Understanding the operation of our planet 1 Who cares 2 Is it useful to know What is plate tectonics segments Continental Drift 2 Early observations 1 Lithospheric plates move in relation to but not independently other plate a Explains many observations including tsunamis a Based on fossil distribution hypothesis of subaerially connected landmass that sunk b Problem hard to explain to distribution of modern mammals on Madagascar India and Africa 3 Development a Alfred Wegner suggested continents were together in geologic past but then drifted Pangaea b Alexander Du Toit focused on the Gondwand sequence bottom of continent 4 Evidence a Continents fit b Floral and faunal similarities i Flossopteris ii Mesosaurus freshwater organisms separated by salt water c Glatial d Geologic similarities between sequences of carboniferous to Jurassic age 5 Science is the business of new ideas but there is nothing that a scientist hates more than a truly new idea Dr Peter Vaill 1983 6 Why was the theory rejected a Mechanism b Timing Continental Drift 1 Paleomagnetism Iron baring minerals orient towards magnetic north a b Magnetic north and south periodically switch c Apparent polar wanter i Geographic north magnetic north Rise of Plate Tectonics 2 1962 Harry Hess felsic continent didn t move over or plow through ocean crust The entire crust moved 3 Evidence a Variable sediment thickness b Central location of mid Altantic ridge 4 Conclusion a MOR form where upward flowing limbs of two adjacent convection cells approach the surface a Everything is driven by convective cells in the slush like mantle material Rise of plate tectonics 1 Hess s model of the structure of a MOR 2 Where is old crust destroyed a Subduction zones 3 Paleomagnetism provided a definitive test a Vine and Matthews in 1963 i Hypothesis newly formed crust should have a normal polarity but that the older crust should have reversed polarity ii Test proved correct Continental Drift 1 New fossil evidence discovered in 1969 a Fossil lystrosaurs heavyset therapsid herbivore were found in Antarctica It lived in marshes and had a beak like jaw i ii Antarctica must have moved from a warm equatorial region to a cold a Fault surfaces along which bodies of rock break from stress and move past a Extensional forces b Graben c Lavas erupt through vents to form volcanoes d Pillow basalts formed from quickly cooled lava underwater e Transform fault offsets a Subduction process where slabs of oceanic lithosphere descends into the polar region Plate Tectonics 1 3 basic fault types each other b Normal c Reverse thrust d Strike slip 2 MOR 3 Subduction zones mantle i Forearc ii Accretionary wedge iii M lange b Volcanoes i Earthquakes 4 Continental convergence a Fold and thrust belts Plate Movements 1 Why do plates move a Convective motion in the asthenosphere applies drag to the base of plates b Push of plate as new plate formed at the elevated ridge c Plate pulled into subduction zone by preceding parent plate is now cold and d Broken plate segments create additional forces creating suction of the slab therefore denser 2 Movements are measureable a Geodetics b Hotspots
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