plate tectonics (plate movements)

Question 1

why do plates move

Answer 1

1. when radioactive materials in the core break down, heat is released. mantle material is heated by the core and expands, rises and spreads out beneath plates.
2. plates are dragged along and move away from each other
3. the hot mantle cools slightly and sinks, pulling the plates along
4. the sinking mantle material heats up again. as it nears the core, the process repeats
5. when a denser oceanic plate is forced beneath a less dense plate in subduction, slab-pull force occurs - the main driving mechanism for plate movement
6. as the plate subducts, it pulls the rest of the plate along. the subducting/sinking plate drives the downward moving portion of convection currents
7. the mantle material found away from where the plates subduct drives the rising portion of convection currents

Question 2

pls describe o-o divergence

Answer 2

1. when two oceanic plates move away from each other, rising convection currents below lift the lithosphere to form a mid-oceanic ridge, rows of submarine mountains or volcanoes
2. tensional forces stretch the lithosphere, producing a deep fissure forming the spreading centre
3. when the fissure opens, pressure on the super-heated mantle material below is reduced, and it responds by melting. new basaltic magma formed flows into the fissure to form new seafloor
4. being less dense than the surrounding older rocks, the new seafloor rises in elevation, resulting in gravitational sliding that pushes older rocks away from the spreading centre - ‘ridge-push’ force
5. shallow earthquakes are often associated with this type of crustal stretching. basaltic magma from the asthenosphere wells up along any crustal fractures to form submarine volcanoes

Question 3

pls describe c-c convergence

Answer 3

1. the two continental plates converge at the convergent boundary. as they are of the same density, no subduction takes place
2. compressional forces cause the edges of the plate to buckle up and fold and get uplifted to form a fold mountain
3. the movement of the convergence of the two plates is not smooth, producing vibrations called earthquakes

Question 4

pls describe o-o convergence

Answer 4

1. when two oceanic plates collide, the older and denser oceanic plate descends beneath the less dense oceanic plate due to ‘slab-pull’ force. a long, narrow and deep oceanic trench is formed where the plate dips into the asthenosphere
2. the tip of the subducted plate melts due to friction with the overriding plate and heat at great depth, producing silicon-rich magma
3. pressure causes the magma to move up through any breaks or fractures on the other oceanic plate
4. rising magma builds up pressure inside the magma chamber
5. build-up of pressure in the magma chamber forces magma up the pipe and escape through the vent on the oceanic crust as lava. lava cools and solidifies. repeated eruptions form a volcano. when the volcano builds up above sea level, it forms a volcanic island (arc)
6. movement of the subducting plate is not smooth, producing vibrations called earthquakes along the subduction zone

Question 5

pls describe o-c convergence!

Answer 5

1. when a thinner and denser oceanic plate converges with a thicker and lighter continental plate, the former descends beneath the latter due to ‘slab-pull’ force into the asthenosphere
2. a long, narrow and deep oceanic trench is formed where the oceanic plate dips into the asthenosphere
3. the tip of the subducting oceanic plate melts due to friction with the overriding continental plate and heat at great depth, producing silicon-rich magma
4. magma moves up through any breaks or fractures on the overriding continental plate to form a magma chamber as it is less dense than the asthenosphere and as gases in the magma expand
5. build-up of pressure inside the magma chamber forces magma to escape through the vent on the land surface as lava. lava cools and solidifies around the vent. over time, through repeated eruptions, it builds up to form a volcano.
6. edges of continental plate and sediments near the edges of continental shelf and on the seafloor are contorted and folded to form fold mountains.
7. the movement of the subducting plate is not smooth, producing vibrations called earthquakes along the subduction zone