Transcript 4.2 The Theory of Plate Tectonics

4.2
The Theory of Plate Tectonics
Tectonics – (Greek) meaning “construction”
Tectonics:
The study of the formation of
features in the earth’s crust
Open textbook to p. 72
Two types of crust:
• Oceanic crust
• Continental crust
Lithosphere & Asthenosphere
Lithosphere – made up of the crust
and the rigid upper mantle
The lithosphere is broken into
separate plates that ride on the
denser asthenosphere.
Asthenosphere – layer of plastic
rock; a solid rock that slowly
flows(like putty) when under
pressure.
Plate Boundaries
Divergent boundaries –
where plates move away from each other
Plate Boundaries
Convergent boundaries – where plates collide (3 types)
1. Ocean & Continent – forms a subduction zone;
usually forms an ocean trench and mountains on land
Plate Boundaries
Convergent boundaries – where plates collide
2. Two Continental plates –
neither plate is subducted, so both are crumpled and uplifted
Plate Boundaries
Convergent boundaries – where plates collide
3. Ocean & Ocean – forms deep ocean trench when one plate is
subducted; subducted plate melts and forms volcanic chain
(Island Arc)
Plate Boundaries
Transform fault boundaries – forms where two
plates are grinding past each other.
Can you think of an example?
San Andreas Fault
Causes of Plate Motion
Convection Currents – cycle of warm matter rising and
cool matter sinking
Theory of Suspect Terranes
Continents are a patchwork of terranes,
each with its own distinct geologic history.
3 identifying characteristics:
1. Terrane contains rock and fossils that differ from the rocks
and fossils of neighboring terranes.
2. There are major faults at the boundaries of a terrane.
3. The magnetic properties of a terrane do not match those
of neighboring terranes
See Figure 4-9 on p. 77