Plate movement Flashcards
What is the geological evidence for plate tectonics?
South America and Africa fit together like a jigsaw
Evidence for glaciation from the Carboniferous period 290 million years ago deposits found in South America, Antartica and India. These must have been formed together and then moved.
Rock sequence in Northern Scotland closely agree with those from Eastern Canada
Paleomagnetism
What is the biological evidence for plate tectonics?
Fossil Brachiopods found in Indian limestones are comparable with similar fossils in Australia
Mesosaurus fossils found in South America and southern Africa
Oil and coal deposits only produced on tropical areas yet there is oil in Antartica
Characteristics of continental crust
30-70km thick
Over 1 500 million years old
Less dense
Characteristics of oceanic crust
6-10km
Less than 200 million years old
Denser
What is the lithosphere?
The crust and the rigid upper section of the mantle.
It is split into 7 main plates
80-90km thick
What is the asthenosphere?
The semi-molten mantle on which the tectonic plates float on
How are rift valleys formed?
Convection currents break brittle continental crust apart and split the plate and often produce parallel fractures that some of the land slides into the gap producing rift valleys.
E.g: The East African Rift Valley
How are island arcs formed?
Oceanic plates collide, one of which is denser and this leads to subduction. The subduction causes the build up of molten magma as the crust is melted. This build up produces volcanoes and they eventually poke out the surface.
How are fold mountains formed?
2 continental plates collide and as they are of a similar density there is on subduction and so they just push up and crumple, producing fold mountains.
What is a hotspot?
A concentration of radioactive elements inside the mantle can cause a hot spot. These elements can cause a mantle plume to shoot up through the mantle and eat away at the crust.
How are chain islands like Hawaii formed?
The plate moves, but the hotspot doesn’t, producing a line where the plate has passed over the hotspot.
