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Plate Tectonics

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Title: Plate Tectonics


1
Plate Tectonics
  • Chapter 8

2
What Is Plate Tectonics?
Section 1
  • Theory that describes the formation, movements,
    and interactions of Earths lithospheric plates.
  • Lithosphere is broken into large plates that
    move (float) on top of the asthenosphere.
  • 3 ways
  • Away from each other (divergent plate boundaries)
  • Toward each other (convergent plate boundaries)
  • Slide past each other (transform plate
    boundaries)

3
Early Ideas About Plate Movements
  • Have you ever noticed that the continents look
    like they would fit together like the pieces of a
    puzzle??? If you have, youre not alone.
  • 1912 Alfred Wegener
  • hypothesis ? continental drift
  • Continents have drifted over time
  • Observations to support hypothesis
  • Shape of continents
  • Fossils
  • Mesosaurus
  • South America Africa
  • Distinctive rock formations
  • Climate change evidence
  • coal deposits

Continental Drift Video
4
Evidence for Joined Continents Interaction
5
The Theory of Plate Tectonics
  • Continents (and ocean basins) are part of
    lithospheric plates.
  • Plate movement continent movement
  • Evidence/Explanations of many geologic processes
  • Location of volcanoes earthquakes
  • Formation of new crust (ocean floor)

6
Locations of Earthquakes Volcanoes
  • Occur in concentrated areas
  • Mark locations of plate boundaries
  • Where plates move apart, together, or past each
    other
  • Strain builds up ? releases causing EQs
  • Molten rock rises ? volcanic activity
  • Pacific Ocean
  • Ring of Fire

Plates Volcanoes Video
7
Locations of Earthquakes Volcanoes
8
Magnetism the Age of the Ocean Floor
  • Magnetic properties ages of igneous rocks on
    the ocean floor provide evidence for theory of
    plate tectonics.
  • Some igneous rocks contain magnetic minerals.
  • Provide record of direction of Earths magnetic
    field when rock formed

9
Magnetism the Age of the Ocean Floor
  • Records of Earths magnetic field
  • Some rocks recorded reversals in magnetic field
  • normal polarity
  • what we know today as N S magnetic poles
  • reversed polarity
  • present N magnetic pole became the S magnetic
    pole
  • present S magnetic pole became the N magnetic
    pole
  • A of magnetic reversals have taken place at
    different times over millions of years

10
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11
Magnetism on the Ocean Floor
12
Magnetism the Age of the Ocean Floor
  • Mid-ocean ridge long chain of volcanic
    mountains on the ocean floor with a deep central
    valley
  • Magnetic reversals are recorded in bands of rock
    on opposite sides of the ridge
  • Mirror image
  • Center of ridge shows current orientation of
    Earths magnetic field (normal or reversed)
  • Rocks at center of ridge are youngest (most newly
    formed)
  • As move further from center rocks get older

Magnetic Polarity Recorded in Rocks Animation
13
Magnetism the Age of the Ocean Floor
  • Mid-ocean ridges ? boundaries between
    lithospheric plates
  • New rock along ridge is formed by hot, molten
    rock which rises up between the plates (because
    it is less dense)
  • As new rock forms plates spread
  • Older rocks pushed away from ridge (both sides)
  • Rock at center of ridge hottest
  • Temperature decreases as move out from center

14
  • HW
  • Read pgs 172-175
  • Answer s 1, 2, 3

15
Types of Plate Boundaries
Section 2
  • Earths lithosphere is broken in to large plates
  • move in 3 ways
  • Divergent plate boundaries
  • Convergent plate boundaries
  • Transform plate boundaries

16
Divergent Boundaries
  • Plates move apart
  • Sometimes called spreading centers
  • Most are along ocean floor
  • Creates mid-ocean ridge

17
Divergent Boundaries
  • Rift valley
  • Center of mid-ocean ridge
  • Border between 2 diverging plates
  • Sea-floor spreading ? molten rock forces through
    cracks (rifts) in valley
  • Oceanic crust forms as rock cools
  • older crust moves away from mid-ocean ridge as
    the new crust is formed

18
Divergent Boundaries
  • Rift valley (continued)
  • Broken into sections
  • offset from each other by breaks (fracture zones)
  • Perpendicular (right angle) to ridge
  • Source of earthquakes at mid-ocean ridges

Divergent Plate Boundary Animation
19
Mid-Ocean Ridges
  • Mid-Atlantic Ridge
  • East Pacific Rise

20
Convergent Boundaries
  • 2 plates move towards each other
  • 2 broad classifications
  • Subduction boundaries
  • Collision boundaries

21
Subduction Boundaries
  • Oceanic plate subducts (plunges) below another
    plate
  • Boundary between the 2 plates is called a
    subduction boundary
  • Features of subduction boundaries
  • Deep-sea (or ocean) trenches
  • Deepest part of the ocean
  • Volcanic activity
  • Island arcs
  • Along the coast of continents
  • Earthquakes

22
Subduction Boundaries
  • Ocean-Ocean subduction
  • 2 Oceanic plates collide
  • Deep-sea trench formed
  • accompanied by chain of volcanic islands
    (volcanic island arc) on the overriding plate
  • Example
  • Pacific Plate subducts under Phillippine Plate
  • Pacific Plate pulled down
  • Forms Mariana Trench
  • Phillippine Plate overrides Pacific Plate
  • Forms Mariana Islands (volcanic island chain)

Subduction and Collision Boundary Animations
23
Ocean-Ocean Subduction Boundary
24
Ocean-Continent Subduction Boundary
  • Ocean-Continent Subduction
  • The denser oceanic plate subducts below the
    less-dense continental plate
  • Ocean trenches form.
  • Volcanoes mountains are formed on the
    continental plate.
  • Example
  • Nazca Plate (off west coast of S. America)
    subducts under the South American Plate
  • Nazca Plate pulled down
  • Forms Peru-Chile Trench
  • South American Plate overrides Nazca Plate
  • Forms Andes Mountains and volcanoes (along
    western edge of S. America)

Subduction and Collision Boundary Animations
25
Ocean-Continent Subduction Boundary
26
Collision Boundaries
  • Continent-continent collision
  • Neither plate subducts, so the crust piles up
    (because the continents join to form a single
    larger continent)
  • Mountains are formed.
  • Example
  • Indian subcontinent colliding into Eurasian Plate
  • Formed Himalaya Mountains

Subduction and Collision Boundary Animations
27
Continent-Continent Collision
28
Transform Plate Boundary
  • 2 plates slide past each other at a fault.
  • Stress is released as an earthquake.
  • Example
  • CaliforniaSan Andreas Fault
  • Pacific Plate (Southwestern Cali.) is moving NW
  • N. American Plate (rest of N. Amer.) moving SE

29
Transform Plate Boundary
Transform Boundary--San Andreas Fault Animation
N
30
  • HW
  • Read pgs 176-179
  • Answer s 1, 2, 3, 4, 6

31
Causes Of Plate Movement Ch. 8.3
Convection cells (caused by density differences)
in the asthenosphere (mantle) cause hot material
to rise, move outward (pushing the plates/ridge
push), sink as the material cools (pulling
plates down/slab pull).
Convection in the Mantle Animation
32
The Big Picture
33
  • HW
  • Read pgs 180-181
  • Answer 1

34
Plate Movements Continental Growth Sec 4
  • Reconstructing the Past
  • Many different kinds of evidence give clues as to
    what Earth looked like in the past
  • Rocks in Ural Appalachian Mountain
  • evidence of past subduction ? formed at
    convergent boundary, but neither mountain range
    is located near a plate boundary today
  • Ages of rocks that form in ocean basins
  • Magnetic record of igneous rocks
  • Can reveal latitude of formation
  • Fossils
  • Organisms that lived in shallow seas ? fossils
    found on high mountaintops
  • Rocks that show evidence of having been covered
    by glaciers, but now are in tropical areas

35
Plate Movements Continental Growth
  • Plate Tectonics Pangaea
  • Evidence suggests 250 million years ago (mya)
    that all the continents were welded together into
    one land mass ? Pangaea

36
Plate Movements Continental Growth
  • Formation of Pangaea
  • Use data from continents to make models of what
    Earth may have looked like before Pangaea
  • A large continental mass stretched between the
    south pole the equator ? Gondwana
  • made of smaller landmasses (S. America, southern
    Europe, Africa, the Near East, India, Australia,
    New Zealand, Antarctica)
  • Other small landmasses ranged across the globe
  • Gondwana moved northward and converged w/ the
    other landmasses to form Pangaea

37
Plate Movements Continental Growth
  • Break up of Pangaea
  • 2 separate landmasses
  • Gondwana
  • Laurasia
  • Over time both broke into smaller landmasses
    which began to resemble the continents today
  • Pangaea is still breaking up
  • The formation break up may have happened many
    times in the past

Break up of Pangaea animation
38
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39
Plate Movements Continental Growth
  • Plate Tectonics Continental Growth
  • P.T. affects shape of continents as well as
    position
  • Added rock materials to the margins of ancient
    continent cores (cratons)
  • 2.5 billion years ago (bya) core continental
    material stabilized
  • Ex. North American craton
  • at surface in most of eastern Canada ? Canadian
    Shield
  • Some of the oldest rock material (4 billion
    years old)
  • Rest of the craton is buried under a platform of
    sediments
  • Remainder of the continent is material added to
    the craton

40
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41
Plate Movements Continental Growth
  • Sources of Growth Material
  • Deep-sea sediments
  • Added when an oceanic plate plunges under a
    continental plate at a subduction boundary
  • Sediments from ocean floor scraped off left
    behind on edge of continent
  • Igneous Rock
  • Magma rises beneath surface cools ? pluton
  • Volcanoes at subduction boundaries add to edges

42
Plate Movements Continental Growth
  • River Sediments
  • Weathered eroded materials deposited at edges
  • Terrane
  • large block of lithospheric plate that has been
    moved attached to continent
  • 3 characteristics to ID a terrane
  • 1. bounded on all sides by faults
  • 2. rocks fossils found in terrane do not match
    those of neighboring terranes
  • 3. magnetic record of terrane does not match
    surround terranes

Growth of a Continent Animation
43
  • HW
  • Read pgs 182-187
  • Answer 3
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