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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

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• 4. Crust– basalt (fine grained igneous rock, volcanic)

• 5. Hydrosphere• 6. Atmosphere

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Earth made of concentric spheres review

• 1. Inner core• 2. Outer core• 3. Mantle

– Asthenosphere – Lithosphere

• 4. Crust• 5. Hydrosphere• 6. Atmosphere

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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 23 T-20

• Play the game of isostasy before class!

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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)

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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).

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

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

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Continents

• Thick accumulations of granitic rocks• Oldest rocks on Earth - about 3.8 billion

years

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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

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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

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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

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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

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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

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

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• START HERE FOR WEDNESDAY

• If you are interested in a 9th edition of our book.

• bmichael23@aol.com.

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I want you to print out an article on hot spots

• Go to google and look up hot spots.

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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)

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

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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

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Earth’s magnetic field

• Fig 2.7 and 2.9 p 40 and 43

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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

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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

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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

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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)

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• Volcanic eruptions occur more frequently on rapidly spreading segment than on slow spreading ones.

• A hydrothermal vent is a geyser on the seafloor.

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Three types of hydrothermal vents p 94

• black smokers• white smokers• cooler discharge

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black smokers

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White smoker

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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.

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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

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Tube worms T 134

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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

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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

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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?

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All three vents support abundant growths of bottom-dwelling organisms.

• Chemosynthesis: the process by which certain microbes create energy by mediating chemical reactions

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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.

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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

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ACTIVE MARGINS

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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

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Subducting plate is old and dense -

• it sinks into the mantle as a steeply dipping slab

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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

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Exotic terranes• terranes have a history distinct from adjoining crustal

fragments are welded onto continents during subduction (A&S-41)

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Go to web for animation

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PASSIVE MARGINS

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Passive margins of continents

• No earthquakes, no volcanoes. Fig 3.7 p 81 book • Called Atlantic-type margins• Form after continents are rifted apart and tend to

be wide• Thick sediment deposits and old oceanic crust

– trenches do not form, – sediment is folded into mountain ranges (Appalachians,

Alps, Himalayas, and Urals)

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Passive margins cont.

• Economically, they are important because of the accumulations of oil and gas that they often contain. Most of the world's giant oil and gas fields occur in such deposits.

• Found on Atlantic Ocean, Antarctic Ocean. Arctic Ocean, and Indian Ocean

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Mantle convection (Fig 2.10 p 44)

• Occurs in mantle, causing plate movements• Supplies molten rock to midocean ridges,

causing volcanism• 1. hot-spot volcanoes originate at unusually

hot areas of the core mantle boundary• 2. the overlying mantle melts, forming

plumes of magma that rise and penetrate the crust as volcanoes.

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Mantle convection cont.

• 3. these hot spots do not move with the overlying mantle and thus remain fixed in location for tens of millions of years

• 4. red patches - continental flood basalts and oceanic lava plateaus T 54

• Crust cools as it ages, and grows denser• Oldest, densest rock sinks into the mantle at the

trenches

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Formation of ocean basins (Fig 2.17 abcd)

• Formed through the breakup of continents. Begins when a continent remains in one location for >100 million years continent impedes heat flow from the earth's interior.

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Formation of ocean basins cont

• a. underlying mantle heats, expanding and uplifting the overlying lithosphere

• b. continents rift, forming narrow valleys (rift valley in Africa)

• c. valleys widen into narrow ocean basin, e.g., Red Sea midocean ridges in the middle of ocean - actively widening

• d. ocean continues to widen until the oldest crust becomes dense enough to sink, causing the ocean to gradually narrow

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Destruction of ocean basins Fig 2.20 abc p 56

• Ocean - continent convergence• Ocean - ocean convergence• Continent - continent convergence• Mountains form when basin closes• Appalachian Mountains mark site of ancient

ocean that closed about 400 million years ago Can see the sedimentary rocks on the AT

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• START HERE ON MONDAY

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Mantle convection (Fig 2.10 p 44)

• Occurs in mantle, causing plate movements• Supplies molten rock to midocean ridges,

causing volcanism• 1. hot-spot volcanoes originate at unusually

hot areas of the core mantle boundary• 2. the overlying mantle melts, forming

plumes of magma that rise and penetrate the crust as volcanoes.

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• 3. these hot spots do not move with the overlying mantle and thus remain fixed in location for tens of millions of years

• 4. red patches - continental flood basalts and oceanic lava plateaus T 54

• Crust cools as it ages, and grows denser• Oldest, densest rock sinks into the mantle at

the trenches

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Boundaries Table 2.2 p 53

• a. divergent - plates move apart• b. convergent - plates collide• c. transform - plates slide past one another• d. Study this table (It is on this exam)

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Points to remember

• Continent - from granite• Ocean - from basalt• Heat flow - Fig 2.10 p 44• Table 2.1 p 51 This is the culture vulture

question

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Breakup of Pangaea on to present

• Began about 225 million years ago, with the breakup of Pangaea about 180 million years ago T 21 - 23 and 15

• North Atlantic formed first, South Atlantic later

• Indian Ocean is the youngest basin• Pacific is the remnant of Panthallasia,

previous cycle

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Present spreading cycle cont.

• Mediterranean is the remnant of Thetys Sea

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END Plate Tectonics

We have seen all the material that will be covered on Exam I