Plate tectonics Flashcards
Earths structure core composition
-dense rocks containing iron & nickle
-5000 degrees
How is heat created in the core
-primordial heat (left from formation of Earth)
-radiogenic heat (decay of radioactive isotopes)
Earths structure mantle composition
-molten and semi molten
-iron and magnesium
What is the upper part of the mantle called
asthenosphere
Oceanic crust
-younger
-heavier
-basalt
Continental crust
-older
-lighter
The Theory of Plate Tectonics
-The Earths crust is made of several rigid plates moving relative to one another
-Pangaea-> Laurasia + Gondwanaland
-Continental drift
Geological evidence of continental drift
-‘jigsaw fit’ of South America and Africa
-Similar ancient glacial deposits found in South America, Antarctica and India
-Similar rock sequences in northern Scotland and eastern Canada, suggests they formed under the same conditions
Biological evidence of continental drift
-Fossils in India comparable with Australia
-Identical plant fossils found in coal deposits in Antarctica and India
Sea-floor spreading
-molten material adds new oceanic crust to the ocean floor, yet crust is destroyed at oceanic trenches, where ocean floor is pulled down by subduction
-evidence= alternating polarity of the rocks that form the oceanic crust due to iron particles in lava
Palaeomagnetism
-record of history of Earths magnetic field , preserved in magnetic minerals in volcanic rocks
Subduction
The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.
Convection currents
Circular currents in the mantle caused by the magma being heated by the core off the Earth.
Slab pull
-destructive plate boundaries
-downward gravitational force acting on the cold and dense descending plate as it sinks into the mantle
-This gravity generated force pulls the whole oceanic plate down as a result of the negative buoyancy of the plate.
-pushing of the subducting plate against the overriding plate= frictional resistance for shallow and deep earthquakes
Ridge push
When the force of gravity moves a plate downward and away from a ridge
Gravitational sliding
When the force of gravity moves a plate downward and away from a ridge
