Plate Tectonics-AQA

Plate Tectonics-AQA

1. Earth Structure

   • The earths structure is made from the CRUST, MANTLE, LIQUID OUTER CORE, SOLID INNER CORE
     • MANTLE is the widest section, thickness aprox. 2900KM, made up of semi molten rock of silicate, iron and nickel
     • CRUST is the outer layer, aprox. 5-70KM thick, the rocks are less dense, rocks rich in silica, oxygen, aluminium, potassium and sodium
       • CONTINENTAL
         • Age: over 1500mil thickness: 30-70km, less dense, composition: granite rich in silicon, aluminium (sial)
       • OCEANIC
         • Age: less than 200mil, thickness: 6-10KM, more dense, composition: basalt rocks rich in silicon, magnesium, oxygen (sima)
     • LIQUID OUTER CORE is a liquid due to changes in pressure, aprox. 2000KM thick, made out of iron and nickel, extremely hot
     • SOLID INNER CORE is the hottest, with temperatures of 5500-6000, made out of iron and nickel, 1300KM thick

2. DESTRUCTIVE PLATE MARGIN

   • O-O TWO PLATES CONVERGE, DENSER OF THE TWO WILL BE SUBDUCTED
     • PACIFIC AND PHILIPPINE PLATE
     • MOVING TOWARDS EACHOTHER, THE DENSER OF THE TWO WILL BE SUBDUCTED, CREATES: DEEP SEA TRENCHES AND ISLAND ARCS
     • EARTHQUAKES; YES VOLCANOES:YES
   • 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
     • MOVING TOWARDS EACHOTHER, FOLD MOUNTAINS
     • INDO-AUSTRALIAN AND EURASION PLATE
     • EARTHQUAKES:YES VOLCANOES:NO
   • O-C PLATES CONVERGE, MORE DENSER OCEANIC CRUST IS SUBDUCTED UNDER THE LESS DENSE CONTINENTAL
     • NASCA AND SOUTH AMERICAN PLATE
     • EARTHQUAKES:YES VOLCANOES: YES
     • MORE DENSER OCEANIC CRUST IS FORCED UNDER THE LESS DENSE CONTINENTAL (SUBDUCTED) CREATES: DEEP SEA TRENCHES AND YOUNG FOLD MOUNTAINS
       • DEEP SEA TRENCH- PERU CHILE TRENCH IN THE PACIFIC OCEAN

3. CONSERVATIVE PLATE MARGIN

   • TWO PLATES SLIDE PASS EACHOTHER EITHER IN THE SAME DIRECTION AT A FAST SPEED OR IN OPPISITE DIRECTIONS
   • EARTHQUAKES: YES VOLCANOES:NO
   • CREATES LOW RIDGES
   • NORTH AMERICAN AND PACIFIC PLATE SAN ANDREAS FAULT

4. Theory

   • Wegener
     • 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
     • Why was he not believed?
       • 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)
     • Evidence
       • 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
       • BIOLOGICAL, SIMILAR FOSSIL FORMATIONS FOUND ON EITHER SIDE OF ATLANTIC-MESOSAURUS, PLANT GLOSSOPTERIS IS A FERN THAT HAS BEEN FOUND IN AFRICAAUSTRALIA, SOUTH AMERICA
       • GEOLOGICAL, SIMILAR GLACIAL DEPOSITS- AMERICA INDIA ANTARCTICA, ROCKS OF SAME AGE AND TYPE AND DISPLAYING SAME FORMATION- SE BRAZIL AND SOUTH AFRICA
       • JIGSAW FIT OF CONTINENTS, THE WESTERN SEABOARD OF AFRICA AND EASTERN SEABOARD OF SOUTH AMERICA
   • Further evidence to prove
     • Mid-Atlantic ridge was discovered in 1948, it ran from the north to the south of the Atlantic Ocean (1000KM WIDTH 2.5KM HEIGHT)
       • 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)
     • Palaeomagnetism confirmed sea floor spreading, it studies the earth magnetic field. Changes every 400,000 years, magnetite align themselves with it

5. CONSTRUCTIVE PLATE MARGIN

   • DIVERGING PLATES, THE MANTLE BENEATH IS UNDER PRESSURE THEN RELEASED AT THE MARGIN
   • CREATES MID-OCEAN RIDGE AND RIFT VALLEYS, EAST AFRICAN RIFT VALLEY
   • EURASIAN AND NORTH AMERICAN PLATE