Transcript Document
Age of the Earth Geologic time scale • Subdivisions of geologic time – Eon, Era, Period, Epoch – Eons • Precambrian: 4.5 b.y. to ~0.5 b.y. • Phanerozoic: ~0.5 b.y. to today Geologic time scale • Subdivisions of geologic time – Eon, Era, Period, Epoch – Eras • Paleozoic: ~560 m.y. to ~250 m.y. • Mesozoic: ~250 m.y. to ~65 m.y. • Cenozoic: ~65 m.y. to today Image source: http://www.gly.fsu.edu/~salters/GLY1000/12Rock_record_time/Slide27.jpg Plate Tectonics- Overview • Plate Tectonics–General Principles • Plate Movements–Accumulating Evidence • Types of Plate Boundaries • How Far, How Fast, How Long, How Come? • Plate Tectonics and the Rock Cycle Plate Tectonics–General Principles • Stress and Strain in Geologic Materials • Lithosphere and Asthenosphere • Locating Plate Boundaries Tectonics • Stress- application of a force – Compressive (pushing together) – Tensile (pulling apart) • Strain- deformation response of the force – Elastic deformation: ‘rubber band’ – Plastic deformation: permanent strain – Rupture: the breaking point Folding Rock Source: Photograph courtesy of M.R. Mudge; courtesy USGS Photo Library, Denver, CO. Folding and Faulting, Cook Inlet, Alaska Source: Photograph by N.J. Silberling, USGS Photo Library, Denver, CO. Rock Failure Under Stress Source: Photograph courtesy of W.B. Hamilton; courtesy USGS Photo Library, Denver, CO. Effect of tectonics on rocks • Depends of physical conditions – Temperature & pressure – composition, time, fluids Lithosphere- Asthenosphere Lithosphere-Asthenosphere • Lithosphere (lithos = rock) – Brittle, elastic outer layer – ~50 km under oceans, ~100 km under continents • Asthenosphere (asthenes= without strength) – Plastic domain – ~300 km in mantle – Discovered by seismic wave studies Plate boundaries • Deformation, earthquakes, and volcanoes are not evenly distributed around the Earth • Mostly concentrated in linear belts, chains • Can use distribution to ‘map out’ plates • ~8 major plates, several smaller ones World Locations of Volcanoes and Earthquakes Source: Map plotted by the Environmental Data and Information Service of NOAA; earthquakes from U.S. Coast and Geodetic Survey. Plate Movements–Accumulating Evidence • • • • • • The Topography of the Sea Floor Magnetism in Rocks–General Paleomagnetism and Seafloor Spreading Age of the Ocean Floor Polar-Wander Curves Other Evidence Shaded Relief Map of the World Source: Photo courtesy of NOAA National Geophysical Data Center. Shaded Relief Map of the World Source: Photo courtesy of NOAA National Geophysical Data Center. The Earth is a large bar magnet… And sometime it flips…! Minerals: the ‘Curie Temperature’ (1) Minerals oriented randomly in a melt (2) Minerals aligned in the magnetic field First magnetic survey of the oceans Age Distribution of the Sea Floor Source: Marine Geology and Geophysics Division of the NOAA National Geophysical Data Center. World Locations of Volcanoes and Earthquakes Source: Map plotted by the Environmental Data and Information Service of NOAA; earthquakes from U.S. Coast and Geodetic Survey. World Lithospheric Plates Source: After W. Hamilton, U.S. Geological Survey. Polar Wander Source: http://www.mq.edu.au/scienceresearch/lackie.htm Plate Movements — Today Source: After R.S. Dietz and J.C. Holden, “Reconstruction of Pangaea,” Journal of Geophysical Research, 75:4939-4956, 1970, copyright by the American Geophysical Union. Plate Movements — 100 Million Years Ago Source: After R.S. Dietz and J.C. Holden, “Reconstruction of Pangaea,” Journal of Geophysical Research, 75:4939-4956, 1970, copyright by the American Geophysical Union. Plate Movements— 200 Million Years Ago Source: After R.S. Dietz and J.C. Holden, “Reconstruction of Pangaea,” Journal of Geophysical Research, 75:4939-4956, 1970, copyright by the American Geophysical Union. Glacial Deposits Across Southern Continents Source: After Arthur Holmes, Principles of Physical Geology, 2d ed., Ronald Press, New York, NY, 1965. Types of Plate Boundaries • Divergent Plate Boundaries – Rifts, Mid ocean ridges, lots of volcanism • Transform Boundaries – Sliding plates, lots of earthquakes • Convergent Plate Boundaries – Subduction zones, mountain belts Divergent plate boundary: East African Rift Satellite Image of Lake Tanganyika, Africa Source: © NASA Transform plate boundary: San Andreas strike-slip fault Convergent plate boundary: Subduction Zone in Alaska Source: Image courtesy of NOAA National Geophysical Data Center. Convergent plate boundary: Where are we? Current Motions of Major Plates: Satellite laser data Source: Data from NASA.