Earthquakes are great indicators of plate boundaries and are associated with all three

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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

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 2.7) 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

2.7.

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

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

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.

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.

1. 2.42 g/ml 2. 2.67 g/ml 3. 2.81 g/ml 4. 2.93 g/ml

18. Based on the choice you made for question 16, what is the density of the rocks that

make up oceanic plates.

1. 2.42 g/ml 2. 2.67 g/ml 3. 2.81 g/ml 4. 2.93 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.

20. Which of the following places represent a Benioff Zone?

1. 10°S, 110°W 2. 0°, 0° 3. 15°S, 180° 4. 30°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

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?

1. 1200 miles 2. 1700 miles 3. 2100 miles 4. 2700 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?

1. 300 million years old 2. 200 million years old 3. 100 million years old

4. 60 million years old 5. 30 million years old

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.

1. 400 million cm. 2. 460 million cm. 3. 510 million cm. 4. 560

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?

1. 1.9 cm/year 2. 2.1 cm/year 3. 2.55 cm/year 4. 2.9 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)

1. 650 million cm 2. 760 million cm 3. 870 million cm 4. 980 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.

1. 230 million years 2. 300 million years 3. 360 million years 4. 440 million years

Fly to 34 46 16.16 N 118 44 58.19 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).

1. 1100 meters 2. 2000 meters 3. 4050 meters 4. 5800 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 (http://pubs.usgs.gov/gip/earthq3/safaultgip.html) 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.

1. 172 2. 297 3. 501 4. 633

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

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 http://pubs.usgs.gov/gip/earthq3/safaultgip.html

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

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 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

42. What type of plate tectonic boundary is present?

1. Transform 2. Convergent 3. Divergent

43. 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

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 28 04 27.04N 86 55 26.84E. 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 46 55 25.66 N 152 01 25.17 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

49. Fly to 43 41 07.81 N 128 16 56.29 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