GEOGRAPHY

Plate Tectonics Lab Assignment After reading the introduction to the Plate tectonic exercises in the manual, complete the questions on a hard copy of this Lab Assignment. When finished, transfer your answers to the lab assessment in BB Vista, save each answer individually if you feel that you are not to going to complete the whole assignment in one sitting. Do not press the “FINISH” button until you have filled all the answers and are ready to get it graded. Before the submission deadline, you can open the incomplete lab assignment for modifications as many times as you wish, but you will only be able to submit it once for a grade. Part 1- Lab Manual The exercises that follow are adaptations of the Plate Tectonics exercises contained in the lab manual. Note that the number that precedes the text of the question corresponds to the identifying number of that question in the lab manual. Lab Manual (Busch 9th Edition) Activity 2.8: The Origin of Magma 1. (Question A1, Figure 2.7) According to the continental geothermal gradient, rocks buried 80 km beneath a continent would normally be heated to what temperature? At 80 km depth, rocks will be heated to about _______ degrees Celsius 1. 1500 2. 1000 3. 750 4. 200 2. (Question A2, Figure 2.7) According to the oceanic geothermal gradient, rocks buried 80 km beneath an ocean basin would normally be heated to what temperature? At 80 km depth, rocks will be heated to about _______ degrees Celsius 1. 1500 2. 1000 3. 750 4. 200 3. (Question A3, Figure 2.7) What is the physical state of the peridotite at point X? 1. 100% liquid 2. a mixture of solids and liquid 3. 100% solid 4. (Question A4, Figure 2.7) What happens when the peridotite in point X is heated to 1750 °C? 1. no change 2. partial melting 3. complete melting 5. (Question A5, Figure 2.7) What happens when the peridotite in point X is heated to 2250 °C? 1. no change 2. partial melting 3. complete melting 6. (Question B1, Figure 2.7) At what depth and pressure will peridotite at point X begin to melt if it is uplifted closer to Earth’s surface and its temperature remains the same? 1. 75 km, 24,000 atm 2. 65 km 20,000 atm 3. 40 km 13,000 atm 4. 20 km 8,000 atm 7. (Question B2 and B3) When mantle peridotite melts as a result of being uplifted in the way described in the previous question, the process is called__________ and is likely to happen at ____________. 1. solidus crystallization, divergent boundaries 2. solution, convergent boundaries and hot spots 3. recrystallization melting, hot spots 4. decompression melting, divergent boundaries and hot spots 8. (Question C, Figure 2.7) According to your answers to the previous four questions related to the peridotite at point X being subjected to changes in pressure and temperature, which two processes would lead to melting? 1. decrease in pressure and temperature 2. increase in pressure and temperature 3. decrease in pressure and increase in temperature. 4. increase in pressure and decrease in temperature Lab manual (Busch, 9th Edition) Activity 2.8 part D: A few modifications will allow you to run the experiment described in this section using materials readily available in your home. The hot plate can be replaced by a foil lined frying pan on the stove burner. The two sugar cubes can also be replaced by two teaspoonfuls of sugar; the secret is not to add excessive water to the sample that needs to be wet. Extra water will dissolve the sugar and obscure the interpretation of your results. Prepare all the experiment materials directly on the cool burner to avoid mixing of the two samples when you move the foil. Place on the stove burner the foil lined pan, the two separate heaps of sugar and add the drops of water on one of the heaps. Then turn the stove on at medium heat, and observe. 9. (Question D1) Which sample melted first? 1. the dry sample 2. the wet sample 10. (Question D2) The rapid melting that you observed in the sample that melted first is called “flux melting,” because flux is an added component the speeds up a process. What was the flux? 1. sugar 2. water 3. silicates 11. (Question D3, Figure 2.8) The effect of water on peridotite is similar to its effect on the sugar experiment, therefore when peridotite is heated in “wet” conditions, the line of the “wet solidus” would be located to the _____________ of the “dry solidus” in Figure 2.8. 1. right, to higher temperatures 2. left, to lower temperatures 12. (Question D4) Looking at Figure 2.1 for a hint, indicate in what tectonic setting may water enter the mantle and produce flux melting of peridotite? 1. hot spots 2. subduction zones 3. mid-oceanic ridges 4. transform faults 13. (Question E3, Figure part E). Which choice best describes the sequence of processes leading to the formation of mid-oceanic ridge volcanoes? 1. “ wet” seafloor basalt subducts and dehydrates, water induces flux melting of mantle peridotite above, basaltic magma ascends and forms volcanoes. 2. flux melting, magma ascends to the surface forming volcanoes, peridotite rises, subduction 3. magma ascends, decompression melting of peridotite, peridotite pushes the basalt open and forms volcanoes. 4. peridotite ascends, decompression melting forms basaltic magma, magma pushes and cracks the ocean floor basalt open, and erupts forming volcanoes 14. (Question F3, Figure part F). Which choice best describes, the processes leading to the formation of a continental volcanic arc, in chronological order? (Beware of error in F3: the words between brackets “oceanic ridge” should be replaced with “continental volcanic arc”). 1. “ wet” seafloor basalt subducts and dehydrates, water induces flux melting of mantle peridotite above, basaltic magma ascends and forms volcanoes. 2. flux melting, magma ascends to the surface forming volcanoes, peridotite rises to shallow depth and melts, subduction. 3. magma ascends, decompression melting of peridotite, peridotite pushes the ocean floor basalt open and forms volcanoes. 4. peridotite ascends, decompression melting forms basaltic magma, magma pushes and cracks the ocean floor basalt open, and erupts forming volcanoes Lab manual (Busch, 9th Edition) Activity 2.3: Using Earthquakes to identify Plate boundaries 15. Refer to the figure in activity 2.3. Which of the following places represent a Benioff Zone? (Hint: refer back to the notes for unit 3) 1. 10°S, 110°W 2. 0°, 90°W 3. 0°, 80°W 4. 20°S, 100°W 16. The Benioff zone is associated with which type of plate boundary? 1. Divergent 2. Convergent (Continent-Continent) 3. Convergent (Continent-Ocean) 4. Transform Lab manual (Busch, 9th Edition) Activity 2.4: Analysis of Atlantic Seafloor Spreading To solve questions in this section, review how to work with graphic scales and the metric system in Unit 2. Use a ruler to measure the distance between features and determine the equivalent distance in the ground using the graphic scale. (A ruler is contained in the GEOTOOLS Sheet 1, at the end of your lab manual). The distance you determine will be in kilometers (km). Convert the distance to centimeters (cm), remember 1000 meters = 1 kilometer. Remember that the rate of movement is equivalent to the plate velocity. Velocity can be calculated dividing the distance the plate traveled by the time it took to cover that distance: velocity = distance/time. Choose the answers that best approximate to your calculated values, make sure you use the required units. 17. (Question B, Figure page 49). Notice that points B and C were together 145 million years ago, but did the sea floor spread apart at the same rate on both sides of the mid-ocean ridge? 1. Same Rate 2. Faster on the East 3. Faster on the West 18. (Question C, Figure page 49). How far apart are points B and C, today in kilometers? 1. ~3,250 km 2. ~3,850 km 3. ~4,250 km 4. ~4,550 km 19. (Question C.1, Figure page 49). Calculate the average rate, in km per million years, at which points B and C have moved apart over the past 145 million years. 1. 8 km/my 2. 16.4 km/my 3. 27.6 km/my 4. 31.8 km/my 20. (Question C.2, Figure page 49). Convert your answer above from km per million years to mm per year. The result is ________ in mm per year. 1. 10 times less than the previous answer 2. Same as the previous answer 3. 10 times more than the previous answer 4. 100 times more than the previous answer 21. (Question D, Figure page 49). Based on your answer in question 19, how many millions of years ago were Africa and North America part of the same continent? (Hint use points D and E). 1. ~150 million years 2. ~165 million years 3. ~180 million years 4. ~200 million years 22. (Question E, Figure page 49). Based on your answer in question 20, how far in meters have Africa and North America moved apart since the United States was formed in 1776 to 2011? 1. ~0.6 meters 2. ~6 meters 3. ~15 meters 3. ~25 meters Lab manual (Busch, 9th Edition) Activity 2.5: Plate motion along the San Andres Fault Part A. The two bodies of Late Miocene rocks (~25 million years old) located along either side of the San Andres Fault (map- page 51) resulted from a single body of rock being separated by motions along the fault. Note the arrows show the relative motion. 23. (Question A1, Figure page 51). Estimate the average annual rate of movement along the San Andres Fault by measuring how much the Late Miocene rocks have been offset by the fault and by assuming that these rocks began separating soon after they formed. What is the average rate of fault movement in centimeters per year (cm/yr)? 1. ~0.1 cm/year 2. ~1.3 cm/year 3. ~13 cm/year 4. ~25 cm/year

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