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Tectonic Plate Theory

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Tectonic Plate Theory Understanding Basic Principles of Earth Science Related to Geology Earth s Crust Earth s crust is the outermost layer. – PowerPoint PPT presentation

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Title: Tectonic Plate Theory


1
Tectonic Plate Theory
  • Understanding Basic Principles of Earth Science
    Related to Geology

2
Earths Crust
  • Earths crust is the outermost layer.
  • The rigid crust floats on the molten part of
    the mantle called the asthenosphere.

3
Pangea
  • Pangea was the supercontinent from which all
    continents have split.
  • In 1915 Wegener proposed Earths continents
    looked this way about 225 million years ago.
  • The theory of continental drift was used to
    explain the current positions of the continents.
  • Wegener could not come up with a mechanism for
    continental drift.

4
Evidence that Pangea Existed
  • Fit of the continents
  • Fossil similarities
  • Rock similarities
  • Mountain chains
  • Paleoclimatic evidence
  • Paleomagnetism
  • Theory of Plate Tectonics

5
Fit of the Continents
  • North and South America match almost perfectly
    with Africa and Europe

6
Fossil Similarities
  • Mesosaurus, a reptile similar to an alligator
    once lived in the shallow waters of both South
    America and Africa.

7
Rock Similarities
  • Rocks of same age are found in locations of South
    America and Africa that were once joined in
    Pangea.

8
Termination of Mountain Chains
  • The map shows location of Pangean mountain chains
    (dark blue) that correspond with current mountain
    chains.

9
Paleoclimatic Evidence
  • Glacial deposits at the equator
  • Coral reefs in Antarctica
  • Therefore the landmasses must have been in
    different locations in the past.

10
Magnetism
  • Earth is a bar magnet
  • Magnetic north and south poles
  • These are not the same location as the geographic
    north and south poles
  • Exact location varies year-to-year

11
Paleomagnetism
  • This is magnetism frozen in the rock at the
    time it was formed.
  • Geologists can determine pole reversals by
    studying rock all over the globe.

12
Sea Floor Spreading
  • Surveys of the ocean basins showed a system of
    ridges and trenches.
  • This led geologists to come up with the idea of
    Sea Floor Spreading.
  • Symmetrical magnetic stripes were discovered on
    either side of the Atlantic Mid-ocean ridge.

13
Sea Floor Spreading
14
Magnetic Reversals along a Mid-Ocean Ridge
(stripes)
Youngest, newest rock is along the ridge.
Oldest rock is farthest from ridge.
15
Theory of Plate Tectonics
  • A rigid piece of lithosphere (outer crust) is
    floating on a partially plastic (molten, soft)
    asthenosphere
  • Seven Major Plates
  • 3 types of Plate Boundaries

16
Plate Boundaries
  • Divergent-Spreading Center- Ocean ridges and
    seafloor spreading (Atlantic Ocean)
  • Convergent-Creates trenches and island arcs
    (Pacific Ocean)
  • Transform-Plates move past one another (San
    Andreas Fault in California)

17
Divergent Boundaries
  • Magma from deep within Earth forces its way
    between two plates, pushing them apart.
  • The magma cools and forms new seafloor.
  • More magma emerges and pushes apart the cooled
    rock.
  • Seafloor Spreading/mid-oceanic ridges

18
Rift Valley
  • A rift valley forms when a continent is slowing
    splitting apart along a divergent boundary.
  • The African Rift Valley is an example.

19
Locations of Seafloor Spreading
20
Convergent
  • Plates move together
  • Oceanic crust slides under continental crust.
  • Subducting crust slides under.
  • Andes Mountains Chain in South America is an
    example.
  • Mountains formed from volcanoes along the
    convergent boundary.

21
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22
Convergent Boundaries
  • The Pacific Ocean by several continental plates.
  • The ocean basin is sliding under the continental
    plates along the plate boundaries.
  • As a result, the Pacific Ocean is growing smaller.

23
Why the Pacific is Shrinking and the Atlantic is
Growing
24
Hawaiian Islands are an island arc.
25
More Examples of Convergent Boundaries
  • Japanese Islands (Pacific Ocean)
  • Cascade Mountains (Northwestern U.S.A.)
  • Himalaya Mountains (Nepal-Asia)

26
Transform Plate Boundary
  • Plates move past one another along strike-slip
    faults

27
What Drives the Tectonic Plates??
  • Convection Cells
  • Hot Spots
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