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Plate Tectonics
Theory of Plate Tectonics
• Plate tectonics – Theory that the lithosphere
is made up of plates that float on the
asthenosphere and that the plates possibly
are moved by convection currents.
Types of Lithospheric
• Oceanic crust
• Continental crust
• Lithosphere broken into plates
~30 identified
Major Plates
3 types of Plate Boundaries
• Divergent – plates move away
• Convergent – plates collide
• Transform-fault – plates grind past each
other
Divergent Boundary
• Two plates moving
away from each other;
most found in the
ocean; forms rifts
valleys
• Ex. – Mid-Atlantic
Ridge
Convergent Boundary
• Direct collision of one
plate with another
• 2 types of crust; 3
types of collision
1. Oceanic – Continental
Collision
•
More dense ocean
crust subducted
beneath less dense
continental crust
forming an oceanic
trench
2. Oceanic-Oceanic Collision
• More dense crust is
subducted, melts,
rises, forms island arc
3. Continental – Continental
collision
• Collision forces crust
upwards forming
mountains (orogeny)
ex. Himalayas
Transform – Fault Boundary
• Plates slide past each
other
ex. San Andreas Fault,
California
Convection Currents
• The transfer of heat
through the movement
of heated fluid;
convection currents in
the asthenosphere may
be responsible for
lithospheric plate
movement.
Theory of Suspect Terranes
• Theory that continents are a patchwork of
pieces of land (lithosphere) that have
individual geologic history
• Connected to form continents (blocks of
terrane are scraped off oceanic crust and on
to the continent as the crust is being
subducted).
Characteristics of Terranes
• Differing rock and fossil content
• Major faults at boundaries
• Differing magnetic properties