Kami Export - annotated-Plate%20Tectoincs%20Lab (1)

L.A. Mission College Seemayer, Jessica This lab is modified from Interpreting Earth History: A Manual of Historical Geology (Exercise 11) by Ritter and Peterson 1 Plate Tectonics Lab Name:________________________________________________________________ Score________ For this lab activity you will look at the different types of plate tectonics boundaries and you will use different techniques to determine how fast the plates are moving. Tectonic Plates The Theory of Plate Tectonics is relatively new (geologically speaking). The core concept of the idea was first proposed by Alfred Wegner in the early 1900 ’ s he called this the “ Continental Drift Hypothesis ” . He believed that the continents were moving independently from one another and “ drifting ” around the surface of our planet. This idea was not that far from the theory that would later develop. However, Wegner did not have the technology to determine what was causing the continents to move he just knew that the evidence suggested that they were not in their original locations. Through advancements in science and development of technology we were able to determine that in fact all the land masses, even the land beneath the oceans were moving and shifting constantly. This idea was tested over and over and eventually became the Theory of Plate Tectonics, which states that the surface of our planet is made up of several large plates and hundreds of smaller plates, they are constantly shifted by the convection cells of molten material in the asthenosphere . Seafloor Spreading The first step of final getting to the Theory of Plate Tectonics was the discovery of seafloor spreading . Advancements in sonar technology allowed oceanographers to discover that some portions of the ocean floor are moving away from one another. This is was will be determined to be a divergent plate boundary. As new magma comes from deep in the asthenosphere to fill in the gap, the magnetic signature of the earth is recorded in the magnetic minerals in the rocks. While recording the data scientists discovered that the magnetic signatures are symmetrical and mirror images of one another along the divergent plate boundary that runs along the length of the Atlantic Ocean, this was named the mid-Atlantic ridge (a ridge is another name for mountain chain). Types of Plate Boundaries As you have learned through your readings there are three types of plate boundaries (or margins) They include the divergent boundaries where two plates are moving in opposite directions from one another. Convergent boundaries where the two plates are moving towards one another, and transform boundaries where plates are sliding past one another. You can further subdivide these three types based on the types of crust involved in either Oceanic Crust or Continental Crust . If you could not infer from the names are found either at the bottom of the ocean or on the continent, respectively.

L.A. Mission College Seemayer, Jessica This lab is modified from Interpreting Earth History: A Manual of Historical Geology (Exercise 11) by Ritter and Peterson 2 Part 1: Seafloor Spreading and the Magnetic Timescale Overview: This part of the lab you will look at a side view of a section of the mid-Atlantic ridge that shows the topography and patterns of paleomagnetic data. You will determine the rate at which these two plates are moving based on the magnetic data. Procedure: 1. You will need to use figures 11.2, 11.3, and 11.4 on the following pages. 2. The black and white bands on figure 11.3 represent the reversal of polarity we see every 5,000 years or so on our planet. You will see that the point in the middle of the profile is labeled as the rift valley. Answer question 1. 3. Look at the polarity reversals on figure 11.3 and compare them to the time of each reversal event on figure 11.4 to determine how long each event took. 4. Use the scale on figure 11.3 to determine the rate (in cm/year) 5. You should be able to determine exactly how long it took for one of the plates to move in the opposite direction of the other. Answer question 2 6. Enter the rate you determined for questions 2 on the map on figure 11.2 in the box labeled “b” . 7. Look at the red line connecting South America and Africa and the scale on the map to determine the distance in figure 11.2 8. Use the rate calculated in question 2 and determine the present separation of these two continents to answer question 3. 9. Use the ages of the rocks in figure 11.3 to determine the estimated ages of the rocks at points “A”&”B”. 10. Given the calculated rate of spreading in question 2. Answer question 4 Questions: 1. Why are the belts of polarity contrast situated symmetrically on either side of the rift zone on the mid-Atlantic ridge? 2. What is the calculated rate in cm/year at which the seafloor spreading is occurring in the Atlantic Ocean based on the data provided in Figures 11.3 and 11.4?

L.A. Mission College Seemayer, Jessica This lab is modified from Interpreting Earth History: A Manual of Historical Geology (Exercise 11) by Ritter and Peterson 4

L.A. Mission College Seemayer, Jessica This lab is modified from Interpreting Earth History: A Manual of Historical Geology (Exercise 11) by Ritter and Peterson 5 Part 2: Hot Spot and Plate Motion Overview: This part of the lab you will look at the plate tectonic movement directly below a hot spot and how this can help determine the rate if the rate and direction of movement. Procedure: 1. You will need to use figure 11.6 and table 11.3 on the following pages. 2. Draw a line from the white dot adjacent to the recent basalt flows on the island of Hawaii and the white dot on the north side or Kauai. 3. Using a protractor and the North arrow on the map answer question 1. 4. Use figure 11.6 and fill in the data pertaining to distance and age differences between the sample stations located on each island. Fill this data in on table 11.3. 5. Calculate the rate of the plate motion that occurred between the extrusion of lavas at each sample area on the table 11.3. 6. Calculate the average rate of plate motion between Hawaii and Kauai, fill this data in on table 11.3. 7. Answer questions 2 and 3. 8. Enter the average rate of motion into the blue box labeled “ a ” on figure 11.2 on the previous page. Questions: 1. Based on the map what is the average direction of plate movement of the Pacific Plate over the past 5.1 million years? 2. Has the rate of plate motions been constant for the past 5.1 Million years? 3. What is the range of values of plate motion?