week 3 - intro to plate tectonics

Question 1

plate tectonic theory

Answer 1

the outermost division of the earth consists of cool, rigid lithospheric plates that are in constant motion
- driven by the internal heat of the earth
- about 100 km thick
- plate tectonics float on a hotter, more plastic region of the upper mantle called the asthenosphere

Question 2

lithospheric plates

Answer 2

regions of earth’s crust and upper mantle that are fractured into plates that move across a deeper plasticine mantle

Question 3

asthenosphere

Answer 3

denser, weaker layer, beneath the lithospheric mantle
- temperature and pressure are so high that rocks soften and partly melt so the ayer is thin and almost liquid

Question 4

subduction/subduction zone

Answer 4

where one lithospheric plate is forced down into the mantle beneath the other plate
- subduction zones are visible on the seafloor as deep ocean trenches
- seismically active areas that have shallow, intermediate and deep focus earthquakes
- generates magmatic arcs

Question 5

magmatic arcs

Answer 5

chains of volcanoes lying parallel to trenches and above subducted slabs of lithosphere
- partial melting of the mantle produces magma
- high heat flow

Question 6

three types of plate interaction

Answer 6

1. divergence
2. convergence
3. transform

Question 7

divergence

Answer 7

plate boundary where two plates are moving away from each other

Question 8

types of divergent plate boundaries

Answer 8

1. mid ocean ridges
   - slow rates of spreading
2. young ocean basins
   - more limited mid ocean ridges that go through noses and tips of continents
   - very young rift and ridge systems
3. on land rifting
   - continental areas characterized by really high heat flow, pull apart faulting and volcanic activity
   - continents spreading apart
   - new ocean basin is made between land masses as they separate (ex. east african rift valley)

Question 9

convergence

Answer 9

plate boundary where two plates are moving toward each other, usually when one plate is subducted beneath the other
- makes ocean trenches

Question 10

three types of convergent boundaries

Answer 10

1. oceanic oceanic
2. oceanic continental
3. continental continental

Question 11

oceanic oceanic convergent boundary

Answer 11

characterized by subduction of one oceanic plate beneath another which forms deep ocean trenches and volcanic island arcs
- older, colder, and more dense plate is subducted and the less dense, warmer, younger crust forms the overriding plate
ex. tonga

Question 12

oceanic continental convergent boundary

Answer 12

characterized by subduction of high density oceanic plate beneath lower density continental palte
- leads to formation of ocean trench adjacent to the continent with chain of volcanic mountains on the continent
ex. south american andes

Question 13

continental continental convergent boundary

Answer 13

intense compression of pre existing continental rocks that forms linear belts of folded mountains along the boundary (suture zone) where convergence occurs
- forms mountains because they get pushed up
- ex. the alps
- neither of the plates can be subducted and no volcanic activity

Question 14

transform

Answer 14

two plates moving in parallel but opposite directions
- when plates slide past each other
- fault boundaries found on continents where two blocks of continental crust slide past each other
- intermittent shallow seismic activity
- low heat flow

Question 15

two types of transform boundaries

Answer 15

1. ridge transforms
2. on land transforms

Question 16

ridge transforms

Answer 16

faults perpendicular to axes of mid ocean ridges, offsetting ridge axes
- fault between offset ridges is seismically active
- associated with shallow focus seisimic activity

Question 17

on land transforms

Answer 17

develop where two continental blocks slide past each other
ex. san andreas fault

Question 18

sinistral strike slip fault

Answer 18

when top continental plate is moving to the left

Question 19

dextral strike slip fault

Answer 19

when top continental plate is moving to the right

Question 20

fracture zone

Answer 20

where two plates are moving along the boundary

Question 21

intraplate regions

Answer 21

the interiors of plates

Question 22

hotspots

Answer 22

large pulses or plumes where basaltic magma rises up from deep mantle sources
- produces source of volcanism and shallow earthquakes
- chains of volcanic islands form as lithosphere passes over the stationary volcanic source at the hotspot

Question 23

moving rate calculatin

Answer 23

distance in kilometers/difference in age

2000 km/20 mya = 10 cm/year

Question 24

how deep is a shallow earthquake?

Answer 24

0 to 30 km

Question 25

how deep is an intermediate earthquake?

Answer 25

30 - 400 km

Question 26

how deep is a deep earthquake?

Answer 26

400 - 700 km