GEO 101 The Solid Earth Week 2 Plate Tectonics Lab (25 points) Introduction Plate tectonics is a set of related concepts that explains how the Earth works including where and why earthquakes and volcanoes occur and how the continents and oceans have changed over time. Learning Outcomes Become familiar with Earth s tectonic plates by identifying and locating plates (by name) and plate boundaries (by type) on a map Interpret the location and types of plate boundaries based on the location of surface features such as ridges, trenches, and volcanic arcs Infer direction of plate motion based on distribution of plate boundaries and types Graph a dataset and use the graph to identify trends in the data Explain how hotspot tracks are used to infer velocity and direction of plate motion Explain the age distribution of oceanic crust in relation to tectonic features on the seafloor such as ridges and trenches Compare the age of oceanic crust to the age of continental crust and the age of the Earth Exercise 1 Plates and Plate Boundaries 1. Identify the tectonic plates on the map of plate boundaries (page 2). Refer to the information in the lecture slides or textbook. Record your answers in the answer sheet by identifying each lettered plate by its name. 2. Label each plate boundary as convergent, divergent, or transform (again, referring to the lecture to textbook) using arrows to indicate the relative motion of the plates. Use the following key. Record your answers on the answer sheet by identifying each numbered plate boundary as convergent (subduction zone or continental collision), divergent (mid-ocean ridge or continental rift), or transform by placing an X in the appropriate column of the table. GEO 101 The Solid Earth Page 1 of 8
Map of plates (letters A-N) and plate boundaries (numbers 1-27). GEO 101 The Solid Earth Page 2 of 8
3. Based on the distribution of divergent and convergent plate boundaries, indicate which of the following locations are moving closer together, further apart or show no change by placing an x in the appropriate column. If the two cities are on the same plate, they will show no change (they will both be moving in the same direction at the same speed). If they are not on the same plate, determine what type of plate boundary lies between them. If there is a divergent boundary, this means that the two plates are moving away from each other as new crust is being produced, pulling the two cities further apart. If there is a convergent boundary, this means the two plates are moving towards each other and old crust is being destroyed, bringing the two cities closer together. If there is a transform boundary between the two cities, you need to look at the relative directions of the plates to determine if the two cities are moving closer or further apart. Locations Closer Further No Change London (UK) & New York Honolulu, Hawaii & Tokyo, Japan Mecca, Saudi Arabia & Cairo, Egypt New York & Mexico City Rio de Janeiro, Brazil & Cape Town, S. Africa Honolulu, Hawaii & Los Angeles Cape Town, S. Africa & Bombay, India Los Angeles & San Francisco, California Sydney, Australia & Bombay, India Examine the figure and answer the questions that follow. The patterned areas labeled X, Y, and Z represent continents; assume the rest of the map is ocean. 4. How many plates are present? 5. Draw arrows on the map showing the relative directions of plate motions. Record your answers in the answer sheet by indicating whether each numbered boundary is convergent, divergent, or transform. 6. Where is subduction taking place? Describe which plate(s) are being subducted and by which other plate by referring to the lettered continent it contains or the numbered boundaries that surround it. GEO 101 The Solid Earth Page 3 of 8
Exercise 2 Hot Spots The volcanic rocks of the Hawaiian- Emperor volcanic chain are all younger than the surrounding oceanic crust. This volcanic chain also defines two linear trends (Figure 1). In 1963, a geologist named J. Tuzo Wilson suggested that this chain of volcanoes formed as the Pacific Plate moved over a stationary plume or hot mantle rock, called a hot spot. Basalt magma from the mantle plume ascended through the oceanic crust forming the island chain. This is a testable hypothesis because if this hypothesis is correct, then: 1) the volcanoes should be progressively older farther away from the current location of the hot spot (the Kilauea volcano); 2) this age-distance Map of the Hawaiian-Emperor chain. relationship can be used to measure the rate of movement (velocity) of the Pacific Plate; 3) the trends of the Hawaiian-Emperor chain should define the direction of movement of the Pacific Plate. Procedure: 1. Plot the data in Table 1 (next page) on the graph paper provided. The x-axis (horizontal axis) will be age in millions of years and the y-axis (vertical axis) will be distance from Kilauea in kilometers. Choose a scale for the x and y axis so that the data fills most of the page. 2. Label the axes (x = age in millions of years; y = distance from Kilauea in kilometers). 3. Label the points for Kilauea, Brooks Bank, Gardner Pinnacles, and Suiko with their names. 4. Using a straight edge, draw a best fit straight line for the data between Kilauea and Brooks Bank. Remember, a best fit line means that not all the points will be on the line. Place your line so that an approximately equal number of points fall on either side of the line. A straight piece of (uncooked) spaghetti works well for adjusting the fit of your line BEFORE you draw it. 5. Draw a second best fit line for the data between Gardner Pinnacles and Suiko. 6. Use your graph to answer the following questions on the answer sheet. If you prefer, you can graph the data using Microsoft Excel or a similar program; the data is provided as Excel and tab-delimited text files in the assignment materials in Blackboard. Step-by step directions for plotting the data in Excel are provided as separate documents in the assignment materials (Excel 2003 and earlier for Windows XP, or Excel 2007 for Windows 7/Vista). GEO 101 The Solid Earth Page 4 of 8
Table 1: Age and distance from Kilauea (along the chain) of selected volcanoes from the Hawaiian- Emperor Chain, obtained from Volcanism in Hawaii (Volume 1, 1987). Volcano Name Age in millions of years (my) Distance from Kilauea (km) Kilauea 0 0 Kohala 0.43 100 West Maui 1.3 221 West Molokai 1.9 280 Oahu 3.7 374 Kauai 5.1 519 Nihoa 7.2 780 Unnamed 9.2 913 Necker 10.3 1058 La Perouse Pinnacle 12 1209 Brooks Bank 13 1256 Gardner Pinnacles 12.3 1435 Laysan 19.9 1818 Pearl and Hermes Reef 20.6 2281 Midway 27.7 2432 Abbott 38.7 3280 Daikakuji 42.2 3493 Yuryaku 43.4 3520 Koko 48.1 3758 Jingu 55.4 4175 Nintoku 56.2 4452 Suiko 64.7 4860 GEO 101 The Solid Earth Page 5 of 8
Graph Paper for Exercise 2 Hot Spots GEO 101 The Solid Earth Page 6 of 8
Answer the following questions on the answer sheet. 7. What does this graph indicate about the general relationship between age and distance from Kilauea? In other words, how does age change with distance from the hot spot? 8. Describe (in words) how the two lines differ in terms of slope. What does this difference in slope tell you about the motion of the Pacific Plate? 9. Using the data in Table 1, calculate the velocity of the Pacific Plate in kilometers per million years (km/my) for each line segment. Remember, velocity is distance divided by time (in this case, age expressed in millions of years). a. The first is from Kilauea to Brooks Bank. To do this, determine the distance between Kilauea and Brooks Bank. Then divide by the difference in age between Kilauea and Brooks Bank. b. The second is from Gardner Pinnacles to Suiko. Determine the distance between Gardner Pinnacles and Suiko. Then, divide by the difference in age between Gardner and Suiko. c. Convert the plate velocity for each segment from km/my to centimeters per year (cm/yr). To do this multiply your results in 3a and 3b by 0.1. d. Compare the plate velocity between Kilauea and Brooks Bank to the plate velocity between Gardner and Suiko. Are the velocities the same? What does this mean? 10. In map view, the Hawaiian-Emperor chain bends at Daikakuji seamount where the Hawaiian and Emperor chains meet. a. What does this bend represent? b. What direction was the plate moving while the Emperor Seamounts formed? c. What direction is the plate moving after the bend (and currently), while the Hawaiian Ridge was forming? d. How long ago did the bend, or change in the direction of motion of the Pacific Plate, occur? Hint: Find Daikakuji in the table. e. Compare the timing of the bend with the timing of the velocity change. Which happened first, the change in velocity or the change in plate motion? GEO 101 The Solid Earth Page 7 of 8
Exercise 3 - The Age Distribution of Oceanic Crust 11. Near what major geologic feature of the Earth s surface is older oceanic crust always located? 12. What is the age of the oldest oceanic crust found on Earth? 13. How does this age compare with the oldest continental rocks? 14. Assuming that the Earth is 4.6 billion years old, what percentage of Earth history is recorded by the rocks of the ocean basins? Hint: Determine the age of the oldest rock in the ocean basins by referring to the second figure in section 3.4.5 of the lecture. Divide the age of the oldest oceanic crust by the age of the earth to determine what fraction of earth's history is recorded by the rocks of the seafloor. Multiply the result by 100 to express your answer as a percent. 15. Why are there no old rocks found on the ocean floor? GEO 101 The Solid Earth Page 8 of 8