Chapter 4 :Chapter 4 Plate Tectonics


Continental Drift :Continental Drift 1912 Wegner proposed Plate Tectonics, which said that all continents had once been connected in a single huge landmass he named Pangaea (all lands) surrounded by Panthalassa (all sea)


Evidence :Evidence Similarities in coastlines Fossils of Mesosaurus along coast of E South America and W Africa Age and type of rock along coast of E South America and W Africa


Slide 6:Appalachians continue into Greenland Glaciers in Africa, South America Coal in Siberia, Europe, North America


Slide 7:Wegner died before the idea was accepted Wegner was a meteorologist and was not taken seriously


Sea Floor Spreading :Sea Floor Spreading Mapping the Mid Atlantic ridge, the sea floor was found to be very young. 150 million years Deitz suggested that magma pushing upward would spread the Crust


Paleomagnetism :Paleomagnetism When iron bearing rock is molten, the iron particles align North-south Some particles were found that were aligned, South-North, indicating that the poles had shifted. Bands of rocks along the sea-floor alternated orientation


Theory of Plate Tectonics :Theory of Plate Tectonics The Earth’s crust is of two types, oceanic and continental, these make up the lithosphere, (rock, sphere) The lithosphere floats on the asthenosphere, a layer of plastic, molten rock 30 lithospheric plates (so far)


Lithospheric Plate Boundaries :Lithospheric Plate Boundaries 3 types, Divergent, Convergent and Transform Divergent Boundaries occur where plates are separating, and magma fills the gap. Usually on ocean floor. Continental plates diverging form rift valleys. Red Sea


Slide 15:Convergent Boundaries occur when two plates are coming together, 3 types of collisions occur Oceanic and continental plates form a subduction zone, with the more dense oceanic plate being forced down, the friction melts the plate, forming an ocean trench


Slide 17:Continent to continent plate does not form a subduction zone because the plates have the same density Instead they uplift forming mountain ranges like the Himalayas Oceanic crust and oceanic crust converging form a subduction zone, the molten rock forms Island arcs like Hawaii


Slide 19:Transform Fault boundary Area where plates are grinding past each other, movements are sudden, creating earthquakes Causes of plate movement Convection is the movement of liquids due to changes in density caused by heat


Suspect Terrane :Suspect Terrane Theory of suspect terranes-Continents are made up of terranes, pieces of lithosphere each with their own history


Slide 21:Three characteristics, terranes contain rocks and fossils that differ from the terranes around it, there are major faults at the boundaries Finally magnetic properties do not match those of the terranes around it


Slide 22:. Evidence-10 terranes around San Francisco, some having limestone formed at the equator The terranes are scraped off the subducting plates, adding mass to the continent and forming mountains


Slide 23:Suspect terranes also called microplate terranes Plate tectonics is to geology what evolution is to biology and atomic theory is to chemistry