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
4. Crust • basalt (fine grained igneous rock, volcanic) • 5. Hydrosphere • 6. Atmosphere
Earth made of concentric spheres review • 1. Inner core • 2. Outer core • 3. Mantle • Mesosphere • Asthenosphere • Lithosphere • 4. Crust • 5. Hydrosphere • 6. Atmosphere
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! We went over this last time.
Isostasy cont • Crustal materials float in asthenosphere (Fig. 1.14) 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)
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).
"Moho" - the boundary, which geologists refer to as the Mohorovicic discontinuity, between Earth's brittle outer crust and its hotter, softer mantle • http://geology.com/articles/mohorovicic-discontinuity.shtml • Go to this web page and read the article. It is only one page.
Continents • Thick accumulations of granitic rocks • Oldest rocks on Earth - about 3.8 billion years • Oldest continent today is Australia.
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) http://www.youtube.com/watch?v=Kpoko_l34ZE • Crust and upper mantle constitute the rigid lithosphere float on nearly molten asthenosphere
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 located where plates converge • Plates move past each other along transform faults (Fig. 2.23) p 61 • Plate movements shape ocean basins T-30 (Fig. 2.13 b) p 48
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
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) Go back to youtube and look at this again • San Andreas Fault (Fig. 2.23) p 59
Continental Rifting Fig 2.17 p 52 • a. upwarping • b. rift valley (fig 2.18) p 54 read and understand http://www.youtube.com/watch?v=_3K7LtP4cds • c. linear sea • d. mid-ocean ridge • e. Table 2.1 p 51
Pillow lava along Juan de Fuca Ridge. Photo courtesy of Submarine Ring of Fire 2002 Exploration, NOAA-OE.
I want you to go to google and look up hot spots. • Go to google and look up hot spots. http://www.youtube.com/watch?v=D1eibbfAEVk
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)
Plates moving across hot spots cause chains of volcanic islands Hawaiian Islands
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
Earth’s magnetic field • Fig 2.7 and 2.9 p 40 and 43 S&A 30
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
Earth's magnetic field cont. • Form bands with same magnetic oriantation S&A 31 • 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
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
Hydrothermal circulation p 93 • Sea water circulates through hot, newly formed rocks (Fig 3.17 a) p 93 (book) • 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)
Volcanic eruptions occur more frequently on rapidly spreading segment than on slow spreading ones. • A hydrothermal ventis a geyser on the seafloor.
Three types of hydrothermal vents p 94 • black smokers • white smokers • cooler discharge
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.
Hydrothermal Vents cont. • d. Color the mounds with yellows and blacks (like Halloween decorations) Read Recovery of Black Smokers Box 33 p 92 • 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
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
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
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?
All three vents support abundant growths of bottom-dwelling organisms. • Chemosynthesis: the process by which certain microbes use energy stored in sulfur compounds to power the conversion of CO2 to organic compounds
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. (review this again)
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
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
Subducting plate is old and dense - • it sinks into the mantle as a steeply dipping slab
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
Exotic terranes • terranes have a history distinct from adjoining crustal fragments are welded onto continents during subduction (A&S-41)