDivergent plate boundary
• 2 plates are moving AWAY from each 2 plates are moving AWAY from each otherother
• Seen in mid-ocean ridgesSeen in mid-ocean ridges and rift valleysand rift valleys
Where in the world?Where in the world?
Divergent plate boundaryDivergent plate boundary(forming a rift valley)(forming a rift valley)
Mid ocean ridgeMid ocean ridge
Divergent plate boundaryDivergent plate boundary
Features:Features:
1)1) 2)2) 3)3)
Divergent plate boundaryDivergent plate boundary
Features:Features:
1)1) Mid ocean ridgesMid ocean ridges2)2) Undersea volcanoes—may make islandsUndersea volcanoes—may make islands3)3) Rift valleys, on landRift valleys, on land
Convergent plate boundariesConvergent plate boundaries
Convergent plate boundariesConvergent plate boundaries
• 2 plates move TOWARD each other2 plates move TOWARD each other
What is happening at the plate What is happening at the plate boundary?boundary?
Oceanic Plate
Oceanic Plate
SubductionSubduction• When 2 plates converge, one plate MAY move When 2 plates converge, one plate MAY move
downwards UNDER the other – this is called downwards UNDER the other – this is called SUBDUCTIONSUBDUCTION
SubductionSubduction
Earthquakes are Earthquakes are deeperdeeper the farther inland you go. the farther inland you go.
SubductionSubduction
Accretion—some of the lightest oceanic crust Accretion—some of the lightest oceanic crust joins the continentjoins the continent
• WhichWhich plate is subducting? plate is subducting?• What is What is happeninghappening to the subducted plate? to the subducted plate?
Convergent plate boundariesConvergent plate boundaries
Features:Features:
1)1) 2)2) 3)3)
Convergent plate boundariesConvergent plate boundaries
Convergent plate boundariesConvergent plate boundaries
Convergent plate boundariesConvergent plate boundaries
Features:Features:
1)1) … …in ocean/ocean convergencesin ocean/ocean convergences2)2) … …in ocean/continent convergencesin ocean/continent convergences3)3) … …in continent/continent convergencesin continent/continent convergences
Convergent plate boundariesConvergent plate boundaries
Features:Features:
1)1) Ocean trenches and volcanic island arcsOcean trenches and volcanic island arcs2)2) Benioff zone earthquakes, continental rim Benioff zone earthquakes, continental rim
volcanoes and accretionvolcanoes and accretion3)3) High plateaus, thrust faults and mountainsHigh plateaus, thrust faults and mountains
Transform Transform plate plate
boundaryboundary• 2 plates 2 plates slide pastslide past
each othereach other Pacific Plate
North American Plate
Transform Plate BoundariesTransform Plate Boundaries
• The area where these plates meet is called a The area where these plates meet is called a transform faulttransform fault
• The San Andreas Fault in California is The San Andreas Fault in California is possibly the most famouspossibly the most famous
Transform PlatesTransform Plates
Point Reyes, California Point Reyes, California
Transform plate boundariesTransform plate boundaries
Features:Features:
1)1) 2)2) 3)3)
Transform plate boundariesTransform plate boundaries
Features:Features:
1)1) Major earthquakesMajor earthquakes2)2) Offset linear featuresOffset linear features3)3) Fracture zonesFracture zones
What kind of boundary?What kind of boundary?11 22 33 44 55
What features do they make?What features do they make?11 22 33 44 55
Plate Boundary TypesPlate Boundary Types
Why do the plates move?
1) 2) 3)
Why do the plates move?
1) Heat2) Differences in density3) Gravity
Why do the plates move?
Inner core
Outer core
Mantle
Crust
Mantle and outer core are melted
Heat
• The Earth was originally molten• The heat within the Earth is left over from then• Radioactivity adds some heat
Density
• D=mass/volume• Less dense floats on more dense • If you heat an object or fluid, it expands, the
density decreases• A more dense fluid will force a less denseto rise
• The average density of the Earth provides evidence of the relative densities of the different layers of Earth
- crust, (lithosphere)-mantle (asthenosphere) and -core.
• The average density of the Earth provides evidence of the relative densities of the different layers of Earth
- crust, (lithosphere)-mantle (asthenosphere) and -core.
The whole Earth is more dense than the rocks we see
Density
• Mantle is more dense than crust
• Oceanic crust is more dense than continental crust
Gravity
g=Gm1m2/d2
If anybody cares. What we do care about is that
a) if you heat a fluid, its density decreases,
b) the cooler fluid is more dense, so it sinks.
All together--
Convection happens!
Why do the plates move?
Why do the plates move?
Convection happens!
• The accepted mechanism for plate motion is: convection in the asthenosphere.
Convection happens!
Convection happens!
This plate is pulled this way…
Convection happens!
…and this plate is pulled this way.
Wegener’s Evidence
• Wegener supported his hypothesis of continental drift with evidence from the puzzle fit of the continents, rock units, geologic structures, fossils and glacial evidence.
Evidence
The modern theory of plate tectonics is supported by evidence from:
Evidence
The modern theory of plate tectonics is supported by evidence from:
A. paleomagnetism, B. C. D.
a. b. c.
Seafloor crust shows the direction of the magnetic field
when the crust was formed
Evidence
The modern theory of plate tectonics is supported by evidence from:
A. paleomagnetism, B. age of ocean floor sedimentsC. D.
a. b. c.
Seafloor crust is older farther from the mid-ocean ridge
Evidence
The modern theory of plate tectonics is supported by evidence from:
A. paleomagnetism, B. age of ocean floor sedimentsC. ocean floor topography D.
a. b. c.
You can see the ridge and the suture zone around it
Evidence
The modern theory of plate tectonics is supported by evidence from:
A. paleomagnetism, B. age of ocean floor sedimentsC. ocean floor topography D. Wegener's evidence.
a. b. c.
Wegener had none of the above. He had to do it the hard way
Evidence
The modern theory of plate tectonics is supported by evidence from:
A. paleomagnetism, B. age of ocean floor sedimentsC. ocean floor topography D. Wegener's evidence.
a. fossils b. c.
Tropical fossils show up in polar regions
Evidence
The modern theory of plate tectonics is supported by evidence from:
A. paleomagnetism, B. age of ocean floor sedimentsC. ocean floor topography D. Wegener's evidence.
a. fossils, b. jigsaw continents, c.
They fit together pretty well
Evidence
The modern theory of plate tectonics is supported by evidence from:
A. paleomagnetism, B. age of ocean floor sedimentsC. ocean floor topography D. Wegener's evidence.
a. fossils, b. jigsaw continents, c. rock types Similar rocks show up on
different continents