Geology 101 539 Class 2 Test 1 Thursday September 4 14 Chapter 2 Plate Tectonics The Unifying Theory Part 1 of 2 Outline The discovery of plate tectonics o Continental drift o Seafloor spreading o The great synthesis 1963 1968 Earth s tectonic plates o Divergent boundaries o Convergent boundaries o Transform fault boundaries Continental Drift Large scale horizontal movements cause earth s major topographical features o Mountains o Oceans basins Alfred Wegener 1880 1930 Proposed in 1912 based on observation of drifting ice sheets His analogy was used with icebergs floating on the water and drifting around Geographic Fit Of The Continents o One of the first pieces of evidence use to argue for continental drift o All continents were once together in a supercontinent called Pangea North America South America Africa Europe example map Fossil Match Across The Atlantic o Paleontologists Animals and plants diverge in evolution after the postulated breakup time Rejection and Acceptance of Continental Drift o Initially rejected by geologists Geologists said it is too good to be true New data after WWII led to 1960s plate tectonic revolution Ocean Drilling started happening Different data from magnetic sonar ocean drilling etc led to this revolution Earth Science Revolution o Now fully embraced Textbooks re written Seafloor Spreading Convection in the Earth s mantle could break up and push continents apart Arthur Holmes 1890 1965 He worked with the idea of convection o Heat rises and cool sinks Harry Hess 1906 1969 He used the hypothesis of mantle convection to explain seafloor spreading island arcs gravity anomalies and serpentine rocks He worked on a cruise ship and use that to his advantage to create and collect data History of the ocean basins 1962 He is the father of modern plate tectonics Iceland o An opening rift along the Mid Atlantic ridge o new ocean crust forms at mid ocean ridge Earthquakes and Volcanoes o Their locations are predicted by plate tectonics o The Pacific Ring of Fire shows the volcanic and earthquake activity now know to be associated with convergence and destruction of lithospheric plates Plate Tectonics The Great Synthesis Plates comprises top of the mantle oceanic crust and or continental crust called lithosphere Could Be Test Question Plates slide over partially molten weak mantle region called asthenosphere Plates are tens of km thick In relative motion w r t each other driven by mantle convection Lithospehere o Cold outer rigid brittle shell of the Earth 100km containing the plates The coldest part Asthenosphere o Heat softened viscous part of the mantle beneath the lithosphere plate motion causes earthquakes and builds mountains Plate Boundaries and Displacement Rates relative plate motions shown in mm year Number associated with arrow What is the explanation for why the Pacific Plate is larger than the other plates o Pacific Plate is the fastest moving growing plate The 3 Types of Plate Boundaries Transform o At transform fault boundaries plates slide horizontally past each other Ex California Divergent o At divergent boundaries plates move apart and create new lithosphere Ex Iceland Convergent o At convergent boundaries plates collide and one is pulled into the mantle and recycled Ex Alaska Transform Plate Boundary o San Andreas Fault runs along the coast of California o Ones that occur in the ocean floor South American Plate African Plate o Makes the rocks on either side different ages Divergent Plate Boundary o Volcanoes and earthquakes concentrate o Mid Atlantic Ridge North American Plate African Plate o East African Rift Valley African Plate Somali Subplate Africa continent is breaking into opposite directions o Parallel valleys volcanoes and earthquakes Convergent Plate Boundaries o Ocean continent Continental arc volcanoes are formed Most common form of convergent plate boundaries o Peru Chile trench Nazca Plate South American Plate o Andes Mountains South American Plate o Ocean Ocean Island arc volcanoes are formed o Japan Trench Eurasian Plate Pacific Plate o Japanese Islands Island arc Eurasian Plate o Continent Continent Fold and thrust mountains are formed ex Himalayas Which of the locations listed below is least associated with a volcanically active plate boundary a mid ocean ridge b deep ocean trench c transform fault Quietest boundary d continental rift Which kind of plate boundary is associated with earthquake activity a Divergent boundary b Convergent boundary c Transform fault boundary d All of the above At which kind of plate boundary is new oceanic lithosphere formed a Oceanic transform boundary b Oceanic divergent boundary c Ocean ocean convergent boundary d Ocean continent convergent boundary