Download Plate Tectonics Theory

Plate Tectonics Theory
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Plate: large, rigid slab of rock
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Tectonics: “to build”
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Theory of Plate Tectonics: refers to how the Earth's surface is built of a dozen or more large
and small plates. The plates are moving relative to one another as they ride atop hotter, more
mobile material
Lithosphere: the
uppermost mantle and
overlying crust behave as
this strong rigid layer.
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-oceanic lithosphere is
thinnest in the oceans (5-10 km
thick).
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-continental lithosphere
is thickest (>200 km thick)
Earth’s major lithospheric plates
15 Solid Plates
"float" on an
Asthenosphere,
of underlying
rock that is under
such high
pressure and
high temperature
conditions as to
permit slight
flows of
movement
Plate Boundaries and relative motion at each
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Convergent Boundaries
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Convergent: two plates move together, a. oceanic lithosphere being reabsorbed into the mantle -orb. possibly collide with two continental blocks to create a mountain system.
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Oceanic-oceanic convergence:
• Deep ocean trenches are a product as oceanic lithosphere descends into the mantle
(also called subduction zones).
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• 1 oceanic + 1 oceanic plates (produce volcanic island arcs; mostly in Pacific like
Japan, Indonesia, Phillipines)
Convergent Boundaries
Oceanic-continental convergence:
• 1 oceanic + 1 continental plates (produce volcanic mountains like Mount St.
Helens)
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Continental-Continental convergence:
• 2 continental plates (produce spectacular mountain ranges like Alps,
Appalachians, Himalayas).
Oceanic-continental convergence
Divergent Boundaries
Divergent: two plates move apart, resulting in upwelling of hot
material to create new seafloor; associated with
• oceanic ridges and volcanism
• seafloor spreading
• continental rifting (landmass may split apart separated by an
ocean basin).
Transform Boundaries
Transform: two plates grind past each other without the production or destruction of
lithosphere.
Forces that Drive Plate Motion
Plate-Mantle Convection - driven by 3 processes
1.
heating at the bottom by heat loss from Earth’s core
2.
heating from within by the decay of radioactive isotopes
3.
cooling from the top that creates thick, cold lithospheric slabs
that sink into the mantle.
Forces
that
Drive
Plate
Motion
(cont.)
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•
slab pull - as cold, dense slabs sink into asthenosphere, they “pull”
the trailing plate along
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•
ridge push - due to gravity, the slabs of lithosphere “slide” down
the flanks of the ridge.
•
“mantle drag” - when flow
in the asthenosphere is
moving faster than that of
the plate.
Which contributes more
to plate motion? Slab
pull or ridge push?
Slab pull. Fast-moving plate are
being sub ducted along a larger
percentage of their margins than
slow-moving plates