HOMEWORK 7

NATS 102-3,4H

Due: November 22, 2002

 

You are encouraged to discuss the homework problems with other students.  However you must do the problems by yourself.   That is use your own choice of words, your own elegance of phrase, and construct your own calculations.  Make sure that the answers are clearly indicated.

 

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1) Ch18 DQ1: Identify two volcanic mountain chains that bear a close relationship to plate boundaries.


Possible answers: Andes, Cascades, Aleutian Islands, Japan, Phillipines, others.

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2) Ch18 DQ2: What plate do you live on? How many adjacent plates are there? What kinds of boundaries do you find to the north, south, east, and west?


Tucson is on the North American Plate, and is bounded on the West by the Pacific Plate (transform boundary) and the Juan de Fuca plate (convergent boundary). There is no Northern boundary. To the East, the North American Plate touches the Eurasian Plate and the African Plate at the Mid-Atlantic Ridge, a divergent boundary. The Carribean Plate (transform boundary) is the major Southern border for the North American Plate, but there are some stretches of Cocos and the South American Plate as well.

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3) Ch18 DQ4: Volcanic islands, including the Azores, the Canaries, and Iceland, lay scattered across the Atlantic Ocean. If you were to date the rocks on these and other Atlantic islands, what pattern do you predict you would find.


New oceanic crust is created at the mid-Atlantic Ridge and moves away from the ridge as a function of time. Therefore, you would expect the rocks on islands closest to the ridge to be the youngest, and those farthest away from the ridge to be the oldest.

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2) Ch18 P9: About 50 million years ago, the Indian subcontinental plate was about 2500km from its present location. How fast (in cm/yr) was the Indian subcontinental plate moving before it collided with the Eurasian plate? Is your answer reasonable?


2500km / 50 Myr = 2.5x108cm / 5x107 yr = 5 cm/yr
That's pretty fast as far as plates go, but not beyond the realm of reasonability.

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4) Ch20 R2: What are the three principal kinds of rocks and how do they form?


  • Igneous -- rocks crystallized from a magma.
  • Sedimentary -- rocks that formed by the addition of layers of material to the top.
  • Metamorphic -- Igneous or Sedimentary rocks that have been altered by heat and pressure.

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    5) Ch20 DQ1: Describe three places where you might find volcanic rocks forming today.


    Some of the choices: Mt. Etna in Italy, Hawaii, Central America, the Phillipines, East Africa, the Cascades, the Andes, Iceland, others.

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    6) Ch20 DQ2: Describe three places where you could watch sedimentary rocks forming today.


    Mississippi delta (siltstone or shale), the Sahara (sandstone), the Carribean Sea (carbonates), the Tucson basin (pebbly conglomerates), others.