Section 10.3 – Theory of Plate Tectonics
Plate Tectonics – Theory that Earth’s crust and part of the upper
mantle are broken into sections
Plates –
- Sections that move on a plastic-like layer of the mantle
- Made of the crust and the upper mantle
- LITHOSPHERE
Asthenosphere – Layer below the Lithosphere
- Plates of the Lithosphere float and move around on the
Asthenosphere
Plate BoundariesPlates can:
1) Move toward each other (Converge)
2) Pull apart (Diverge)
3) Slide past each other (Transform)
Divergent Boundary- 2 plates are moving apart
- Examples – North American Plate and Eurasian and African
Plates
- Boundary is called Mid-Atlantic Ridge
** Crust disappears when: The seafloor cools, becomes denser and
sinks.
Convergent Boundary –
- 2 plates move together
- Oceanic Plate converges with less dense Continental Plate –
Oceanic Plate sinks
Subduction Zone –
- Area where an oceanic plate subducts or goes down
- Some volcanoes form here
- Can also occur where 2 oceanic plates occur. This will form
mountains
- Earthquakes are common at convergent boundaries
Transform Boundary –
- Occurs where 2 plates slide past each other
- They can move in opposite directions or in the same
direction
- Example – San Andreas Fault – earthquakes occur
Convection Current
- The cycle of heating, rising, cooling, sinking
- Force behind tectonic plates
Features Caused by Plate Tectonics
-
Mountains
Ocean Basins
Volcanoes
Earthquakes
Faults
- Form when rocks break and move along surfaces
- Interrupt rock layers by moving them out of place
Rift Valleys and Mid Ocean Ridges
- Forms where Earth’s crust separates
- Example – Great Rift Valley – Africa
- Normal Fault – Divergent – plates pull apart
Mountains and Volcanoes
- Mountains occur where 2 continental plates collide
- Reverse Fault – Convergent (plates come together)
- Volcanoes occur where 2 oceanic plates collide
o Denser plate sinks
o Island Arcs form above the sinking plate
- Strike –Slip Fault – Transform – rocks on opposite sides move
in opposite directions or in the same direction but at
different rates
o Causes earthquakes