topic 1 : plate tectonic

internal structure of the earth

core, mantle, crust

core

innermost

4400-6000 °C

3300km thickest

Mantle

between core and crust

1000 - 3700°C

2900km

crust

outermost

lowest temperature

6-70km

convection currents

-heat from earth's core causes mantle material to become less dense

- mantle material rises towards the surface

- it spreads beneath plates and drag them apart causing divergent plate movement

- mantle material then loses heat ,collide and sink towards the core causing convergent plate movement

- material then get heated up again and the process repeats

- rising and sinking of mantle material causes convection current

slab-pull force

- 2 plates converge , denser oceanic crust is pulled down by gravity

- subducts beneath less dense crust

- denser oceanic crust sinks into mantle

- it pulls rest of the plate downwards

sea-floor spreading

- divergent plate moves away from each other

- magma rises

- iron rich lava erupts from the center of mid- oceanic ridge

- lava cools and solidifies forming new oceanic crust

- crust is pushed away from ridge

- rocks nearest to the mid- oceanic ridge are the youngest

- rocks further away are older

- new crust formed at mid-oceanic ridges

- older crust destroyed at oceanic trench

magnetic stripping

- normal polarity, magnetic north towards the geographic north and the magnetic south towards the geographic south

- reverse polarity, magnetic north towards the geographical south and magnetic south towards the geographical north

- oceanic plates move away from each other

- iron-rich lava erupts from the center of the ridge

- lava cools and solidifies forms new oceanic crust

- crust is pushed away from the ridge

-new iron rich rocks record reversals in earth's polarity

- over long time, more lava moves away from ridge forms a symmetrical zebra- like pattern

divergent boundary: continental- continental

- 2 continental rift valley move apart from each other

- rocks fracture ( faulting) to form parallel faults

- the rocks in between these faults collapses with steep sides

- decrease in overlying pressure causes underlying mantle to melt forming magma

- magma rises through weak crust forming volcanoes

- eg. The East African Rift Valley

divergent boundary: oceanic-oceanic

- 2 oceanic plates move apart

- decrease in overlying pressure causes underlying mantle to melt

- magma rises through crust

- lava cools and solidifies to form balistic rocks

- forms new oceanic crust

eg North American and Eurasian plates movement

transform boundary

- plates slide past each other

- builds up tremendous stress

- faulting occurs

- sudden release of energy results in earthquake

- san andrew fault

Convergent Boundary (Continental/Continental)

- two continental plates collide

- subduction does not take place because plates too buoyant to subduct

-pressure causes rocks to be uplifted and buckled to form fold mountains

- friction along convergent plate boundary also causes earthquakes

- magma does not rise to the surface so no volcanoes formed

Convergent Boundary (Oceanic/Oceanic)

- 2 oceanic plates move towards each other

- denser plates subducts under less dense plate

- denser plate at subduction zone melts forming magma

- magma rises through weak crust-forms volcanoes

- oceanic trench is found along subduction zone

Convergent Boundary (Oceanic/Continental)

- oceanic plate collides with continental plate

- denser oceanic plate subducts beneath the continental plate forming oceanic trench at subduction zone

- subducting plate sink into mantle and high pressure forces water out of its oceanic crust, water lowers the mp of the overlying mantle causing it to melt , magma formed

- magma rises through weak crust and forming vocalones at continental plate