Title: Plate Tectonics
1Plate Tectonics
2What 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)
3Early 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
4Evidence for Joined Continents Interaction
5The 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)
6Locations 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
7Locations of Earthquakes Volcanoes
8Magnetism 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
9Magnetism 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
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11Magnetism on the Ocean Floor
12Magnetism 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
13Magnetism 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
15Types 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
16Divergent Boundaries
- Plates move apart
- Sometimes called spreading centers
- Most are along ocean floor
- Creates mid-ocean ridge
17Divergent 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
18Divergent 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
19Mid-Ocean Ridges
20Convergent Boundaries
- 2 plates move towards each other
- 2 broad classifications
- Subduction boundaries
- Collision boundaries
21Subduction 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
22Subduction 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
23Ocean-Ocean Subduction Boundary
24Ocean-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
25Ocean-Continent Subduction Boundary
26Collision 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
27Continent-Continent Collision
28Transform 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
29Transform Plate Boundary
Transform Boundary--San Andreas Fault Animation
N
30- HW
- Read pgs 176-179
- Answer s 1, 2, 3, 4, 6
31Causes 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
32The Big Picture
33- HW
- Read pgs 180-181
- Answer 1
34Plate 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
35Plate 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
36Plate 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
37Plate 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
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39Plate 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
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41Plate 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
42Plate 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