apple Concept - we can use earthquake patterns to define/locate plate boundaries

Transcription

1 Geol 108 Lab 1 Plate Tectonics Week of Sept. 3-7, 2012 PART I. Introduction to Plate Tectonics World Seismic Map apple Concept - we can use earthquake patterns to define/locate plate boundaries 1. a. Draw (in colored pencil) the major plates of the Earth (as instructed by your TA) on the World Seismic Map (attached). b. Make a note of the types of plate boundaries as you draw (convergent, divergent, transform). PART II. Topographic features on the land and ocean floor use your paper map and the plastic relief maps for this section apple Concept - physiographic features are related to plate interaction A. Divergent plates move apart 1. Find a divergent plate boundary on the plastic relief map and give the location. 2. What obvious feature do you see on the plastic relief map at the divergent plate boundary? describe the general shape. 3. Label the Mid-Atlantic Ridge and the East Pacific Rise on your paper map. B. Convergent plates come together 1. Locate the Tibetan plateau (notice the very thick crust), and label on your paper map. Which two plates come together here? What type of convergent plate boundary is this (oceanic to continental, oceanic to oceanic, or continental-to-continental)? 1 of 6

2 2. Locate the Pacific Plate on the plastic relief map. What ocean-floor feature do you notice (plastic relief map) where the Pacific meets the Aleutian Islands (near Alaska)? (i.e., what obvious ocean floor feature indicates subduction?) What type of convergent plate boundary is this? C. Overview of the relief map 1. What do you notice, in terms of elevation, about the ocean floor compared to the continents? Now that you have your paper map complete: Which plate is almost totally surrounded by divergent (spreading) plate boundaries? Which plate is totally surrounded by convergent boundaries? Name the plates that are bounded in part by the Mid-Atlantic Ridge. 2 of 6

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4 PART III: Determining Directions and Velocities of Plate motions using hot spots Hot Spots: Linear chains of volcanoes are locally developed within interior portions of lithospheric plates. Because these do not occur along plate boundaries, they cannot be related to plate divergence or convergence. Most geologists agree that these features develop from magmas which reach the earth's surface from upwellings deep within the mantle. These upwellings are termed mantle plumes or hot spots. Assume, for this exercise, that the hot spot is relatively stationary. If a stationary hot spot is overridden by a lithospheric plate, a linear chain of volcanic features develops. The volcanoes will systematically increase in age away from the hot spot and their trend and variation in age may be used to help determine both the directions and the rates of lithospheric plate movement. Use Figure 1 on the next page for the following questions. 1. What is the rate in centimeters per year (cm/yr) and direction of plate motion in the Hawaiian region from 4.7 to 1.6 million years ago? 2. What is the rate in centimeters per year (cm/yr) and direction of plate motion in the Hawaiian region from 1.6 million years to the present time? 3. How does the rate & direction of Pacific Plate movement during the past 1.6 million years differ from the older rate & direction ( m.y.) of plate motion? 4. Based on the distribution of the Hawaiian Islands and Emperor Seamount chains, suggest how the direction of the Pacific Plate movement has generally changed over the past 60 million years. 4 of 6

5 Fig. 1. Map of the northern Pacific Ocean and the Hawaiian Islands chain. Notable geologic hazards from the 1990 s are indicated. 5 of 6

6 PART IV. Using rock units to measure displacement along the San Andreas fault The Pinnacles Volcanic Formation rock unit, located north of Paso Robles in the central Coast Ranges, is an excellent example of tectonic plate movement. The Pinnacles Rocks are believed to be part of the Neenach Volcano that erupted 23 million years ago near present-day Lancaster, California. 1. a. Use Figure 2. If Pinnacles Rocks, and Neenach Volcanic Formation were once one unit, what can you conclude about the total displacement along the San Andreas? (Note the scale in kilometers at bottom of figure) b. Calculate the rate in cm per year. Fig. 2. Location of Pinnacles and Neenach Formations. Also shown is the La Honda Basin an offset segment of the San Joaquin Basin. From: W.P. Irwin, Geology and Plate- Tectonic Development, in, The San Andreas Fault System, USGS Prof. Paper 1515, of 6