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Plate TectonicsPlate Tectonics
Wegener, Continental Drift and Wegener, Continental Drift and PangaeaPangaea
Video shows a fast motion animation over the past 740 million years
Evidence for Continental DriftEvidence for Continental Drift
Jigsaw Puzzle fit of Jigsaw Puzzle fit of continentscontinents
Alfred Wegener during Greenland expedition
More evidenceMore evidence
Matching fossils on Matching fossils on continents now continents now located thousands located thousands of miles apart. of miles apart. Example = Example = Mesosaurus, a Mesosaurus, a freshwater reptilefreshwater reptile
Many othersMany others
More evidenceMore evidence
Matching geologic Matching geologic structures including:structures including:– Mountain chainsMountain chains– Ore depositsOre deposits– Same rocks of same Same rocks of same
ageage
More evidenceMore evidence
Climate change Climate change evidenceevidence– Glacial deposits at Glacial deposits at
current equatorcurrent equator– Fossilized palm Fossilized palm
trees in Greenlandtrees in Greenland Map shows why Map shows why
according to the according to the placements of placements of current continents current continents within Pangaeawithin Pangaea
Wegener not believedWegener not believed
Why? -Why? -– What could possibly force the continents What could possibly force the continents
to move across the ocean floor in this to move across the ocean floor in this way. They would be crushed.way. They would be crushed.
– He was a meteorologist, not a geologistHe was a meteorologist, not a geologist
Developments 50s and 60sDevelopments 50s and 60s World war 2 submarines found World war 2 submarines found
mountains under the oceans – the mountains under the oceans – the midocean ridgesmidocean ridges
Sea floor drilling showed rocks Sea floor drilling showed rocks younger than expected and youngest younger than expected and youngest towards the center of the mid ocean towards the center of the mid ocean ridgeridge
Theory of seafloor spreading Theory of seafloor spreading suggested by Princeton professor Dr. suggested by Princeton professor Dr. Harry HessHarry Hess
Seafloor spreadingSeafloor spreading
First look at the earth’s layers as shown here. Let’s draw them. How do we know about them? Animation and Video
Evidence for sea floor spreadingEvidence for sea floor spreading Alvin and other submersibles Alvin and other submersibles
found cracks and lava showing found cracks and lava showing spreading and volcanism at mid spreading and volcanism at mid ocean ridges and odd life formsocean ridges and odd life forms
Matthews and Vine’s survey of Matthews and Vine’s survey of the Indian Ocean sea floor the Indian Ocean sea floor showed matching stripes of showed matching stripes of reversing polarities on either reversing polarities on either side of ridge – what caused side of ridge – what caused these?these?– Lava spreading during Lava spreading during
alternating magnetic periodsalternating magnetic periods Discussion of Discussion of
electromagnetism, electromagnetism, paleomagnetism and earth’s paleomagnetism and earth’s corecore
The Earth’s magnetic fieldThe Earth’s magnetic field It is produced by the It is produced by the
outer core of the earth outer core of the earth which is made of liquid which is made of liquid iron and nickeliron and nickel
This moving magnetic This moving magnetic material produces a material produces a moving magnetic field, moving magnetic field, which in turn produces which in turn produces a moving electric field. a moving electric field. It is a dynamo!It is a dynamo!
Earth’s magnetic field Earth’s magnetic field varies over time and it varies over time and it protects us from protects us from cosmic radiationcosmic radiation VIDEO TRUE or FALSE?
Seafloor spreading and Seafloor spreading and paleomagnetismpaleomagnetism
Pangaea revisitedPangaea revisited
By piecing together By piecing together this information, this information, we can see how we can see how the continents the continents have moved over have moved over the past 200 the past 200 million years, due million years, due to seafloor to seafloor spreadingspreading
Plate tectonicsPlate tectonics Sea floor spreading provides the Sea floor spreading provides the
driving mechanism for movementdriving mechanism for movement However, it is not the continents that However, it is not the continents that
are moving, but the “plates” of are moving, but the “plates” of lithosphere “floating” in effect on the lithosphere “floating” in effect on the asthenosphereasthenosphere
The lithosphere is made up of about The lithosphere is made up of about 20 plates which move relative to 20 plates which move relative to each other in several wayseach other in several ways
Let’s look at a generalized sketchLet’s look at a generalized sketch
The PlatesThe Plates
Sea-Floor Spreading and Plate Sea-Floor Spreading and Plate BoundariesBoundaries
3 types of boundaries3 types of boundaries
Convergent – Convergent – where plates come where plates come together. See together. See example next slideexample next slide
Converging Margins: India-Asia Converging Margins: India-Asia CollisionCollision
Interesting plate collisionInteresting plate collision This picture shows a This picture shows a
place in place in Newfoundland where Newfoundland where a massive collision a massive collision actually forced actually forced mantle rock on top of mantle rock on top of the crust, during the the crust, during the collision that formed collision that formed Pangaea and the Pangaea and the Appalachian Appalachian mountains. This mountains. This looks down the old looks down the old plate boundary.plate boundary.
Mantle rocks are toxicMantle rocks are toxic These rocks have very These rocks have very
different compositions different compositions than crustal rocks.than crustal rocks.
They contain heavy They contain heavy metals, which do not metals, which do not support life forms on support life forms on the earth’s surface, so the earth’s surface, so few organisms live few organisms live there.there.
However, in some However, in some places their heavy places their heavy metal concentrations metal concentrations produce rich metal produce rich metal deposits and are mineddeposits and are mined
Divergent BoundariesDivergent Boundaries Found at spreading Found at spreading
centers – either mid centers – either mid ocean ridges or mid ocean ridges or mid continental rift zonescontinental rift zones
Transform fault boundaryTransform fault boundary
This shows the San This shows the San Andreas Fault.Andreas Fault.
It is a transform fault It is a transform fault boundary, where the boundary, where the plates move sideways plates move sideways past each other, rather past each other, rather than away from each than away from each other (at divergent other (at divergent boundaries), or towards boundaries), or towards each other (at each other (at convergent boundaries)convergent boundaries)
Transform Faults and Seafloor Transform Faults and Seafloor SpreadingSpreading
Review of different boundariesReview of different boundaries Divergent –mid ocean ridge like Iceland or Divergent –mid ocean ridge like Iceland or
continental rift zone like the African Rift continental rift zone like the African Rift ValleyValley
ConvergentConvergent– Ocean/ocean like Japanese IslandsOcean/ocean like Japanese Islands– Continent/ocean like Andes and CascadesContinent/ocean like Andes and Cascades– Continent/continent like the HimalayasContinent/continent like the Himalayas
Transform fault like the San Andreas faultTransform fault like the San Andreas fault Hot spots are not at plate boundaries, but Hot spots are not at plate boundaries, but
give us information about plate motiongive us information about plate motion Activity Activity
What causes plate tectonics?What causes plate tectonics? Convection in the mantle, as Convection in the mantle, as
the plastic asthenosphere the plastic asthenosphere flows, carrying the plates with flows, carrying the plates with it.it.
This is probably aided by slab This is probably aided by slab pull at subduction zones and pull at subduction zones and ridge push at mid ocean ridges ridge push at mid ocean ridges and rising plumes in the mantleand rising plumes in the mantle
This diagram shows several This diagram shows several different model hypothesesdifferent model hypotheses
Plate tectonics causes Plate tectonics causes volcanic activityvolcanic activity
and earthquakesand earthquakes
It causes rocks to be tiltedIt causes rocks to be tilted
Or even to fold or breakOr even to fold or break
What will the future bring?What will the future bring?
Link to animationLink to animation
Volcanoes and Earthquakes and Volcanoes and Earthquakes and Plate Boundaries – GIS activityPlate Boundaries – GIS activity
Structural GeologyStructural Geology
IsostasyIsostasy MountainsMountains Stress and strainStress and strain FoldsFolds FaultsFaults
Formation of mountainsFormation of mountains
Two forces are Two forces are constantly at constantly at work on the work on the earth.earth.– Weathering Weathering
and erosion and erosion tear structures tear structures down whiledown while
– Plate tectonics Plate tectonics builds them upbuilds them up
So we have mountains!So we have mountains!
But they will not last forever.
Mountains form in different waysMountains form in different ways-Volcanic mountains--Volcanic mountains-
Volcanoes form by subduction and mVolcanoes form by subduction and melting of plates elting of plates
Volcanic mountains form over hot spVolcanic mountains form over hot spotsots
Volcanic mountains form at rift zonesVolcanic mountains form at rift zones
Other mountain typesOther mountain types
Folded mountains form From converging Folded mountains form From converging continents like the Himalayascontinents like the Himalayas
How do these look?How do these look? Direction?Direction? Fault block mountains form where blocks of Fault block mountains form where blocks of
rock drop at faults – mostly near plate rock drop at faults – mostly near plate boundaries, but not alwaysboundaries, but not always
Uplifted mountains – where large sections Uplifted mountains – where large sections of the crust are pushed up, perhaps by of the crust are pushed up, perhaps by magma, or other forcesmagma, or other forces
IsostasyIsostasy Just as a boat sinks or rises with changes in Just as a boat sinks or rises with changes in
weight, so does the crust sink or rise with weight, so does the crust sink or rise with changes in weight. Plate tectonics builds changes in weight. Plate tectonics builds mountains and the extra weight causes the crust mountains and the extra weight causes the crust to sink. As erosion occurs the weight of the to sink. As erosion occurs the weight of the mountains decreases and the crust rises again. mountains decreases and the crust rises again. This process is called isostasy or isostatic changeThis process is called isostasy or isostatic change
IsostasyIsostasyIsostasy is balance. A floating object is balanced in the water, like an iceberg. If some of the top melts, the iceberg rises in the water to stay in balance. If you get into a boat, the boat sinks to maintain balance. The same thing happens with mountains. As plate motions push it higher the mountain sinks into the mantle to stay in balance. On the other hand, when the mountain erodes, it will rise in the mantle as the top erodes. So, a mountain may lose 1 meter from erosion, but regain 0.8 meters from rising due to isostasy. It maintains isostatic equilibrium.
•This is also a great example of feedback within a system. Is it positive or negative? Figure it out. Remember that maintaining equilibrium is __ feedback because it keeps the system in balance. So, what is it, positive or negative?
•This is a good example of Newton’s 3rd law. For every force, there is an equal and opposing force. In this case the force of gravity is opposed by the buoyant force.
Right! It’s negative.
Stress Stress
Due mostly to plate movements, the earth’s crust is under a lot of stress. There are 3 types, shown at the right
A occurs where plates pull apart, divergent boundaries, and is called tension
B occurs where plates converge, and is called compression
C occurs where plates move past each other, at transform fault boundaries and is called shearing
StrainStrain This stress leads to strain This stress leads to strain
on the crust which bends it. on the crust which bends it. – –
If it is warm, underground, it If it is warm, underground, it can bend. This called ductile can bend. This called ductile deformation. Features are deformation. Features are called folds. Upturned folds called folds. Upturned folds are anticlines while are anticlines while downturned folds are downturned folds are synclines. synclines.
Or, the rock may break, if it Or, the rock may break, if it is brittle. This causes faults is brittle. This causes faults –breaks of the earth.–breaks of the earth.
A fold above and a fault below
anticline syncline
Stress and strain video
Economic value of folds/faults
Different faultsDifferent faults
Faults move in Faults move in different ways, different ways, depending on the depending on the type of stress on type of stress on them. Here are 3 them. Here are 3 types that form. types that form.
1 is a normal fault1 is a normal fault 2 is a strike slip 2 is a strike slip
faultfault 3 is a reverse fault3 is a reverse fault
2
3
1
MatchingMatching
These form at These form at different plate different plate boundaries. Can you boundaries. Can you figure out which figure out which forms where? Match forms where? Match themthem
A. Convergent
C. Transform Fault
B. Divergent
2
3
3
2
1
1
Can you match the stress and strain?Can you match the stress and strain?
A is 1st, B is 3rd, C is 2nd
2
3
1