Transcript Plate Motion

Plate Motion
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Remember that the planet is divided into four
sections…
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The Inner Core
The Outer Core
The Mantle
The Crust
Convection Currents
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Circular patterns of motion created in the mantle when
material heats, expands, becomes less dense and rises >>>
followed by the cooling, contraction, and sinking of denser
material.
As the moving magma circulates, it runs along the
underside of the crust, pushing it along (ever so
slowly).
Ridge Push
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The movement of tectonic plates away from a
mid-ocean ridge >>> toward an area of
subduction, such as a trench (occurring at
position “B”). Gravity is believed to be playing
a role.
Slab Pull
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The movement of tectonic plates into an area
of subduction (a trench). As the leading edge is
pulled into the mantle and recycled (melted),
the trailing edge is pulled into the trench
(occurring at position “C”). Gravity is believed
be playing a role here as well.
So which is which?
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There is some debate as to whether ridge push
is “pushing” the plates away from the ridges,
or if slab pull is “pulling” the plate into the
trenches.
There is also debate as to whether ridge push
and slab pull are playing a bigger/smaller role
than convection currents.
It is most likely a combination of the three.
Some unanswered questions
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How did these currents
originate?
Are convection
currents permanent
features?
Do they shift positions
over time?
What causes them to
stop?
How big are these
currents?
Is convection only
taking place in the
upper mantle?
Does subduction cause
convection currents?