Transcript Plate Tectonics

Plate Tectonics
Continental Drift
Seafloor Spreading
Plate Tectonics Theory
Continental
Drift
Early evidences:
Fit of continents
Present
Mountain ranges
and rock sequences
Unique organisms
Glacial debris
200 million years ago
Continental glacier
on Pangaea
Current location
of glacial debris
Rock Magnetism
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Wegener’s ideas put on shelf for a while
New magnetism measurement techniques in
mid-20th century
Expected some wobble of magnetic pole
Compared magnetism on distant
continents
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Compare rocks of same age on distant
continents
Found significant drift of pole
Found more than one magnetic pole at
same time?
Confirmed that drift must be occurring
Another discovery from magnetism
Reversals!
No explanation, but real
To the seafloor……Ideas of Harry Hess
Location of mid-ocean ridges, deep sea trenches
age of seafloor
Hess’s ideas
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Took philosophical approach
Explained age by production of new seafloor
at ridges and destruction at trenches
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“Introduced” idea of convection in the mantle
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Called seafloor spreading
Hess’s vision
Trench
Ridge
Trench
Seafloor spreading – version 2
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Vine, Matthews, Morley
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Observed magnetic pattern on seafloor
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Finally noticed symmetry of pattern
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Testable prediction
Magnetic pattern
from magnetometer
Note symmetry about ridge;
seafloor colored by artist
Formation of seafloor magnetic pattern
Another “view” of
seafloor magnetic
pattern
Other evidences of
seafloor spreading
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Chains of islands and ages
Development of types of coral reefs
Satellite imagery
Chains of islands and their ages
Location of hot spots (mantle plumes)
Basic theory of plate tectonics
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Remember layering of earth
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Lithosphere broken into pieces called plates
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Plates move and interact at boundaries
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Find boundaries with earthquakes and
topographic features
Earthquakes (about 10 years)
Plates (puzzle pieces)
Plate Boundaries
Divergent :
mid-ocean ridge
Convergent:
oceanic-continental
oceanic-oceanic
Transform faults:
offsets in
mid-ocean ridges
Divergent and transform boundaries
Convergent
boundaries
Oceanic-continental
(top picture)
Oceanic-oceanic
(bottom picture)