Plate tectonics
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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

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PLATE TECTONICS

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Plate tectonics

PLATE TECTONICS


Earth made of concentric spheres fig 1 14 p 18 t 14

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


Plate tectonics

  • 4. Crust

    • basalt (fine grained igneous rock, volcanic)

  • 5. Hydrosphere

  • 6. Atmosphere


Earth made of concentric spheres review

Earth made of concentric spheres review

  • 1. Inner core

  • 2. Outer core

  • 3. Mantle

    • Asthenosphere

    • Lithosphere

  • 4. Crust

  • 5. Hydrosphere

  • 6. Atmosphere


Isostasy

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!


Isostasy cont

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)


Isostasy cont1

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).


Plate tectonics

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


Moho exposed at the surface located between crust and mantle s a 22

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


Continents

Continents

  • Thick accumulations of granitic rocks

  • Oldest rocks on Earth - about 3.8 billion years


Plate tectonics1

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


Plate tectonics cont

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


Plate boundaries fig 2 14 a b c p50

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

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


Continental rifting fig 2 17 p 52

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


Plate tectonics

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


Plate tectonics

  • START HERE FOR WEDNESDAY

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

  • [email protected]


I want you to print out an article on hot spots

I want you to print out an article on hot spots

  • Go to google and look up hot spots.


Hot spots

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

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


Hot spots cont

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

Earth’s magnetic field

  • Fig 2.7 and 2.9 p 40 and 43


Earth s magnetic field fig 2 12 p 46 t 28

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

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


Neat stuff on the earths magnetic field

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

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)


Plate tectonics

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

  • A hydrothermal vent is a geyser on the seafloor.


Three types of hydrothermal vents p 94

Three types of hydrothermal vents p 94

  • black smokers

  • white smokers

  • cooler discharge


Black smokers

black smokers


White smoker

White smoker


Hydrothermal vents cont

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 cont1

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


Tube worms t 134

Tube worms T 134


Hydrothermal vents cont2

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 cont3

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 cont4

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

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

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


Continental margins

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.


Continental margins two types fig 3 7 p 82

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


Active margins

ACTIVE MARGINS


Earthquakes

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

Subducting plate is old and dense -

  • it sinks into the mantle as a steeply dipping slab


Subducting plate is young

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

Exotic terranes

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


Go to web for animation

Go to web for animation


Passive margins

PASSIVE MARGINS


Passive margins of continents

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)


Passive margins cont

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


Mantle convection fig 2 10 p 44

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.


Mantle convection cont

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


Formation of ocean basins fig 2 17 abcd

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.


Formation of ocean basins cont

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


Destruction of ocean basins fig 2 20 abc p 56

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


Plate tectonics

  • START HERE ON MONDAY


Mantle convection fig 2 10 p 441

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.


Plate tectonics

  • 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


Boundaries table 2 2 p 53

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)


Points to remember

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


Breakup of pangaea on to present

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


Present spreading cycle cont

Present spreading cycle cont.

  • Mediterranean is the remnant of Thetys Sea


End plate tectonics

END Plate Tectonics

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


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