Flashcards in Plate Tectonics Deck (11)
State the two types of crust, what are the made out of?
Oceanic crust - basaltic rock formed from silica and magnesium (sima)
Continental crust- granite rocks formed from silica and aluminium (sial)
What is the lithosphere?
Curst and upper mantle
Give four pieces of evidence for plate tectonics
1) similar fossils found on either side of oceans - mesosaurus (S.africa and S.America)
2) similar landforms and rock patterns e.g. Appalachian mountains fit with mountains in western Scotland
3) jigsaw fit of Africa and south America
4) paleomagnetism - every 72 million years magnetic field flips, rocks have striated patterns of metallic minerals facing north and south along the atlantic ocean shows sea floor spreading
Give three ways in which the tectonic plates move
Convection currents - radioactive decay in the mantle produces convection currents that exert a force on the tectonic plates
Slab pull - destructive margin mass of sinking plate pulls the rest of it down
Ridge push at a constructive boundary new crust formed which cools and condenses gravity cools and pulls denser rock down
What is sea floor spreading?
Magma rises where plates diverge
Fills the gap and forms new crust
New crust is dragged apart
Sea floor gets wider creating ridges
What is another name for a constructive plate margin? What landforms occur in oceanic areas? What about continental areas?
Two plates move towards each other
In oceanic areas ocean ridges will form with transform faults parallel to the margin - magma leaks out solidifies
In continental areas - rift valleys will form e.g. Great African rift valley, stretching from Mozambique to the red sea,
Often volcanoes will be found within them e.g. Mt kenya
What occurs at a oceanic vs continental destructive margin?
Denser oceanic plate subducts underneath the lighter continental plate
Forms an ocean trench
Continental land mass rises = mountains
Oceanic crust melts in the benioff zone due to friction and mantle heat
Pressure can build up and plates can suddenly move past each other = earthquake
What happens at an oceanic vs oceanic destructive margin?
Denser of two plates subducts
Earthquakes and volcanoes
Underwater volcanoes and island arcs
What happens at a continental vs continental plate
Two plates collide
Fold mountains occur
No subduction therefore no volcanoes
Why can earthquakes be bad at conservative margins?
Because the tend to have a very shallow focus