The Theory of Plate
Tectonics
4.2
Plate Tectonics
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Greek tektonikos = “construction”
Tectonics is the study of the
formation of features in the earth’s
crust.
Review of earth’s make up
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2 types of crust:
Continental and oceanic crust
Lithosphere: Crust + ridgid upper mantle.
Athenosphere: Plastic rock that flows
slowly when under pressure.
Lithosphere is broken into separate plates
that “ride” on the athenosphere.
30 plates have been identified.
Some are moving together…some apart
this constant movement has created
earth’s major surface features.
Divergent Boundaries
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Divergent- 2 plates moving apart.
Asthenospere flows upward to fill the
open space.
Forms new rock forms.
Mostly occurs on ocean floors.
Rift Valleys are formed:
Red Sea occupies a huge rift valley of
when African and Arabian plate
seperated.
Convergent Boundries
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2 plates coming together and colliding
3 types:
1) Oceanic vs. Continental: continental crust is
subducted under oceanic crust: Produces Volcanic
mountains or a ocean trench.
2) Continental vs Continental: Neither plate is
subducted. Edges are crumpled upward and
produce large mountains (hymliays)
3) Oceanic vs oceanic: One goes under the other
and the subducted plate produces magma that
forms and rises to form an island arc.
Transform Boundaries
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Transform Boundaries forms when
the two plates are grinding past each
other.
They scrape each other and make
earthquakes.
San Andreas fault
Causes of Plate Motion
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Convection: Transfer of heat through the
movement of heated material.
Cycle of warm water rising and then
cooling create convection currents.
Scientist hypothesize that the earth has
hot low-density plumes from mid-ocean
ridges when it moves away from mid ridge
it becomes more dense and begins to
subduct into asthenosphere.
Questions still remain though.
Microplate Terranes
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Theory of Microplate Terranes:
Continents are actually a patchwork
of the lithosphere.
1)Terrane contains rock and fossils
that differ from neighboring terranes.
2)Major faults at the boundaries of
the terrane
3) Magnetic properties do no match
those of neighboring terranes.