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GEOL 208 Lecture 2

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GEOL 208 Lecture 2

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  1. 0 Geology 208: The Earth, Moon and Planets • Today • Diary (letter of intent) submission • Geology of the Earth: Skinner (2005 ed.), chap 1: 17-20, 23-28; chap. 2: 33-61 • Next class (May the 19th) • a. Climate change: • Strahler (Canadian ed.) chap. 5: 122-130 • b.Glacial processes & landforms: • Strahler (Canadian ed.), chap.20: 593-621 “The Origin of the Solar System”

  2. Geological history of the Earth • History • formed ~4.6 GYA (phase A) • partly molten, due to debris bombardment & gravitational infall • ~4 GYA (phase B) • - “period of heavy bombardment” - • …cooling surface layers rendered molten again to tens of kilometres of depth 2

  3. Geological history of the Earth • History • Radioactivity, • (loss of energy by unstable atomic nuclei) • a continuing (internal) source of heat • - caused much of Earth’s interior to liquefy • heavy metals to sink to core • lighter metals float to surface 3/6/2014 3 3

  4. Solid crust Solid mantle Liquid core Solid inner core The Earth’s interior Basic structure: melting point - temp. at which an element melts (transition from solid to liquid)- increases as pressure rises towards centre… …inner core solid FYI: Core as hot as the sun’s surface 4

  5. The Earth’s interior Earth(radius) = 6400 km ------------------------------ Core(radius): 3500 km - Fe, some nickel - ----- Mantle (radius): ~2900 km - solid, outer layer is brittle 3/6/2014 5 5

  6. The Earth’s crust Crust(two types) floats on the mantle = ~5-70 kms deep a. oceanic - thinner but heavier (basalt-rich) b. continental - thicker but lighter (granite-rich) 3/6/2014 6 6

  7. The lithosphere - solid upper part (100 km) of the mantle + lower part of crust(rocks are cooler, stronger, more rigid than asthenosphere) asthenosphere - weak, hot (but relatively solid) sphere beneath lithosphere - FYI = “Plate tectonics”derived from “litho-astheno” relationship… 3/6/2014 7 7

  8. The lithosphere & tectonics • The lithosphere • (fragmented into tectonic plates) • moves over… • the asthenosphere • (which flows viscously) • convection = source of flow/movement 3/6/2014 8 8

  9. The lithosphere & tectonics • convection = source of flow/movement • hot rocks (lower/deeper in mantle), less dense • cooler rocks (higher in mantle), more dense • due to gravity • hot rocks rise, cool rocks sink

  10. FYI • Magma • molten rock/suspended mineral grains (usually silicates) & gases (mostly water vapour and C02) • Lava = magmathat reaches the Earth’s surface 10

  11. Plate tectonics (continental drift) Alfred Wegener (1915) proposed that landmasses were once united (Pangea)… …then split into Laurasia & Gondwanaland 11

  12. Plate tectonics: continental drift • Land masses continue to aggregate & disaggregate • some interesting fits - • Greenland/eastern Canada • Africa/Asia • South America/Africa • Australia/NewZealand 12

  13. fossils http://www-tc.pbs.org/kcet/wiredscience/blogs/driftmap.gif Continental drift: evidence http://www.gtj.org.uk/en/small/item/GTJ30473/ 13

  14. Volcanoes Occur at hotspots, rifts or where plates subduct

  15. Volcanoes

  16. Volcanoes on Mars

  17. http://pubs.usgs.gov/of/2004/1007/images/volcanic.gif Volcanoes volcano - surface vent, through which lava flows pluton - constrained body of “intrusiveigneous” rock sill - intrusive igneous rock parallel to layering of intrusive rock dike - ibid., cuts across the layering of intruded rock 17

  18. Volcanoes Sill bleaching (above & below sill) is “contact” metamorphism Dyke intruding basalt lava flows

  19. Volcanoes • “Breadknife” • igneous dyke exposed by weathering & erosion • part of Warrambungle volcano (Australia) • erupted 18 MYA • injected into loose accumulation of ash & cinders • on volcano flank

  20. Volcanoes • Mt. St-Helen’s, Washington State (1980) • explosive eruption • high dissolved-gas contents • high-viscosity magmas Viscosity = property of resistance to flow in a fluid or semi-fluid i.e. high viscosity = highly resistant to flow 20

  21. Volcanoes • Mauna Loa, Hawaii • non-explosive eruption • low dissolved-gas contents • low viscosity magmas 21

  22. Plate divergence • New crust is constructed & forced outwards from a • rift • “magma” • (less dense than surrounding rock) rises from mantle… • (by convection) • …fills crack • Spreading speed (i.e. Mid-Atlantic ridge) = 1.8 cm/yr 22

  23. Plate divergence Oceanic crust (A) (1) basaltic (extrusive), lava on rift floor (2) gabbro (intrusive), at greater depths

  24. Plate tectonics: convergence Ocean-land convergence(subduction zone) - continental crust lighter than oceanic crust  …oceanic crust subducted friction between plates + heat from interior… …melt subducting plate… …magma created 24

  25. http://virgil.org/dswo/fs/japantour/shared/ring-of-fire-plates.jpghttp://virgil.org/dswo/fs/japantour/shared/ring-of-fire-plates.jpg http://msnbcmedia3.msn.com/i/msnbc/Components/Interactives/Technology_Science/Science/Ring_of_fire.jpg Plate convergence Margins - distribution of active volcanoes coincides with them

  26. Plate convergence Land-land convergence (collision) 10 Mya Indian plate collided with Eurasian plate  - continental crusts equally dense - (buckling and piling-on follow) - collision velocity ~5 cm/yr

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