Transcript CH 9 Plate tectonics

*Plate Tectonics
* 1915- Wegener proposes his hypothesis of
continental drift.
* Not widely accepted because he could not
explain WHY?
* Died in 1930 still trying to figure it out.
*
Continental Drift - 240 million years ago there
was one supercontinent called Pangaea. Over time
the continents have moved to their present
locations and continue to move.
*
* South America and Africa fit together.
*
* Mesosaurus and Glossopteris
- Matching fossils found in patterns across
different continents
*
* Glaciers and Coal Deposits
Signs of glaciers on multiple continents,
some near equator.
Found in cold areas but need tropical
climate to form.
* Age, Type, and Alignment of
Mountains
* Appalachian Mtns. Same age
and type as mtns. in Greenland
and Europe
*
*Plate Tectonics
* Move slowly about 5 cm or 2.5” per year
* Plate movement causes EQs, volcanoes, & create
mountains
* Lithosphere – plates
* outer and rigid
* Crust and upper mantle
* Moves over the
asthenosphere
* Asthenosphere
* below and plastic like
* Lower mantle
*Earth’s Interior
1.
Transform
*
*
*
*
Plates slide past one another
Stress involved is shearing
Forms Eqs
Ex: San Andreas Fault
*Boundary Types
1.Divergent
*
*
*
*
Plates move away from
each other
Stress involved is tension
Forms mid ocean ridges
and rift zones
Ex: Mid-Atlantic Ridge
and Iceland
*Boundary Types
3. Convergent
*
*
*
Plates move towards each other
Stress involved is compression
3 different results!
*
A)oceanic-continental
crusts meet
* Subduction (denser plate
*
*
*
[oceanic] dives below)
Ocean trench forms offshore
Continental volcanic arcs
Ex: Cascades, Andes
*Boundary Types
B) Oceanic-oceanic
crusts meet
* Subduction occurs and
one plate dives down
* Ocean trench forms
* Volcanic island arcs
* Ex: Japan, Aleutians
*Boundary Types
C) Continental-continental crusts
meet
*
*
*
*
No subduction
Collision boundary
Mountains form
Ex: Appalachians, Himalayas
*Boundary
Types
*Plate Tectonic Evidence
1. Paleomagnetism
*Polar wandering & Polar reversals
2. Earthquake patterns
*Earthquakes occur @ plate boundaries
3. Ocean Drilling
*Glomar Challenger & Harry Hess
*180 million (oceanic) vs. 4 billion (continental)
4. Hot spots—example = Hawaii
*Only one active volcano
*Evidence of movement & direction
*Islands further from hot spot are oldest
* Scientists generally agree that convection in
the mantle is the basic driving force for plate
movement.
* The unequal heating within the earth causes
this.
* Read about slab-pull & ridge-push.
* Read about mantle convection.
*Causes of Plate
Motion