Tectonic Processes

Divergent Plate Boundaries

Plates move apart:

• Oceanic-oceanic

• Continental-continental

Convergent Plate Boundaries

Plates move towards each other:

• Oceanic-oceanic

• Continental-continental

• Oceanic-continental

Divergent (Oceanic-oceanic)

• Move apart

• Rising convection current lifts lithosphere

• Forms mid-oceanic ridge (submarine mountains/volcanoes)

• Tensional forces stretch lithosphere and produce a deep fissure

• Opened fissure reduces overlying pressure

• Underlying mantle melts

• Basaltic magma fills fissure

• Cools and solidifies into sea floor

• Less dense, new seafloor rises into mid-oceanic ridge

• Ridge push force pushes older rocks away from spreading centre

• Causes shallow earthquakes

Divergent (continental-continental)

• Move apart

• Form parallel faults

• Rock between faults collapse to form deep rift valleys

• Decrease in overlying pressure

• Underlying mantle melts

• Magma rises

• Forms volcanoes

• Stress and tensions cause earthquakes

Convergent (oceanic-continental)

• thinner, denser oceanic plate descends thicker, lighter continental plate

• Due to slab-pull force

• Forms oceanic trench

• Tip of subducting oceanic plate melts due to friction

• Silica-rich magma rises to form magma chambers

• As it is less dense and gases within expand

• Magma escapes through vent

• Cools and solidifies

• Accumulate to form volcano

• Edges of continental plate and nearby sediments are contorted and folded to form fold mountains

Convergent (Oceanic-oceanic)

• Collide

• Denser plate subducts

• Forms deep depression of oceanic trench

• High pressure forces water out of oceanic crust

• Lowers melting point of overlying mantle

• Melts to form magma

• Rises through weak areas in crust

• forms chain of volcanoes (a volcanic island)

• Friction causes earthquakes

Convergent (continental-continental)

• Collide

• No subduction as both are too buoyant

• High pressure causes rocks to be uplifted and buckled

• To form fold mountains

• Friction causes earthquakes

• No magma rises And hence no volcanoes form

Transform Boundaries

• Slide past

• No crust created or destroyed

• Stress from movement produces a fault (zone of fractures)

• Earthquakes occur when one suddenly slips past another

• No magma rises and hence no volcanoes