Geog Revision

Plate Tectonics Revision

Wegener’s continental drift theory stages:
200 million years ago - Supercontinent Pangaea, Australia touching Antarctica and Indian Asia
180 million years ago - Split into Laurasia up north and Gondwanaland south
135 million years ago - Continents began to break up, Australia attached to Antarctica
65 million years ago - Further breaking up, Australia moved north-east into isolation
Today - Current positions
50 million years later – Australia to move further north
Types of plates:

Continental Plates:
 Carry land masses, continents, above
 Some also hold oceans, but they are named after the land. Eg. North American Plate
 Made of lighter, less dense rock. Eg. Quartz and feldspar
 Normally do not subduct
Oceanic Plates:
 Carry oceans above
 May carry small land masses, islands, but named after the ocean. Eg. Pacific Plate
 Made of heavier, denser rock. Eg. Mainly basalt, (granite?)
 Tend to subduct in a collision

Important information:
-Rocks deep underground can be studied through rocks from volcanoes and by looking at seismographs or seismic waves (shifting rocks create energy)
-Deep underground, the high pressure keeps rocks solid by compacting and compacting particles (liquid takes up more space than solid)
-Middle of earth probably made of iron, as rock alone would not be able to make up the weight (measured using Cavendish balance) and magnetism of the earth which make compasses work is based on this iron core. The field of magnetism from N to S poles protect the earth from solar winds
-The middle of the earth is liquid outside and solid inner section
-Like gases, hot molten rock will rise (to form volcanoes) and cool rock will sink
-Volcanoes are created when molten rock rises through up through the crust
-When a plume of hot rock pushes through the mantle, cooler rock is forced aside causing volcanic ridges. The old crust moves aside and magma fills the gap to develop new crust
-Positions on the edge of a plate are more tectonically active. Australia is in centre so it is not
-A normal fault is where rocks are pulled apart and one side drops down
-Large faults can cause earthquakes
-Folding and breaking of rocks plus grinding of one plate under another can cause earthquakes to occur
-When rocks break and slip, earthquakes can occur
-Trench is a long narrow valley on the ocean floor
-Subduction is the action of a plate (usually oceanic) sliding beneath another plate upon collision
-When an oceanic plate subducts and causes an earthquake, a tsunami can also occur
-Subduction zone is the area where a plate subducts
-Plates are constantly on the move, they move at a rate of 5 to 15cm per year

Convection Currents:
This is the heat-driven motion that causes plates to move and rocks to travel in a circular motion within the earth. They are within the mantle
Currents moving away from each other = diverging = crust pulled apart
Currents moving toward each other = converging = crush pushed together

Plate Boundaries:

1. Divergent/Constructive Boundary
-Movement of plates away from each other
-Plates can be oceanic or continental
-Gap caused called a rift or ridge
-Magma fills rift, volcano formed
-New crust created
-e.g. Mt Kilimanjaro, East African Rift, Mid-Atlantic Rift, Iceland

2. Convergent/Collision/Destructive Boundary

-Plates move toward each other
-Ocean to continent = oceanic crust subducts and melts, land on continental crust folds upward, volcano and rift forms. E.g. Mt St Helens, USA

-Ocean to ocean = one piece of crust subducts and melts, volcano (underwater) and trench forms. E.g. Japan, Indonesia, Caribbean Islands, Philippines (island arcs)

-Continent to continent = none or very little subduction occurs; continents on top of the plates collide and fold upwards to form mountains. E.g. Himalayas (Indian and Eurasian Plates), Andes (fold mountains?)

3. Transform/Conservative Boundary
-Plates slide alongside each other
-Can be oceanic or continental
-May move in the same or opposite direction
-Causes a fault e.g. Sand Andrea Fault, California (Pacific and North American Plates)

Helpful sites:
http://geology.com/nsta/convergent-plate-boundaries.shtml
http://www.waterencyclopedia.com/Oc-Po/Plate-Tectonics.html