1 / 65

PLATE TECTONICS

PLATE TECTONICS. Earth made of concentric spheres ( Fig. 1.14 ) p 18 T-14. 1. Inner core - rich in iron and nickel, dense 2. Outer core - liquid 3. Mantle Asthenosphere - nearly molten and can flow very slowly

lapis
Download Presentation

PLATE TECTONICS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PLATE TECTONICS

  2. Earth made of concentric spheres (Fig. 1.14) p 18 T-14 • 1. Inner core - rich in iron and nickel, dense • 2. Outer core - liquid • 3. Mantle • Asthenosphere - nearly molten and can flow very slowly • Lithosphere - rigid outer layer of the earth and floats in the asthenosphere. (Fig. 1.16) p 22 T-29 S&A-22

  3. 4. Crust • basalt (fine grained igneous rock, volcanic) • 5. Hydrosphere • 6. Atmosphere

  4. Earth made of concentric spheres review • 1. Inner core • 2. Outer core • 3. Mantle • Asthenosphere • Lithosphere • 4. Crust • 5. Hydrosphere • 6. Atmosphere

  5. Isostasy • Isostatic adjustment • describes the relative elevations that materials of different densities and thicknesses reach at equilibrium with gravity (1.16) p 20 S&A 23T-20 • Play the game of isostasy before class!

  6. Isostasy cont • Crustal materials float in asthenosphere (Fig. 14) p 20 • Weight of volcano bends crust (Fig 2.27) remember from last time. • Glaciers also cause crust so subside (a process by which one plate descends beneath another plate and is ultimately resorbed into the mantle)

  7. Isostasy cont • Scandinavia and Antarctica are rising due to the melting of the glaciers that cover them. • Remember how the block raised when we reduced the height (from isostasy game).

  8. "Moho" - the boundary, which geologists refer to as the Mohorovicic discontinuity, between Earth's brittle outer crust and its hotter, softer mantle

  9. MOHO exposed at the surfacelocated between crust and mantle (S&A 22)

  10. Continents • Thick accumulations of granitic rocks • Oldest rocks on Earth - about 3.8 billion years

  11. Plate tectonics • New crust formed at mid-ocean ridges or spreading centers Convection currents (Fig. 2.10) p 44 (this is a very important diagram) • Crust and upper mantle constitute the rigid lithosphere float on nearly molten asthenosphere

  12. Plate tectonics cont • Lithosphere broken into rigid units and move slowly older lithospheric material is being subducted while new lithosphere is produced along the ridges and rises. • Trenches plates converge • Plates move past each other along transform faults (Fig. 2.23) p 59 • Plate movements shape ocean basins T-30 (Fig. 2.13 b) p 48

  13. Plate boundaries (Fig. 2.14 a. b. c.) p50 • 1. Divergent boundary - Midocean ridges - plates form and move away from each other (Fig. 2.14 a) • 2. Convergent boundary - Trenches - plates move toward each other and are destroyed as they are drawn down into the mantle (subduction) (Fig. 2.14 b, 2.20, 2.21, and 2.22) p 56-58

  14. Plate boundaries cont. • 3. Fracture zones - plates slide past each other (NO earthquakes felt) • 4. Transform faults - plates slide past each other (Earthquakes felt) (Fig. 2.14 c) • Transform faults and fracture zones (Fig. 3.17) p 95 (T 38) • San Andreas Fault (Fig. 2.23) p 59

  15. Continental Rifting Fig 2.17 p 52 • a. upwarping • b. rift valley (fig 2.18) p 54 read and understand • c. linear sea • d. mid-ocean ridge • e. Table 2.1 p 51

  16. Pillow lava along Juan de Fuca Ridge. Photo courtesy of Submarine Ring of Fire 2002 Exploration, NOAA-OE.

  17. START HERE FOR WEDNESDAY • If you are interested in a 9th edition of our book. • bmichael23@aol.com.

  18. I want you to print out an article on hot spots • Go to google and look up hot spots.

  19. Hot spots • plumes of magma that rise from deep within the mantle erupt (Fig. 2.24) p 62 T 54 • Plates moving across hot spots cause chains of volcanic islands Hawaiian Islands (Fig. 2.25) p 62 • Many occur near midocean ridges. Seen today in Iceland. (Fig2.26) p 63 formation of sea mounts and table mounts (guyots)

  20. Plates moving across hot spots cause chains of volcanic islands Hawaiian Islands

  21. Hot spots cont. • Others beneath the continent - gisers in Yellowstone National Park • Flood Basalts - from volcanic activity that produces widespread gently sloping surfaces. Commonly surround volcanic islands

  22. Earth’s magnetic field • Fig 2.7 and 2.9 p 40 and 43

  23. Earth's magnetic field (Fig. 2.12) p 46 T 28 • Changes orientation at irregular intervals, as of today we do not know why. • Minerals record the orientation of Earth's magnetic field at the time when the rocks cooled ~ 100,000 yrs (Fig. 2.11) p 45 • Measure with magnetometers T 48

  24. Earth's magnetic field cont. • Form bands with same orientation - like tape recorder T-26 • Matthews and Vine saw the magnetized rocks and decided that the rocks were younger in the center of the ridge, older at edges • Permits determining age of ocean floor

  25. Neat stuff on the earths magnetic field • http://science.nasa.gov/headlines/y2003/29dec_magneticfield.htm • www.pbs.org/wgbh/nova/magnetic/reversals.html • This shows an interactive. I expect you to do this

  26. Hydrothermal circulation p 93 • Sea water circulates through hot, newly formed rocks (Fig 3.17 a) p 93 • 1. cooling them • 2. removes metals and deposits them in ocean floor vents • 3. ocean water circulates through newly formed crust every 5 - 10 million years. (remember the ocean has been around a very long time)

  27. Volcanic eruptions occur more frequently on rapidly spreading segment than on slow spreading ones. • A hydrothermal vent is a geyser on the seafloor.

  28. Three types of hydrothermal vents p 94 • black smokers • white smokers • cooler discharge

  29. black smokers

  30. White smoker

  31. Hydrothermal Vents cont. • Three types of hydrothermal vents • 1. most spectacular are black smokers. • a. They discharge superheated waters (300 - 400oC) at high rates much like a fire hose. • b. Black because of chem. rx. 2o to those that occur in the water forming sulfur-bearing minerals. • c. form large fragile chimney like mounds up to 10 meters high made of porous silica, native sulfur, and sulfur-bearing minerals.

  32. Hydrothermal Vents cont. • d. Color the mounds with yellows and blacks (like Halloween decorations) Read Recovery of Black Smokers p 90-91 • e. Tube worms: Very fast growing and reach sizes up to 3 m (10 ft) other animals include sea anemone, clams, crabs, fish and bacteria Fig 15.25 p 477 • f. Temperature fluctuations are common occurring in days to seconds. • g. Micro-organisms

  33. Tube worms T 134

  34. Hydrothermal Vents cont. • 2. White smokers • a, are not as hot (200-330 oC) are also common • b. circulating fluids have mixed with cold ocean waters • c. milky discharge thus the name

  35. Hydrothermal Vents cont. • 3. Cooler discharge (cold seep) (5 - 25oC) • a. water flows out through cracks and fissures in the ocean floor. • b. cold seep waters are about the same temperature as the surrounding waters • c. the discharge water is clear

  36. Hydrothermal Vents cont. Hydrothermal circulation continues for millions of years as the rocks cool. • Eventually, fractures fill with mineral deposits and fluids no longer pass through. • Sediments accumulate on the ocean floor. • Where do the minerals come from?

  37. All three vents support abundant growths of bottom-dwelling organisms. • Chemosynthesis: the process by which certain microbes create energy by mediating chemical reactions

  38. Continental Margins • (steep slopes that descend to the sea floor) p 100 - 102 • One of the most outstanding features of the continental slopes are submarine canyons. (Fig 3.9 p 83) Submarine canyons are steep sided and V-shaped in cross section with tributaries similar to those of river-cut canyons.

  39. Continental Margins two types(Fig 3.7) p 82 • 1. Active continental margins lie along edge of plates (Convergent) • Contain many active volcanoes, frequent earthquakes, young mountains • Common along Pacific margins, called Pacific-type margins are frequently narrow • 2. Passive margins of continents lie in middle of plates

  40. ACTIVE MARGINS

  41. Earthquakes: • 1. common near Pacific-type margins • 2. deep earthquakes indicate subduction - in subduction zones, plates move as large slabs and drag against the rocks above and below causing earthquakes in those areas • 3. subduction causes a drag on rocks -> deform the rocks along the margins -> energy buildup -> earthquakes -> energy releases

  42. Subducting plate is old and dense - • it sinks into the mantle as a steeply dipping slab

  43. Subducting plate is young • still warm, and relatively buoyant • slab dips at a shallow angle • occurs along the eastern margin of the Pacific, where the American plate is overriding recently formed crust • volcanoes occur on land • many of earthquakes

  44. Exotic terranes • terranes have a history distinct from adjoining crustal fragments are welded onto continents during subduction (A&S-41)

  45. Go to web for animation

  46. PASSIVE MARGINS

More Related