worksheet 4 Flashcards
what are plate tectonics
one of the grand theories of the natural world
what are the 7 commonly major plates
pacific, north america, eurasian, african, antarctica, indo-australian, south american
what happens at a constructive/divergent plate boundary
crust is made
what happens at subduction zone
oceanic crust is destroyed
what is another name for a transform plate boundary
strike-slip or conservative boundaries
what plate tectonic event made the himalayans
continental collision
what are the theories behind plate movement
- mantle convection
- ridge push
- slab pull
what is mantle convection
where currents in the mantle (made my differences in temperature) carry the plates like a conveyor belt
what is ridge push
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
what is slab pull
sinking (subducting) cold dense oceanic crust pulls the crust that is attached to it behind it
where is the thickest crust and how thick
in mountain belts. himalayas and andes have ~70km thickness
where is the thinnest crust and how thin
oceanic crust. <10km in places
how thick is ireland crust
~20-30 km
how does the crust in ireland compare to other crust
it is continental crust with lower than average thickness
what is oceanic crust made from
mafic minerals and basalt.
what is continental crust made from
felsic rocks like granites and other igneous rocks with quartz and feldspar
which is denser: oceanic or continental crust (and how thick are they)
oceanic crust
oceanic crust - 3.0 kgm^-3
continental crust - 2.7 kgm^-3
what is the correlation between crust thickness and elevation
higher above sea level when crust is thicker
what is lighter: continental or oceanic crust?
continental crust
what is isostasy
the idea that crust floats on the mantle like ice floating on water
what are magnetic anomalies and where do they occur
stripy patterns that occur only in the oceanic crust. they align north south with the mid ocean ridge
why do magnetic stripes form symmetrically on the side of ridges?
this occurs due to the polarity of the rocks changing due to geomagnetic reversals when crust is created
where is the youngest crust
at the mid ocean ridges
how old is oceanic crust generally
relatively young <270 my
how old is the oldest continental crust
up to 4500 my old
what are the very old areas of continental crust called
precambrian shields
how does bathymetry vary across the atlantic
gets deeper as you move away from mid ocean ridge. corresponds with age
what is the relation between sea floor age and heat flow
younger seafloor means higher heat flow and will be hotter
where is oceanic crust made
the mid ocean ridge
what is subduction
when crust gets dense as it cools and ages so it sinks into the mantle. when it completely sinks that is subduction
what is the process of opening of the atlantic
- opening between east USA and NW africa
- southern atlantic
- north atlantic (<60 mya)
when did ireland break away from north america
90-120 mya
when did ireland break apart from greenland
60 mya
where is the bay of biscay and what is its opening process
- south of ireland
- started opening 100-110 mya bc of counterclockwise rotation of iberian peninsula
- no longer spreading. oldest oceanic crust is 80 myo
where is the oldest oceanic crust in the world and how old
in the western pacific, either side of atlantic and east mediterranean is 200-270 myo
what are transform faults
east-west trending features that offset the mid-ocean ridge that form valleys on the ocean floor
what do transform faults define
they define plate boundaries
how are transform faults formed
caused by difference in spreading rates or by spreading initiating in different places
what type of boundary is it between african and eurasian plate
convergence (so local subduction and destruction of crust)
what do earthquakes and volcanos suggest
tells us where plate boundaries are
what is the epicenters of most earthquakes in atlantic and europe
shallow - <30 km below surface
what is the ring of fire and why does it occur
ring of fire in the pacific where there are many large earthquakes and volcanoes due to the pacific tectonic plate
what is one of the lowest points on earth and where is it
atacama trench, west of south america
what is the wadati-benioff zone
a dipping zone of seismicity in the pacific near south america where the epicenters for earthquakes are up to 500-600 km deep
how did the andes form
crustal thickening and uplift
what are hotspots
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
