Laboratory #1: Plate Tectonics

Transcription

1 Name: Lab day: Tuesday Wednesday Thursday ENVG /SC L Planet Earth Laboratory Laboratory #1: Plate Tectonics Readings: Tools needed for this lab: ruler and a pencil!!! OBJECTIVE: Understanding plate tectonic features, interpreting seismological and bathymetric maps. This lab builds upon Chapters 3 and 4 in your textbook and is designed to highlight the mechanisms of plate tectonics and hotspots. You have two exercises to complete that are modified from your lab manual. Refer to the relevant maps in your lab manual as they are in color. 96 points total. Question 1: The plate boundary in the SW Pacific Ocean near the Fiji, Samoa, and Tonga Islands is highlighted in this exercise (pages 3 and 4). Shown on the map are bathymetry (water depth or depth to seafloor, indicated by the contour lines), active volcanoes, and epicenters of earthquakes of varying focal depths. (a) What type of plate boundary is this? (2 pts) (b) Given its location, what type of crust (oceanic or continental) do you think lies to the east? (2 pts) (c) What type of crust (oceanic or continental) do you think lies to the west? (2 pts) (d) The top part of the Figure on page 4 gives a topographic profile of the seafloor along the line A-A in the page 3 figure. The topographic profile has a vertical scale of 1 cm to 3,125 m. What tectonic feature does the low part (~4,000 m water depth) of the profile represent ~20-35 mm from A on page 4? Label it on the topographic profile. (4 pts) 1

2 (e) The bottom part of the Figure on page 4 is also a cross section along line A-A, but with no vertical exaggeration. Plot generalized earthquake foci on that cross section by placing dots/circles at the appropriate depths below areas in which earthquakes of various focal groups occur (different color codes in the key to the map on page 3). Assume the following depths: red = km; Orange = ; Brown = ; Green = km; Light Blue = km; Pink = km; Dark blue = km. NOTE: The earthquake zones overlap with each other. Use foci that are on the cross section line as well as those up to 1 cm above it as indicated by the box on the map. Use a sheet of paper to gather the data from the map by lining it up along the cross section and marking A and A. Plot one set of foci at a time and plot earthquakes in each zone so that the one furthest to the left is the lowest and the one furthest to the right is the highest (i.e., each zone dips to the left, so start with the point furthest to the right at the shallowest depth of each depth range and smoothly add the remainder at progressively lower depths as you move to the left until the point furthest to the left is at the deepest point of each depth range). (8 pts) Be careful! Distinguishing the orange from the red dots on the map may be difficult! Why are the earthquakes where they are and what feature do they define? (4 pts for the first answer, 2 pts for the second = 6 pts total) (f) Compare the 2 profiles in the Figure on page 4. What topographic/tectonic feature is present where the zone of earthquakes intersects the surface [i.e., at the low part of the profile (~9,500 m water depth) ~60-70 mm from A in the map on page 3]? (2 pts) (g) Label the trench, forearc, and volcanic arc on the topographic profile. (6 pts) (h) What is the width of the arc-trench gap (assume the horizontal scale is 1 cm to 100 km)? (4 pts) (i) What controls the width of the arc-trench gap? (2 pts) 2

3 3

4 4

5 Question 2: The map on page 6 is of the Hawaiian Islands and other islands and seamounts (submarine volcanoes) that form the Hawaiian-Emperor chain. All the features along the chain have a volcanic origin, and all are younger than the surrounding oceanic crust on which they sit. In 1963, J. Tuzo Wilson proposed that all the volcanoes in the Hawaiian-Emperor chain formed above the same hotspot or thermal plume. This idea was later extended to include the Emperor chain. If this hypothesis is correct, then 1) volcanoes should be older farther away from the hotspot, and 2) the distance-age relation can be used to measure the rate of plate movement, assuming the hotspot is fixed. The Table on page 7 lists the ages of these volcanoes and their distance from Kilauea, a currently active volcano on the island of Hawaii. (a) Plot the data in the Table 17.1 on graph provided (Page 7), and label each of the points with the name of the volcano. (30 pts) (b) What does the graph indicate about the general relation between age and distance from Kilauea (located at 0 km)? (4 pts) (c) Draw 2 best-fit straight-line segments, the first between Kilauea and Laysan and the second between Laysan and Suiko. How do they differ? (6 pts) (d) Calculate the rate of plate movement in centimeters per year for each of the straight line segments (divide the distance traveled by the time interval over which travel took place. Remember to convert to proper units). Show how you arrived at your answer. (6 pts) (e) What do your answers in (d) tell you? (6 pts) (f) Give two explanations for the bend in the Hawaiian-Emperor chain. (3 pts each = 6 pts) 5

6 6

7 7