GEOL 101: Plate Tectonics II
GEOL 101: Plate Tectonics II 101-017
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This 4 page Class Notes was uploaded by Natalee Stanton on Wednesday February 3, 2016. The Class Notes belongs to 101-017 at University of South Carolina taught by in Winter 2016. Since its upload, it has received 28 views. For similar materials see Geology 101-017 in Geology at University of South Carolina.
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Date Created: 02/03/16
GEOL 101 – Lecture 4 Plate tectonics II Oxygen comes from volcanic activity o Not always there Early Plate Tectonics: Continental Drift - First proposed by Alfred Wegener in 1912 based on his observation of drifting sheets of ice - Largescale horizontal movements of the outer portions of the Earth are responsible for major topographical features such as mountains and ocean basins Geographic Fit of the Continents This is the first evidence that supports continental drift Pangea – suggest that all continents were once together in a single supercontinent Geology and Paleontology Matches on Opposite Sides of the Atlantic South America and Africa had the same species fossils The Rejection and Acceptance of Continental Drift Rejected by most geologist New data after WWII led to the “plate tectonic revolution” in 1960’s Now embraced by essentially everybody Today’s geology textbooks radically different than those 50 years ago Evidence from the Oceans: Seafloor Spreading a. Sonar surveying b. Seafloor bathymetry c. Oceanic rifts places where the plates are moving apart d. Harry Hess and Robert Dietz 1960’s Oceanic vs. Continental Curst (lithosphere) - Continental Curst 1. Lighter – 2.8g 2. Weaker 3. Does not easily recycle in the mantle – stays at the surface, doesn’t go back down 4. Long lived - Oceanic curst 1. Denser – 3g 2. Stronger 3. It recycles in the mantle 4. Short lives Three Types of Plate Boundaries 1. Transform – moving side to side not creating or destroying lithosphere – faults are created 2. Divergent – 2 plates moving apart and create new lithosphere 3. Convergent – 2 plates move together – colliding – if oceanic plate, it will be recycled into the mantle go under the continental curst Divergent Boundaries - New oceanic lithosphere is created at mid ocean ridges - Upwelling mantle - Seismically active (shallow earthquakes - Volcanic activity - Rifting – stretching – caused by tensional forces – not making new, breaking it o East African rift Iceland is a volcanic island Midocean ridge exposed on and New oceanic crust is forming where we can see it Convergent Boundaries – Subduction Zones - Three types 1. Ocean – ocean : Japan 2. Ocean – continent : Andes 3. Continent – continent : Himalaya - The most complex type 1. Ocean – Ocean - Subduction of oceanic plates forms a deep –sea trench - Water form subduction plate causes melting and generates volcanoes at surface - Subducting plate cold, rigid, generates deep earthquakes in subduction zones 2. Island arcs: - Tectonic belts of high seismicity - Deep earthquakes in the mantle (<600 km) - Active volcanoes - Bordered by a submarine trench 3. Ocean – continent - Continental crust overrides oceanic plate because it’s lighter (less dense) - Continental edge is uplifted into a mountain chain roughly parallel to deep sea - Earthquakes and volcanoes Ocean – Continent Convergence - Continental arcs o Mountain building o Active volcanoes o Strong and deep earthquakes – Chile 9.2 subduction earth quake Convergent Plate Boundary: : Continent – Continent - Both continents remain afloat - Eurasian plate overrides Indian plate, creating much thicker crust - Crust crumbles, creating high mountains and a wide plateau : Convergence - In ocean – continent boundaries, convergence is taken up by subduction - In continent–continent boundaries, convergence is accommodated by deformation of the crust without subduction - Both plates are too buoyant to be subducted Transform Plate Boundary - Lithosphere is neither created nor destroyed - Horizontal displacement between adjacent plates - Rocks of different types on each side - Crustal shallow earthquakes – strong o Transform faults – San Andreas The Seafloor A Magnetic Tape Recorder - During and after WWII method to measure the local seafloor magnetic field - Regular patterns in the intensity of magnetic field - The seafloor is a magnetic tape recorder - Magnetic stripes are called isochrones – because they mark time - High and low intensity - The earth s magnetic field is reversing itself of tens of thousands of years - Seafloor spreading moves magnetized curst away from the ridge crest o Western specific and south Carolina Atlantic oldest rock Driving Mechanism of Plate Tectonics - Thought to be convection of the mantle - Friction at base of the lithosphere transfers energy from the asthenosphere to the lithosphere The Earth’s Lithospheric plates consist of a. Continental crust b. Oceanic crust c. Continental and oceanic crust d. Continental and oceanic crust and uppermost mantle New lithosphere is created ____ . a. In deep sea trenches b. In subdution zones c. At mid ocean ridges d. Along transform faults What type of plate boundary is shown in the diagram? *This question will be on the Exam* a. a continental collision b. a subduction zone c. a spreading center d. a transform fault On a map of the oceanic crust, the boundaries between normally and reversely magnetized oceanic crusts are called _____. a. Dipoles b. Isochrones c. Isograds d. Sutures What drives plate tectonics? a. Magnetic reversals b. Mantle convection c. Solar energy d. Volcanism
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