worksheet 4

Question 1

what are plate tectonics

Answer 1

one of the grand theories of the natural world

Question 2

what are the 7 commonly major plates

Answer 2

pacific, north america, eurasian, african, antarctica, indo-australian, south american

Question 3

what happens at a constructive/divergent plate boundary

Answer 3

crust is made

Question 4

what happens at subduction zone

Answer 4

oceanic crust is destroyed

Question 5

what is another name for a transform plate boundary

Answer 5

strike-slip or conservative boundaries

Question 6

what plate tectonic event made the himalayans

Answer 6

continental collision

Question 7

what are the theories behind plate movement

Answer 7

1. mantle convection
2. ridge push
3. slab pull

Question 8

what is mantle convection

Answer 8

where currents in the mantle (made my differences in temperature) carry the plates like a conveyor belt

Question 9

what is ridge push

Answer 9

newly formed crust at the mid ocean ridge is at a higher elevation and gravity pulls the new slap down and away from the ridge

Question 10

what is slab pull

Answer 10

sinking (subducting) cold dense oceanic crust pulls the crust that is attached to it behind it

Question 11

where is the thickest crust and how thick

Answer 11

in mountain belts. himalayas and andes have ~70km thickness

Question 12

where is the thinnest crust and how thin

Answer 12

oceanic crust. <10km in places

Question 13

how thick is ireland crust

Answer 13

~20-30 km

Question 14

how does the crust in ireland compare to other crust

Answer 14

it is continental crust with lower than average thickness

Question 15

what is oceanic crust made from

Answer 15

mafic minerals and basalt.

Question 16

what is continental crust made from

Answer 16

felsic rocks like granites and other igneous rocks with quartz and feldspar

Question 17

which is denser: oceanic or continental crust (and how thick are they)

Answer 17

oceanic crust
oceanic crust - 3.0 kgm^-3
continental crust - 2.7 kgm^-3

Question 18

what is the correlation between crust thickness and elevation

Answer 18

higher above sea level when crust is thicker

Question 19

what is lighter: continental or oceanic crust?

Answer 19

continental crust

Question 20

what is isostasy

Answer 20

the idea that crust floats on the mantle like ice floating on water

Question 21

what are magnetic anomalies and where do they occur

Answer 21

stripy patterns that occur only in the oceanic crust. they align north south with the mid ocean ridge

Question 22

why do magnetic stripes form symmetrically on the side of ridges?

Answer 22

this occurs due to the polarity of the rocks changing due to geomagnetic reversals when crust is created

Question 23

where is the youngest crust

Answer 23

at the mid ocean ridges

Question 24

how old is oceanic crust generally

Answer 24

relatively young <270 my

Question 25

how old is the oldest continental crust

Answer 25

up to 4500 my old

Question 26

what are the very old areas of continental crust called

Answer 26

precambrian shields

Question 27

how does bathymetry vary across the atlantic

Answer 27

gets deeper as you move away from mid ocean ridge. corresponds with age

Question 28

what is the relation between sea floor age and heat flow

Answer 28

younger seafloor means higher heat flow and will be hotter

Question 29

where is oceanic crust made

Answer 29

the mid ocean ridge

Question 30

what is subduction

Answer 30

when crust gets dense as it cools and ages so it sinks into the mantle. when it completely sinks that is subduction

Question 31

what is the process of opening of the atlantic

Answer 31

1. opening between east USA and NW africa
2. southern atlantic
3. north atlantic (<60 mya)

Question 32

when did ireland break away from north america

Answer 32

90-120 mya

Question 33

when did ireland break apart from greenland

Answer 33

60 mya

Question 34

where is the bay of biscay and what is its opening process

Answer 34

• south of ireland
• started opening 100-110 mya bc of counterclockwise rotation of iberian peninsula
• no longer spreading. oldest oceanic crust is 80 myo

Question 35

where is the oldest oceanic crust in the world and how old

Answer 35

in the western pacific, either side of atlantic and east mediterranean is 200-270 myo

Question 36

what are transform faults

Answer 36

east-west trending features that offset the mid-ocean ridge that form valleys on the ocean floor

Question 37

what do transform faults define

Answer 37

they define plate boundaries

Question 38

how are transform faults formed

Answer 38

caused by difference in spreading rates or by spreading initiating in different places

Question 39

what type of boundary is it between african and eurasian plate

Answer 39

convergence (so local subduction and destruction of crust)

Question 40

what do earthquakes and volcanos suggest

Answer 40

tells us where plate boundaries are

Question 41

what is the epicenters of most earthquakes in atlantic and europe

Answer 41

shallow - <30 km below surface

Question 42

what is the ring of fire and why does it occur

Answer 42

ring of fire in the pacific where there are many large earthquakes and volcanoes due to the pacific tectonic plate

Question 43

what is one of the lowest points on earth and where is it

Answer 43

atacama trench, west of south america

Question 44

what is the wadati-benioff zone

Answer 44

a dipping zone of seismicity in the pacific near south america where the epicenters for earthquakes are up to 500-600 km deep

Question 45

how did the andes form

Answer 45

crustal thickening and uplift

Question 46

what are hotspots

Answer 46

a place beneath a plate where the crust melts and volcanoes form. they are usually static but the plate moves so where the volcanoes are made changes