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 24. (Question A2, Figure page 51). Most of the movement along the San Andres Fault occurs during earthquakes. An average movement of about 5 m (16ft) along the San Andres Fault was associated with the devastating 1906 San Francisco earthquake that killed people and destroyed property. Assuming that all displacement along the fault was produced by earthquakes of this magnitude, how many Earthquakes are needed to produce the displacement observed in the previous question? 1. ~1,000 2. ~10,000 3. ~65,000 4. ~100,000 Lab manual (Busch, 9th Edition) Activity 2.7: Plate tectonics of the Northwest United States Notice the ages of seafloor rocks in Figure 2.6. The modern seafloor rocks of this region are forming along a divergent plate boundary called the Juan de Fuca Ridge. The farther one moves away from the plate boundary, the older the seafloor rocks. 25. (Question B2, Figure 2.6). Notice the seafloor rocks older than 8 million years are present west of the Juan de Fuca Ridge but not east of the ridge. What could cause their absence from the map? They are absent because ______________. 1. a strike slip fault along the ridge has moved older rocks further north. 2. older rocks have been subducted underneath the North American Plate 3. rifting has produced metamorphism, which obliterated the old age of the seafloor 4. erosion of the sea floor destroyed rocks older than 12 million years 26. (Question B3, Figure 2.6) The type of plate boundary represented by the red line on the figure is a/n __________________ boundary. 1. transform 2. convergent 3. divergent 4. unconformity 27. (Question B4, Figure 2.6) Which of the following best explains the origin of magma that builds Cascade Range volcanoes? 1. As the North American Plate and the Juan de Fuca Plate slide past each other on a horizontal plane, friction produces the heat to generate magma. 2. As the Juan de Fuca plate is rifted apart, lower pressure at the rift produces magma that feeds the volcanoes at the Cascade Range. 3. Subduction of the Juan de Fuca Plate under the North American Plate brings rocks from the ocean floor and marine sediment to depths where partial melting ensues due to the increased temperature and the influence of water. 4. Migration of the North American Plate over a hot spot is responsible for the Cascade Range volcanoes. Part 2- Google Earth The exercises that follow use Google Earth. For each question (or set of questions) paste the location that is given into the “fly to” box. Examine each location at multiple eye altitudes and differing amounts of tilt. For any measurements use the ruler tool, this can be accessed by clicking on the ruler icon above the image. Google Earth: Hawaiian Islands Fly to Hawaii. Please review the section on Hotspots and the Hawaiian Islands in the Lab manual and in the unit notes. Rocks have been dated on each of the Hawaiian Islands and their ages are as follows: Big Island- 0 (active), Maui – 1.1 million, Kauai- 4.7 million, Nihoa (23 03 32.79N 161 55 11.94W)- 7.2 million years 28. Consider the ages and positions of the islands listed above along with what you know about plate tectonics and hotspots. In what general direction is the Pacific Plate moving? 1. Northwest 2. Southeast 3. Northeast 4. Southwest 29. How fast was the Pacific plate moving during the last 1.1 million years between the formation of the Big Island and Maui in cm/year? 1. ~5 cm/year 2. ~10 cm/year 3. ~15 cm/year 4. ~20 cm/year 30. How fast was the Pacific plate moving from 7.2 million years ago to 4.7 million years ago between the formation of Kauai and Nihao in cm/year? 1. ~5 cm/year 2. ~10 cm/year 3. ~15 cm/year 4. ~20 cm/year 31) Examine the headings of the measurements that you took for the previous two questions. The headings indicate the direction the Pacific Plate is moving over the hot spot. How does the direction of motion of the Pacific Plate during the last 1.1 million years differ from direction of movement between 4.7 and 7.2 million years ago? The direction of plate movement in the last 1.1 million years________. 1. shows no change 2. has become more northerly 3. has become more southerly 32) Zoom out and examine the dozens of sunken volcanoes out past Nihoa, named the Emperor Seamounts. As one of these volcanic islands on the Pacific Plate moves off the hotspot it becomes inactive, or extinct, and the island begins to sink as it and the surrounding tectonic plate cool down. The speed the islands are sinking can be estimated by measuring the difference in elevation (tilting the image helps to find the highest elevation) between two islands and dividing by the difference in their ages (this method assumes the islands were a similar size when they were active). Using Maui and Nihoa, how fast are the Hawaiian Islands sinking? 1. ~0.05 cm/year 2. ~0.5 cm/year 3. ~5 cm/year 4. ~10 cm/year 33) Using the speed you calculated in the previous question (and ignoring possible changes in sea level), when will the Big Island of Hawaii sink below the surface of the ocean? 1. ~650,000 years 2. ~1.2 million years 3. ~8 million years 4. ~13 million years 34) Examine the Emperor Seamounts and notice that it is a continuous chain that reaches far north to the Aleutian Islands of Alaska. Using a speed halfway between that which you calculated in questions 29 and 30, calculate the age of the oldest (furthest North) seamount in the Emperor Seamounts? (Hint 1- using the line mode of the ruler tool will not work since the Pacific Plate had a drastic change in direction, try using the path mode of the ruler tool to give a more accurate distance; Hint 2- Since you know the plate does not move at the same speed over time, the age you estimated will differ from the real age based on radiometric dating, therefore your answer will be different from the one given in the lab manual!). 1. ~30 million years 2. ~45 million years 3. ~60 million years 4. ~75 million years Google Earth: Identifying Plate Boundaries 35. Fly to 15 19 48.78 S 75 12 03.41 W. What type of tectonic plates are present? 1. Ocean- Ocean 2. Ocean- Continent 3. Continent- Continent. 36. What type of plate tectonic boundary is present? 1. Transform 2. Convergent 3. Divergent 37. Fly to 6 21 49.68 S 29 35 37.87 E. What type of process is going on at this location? 1. Seafloor spreading 2. Continental rifting 3. Subduction 38. What type of plate tectonic boundary is present? 1. Transform 2. Convergent 3. Divergent 39. Fly to 28 04 27.04N 86 55 26.84E. What type of tectonic plates are present? 1. Ocean- Ocean 2. Ocean- Continent 3. Continent- Continent. 40. What type of plate tectonic boundary is present? 1. Transform 2. Convergent 3. Divergent