Topic 08_colour

Topic 08_colour - Topic 08 Plate Tectonics and Rocks 1....

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Unformatted text preview: Topic 08 Plate Tectonics and Rocks 1. Structure of the Earth Inner core •  solid (mainly Fe) (13 500 kg/m3) Outer core •  liquid (Fe/Ni/S) (10 700 kg/m3) Mantle •  80% of earth’s volume •  4500 kg/m3 Crust •  thin, outer layer •  8 to 40 km deep •  < 8km below ocean floors (higher density) •  deeper under land (up to 40 km) (lower density) ConXnental crust •  2700 kg/m3 Oceanic crust •  3000 kg/m3 Layers of the Earth Lithosphere •  Solid upper part of mantle plus crust •  More rigid than asthenosphere •  Lithosphere moves over asthenosphere •  Lithosphere fragmented into plates •  60–150 km thick Asthenosphere •  Beneath lithosphere •  layer of so], plasXc rock in mantle •  part of mantle •  about 300 km thick Isostasy •  lithosphere (more rigid) floats on denser asthenosphere Geography 211 (Fall 2009) 10/16/09 1 2. Early History of Plate Tectonics •  support by few visionary scienXsts •  rejecXon by established scienXfic leaders Wegener (1912): •  landmasses migrate ‐ Pangaea (225 mya) •  jigsaw fit ‐ geological/fossil similariXes Arthur Holmes (1928): •  thermal convecXon •  lower liquid conveyor belt with conXnents on top Evidence for Plate Tectonics •  mountain chain under ocean •  64 000 km length and 1000 km width •  sea‐floor spreading MagneXc pole changes direcXon: •  recorded in crust Mid‐ocean ridges: •  upwelling magma ‐ cools to form new ocean floor •  aligns with magneXc field •  plates move laterally 3. Plate Boundaries (i) Divergent •  sea‐floor spreading centers •  plates spread apart (ii) Convergent •  plates come together •  One plate subducted (iii) Transform •  horizontal displacement •  no new crust formed or subducted Geography 211 (Fall 2009) 10/16/09 2 Plate Divergence Plate Convergence Lateral (Transform) Boundary Geography 211 (Fall 2009) 10/16/09 3 Mid-ocean ridge features Himalayas San Andreas Fault Geography 211 (Fall 2009) 10/16/09 4 4. Rocks and Minerals Mineral: •  naturally occurring inorganic substance (e.g. quartz) •  specific chemical formula •  20 to 30 common rock‐forming minerals (~ 3000 total) Rock: •  assemblage of minerals bound together (or mass of single mineral) •  •  •  igneous sedimentary metamorphic Rock Types Igneous: •  from molten material Sedimentary: •  from debris eroded from other rocks and other materials Metamorphic: •  rocks changed by heat and / or pressure Constantly transforming from one type to another Igneous rocks Geography 211 (Fall 2009) 10/16/09 5 Sedimentary Rocks •  derived from fragments of exisXng rock or organic material Clas%c Sedimentary Rocks •  derived from parXcles of other rocks/ sediments •  layers o]en visible (straXficaXon) LithificaXon: •  compacXon •  any remaining spaces may be empty or have matrix •  other minerals can hold grains together via precipitaXon of elements in soluXon (cementaXon) Chemical Sedimentary Rocks •  chemically precipitated deposits: evaporaXon of water within which ions are dissolved (new ions added or temp/press changes that affect ability to hold ions) •  biochemical precipitaXon: secreted shells of organisms Sediment Boulders, cobbles, gravels, fines Sand Silt Clay Grain Size Mixture 0.062 - 2mm 0.002 - 0.062 mm < 0.002 mm Rock Conglomerate Sandstone Siltstone Shale Geography 211 (Fall 2009) 10/16/09 6 Metamorphic Rocks Metamorphism: •  physical/chemical changes due to intense heat/pressure •  fault/plate collision zones •  foliated/non‐foliated (alignment) The Rock Cycle •  CirculaXon of rock material between earth's interior and crust Fig 11.21 Geography 211 (Fall 2009) 10/16/09 7 Geography 211 (Fall 2009) 10/16/09 8 ...
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