GSU GEOL 1122K - Chapter 2 Reading Quiz (11 pages)

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Chapter 2 Reading Quiz



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Chapter 2 Reading Quiz

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Pages:
11
School:
Georgia State University
Course:
Geol 1122k - Introductory Geosciences Ii
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Accretionary prisms form due to what process subduction divergence rifting transform motion As sediment on the down going slab is scraped off by the overriding plate during subduction an accretionary prism forms SEC 2 8 Figure 2 22a Asthenosphere is warm enough to flow slowly subducts when it collides with continental lithosphere is the lower layer of both continental and oceanic lithosphere is the uppermost layer of Earth s core Asthenosphere is part of the mantle not the core It supports the lithosphere rather than being part of it or colliding with or subducting under it SEC 2 Choose the FALSE statement Magnetic anomalies are places where the magnetic field strength is either greater or less than the expected strength termed normal if the atomic dipoles match Earth s current magnetic field and point from north to south found only on the seafloor measured with an instrument called a magnetometer Magnetic anomalies are found on continents as well as on the seafloor They create irregular patterns on continents and distinct alternating bands on the seafloor SEC 2 5 Figure 2 10 Earth s magnetic field is created by flow of liquid iron in Earth s molten outer core centrifugal force pushing on Earth s crust convecting iron rich silicates in Earth s mantle the rotation of the planet on its axis The flow of iron alloy in Earth s molten outer core makes it an electromagnet SEC 2 3 Identify the FALSE statement Plate boundaries where subduction occurs are also called consuming boundaries Seafloor spreading behind a volcanic island arc creates a small ocean basin called a back arc basin or marginal sea An accretionary prism is a wedge shaped mass of sediment scraped off a subducting plate as it slides under the overriding plate A spreading boundary must be in the middle of the ocean basin where it is located The Mid Atlantic Ridge is in the middle of its ocean but this is not true for mid ocean ridges in the Pacific and Indian Oceans SEC 2 7 2 8 Identify the FALSE statement Positive magnetic anomalies occur over areas of seafloor when the poles of Earth s magnetic field and the paleopoles preserved in the seafloor basalt agree negative anomalies occur when they are opposite each other All polarity chrons are the same length of time they differ only in the magnetic strengths they represent The series of rock stripes parallel to and bilaterally symmetrical across the midocean ridge record the sequence of Earth s magnetic reversals over time The width of each rock stripe is a measure of how long the polar direction remained constant Time intervals between reversals differ so the lengths of polarity chrons also differ Polarity chrons have nothing to do with magnetic strength SEC 2 5 Identify the FALSE statement Plates shift the continents around as they move so Earth s surface is constantly changing Plates may consist of all ocean floor or both ocean floor and continental crust There are 12 major plates and several microplates The contacts between plates are called passive margins The contact between lithospheric plates is called a plate boundary Passive margins do not occur at plate boundaries SEC 2 6 Identify the FALSE statement As the seafloor spreads the asthenosphere rises melts to become magma and fills the space between plates Some magma generated during seafloor spreading spills out to produce a new layer of seafloor called gabbro Some magma generated during seafloor spreading erupts from submarine volcanoes Observers in research submersibles have seen submarine volcanoes Gabbro does form along the sides of magma chambers in the crust below the ridge axis but the magma that rises to become seafloor cools to form basalt SEC 2 7 Identify the FALSE statement A subducting or down going plate can be either continental or oceanic lithosphere has a trench along its seaward edge can be charted by noting its Wadati Benioff zone has a volcanic arc associated with it A subducting plate is always oceanic lithosphere SEC 2 8 Identify the FALSE statement According to the mantle plume model hot spot plumes stream upward slowly because their hot rock is less dense than the overlying rock can occur beneath ocean plates as well as continental plates produce volcanoes that do not always coincide with a plate boundary are thought to originate at the crust mantle boundary This model proposes that plumes originate deep in the mantle just above the core mantle boundary Alternative explanations of hot spot volcanoes propose plumes at shallow depth or no plumes at all SEC 2 10 Identify the FALSE statement Oceanic lithosphere gets older and thicker as it gets farther from the ridge axis gets cooler as it gets farther from the ridge axis attains its maximum thickness when it is about 800 million years old effectively does not exist beneath the mid ocean ridge axis Oceanic lithosphere attains its maximum thickness when it is about 80 million years old Even if you did not remember the exact age you could identify the false statement if you remember that no oceanic lithosphere is more than 200 million years old SEC 2 7 Figure 2 19 Identify the FALSE statement Plate movement is influenced by mantle convection which creates shear at the base of plates slab pull in which the down going oceanic plate exerts a pull on the rest of the plate mantle plumes which are created when hot rock rises up from the deep mantle and creates melting at the base of the lithosphere ridge push in which the elevated rocks at the ridge axis push on rocks farther from the ridge Mantle plumes are the possible cause of hot spots but they do not affect plate movement in a meaningful way SEC 2 12 Identify the FALSE statement The rate of plate motion can be determined to within millimeters by using the global positioning system GPS can be expressed as relative plate velocity which describes movement of one plate in relation to another plate can range from 100 to 150 cm per year can be expressed as absolute plate velocity which describes movement of a single plate relative to a fixed point Plate motion ranges from 1 to 15 cm per year SEC 2 12 Figure 2 32 Identify the TRUE statement associated with this diagram The apparent polar wander path of Africa is the same as that of Europe Apparent polar wander paths prove that Earth s magnetic poles wandered up to 90 degrees from their current position through geologic time Apparent polar wander paths were created by measuring the paleomagnetism in rocks of different ages from the same location The


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