Theory of plate tectonics

Radiogenic heat - produced by radioactive decay of isotopes

Primordial heat -  heat left over from earth's formation

      Lithosphere - 80-90km thick, divided into large plates (oceanic/continental)

Oceanic crust - 6-10km, 3.0 density, Basalt, silicon

Continental crust - 30-70km, 2.6 density, granite

Palaeomagnitism - magnitism in rocks induced by earth's magnetic field at time of formation

Convection currents - movement caused by radiogenic heat from core, heat causes magma to rise, cooling nearer the surface, and sinks forming a current

Magma - molten rock, located in the mantle

Subduction - denser plate sinks under less dense late (often causes seismic activity)

Gravitational sliding - result of gravity acting down the slope of a ridge, frictional resilience to force causes shallow earthquakes (constructive plate boundaries)

(ridge push another word for gravitational sliding)

Sea floor spreading -formation of oceanic crust via upwelling of magma at mid-ocean ridges

Slab pull - gravitational force on dense decending plate to mantle pulls oceanic plate down, frictional resilience causes earthquakes (destructive plate boundaries)

Young fold mountains - formed by effects of folding layers in crust, no volcanic activity, (constructive plate boundaries)

Rift valleys - plates move apart on continental areas

Ocean ridges - when plates move apart on oceanic areas

Deep sea trenches - oceanic and continental meet - oceanic forced under less dense continental, forms a trench via downwarping

Island arcs - during subduction plate melts from heat (friction) - becoming less dense. This rises and forms explosive volcanoes 

convergent

-oceanic (dense) and continental (less dense) move together

-ocean forced under continental

-friction causes melting (subduction zone)

-magma rises, friction causes earthquakes

-plates move apart, magma rises through gap forming new crust

EG Mid Atlantic Ridge

(typically low VEI, basaltic lava, shield volcanoes)

Constructive plate boundary: plates slide next/opposite direction - friction causes plate to slip in sudden movement (eg. San Andreas Fault - California)

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Volcano - rupture in earth's crust. Allowing magma to escape from magma chamber via vents

Hotspots - concentration of radioactive elements - plume of magma rises and breaks platr surface, forming volcanoes on upper crust

Mantle plume - upwelling of hot rock from mantle - known to form hotspots

Seismicity - frequency of earthquakes in a region

Vulcancity - gas/magma is extrudned onto earth's surface