Plate Tectonics Lab Assignment

Transcription

1 Plate Tectonics Lab Assignment After reading the introduction to the Plate Tectonics exercises in the lab manual, complete the questions on a hard copy of this Lab Assignment. When finished, transfer your answers to the lab quiz in GoVIEW. Do not press the SUBMIT button until you have filled all the answers and are ready to get it graded. You have two attempts to complete this lab assignment. The average score of your two attempts will be recorded. You should save each question individually and only press SUBMIT when you are ready to be graded. 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 (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 (Question A3, Figure 2.7) What is the physical state of the peridotite at point X? % liquid 2. a mixture of solids and liquid % 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?

2 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? km, 24,000 atm km, 20,000 atm km, 13,000 atm 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

3 11. (Question D3, Figure 2.7) 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 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 Part 2- Plates and Density An important property of geological plates is their density (mass/volume). The relative density of two plates can control how they interact at a boundary, and, therefore, the types of geological features found along the border between the two plates. Measuring the density of rocks is fairly easy and can be done by first weighing the rocks and then calculating their volume. The latter is best done by a method called fluid displacement

4 using a graduated cylinder. Water is added to the cylinder and the level is recorded, a rock is then added to the cylinder and the difference in water levels equals the volume of the rock. Density is then calculated as the mass divided by the volume. The information needed to calculate density was collected for four rocks and can be used to answer the following questions including the weight (in grams) as well as the volume of water recorded by a graduated cylinder (in milliliters) before and after the rock was added. Note: each line on the graduated cylinder represents 5 ml.

5 Read the description of the rocks representative of the continental and oceanic plates in in the section on Basics of Plate Tectonics in unit 4 of the ecore course content. 15. The rock that most closely resembles the composition of continental plates is: 1. A 2. B 3. C 4. D 16. The rock that most closely resembles the composition of oceanic plates is: 1. A 2. B 3. C 4. D 17. Based on the choice you made for question 15, what is the density of the rocks that make up continental plates g/ml g/ml g/ml g/ml 18. Based on the choice you made for question 16, what is the density of the rocks that make up oceanic plates g/ml g/ml g/ml g/ml 19. Based on your previous questions, at a boundary the plate subducts below the plate. 1. convergent; continental; oceanic. 2. convergent; oceanic; continental. 3. divergent; continental; oceanic. 4. divergent; oceanic; continental. Part 3- Geological Patterns associated with plate tectonics Earthquakes are great indicators of plate boundaries and are associated with all three types. One type of boundary is unique in having a Benioff zone. Answer the following questions using the following figure from the USGS.

6 20. Which of the following places represent a Benioff Zone? S, 110 W 2. 0, S, N, 75 E 21. The Benioff zone is associated with which type of plate boundary? 1. Divergent 2. Convergent (Continent-Continent) 3. Convergent (Continent-Ocean or Ocean-Ocean) 4. Transform Examine the following figure showing the distribution across Australia and Antartica of a fossil snake (Patagoniophis). Obviously, this small snake was unable to swim the immense distance between the contients and, therefore, lived while Australia and Antartica were still joined together. Use the following figure modified from the

7 Australia Department of Natural Resources and Scanlon (2005), Memoirs of the Queensland Museum to answer the following questions. 22. How far have the fossil snakes moved apart since they were originally deposited? miles miles miles miles 23. Given that this portion of the Australian plate moves at a speed of 2.2 inches per year, how old are the snake fossils? million years old million years old million years old million years old million years old

8 24. Study the section in the ecore Course Content entitled Fossil evidence from widely separated continents. The age and distributions of organisms such as Glossopteris and Lystrosaurus indicate that Australia and Antarctica broke from Gondwanaland during the Triassic. Given your answer to the previous question, Antarctica separated from Australia: 1. before they separated from Gondwanaland. 2. at the same time as they separated from Gondwanaland. 3. after they separated from Gondwanaland. Part 4- 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. 25. Examine the coastlines of Western Africa and Eastern South America. Notice that the shapes match up. What type of plate boundary does this represent? 1. Convergent 2. Divergent 3. Transform 26. Measure in centimeters the distance between the two continents where they used to be connected. This varies along the coast so measure between the eastern most portion of Brazil and Cameroon million cm million cm million cm million cm. 27. Given that Pangaea broke apart 200 million years ago and your previous answer, how fast are South America and Africa separating in cm/year? cm/year cm/year cm/year cm/year 28. The Americas will eventually collide with Asia likely forming the next Supercontinent (prematurely called Amasia). How far apart are North America and Mainland Asia in cm? (measure the distance across the Pacific at 40 degrees north latitude- basically measure between Northern California and Japan- this is easiest to do when you zoom way out) million cm million cm million cm million cm. 29. Given the speed you calculated in question 27 and distance you measured in question 28, calculate when Amasia will likely be formed million years million years million years million years

9 Fly to N W and zoom out to an eye altitude of 30,000 feet. Quail Lake is a dammed river that is sitting directly over top of the San Andres Fault, which is a well-known transform boundary with the North American Plate on the northern side and the Pacific Plate on the southern side. This boundary is running East- West in this area and you may be able to see the boundary better by zooming out. 30. Examine the path or the river that feeds into and flows out of Quail Lake. How much movement has occurred in order to alter the course of this river? (Hint: assume the river originally flowed more or less straight North-South and focus on the river rather than the size of Quail Lake) meters meters meters meters 31. What direction is the North American plate moving in comparison to the Pacific Plate at this location? 1. East 2. West 32. Given that San Francisco is located on the North American Plate and Los Angles is located on the Pacific Plate, are these two cities getting closer together or farther apart over time? 1. Closer 2. Farther 33. Most of the movement along this boundary occurs during earthquakes. According to the USGS ( the catastrophic 1906 San Francisco earthquake resulted in a local movement of the fault 6.4 meters (21 feet). Assuming all displacement along the transform boundary was the result of similar sized earthquakes, how many earthquakes would be required to cause this the amount of displacement you measured in the previous questions 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 ( N W)- 7.2 million years 34. 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

10 35. 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 36. 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 Nihoa in cm/year? 1. ~5 cm/year 2. ~10 cm/year 3. ~15 cm/year 4. ~20 cm/year 37. 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 southerly 3. has become more northerly 38. 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; however you should also zoom in to look for the highest point) 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 39. 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 40. 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 35 and 36, 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

11 the lab manual!) 1. ~30 million years 2. ~45 million years 3. ~60 million years 4. ~75 million years Google Earth: Identifying Plate Boundaries 41. Fly to S W. What type of tectonic plates are present? 1. Ocean- Ocean 2. Ocean- Continent 3. Continent- Continent 42. What type of plate tectonic boundary is present? 1. Transform 2. Convergent 3. Divergent 43. Fly to S E. What type of process is going on at this location? 1. Seafloor spreading 2. Continental rifting 3. Subduction 44. What features would you expect to occur at this type of boundary? 1. Earthquakes and a trench 2. Volcanoes and a valley 3. Mountains and landslides 4. Earthquakes and offset rivers 45. Fly to N E. What type of tectonic plates are present? 1. Ocean- Ocean 2. Ocean- Continent 3. Continent- Continent. 46. What type of plate tectonic boundary is present? 1. Transform 2. Convergent 3. Divergent 47. Fly to N E. What type of tectonic plates are present? 1. Ocean- Ocean 2. Ocean- Continent 3. Continent- Continent 48. What features would you expect to occur at this type of boundary? 1. Earthquakes and a trench 2. Volcanoes and a valley 3. Mountains and landslides 4. Earthquakes and offset rivers

12 49. Fly to N W. What type of tectonic plates are present? 1. Ocean- Ocean 2. Ocean- Continent 3. Continent- Continent 50. What type of plate tectonic boundary is at this exact location? 1. Transform 2. Convergent 3. Divergent 51. This plate boundary isn t as simple as the previous examples, meaning another nearby plate boundary directly influences it. Zoom out and examine the area, what other types of boundary are nearby? 1. Transform 2. Convergent 3. Divergent