Geol 106 life in the age of dinosaurs lab 4: Density, Isostasy, and Plate Tectonics
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- Upon completion of this lab, students will be able to
- 1 mL = 1 cm 3
- Basalt Granite Peridotite
- In your own words , explain why ocean basins
- Block 1 Block 2 Block 3 Plate
- Elevation Depth Thickness Figure 1
- Start Step 1 Step 2 Step 3
- In your own words , explain why regions of high elevation
| GEOL 106 – LIFE IN THE AGE OF DINOSAURS
Lab 4: Density, Isostasy, and Plate Tectonics Introduction: Your aware that there is a difference between the weight of a rock and the weight of an equal-sized chunk of bone or wood. This is because of density, or mass/volume. Rock is much more dense than either wood or bone. But you may not realize that rock densities are not all the same. In fact, relatively small differences in the density of common rock types found in the continental crust, ocean crust, and mantle determine the depth of the ocean basins, the height of mountain ranges, and prevent the continental crust from being recycled. Today we will explore the density differences between common Earth materials and simulate the effects of erosion on the topography of a mountain range in order to grasp the concept of isostasy. Simply put, isostasy is similar to floating: the crust and upper mantle are floating above the slushy asthenosphere. Loading of the crust by folding or deposition of sediment leads to isostatic depression, or downwarping, while removal of sediment or rock causes rebound or upwarping. Learning Goals: To appreciate the variability and importance of density in Earth materials To understand the relationships between density, isostasy, and topography To gain a working understanding of plate tectonics Upon completion of this lab, students will be able to: Calculate the density of a rock (or piece of wood) by measuring mass and volume Describe the relative densities of continental crust, oceanic crust, and the mantle Explain why continental crust cannot be returned to the mantle Predict which of 2 wood blocks will float higher above the surface in a tank of water Describe the effects of erosion on topography Explain why mountains have roots Construct and interpret x/y plots of data collected by the class Part I: Density of Different Rock Types Although the earth has many different kinds of rocks, some are more common than others. These are considered the main constituents of the crust. In order to get a feel for the range of densities in the rocks that make up the crust and upper mantle, weigh and measure 1 sample each of granite, basalt, and peridotite. Fill in the table below and write your data on the board so we can gather class measurements and find averages. Use the electronic balance to weigh the samples, and use water displacement to measure the volume. (Remember that 1 mL = 1 cm3). To get density, then, all you have to do is divide the sample mass by its volume.
* your choices are continental crust, oceanic crust, and mantle In your own words, explain why ocean basins (which have a floor of ocean crust) are areas of low elevation compared to the continents. In other words, why does basaltic ocean crust for low spots on the surface of the Earth? __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ Part II: Mountain Building and Erosion It is a somewhat puzzling fact that we observe piles of sediment, up to several kilometers deep, that was entirely deposited in a shallow ocean environment. In this exercise we simulate a coastal mountain range, such as the Appalachians, and associated coastal margin sedimentation. We will simulate this system using wooden blocks to represent the crust and water to represent the higher-density mantle on which the crust floats. Step 1: Select three thick wooden blocks (be sure to get 3 different types of wood) and approximately 10 thinner wooden plates and determine their densities. The density of the blocks is variable, but the density of all plates should be the same. Therefore you only need to determine the density of one plate. To do this, weigh the block or plate and note the number written on it. Then measure the length, width, and height of the block or plate and record these measurements in the chart below. Calculate the volume (length x width x height) in cm3. Divide the mass by the volume (as in part 1) to compute the density. Step 2: How high does each block float? Stake out on of the clear plastic basins that is about three-quarters full of water. Float each block and the plate, recording the height of the wood above and below the water line.
Step 3: Now calculate a couple of ratios and add them to your chart (above). First, divide the density of the wood by the density of water (the density of water is 1g/cm3). Then divide the height below water by the height above water for each block or plate. Express your values to 2 decimal places! Rounding will not do. Step 4: Graph your results on a piece of graph paper, placing values from the row labeled X on the x-axis (horizontal axis) and values from the row labeled Y on the y-axis (vertical axis). Incorporate 3 additional data points from other teams who used different types of wooden blocks. Based on your graph, describe the relationship between the density ratios and the height ratios. __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ Suppose that the wooden blocks were floating in a tub of honey instead of water. What would you expect to see, and why? __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ Step 5: Return to your basin or water. Choose two of your thick blocks and float them next to each other. This is the crust! Now create a mountain range by piling the plates on top of one of the blocks to simulate thickened continental crust. This might be a bit tricky, but try to pile them as high as you can (see Figure 1 below). Step 6: Measure the thickness of the two piles. Then measure the elevation of the mountains (pile of plates) and the plains (single block) and the depth of the water beneath the two blocks. Record your results below. Step 7: Simulate erosion by moving plates from the mountain range onto the plains. After each step measure the thickness of the piles, the elevation of the mountains and the plains, and the depth of water beneath each. Continue until the mountains and plains are about the same height. Erosion now stops, because there is no relief left! Step 8: Graph the elevation of the mountains and the plains after each erosion step. To do this, put time (erosion step) on the x-axis and height on the y-axis. Now add the total thickness of the mountain crust to your graph. You will end up with 3 lines, one for the elevation of the mountains, one for the elevation of the plains, and one for the total thickness of the mountain crust. 
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Consider the two graphs that you have made, one of density vs. height ratios and one of elevation of the mountains, the plains, and the total thickness of the mountain crust over time. In your own words, explain why regions of high elevation (mountains!) have roots (thick crust that extends far into the mantle below). __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ Directory: files -> uafgov files -> Integer programming and game theory files -> 4 Integer Programming files -> Bpa vehicle Window Repair Scenario #1 task: Procure vehicle window relacement. Objective files -> Pop Warner History files -> North Carolina Inclusion Initiative Mapping Where Children with ieps are Being Served Purpose files -> Fall 2013 Spring 2014 Program Data: Standard 1 Exhibit 4d files -> Hanban – asia society confucius classrooms network 2010 request for proposal files -> Northern England’s set-jetting locations Download 67.36 Kb. Share with your friends:
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