Plate Tectonics-AQA

Earth Structure
1. The earths structure is made from the CRUST, MANTLE, LIQUID OUTER CORE, SOLID INNER CORE
  1. MANTLE is the widest section, thickness aprox. 2900KM, made up of semi molten rock of silicate, iron and nickel
  2. CRUST is the outer layer, aprox. 5-70KM thick, the rocks are less dense, rocks rich in silica, oxygen, aluminium, potassium and sodium
    1. CONTINENTAL
      1. Age: over 1500mil thickness: 30-70km, less dense, composition: granite rich in silicon, aluminium (sial)
    2. OCEANIC
      1. Age: less than 200mil, thickness: 6-10KM, more dense, composition: basalt rocks rich in silicon, magnesium, oxygen (sima)
  3. LIQUID OUTER CORE is a liquid due to changes in pressure, aprox. 2000KM thick, made out of iron and nickel, extremely hot
  4. SOLID INNER CORE is the hottest, with temperatures of 5500-6000, made out of iron and nickel, 1300KM thick
DESTRUCTIVE PLATE MARGIN
1. O-O TWO PLATES CONVERGE, DENSER OF THE TWO WILL BE SUBDUCTED
  1. PACIFIC AND PHILIPPINE PLATE
  2. MOVING TOWARDS EACHOTHER, THE DENSER OF THE TWO WILL BE SUBDUCTED, CREATES: DEEP SEA TRENCHES AND ISLAND ARCS
  3. EARTHQUAKES; YES VOLCANOES:YES
2. C-C two continental plates, much lower density, not much subduction, produce FOLD MOUNTAINS, NO VOLCANIC ACTIVITY, TRIGGER SHALLOW FOCUS EARTHQUAKES, INDO-AUSTRALIAN PLATE 5.8 COM YEAR
  1. MOVING TOWARDS EACHOTHER, FOLD MOUNTAINS
  2. INDO-AUSTRALIAN AND EURASION PLATE
  3. EARTHQUAKES:YES VOLCANOES:NO
3. O-C PLATES CONVERGE, MORE DENSER OCEANIC CRUST IS SUBDUCTED UNDER THE LESS DENSE CONTINENTAL
  1. NASCA AND SOUTH AMERICAN PLATE
  2. EARTHQUAKES:YES VOLCANOES: YES
  3. MORE DENSER OCEANIC CRUST IS FORCED UNDER THE LESS DENSE CONTINENTAL (SUBDUCTED) CREATES: DEEP SEA TRENCHES AND YOUNG FOLD MOUNTAINS
    1. DEEP SEA TRENCH- PERU CHILE TRENCH IN THE PACIFIC OCEAN
CONSERVATIVE PLATE MARGIN
1. TWO PLATES SLIDE PASS EACHOTHER EITHER IN THE SAME DIRECTION AT A FAST SPEED OR IN OPPISITE DIRECTIONS
2. EARTHQUAKES: YES VOLCANOES:NO
3. CREATES LOW RIDGES
4. NORTH AMERICAN AND PACIFIC PLATE SAN ANDREAS FAULT
Theory
1. Wegener
  1. Wegener suggested that all the continents once fitted all together in one super continent, PANGEA, 300 mil years ago. Which later split into North:Laurasia and South:Gondwanaland. Published in 1912
  2. Why was he not believed?
    1. he was a METEOROLOGIST which studies the weather, couldn't explain SEA FLOOR SPREADING, GERMAN didn't help due to the cold war, already EXPLANATIONS approved (land bridges)
  3. Evidence
    1. CLIMATOLOGICAL, ANTARCTICA, NORTH AMERICA, SVALBARD AND UK CONTAIN COAL DEPOSITS OF SIMILAR AGE- COAL IS ONLY FORMED IN TROPICAL CONDITIONS, THEY ARE NO LONGER IN TROPICAL CONDITIONS, MUST HAVE MOVED FURTHER FROM THE EQUATOR
    2. BIOLOGICAL, SIMILAR FOSSIL FORMATIONS FOUND ON EITHER SIDE OF ATLANTIC-MESOSAURUS, PLANT GLOSSOPTERIS IS A FERN THAT HAS BEEN FOUND IN AFRICAAUSTRALIA, SOUTH AMERICA
    3. GEOLOGICAL, SIMILAR GLACIAL DEPOSITS- AMERICA INDIA ANTARCTICA, ROCKS OF SAME AGE AND TYPE AND DISPLAYING SAME FORMATION- SE BRAZIL AND SOUTH AFRICA
    4. JIGSAW FIT OF CONTINENTS, THE WESTERN SEABOARD OF AFRICA AND EASTERN SEABOARD OF SOUTH AMERICA
2. Further evidence to prove
  1. Mid-Atlantic ridge was discovered in 1948, it ran from the north to the south of the Atlantic Ocean (1000KM WIDTH 2.5KM HEIGHT)
    1. HARRY HESS 1962, found the youngest in the middle and the oldest nearest to the USA and the CARRIBEAN, with the newest near ICELAND (rate of spreading 5cm)
  2. Palaeomagnetism confirmed sea floor spreading, it studies the earth magnetic field. Changes every 400,000 years, magnetite align themselves with it
CONSTRUCTIVE PLATE MARGIN
1. DIVERGING PLATES, THE MANTLE BENEATH IS UNDER PRESSURE THEN RELEASED AT THE MARGIN
2. CREATES MID-OCEAN RIDGE AND RIFT VALLEYS, EAST AFRICAN RIFT VALLEY
3. EURASIAN AND NORTH AMERICAN PLATE

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Plate Tectonics-AQA

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