Transcript Mechanisms of Plate Motion

Warm Up 11/26
The Hawaiian Islands were formed when the Pacific Plate
moved over ____.
a. a hot spot
c. the Aleutian Plate
b. a subduction zone d. an ocean ridge
2. Strips of alternating magnetic polarities found in rocks in the
ocean basins ____.
a. conflict with the theory of plate tectonics
b. provide evidence that Earth’s magnetic field has never
reversed polarity
c. indicate changes in Earth’s gravitation field
d. provide evidence for seafloor spreading
3. The formation of the Hawaiian Islands is associated with ____.
a. a convergent plate boundary
c. a transform fault
boundary
b. a divergent plate boundary
d. no plate boundary of
any kind
Answers: 1) a. 2) d. 3) d.
1.
Mechanisms of Plate Motion
Chapter 9, Section 5
Causes of Plate Motion
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Scientists generally agree that
convection occurring in the mantle is the
basic driving force for plate tectonics
Convective Flow – the motion of
matter resulting from convection
The slow movements of the plates and
mantle are driven by the unequal
distribution of Earth’s heat from the
radioactive decay elements
Convective Flow
Slab-Pull and Ridge-Push
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Slab-Pull – old oceanic crust, which is
relatively cool and dense, sinks into the
asthenosphere and “pulls” the trailing
lithosphere along
Slab-pull is thought to be the primary
downward arm of convective flow in the mantle
Ridge-Push – causes oceanic lithosphere to
slide down the sides of the oceanic ridge as a
result of gravity
Mantle Convection
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Mantle Plumes – hot plumes of rock that are
attributed to the upward flowing arms of mantle
convection
Mantle plumes sometimes show themselves on
the surface as hot spots and volcanoes
Whole-mantle convection is when slabs of cold
oceanic lithosphere descend into the lower
mantle, at the same time, hot mantle plumes
originating near the mantle-core boundary move
heat toward the surface
Another model is called the deep-layer model ,
and can be likened to a lava lamp, heat from
Earth’s interior causes the layers to mix and
combine in swirling patterns
The unequal distribution of heat within Earth
causes the thermal convection in the mantle that
ultimately drives plate motion
Whole-Mantle Convection
Deep-Layer Model
Assignment
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Read Chapter 9, Section 5 (pg. 269270)
Do 9.5 Assessment #1-5 (pg. 270)
Study for the Chapter 9 Quiz!