Lecture 4 Flashcards
What are plate boundaries associated with?
faulting
What are the 3 types of faults?
1) Normal faults
2) Reverse faults
3) Strike-slip faults
Describe normal faults, reverse faults, and strike-slip faults.
- Normal: extensional (pulling apart)
- Reverse: compressional (colliding)
- Strike-slip: shearing (sliding past) - transform boundaries
What is a divergent boundary?
Two places move apart, resulting in upwelling of material from the mantle to create new sealer.
Where do divergent boundaries occur?
- occurs mainly at mid-ocean ridges
- can occur under continents at rift valleys
What are meid-ocean ridges the site of? Explain.
- site of crustal formation
- hot mantle material rises to top of lithosphere, cools
- results in the formation of new ocean crust.
Why does new crust formed at mid ocean ridges ‘sit lower’ on the planet?
- very dense and iron rich – heavy
- the density of ocean crust is due to it being derived from the mantle
At mid ocean ridges, why does partial melting occur?
The descending slab undergoes dehydration which causes partial melting of the overlying mantle – molten material is less dense, rises
What are the three types of divergent boundaries?
1) Results from oceanic - continental collision
(mountain building)
2) Results from two oceanic plates colliding (volcanic island arc)
3) Due to collision of two continental plates (intense mountain building)
What do divergent boundaries all result in?
subduction
When are older portions of oceanic plates returned to the mantle?
convergent plate boundaries
What is surface expression of the descending plate?
an ocean trench
What are destructive plate margins called?
subduction zones
What are transform fault boundaries?
plates slide past each other without either generating new lithosphere or consuming old lithosphere
What are enormous faults that result in active seismic activity?
transform fault boundaries
