Transcript 8.3 Causes of Plate Movement

Objectives:
1) Explain the “mantle convection hypothesis”.
2) Compare and contrast ridge push and slab pull.
 3 major hypotheses
describe how tectonic
plates move
 Mantle convection
 Ridge push
 Slab pull
 Asthenosphere
 Provides the plates with a
surface on which they can
move
 Pliable
 Rock materials are hotter
than those in the
lithosphere
 The mantle may be moving
the plates along with it as it
convects
 Magma that is hotter and
less dense than its
surroundings rises upward
at a mid-ocean ridge
 It drags the lithospheric
plate with it as the current
moves away from the midocean ridge
 Cooler, denser rocks of the
lithospheric plate sink
down at a subduction
boundary
 “Gravitational Sliding”
 Molten magma rises at the mid
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ocean ridge
Heats the rock around it
Surrounding rock is heated to
expand and elevate
Creates a slope
New rocks are less dense and
more buoyant
Becomes denser as it cools
Gravity causes older, denser rock
to slide away from the ridge
down the slope
New molten magma wells up
(etc.)
 The edge of the subducting
plate is much colder and
heavier than the mantle
 It continues to sink, pulling
the rest of the plate along
with it
 Definition: the force that
the sinking edge of the
plate exerts on the rest of
the plate
 Scientists think this is a
stronger factor than ridge
push or mantle convection
in driving plate movements
 Answer the following
1) What is the “mantle
questions.
 Use complete
sentences.
 You may NOT use your
book. You MAY use
your notes.
 This is a quiz grade
convection hypothesis”?
2) Compare and contrast
ridge push and slab
pull. (use a Venn
diagram)