Plate tectonics

what is the theory of plate tectonics?

• continental drift theory

• helps expl geolog phenomena such as:

  • occurrence of hazards e.g.earthquakes + volc eruptions

  • form of mountain ranges

  • movem of continents

  • distrib of some mineral resources e.g. diamonds

what is continental drift theory?

1) 1912: AW published theory, sugg Earth’s continents had once been part of pangaea

2) believed continents grad drifted apart over millions of yrs

3) unable to sugg cause of movem + many scientists were sceptic

4) today, theory is recogn as basis of the modern theory of plate tect

what are convection currents?

• In past, convec curr theory used on own to expl tect plate movem

1) heat from radioact decay in core moves upwards in mantle

2) creates convec curr, rise tow surface before spreading in asthenosph, cooling + sinking

3) as they reach asthenosph they carry lithospheric plates above w them

how does slab pull work?

1) subduc zone formed when 2 plates move tow each other

2) heavier, denser oceanic plate subducts under lighter, less dense plate

3) as plate sinks, gravity pulls plate down into mantle - this is known as SLAB PULL

how does ridge push work?

1) New oceanic crust formed at mid-ocean ridges, stands 2-3km above ocean floor

2) As crust moves away from mid-ocean ridge, cools + becomes denser & thicker

3) causes lithosph to slope away from ridge, gravity pulls lithosph down slope, pushing it forw

• known as gravitational sliding (or ridge push)

how does sea floor spreading work?

1) palaeomagnetism prov evid sea floor has grad moved apart at mid-ocean ridge

2) lava cools + solidifies w minerals lining up with magnetic field

3) direction of minerals on either side is a mirror image