theory of plate tectonics

what is Ridge push

heat from radioactive decay moves upwards into mantle, creatin g convection currents which pushes up into spreading mid ocean ridges forcing them further apart

what is seafloor spreading

movement of oceanic crust away from a constructive plate boundary, as recorded by magnetic stripes in basaltic rock (palaeomagnetism)

what is the subduction zone

where 2 plates meet

what is slab pull

at destructive margins, lithosphere descends into mantle. Collision with other plate boundary causes both shallow and deep seismic acitivity

convergent plate boundary

plates moving towards each other, oceanic plate subducts under continental plate forming deep ocean trenches in the subduction zone. Earthquake and volcanoes occur

constructive plate boundary

plates moving apart, volcano and earthquakes occur here

collision plate boundary

plates move towards each other, plates are same density so they’re forced upwards. no volcanic activity as no subduction zone. earthquakes occur

conservative boundary

plates move past each other, they become stuck and pressure builds causing plates to snap past each other. friction causes earthquakes but not volcanoes

magma property at divergent boundary

earthquakes are mild, basalt lava has low viscosity, high temp

magma property at convergent boundary

friction and pressure builds in benioff zone causing strong earthquakes, magma is high viscosity, low temp

magma property at transform boundary

plates can stick cause build up of pressure and powerful earthquakes

the crust

continental- thicker, less dense layer

oceanic- thinner, denser layer

upper mantle

asthenosphere- semi molten layer which moves under high pressure

Lithosphere- rigid layer above astehnosphere

lower mantle

hotter and denser,

core

inner core- solid centre, composed of iron

outer core- semi molten, liquid iron and nickel

what are convection currents

hot, liquid magma currents moving into the asthenosphere