Plate Tectonics:

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Plate Tectonics Grand Unifying Theory of
everything... for the Geosciences, at least!
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A video
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Plate tectonics theory says that the Earths core
is broken up into pieces that move by plowing
through the other rocks on Earths surface?

1. True
2. False

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Introduction

Plate Tectonics Theory
gt
explains location of and actions associated
with....
-
Volcanoes (distribution and composition)
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Earthquakes (distribution, strength, depth)
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Mountain Ranges (of all types)
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Natural resources (distribution and formation of

Coal, Mineral Resources, Oil)
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Ocean basins ( age, shape, and size)
biologic
-

distribution and behavior

(fossils and modern animals)
-
seemingly incompatible climate records
A theory that unified the geosciences by
explaining
nearly all geological phenomena
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• Plate Tectonics and Continental drift are NOT the
  same thing!
• Continental drift was the hypothesis postulated
  by Alfred Wegener that was rejected due to the
  wrong explanation for how the continents were
  moving
• Plate tectonics built upon Wegeners rejected
  hypothesis and added a lot of new information
• Sea floor spreading
• Paleomagnetism
• Age of sea floor along oceanic ridges

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Plate Boundaries, Earthquakes and Volcanoes

• Red boxes show the location of the next three
  slides

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• A small shield volcano in Iceland
• thin lava is created at a divergent plate
  boundary
• The low viscosity lava creates the shield volcano

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Confirmation of Sea-Floor Spreading


Deep sea drilling supports the hypothesis that
ocean crust is forming at
the ridges and moving away from the ridges.
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• Mt Rainier in Washington State- a classic example
  of a stratovolcano
• The lava associated with this type of volcano is
  created as oceanic crust melts and pushes through
  continental crust along convergent subduction
  plate boundaries

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Convergent Subduction (Oceanic-Continental) Plate
Boundary
?
Denser oceanic crust subducted beneath
continental crust.
?
Denser oceanic crust subducted beneath
continental crust.
?
Andesitic volcanic arcs form on the leading edge
of the
?
Andesitic volcanic arcs form on the leading edge
of the
continental plate.
continental plate.
?
Andes Mountains, Cascades
?
Andes Mountains, Cascades
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• A couple of cinder cones and a lava flow in New
  Mexico
• This type of volcanic cone is often found
  associated with other volcanoes, and commonly
  where plates have been completely subducted and
  the melted material is in its last gasps.

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Alfred Wegener Continental Drift Hypothesis

1912-1915
Alfred Wegener
proposed a hypothesis called "continental drift".
gt

Continents were once together
Supercontinent
Pangaea
all,
Gaea
land).
(Pan
gt



Based on a lot of geological evidence
gt
mountain ranges, fossils, continental fit,
similar rocks

Wegener's theory lacked a scientifically valid
explanation for how the continents could move.
-
Hypothesis was rejected for the above reason
An alternative to the Contracting Earth model
favored by many geoscientists at the time
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Continental Fit
1965 Edward
Bullard proposed
modification of
Wegeners idea of
fitting continents by
using the 2,000 m
isobath, which
corresponds to the
continental slope
and the edge of
continental crust.
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Similarity of Rock Sequences
Identical Carboniferous rocks on Gondwana is
tough to explain
if the continents were not joined at that time
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Various mountain ranges are currently
widespread. Rejoining separated continents
shows the linear nature of the mountain chains.
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Tropical locations have geological evidence of
Carboniferous glaciation.
The former parts of Gondwanaland are widely
separated today, but were not in the distant
geological past.
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The Gondwana Ice Cap
The Gondwana Ice Cap

If the continents
are reassembled,
the glacial
evidence makes
sense.

At the same time
most of Laurasia
was in the tropics.
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Gondwanaland Animal and Plant Fossils
Gondwanaland Animal and Plant Fossils
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Sea-Floor Spreading

Sea floor mapped during the 1950s
-
revealed the Mid oceanic ridge system.
The mountain chain had a down-dropped valley in
the middle, called a rift valley. could only be
caused by pulling apart

1962 Captain Harry Hess (US Navy)
gt
proposed Sea-floor Spreading to account for
continental movement and size of oceans.
Magnetic reversals recorded in the rocks were
discovered later and verified Hess hypothesis
gt
patterns were symmetrical with respect to the
ridge axis.
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Magnetic Data and the Mid Ocean Ridge Rift
valley an example of an Oceanic crust divergent
boundary

proof for sea floor spreading and a mechanism to
move continents as Part of the larger tectonic
plates
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(No Transcript)
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Age of the Ocean Basins
Final verification of sea floor spreading.
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Which is not something that was used to support
Continental drift hypothesis?

1. The fit of the continents
2. The alignment of mountains
3. The locations of fossils on various continents
4. The arrangement of unique rocks on continents
5. All of the above were used to support Continental
   Drift hypothesis

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Plate Boundaries


Convergent where two plates meet, with one
being subducted or both being forced upward
gt

• oceanic-oceanic subduction
• gtcontinental-oceanic subduction
• Continental-continental collision

.
Divergent where two plates spread apart at a
ridge or rift valley.

• oceanic
• gtcontinental

Transform where two plates or plate segments
slide past each other.
gt driven by convection cells within the mantle,
the plates interact with each other gt faults and
earthquakes often occur along plate boundaries
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• Earthquakes
• Occur along breaks in the Crust known as faults
• Energy stored along faults released as rock
  strength and friction are overcome releasing
  energy waves
• Three kinds of energy waves
• P-waves (fastest)-move through any substance
• S-waves (next fastest)-move through solids ONLY
• Surface waves (slowest)-move along the Earths
  surface

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Convection currents drive plate motion
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Earthquake waves allow us to determine what the
internal structure of Earth looks like concentric
spheres of material, each layer with specific
characteristics that influence seismic wave
movement
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3D maps of the Earths convection currents based
on seismic wave analysis-complicated, but likely
more realistic!
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Convergent Continental-Continental Plate Boundary
Continental-Convergent Plate Boundary
Continental crust
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Himalayas
Himalayas
Tibet
Tibet
Indian
Indian
Plateau
Plateau
subcontinent
subcontinent
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Convergent Subduction (Oceanic-Continental) Plate
Boundary
Western coast of South America
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Oceanic-Oceanic Plate Boundary
Convergent subduction Oceanic-Oceanic Plate
Boundary
?
Volcanic island arcs form nearly parallel to the
subduction
?
Volcanic island arcs form nearly parallel to the
subduction
zone, which is expressed as a deep ocean trench.
zone, which is expressed as a deep ocean trench.
?
Most modern island arcs are in the Pacific Ocean.
?
Most modern island arcs are in the Pacific Ocean.
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Island Arc
N
Sea of Japan
To RoC
Pacific Ocean
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Continental Divergent boundary
East African Rift Valley
East African Rift Valley
? Eastern Africa
appears to be
rifting away from
the rest of the
continent.
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San Andreas Fault- a Transform Boundary
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Which type of plate boundary is not commonly
associated with volcanoes?

1. Continent-Oceanic convergent subduction
2. Divergent
3. Transform