Tectonic Lab Key S21
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Palomar College *
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Geology
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Feb 20, 2024
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PLATE TECTONICS AND SEA FLOOR TOPOGRAPHY: INVESTIGATION AND QUESTIONS WORKSHEET 20§ Open the file containing the “Global Tectonic and Volcanic Activity Map”. This map will be used throughout the entire lab. Note that you can zoom in on the map to highlight and read information specific to a particular region. Be sure to read the map legend. Reference Page #1 (Tectonic plate boundaries and their related processes and features) will also be used throughout the lab activity. Note: This is a worksheet only; your final answers should be submitted via the Canvas Quiz link. 1. Use the “Global Tectonic and Volcanic Activity Map” as a reference and locate the Mid- Atlantic Ridge. What tectonic process occurs in this region? (select one): rifting subduction / collision / transform faulting Visualize traveling by boat across the Atlantic Ocean from New York City, US to Casablanca, Morocco (northwest Africa). If you are unsure of the locations of these cities, please look them up on a world map. The figure below is a cross-section (profile view) of the sea floor drawn across the North Atlantic along the path traveled from New York City to Casablanca. The location of the mid-ocean ridge (MOR) is indicated for you. N?York City Casahlegc‘al o ] i 1! 1 | ! (I O B I { North American Plate | _African Plate MOR g8 g ] 2‘ 180 m.y. 180 m.y. 8 , i -0 2000 4000 6000 Distance, km Cross-section of North Atlantic Ocean sea floor from New York City, US to Casablanca, Morocco. a. On the figure provided above, complete the following: O Draw arrows to show the appropriate direction of plate motions at the MOR. QO In the boxes provided, write the names of the plates involved. QO Use Reference Page #2 (Age map of the ocean floor in millions of years before present) to fill in the boxes with the age of the ocean floor at the base of the continental slope. Note: the ages should match on both sides. b. Using Reference Page #2, visualize how the age of the ocean floor changes as you travel from New York City to Casablanca. Complete the following chart. Use simple “older” vs “younger” descriptions. Sea Floor Edge of North America Mid-Ocean Ridge Sea Floor Edge of Northern Africa Older Younger Older
Given that the width of the ocean floor between New York City and Casablanca is approximately 4500 kilometers, calculate the rate at which the Atlantic Ocean grew in units of centimeters per year. Use the formula: Distance = Rate x Time. (ZXHINTS: For the variable “Time” use the age that you determined in question 2a above but remember this value is in millions of years! Also, remember that units must match when doing calculations so kilometers must be converted to centimeters in order to determine a rate with the units of cm per year; there are 100,000 cm in 1 km. Use the formula: Distance = Rate x Time; you are calculating “Rate.” Distance is 4500 km = 450,000,000 cm; Since 1 km = 1000 m and 1 m =100 cm Age = 180 million years or 180,000,000 years Thus Rate is 450,000,000 cm / 180,000,000 years Which simplifies to 45 cm /18 years or 2.5 em/yr Answer=_ 2.5 cm/yr Describe how your calculated value above compares with the value listed on the “Global Tectonic and Vol¢anic Activity Map” for that area. The calculated answer is very close (within 1 em/yr) to the rates listed on the map in the northern hemisphere, but significantly lower than rates listed on the map in the southern hemisphere. 3. Use the "Global Tectonic and Volcanic Activity Map" map as a reference. a. b. 5000 Elevation, m C. Locate the Peru-Chile Trench. Based on Figure 4 in the Lab_Introduction, which process is occurring in this region? (select one): Figure 4a / 4@ Figure 4c The plate tectonic process here is called (select one): rifting / sea floor spreading W collision / transform faulting Wt Andes Mnts. S. American Plate J - T ¥ Faa— 1200 Distance, km Cross-section for western margin of South America near latitude 20°S. On the figure provided above, complete the following: O Label the Andes Mountains and the Peru-Chile Trench in the boxes provided. O Label the two major plates that are involved. O Draw arrows to show the appropriate direction of plate motions at this boundary type.
Based on the figure for Question 3c, the depth of the trench off the coast of South America is approximately 7000 meters. Given that 1 meter equals 3.28 feet, convert the depth of the trench into feet. Show your work. 7000 m x 3.28 m/ft = 22,960 ft 4. Use "Global Tectonic and Volcanic Activity Map" map as a reference. a. Locate the Aleutian Trench and Aleutian Islands. Based on Figure 4 in the Lab Introduction, which tectonic process is occurring in this region? (select one): l; Figure 4b / Figure 4c The plate tectonic process that occurs here is called (select one): rifting / sea floor spreading / collision / transform faulting The Aleutian Trench and Aleutian Islands are the result of the same tectonic process as the Peru-Chile Trench and Andes Mountains, but due to the type of crust involved the tectonic setting is different in each location. Select the correct tectonic setting for each location. Aleutian Trench / ocean-continent | continent-continent Peru-Chile Trench ocean-ocean continent-continent 5. Use "The Global Tectonic and Volcanic Activity Map" map as a reference. a. Locate the Himalayan Mountains and the Mariana Trench. Both of these features are a result the same general tectonic process (select one): divergence ' transform faulting List the two plates involved in the tectonic processes in each region: » Himalayan Mountains: __ Indian-Australian _and ___ Eurasian __ plates. » Mariana Trench: __ Philippine and Pacific plates. The Himalayan Mountains are the highest continental mountain range in the world. The Mariana Trench is the deepest part of the world’s ocean basin. Explain how the same general tectonic process can produce such distinctively different landforms. (7. HINT: consider the types of crust involved.) The crust that is tectonically interacting at the Himalayas is thicker and less dense than the thinner, more dense crust involved at the Mariana Trench.
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10 6. The figure below shows tectonic features of the U.S. Pacific Northwest region. You will be uploading this completed page. Profile View A Juan de Fuca Ridge Mount St. Helens \E; /Mount Adams —— ] — ’ North Pacific Juan de Fuca American Plate Plate Plate Map View Cascade Range A A& _ Mount St. Helens ‘f,: Mount Adams P\?&&, Nor{: Am riccn Plite . 1 - Segment 1 Segment 2 Tectonic map of the Pacific Northwest U.S. region. The upper portion of the figure shows a side or profile view of the area. The lower portion of the figure is a map view of the area along line A—B. Modified from the USGS. a. Complete the following directly onto the figure above. 206HINT: To assist in your identification, use Reference Page 3 — Pacific Northwest Tectonic Features. On the profile view, shade all three tectonic plates a different color. On_the map view, label the names of each tectonic plate and shade each plate with the same color you used for the profile view. Color the three sections of the spreading zone red. Color the subduction zone blue. For each plate, draw several arrows to indicate directions of plate motion. ooo 0d
11 b. The Blanco Fracture Zone is a historic name that predates the theory of plate tectonics. Use Reference Page #3 — Pacific Northwest Tectonic Features to help you locate this feature. QO On the tectonic map on the previous page, use a green color to shade only that portion of the Blanco Fracture Zone that is a transform fault boundary. c. According to Reference Page #4 — Pacific Northwest Volcanic and Earthquake Activity, what kinds of tectonic activity occur at the following locations? (ZOEHINT: select only those activities that apply.) Juan de Fuca Ridge Cearthquakes Yolcanic activind Gorda Ridge Cearthquakes Xolcanic activi Blanco Fracture Zone C earthquakes) volcanic activity d. The Mendocino Fracture Zone is similar to the Blanco Fracture Zone in that its name predates plate tectonics. Use Reference Page #3 to locate the Mendocino Fracture zone. Only a portion of the Mendocino Fracture Zone region is tectonically active as evidenced by the information provided in Reference Page #4. 0O Two segments are indicated along the Mendocino Fracture Zone region. Select the appropriate choice for each of the two segments as either a transform fault or a fracture zone. (;LSHINT: Review the lab introduction to refresh your memory about the distinction between transform faults and fracture zones.) Segment 1 is a transform fault CEacture zoned Segment 2 is a Caransform fauld! fracture zone O On the tectonic map on the previous page, use a green color to shade only that portion of the Mendocino Fracture Zone that is a transform fault boundary. e. Based upon your analysis of this region, along which segment of the “Mendocino Fracture Zone” is earthquake activity most common? (select one): Segment 1 Reference Page #5 shows the historical occurrence of tsunamis worldwide. Use this information along with "The Global Tectonic and Volcanic Activity Map" as a reference to answer the following questions. a. Based on the distribution of tsunami-generating earthquakes, which tectonic process is responsible for producing most tsunami events? (select one): rifting / sea floor spreading collision / transform faulting b. Which sea floor feature is associated with the generation of tsunamis? (select one): rift / ridge fracture zone
12 7. c¢. Although most tsunamis are generated in the Pacific, several tsunamis have occurred in the Atlantic. Using "The Global Tectonic and Volcanic Activity Map" as a reference, locate the two potential sources of tsunamis in the Atlantic. (206 HINT: Use your answer from the previous question to assist in locating these sources.) Which two geographic locations are most likely to be potential sources of tsunami activity? (select two) Q Where the North American Plate meets the Eurasian Plate @ Where the North American Plate meets the Caribbean Plate _—> 0O Where the African Plate meets the South American Plate @ Where the South American Plate meets the Sandwich Plate = O Where the Eurasian Plate meets the Azores Fault Zone d. Locate the Mediterranean Sea. Using Reference Page #5, how many tsunami events resulting in “serious destruction” have occurred in that region? 3 8. Use "The Global Tectonic and Volcanic Activity Map" as a reference. Locate the Red Sea. a. Based on the map, the plate tectonic process here is called (select one): subduction / collision / transform faulting b. Name the two plates involved in this process: 1) Arabian Plate 2) African Plate ¢. Which of the following locations has a plate boundary process most similar to the Red Sea? (select one): Mediterranean Sea ulf of CaliforniqY Persian Gulf / Gulf of Mexico 9. Refer to Reference Page #6 - Hotspot Activity & the Hawaiian Islands a. Look at the distribution of hotspots shown in Reference Page #6A. What do you observe in the distribution? Are hotspots unique to either continental or oceanic settings? (select one) unique to continental / unique to oceanic Lnot unique to either setting b. Hotspots are not by definition associated with a specific type of plate boundary. However, if a hotspot is found near a plate boundary, it is typically which kind of boundary (select one) convergent | transform fault c. With this answer in mind, look carefully at Reference Page #6A. Notice that the eastern side of the African continent currently has quite a large number of active hotspots. What general tectonic process appears to be happening here? (select one) continental riftingy sea floor spreading / subduction / continental collision As a result, what do you predict for the tectonic future of this region? (Z0§HINT: Figure 3 in the Lab Introduction also provides relevant information.) Eastern Africa will begin to split apart from the main African continent and become flooded as a new sea forms.
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10. 11. 13 Refer to Reference Page #6B showing the bathymetry of the Pacific basin and the trend of the Hawaiian-Emperor seamount chain. The motion of the Pacific Plate over the Hawaiian hotspot has produced the entire volcanic chain. As a result of this motion, the Emperor Seamounts and Hawaiian Islands to the northwest. (select one) : get younger Refer to Reference Page #6C, which shows the detail of the Hawaiian Islands including the ages of each of the islands. These ages reflect the time period during which that portion of the Pacific Plate was sitting over the hotspot. The “Big Island” of Hawaii is currently volcanically active thus some of the rocks have nearly a zero age in millions of years. To the northwest by 280 kilometers is the island of Molokai. a. Based on the information in Reference Page #6C, Molokai was last active 1.8 million years ago (Ma) b. If we know the time between the volcanic features (their age difference) and we know the distance between the volcanic features (280 kilometers), then the rate at which the Pacific Plate has moved can be determined. Using the equation Distance = Rate x Time, calculate the rate of plate motion. Show your work and remember that rate is given in units of centimeters per year. Refer back to Question 2¢ for additional hints. Distance is 280 km or 28,000,000 cm Age is 1.8 million years or 1,800,000 years Thus Rate is 28,000,000 cm / 1,800,000 cm which equals 280 cm / 18 yrs or 15.5 em/yr 15.5 cm/yr ¢. Using your data from Question 11b and 2c¢, what conclusion about rates of tectonic processes can you draw from your calculations? Tectonic processes (i.e. plate motion) eccur at different rates around the world.