Download 1 IDS 102 Plate Tectonics Questions Part I: Observations

IDS 102
Plate Tectonics Questions
Part I: Observations- Four maps of world are positioned around the room. Answer the
questions associated with each map and record your general observations about the maps.
World topography- this map portrays the elevation of the Earth’s surface by color. See the scale
along the side of the map for the elevations. The elevations are in meters. Recall that a meter is
slightly longer than 3 feet, so if you multiply the values given by 3 you will have a rough
estimate of the height of the land or depth of the ocean in feet.
1. Notice that there are two predominate colors on this map. What are the elevations represented
by these two primary colors on this map?
2. Explain why there are these two predominate elevations. (Hint: think about isostasy and the
type of materials we used to demonstrate buoyancy).
3. Does the continental crust end at the shoreline? What is your evidence?
4. Look carefully at the elevations in the ocean basins. Are there mountains in the ocean basin? If
so, describe those mountains—are they part of a chain of mountains or are they randomly
distributed on the ocean floor?
5. Where do you find the deep purple colors on the map? Explain where this color is found and
the shape of the region illustrated by this color.
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Earthquake (Seismology) Map:
1. Are the earthquake epicenters randomly distributed on this map? If not, describe the patterns
of the earthquake epicenters.
2. The colors of the epicenters indicate the depth of the earthquake focus. Are there more
shallow foci or deep foci?
3. Describe where you find the shallow earthquake foci. Describe where you find moderate to
deep earthquake foci.
4. What do you notice about the patterns of colors in the places that have moderate to deep
earthquake foci—in other words, is a there specific pattern to the colors relative to the ocean and
land area when there are moderate to deep foci?
5. Are the shallow foci more or less random on the continents or in the ocean basins?
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Volcanoes:
1. What do you notice about the distribution of volcanic eruptions of the Earth’s surface? Is the
distribution random, in specific patterns, or both? If you picked specific patterns or both,
describe the patterns and where one finds the patterns and random distributions.
2. When volcanoes are found in a line, are the lines on land or in the ocean? Are the lines of
volcanoes running through the middle of the continents or along the edges?
3. Many people have heard the expression of the Pacific “Ring of Fire”. Where else do we find
lines or chains of volcanoes?
4. Would Yellowstone in NW Wyoming be a part of the chain of volcanoes?
Ocean Floor Ages (Geochronology):
1. Describe the age of the rocks that compose the crust west of South America. Where do we find
the youngest rocks and where do we find the oldest rocks? Describe the patterns of the ages.
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2. Where do we find the youngest rocks on the ocean floor?
3. What is the age of the oldest rocks found on the ocean floor? Where are those rocks found on
the map?
4. What do you notice about the width (distance across) of the red portion of the map? Where do
you tend to find the widest red color pattern? Where do you find a narrow red color width?
Part II: Plate boundary map
Plate boundaries are divergent, oceanic-continental convergent, oceanic-oceanic convergent,
continental-continental convergent, and transform. From our discussions of the plate boundary
characteristics in class and your observations in Part I of this handout, label the boundaries of the
plates shown on the plate boundaries handout distributed.
Use the following colors to label the boundaries on your map.
Red: Divergent
Blue: Ocean-continental convergent
Orange: Ocean-ocean convergent
Green: Continental-continental convergent
Yellow: Transform
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Part III: Questions about Plate Boundary Features:
Divergent boundaries:
1. Explain why there are mountains at divergent boundaries. (Out pouring of lava from the
divergent boundary alone does not explain why there are mountains here.)
2. There is a down-dropped valley along the crest of the ridge, what is the origin of this valley?
3. One of the observations that we made about the depth of the earthquake foci at divergent
boundaries is that they are all shallow. Why are there no deep earthquakes at divergent
boundaries?
4. Why is there very little sediment covering the pillow basalts at a divergent boundary?
5. Explain how we could use marine magnetic anomalies (magnetic reversal patterns on the sea
floor) to tell us that divergence is happening at one of these boundaries.
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6. How could we determine the past velocity (speed) of plate motion using the marine magnetic
anomalies?
7. Explain how basaltic magmas are formed in the upper mantle.
8. How are the chimney-like structures in the deep-sea hydrothermal vents (so-called "Black
Smokers") formed?
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Ocean-continental Convergent Zone:
1. Which of the two plates (the one with oceanic crust or the one with continental crust)
subducts? Why does it subduct?
2. What is a Benioff-Wadati zone and how it is formed?
3. Explain how intermediate to high silica magmas (andesitic, dacitic, or rhyolitic) form at this
type of plate boundary.
4. Explain why the density of the oceanic crust continues to increase as the plate is subducted.
5. What is a modern example of this type of convergent zone?
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Ocean-Ocean Convergent Zone:
1. If both of the plates have oceanic crust, why does one plate subduct? Could we predict which
oceanic plate will subduct? How?
2. In what ways is this type of boundary similar to a oceanic-continental convergent zone? Be as
specific as possible.
3. What is a modern example of this type of convergent zone?
Continental-continental convergent zone:
1. This type of boundary is sometimes referred to as a “suture” zone. Explain the use of this
term. Does one of the plates subduct? Why/Why not?
2. Would you expect to find a Benioff zone at this type of plate boundary? A deep-sea trench? A
volcanic arc? Explain your answers.
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3. What is a modern example of this type of convergent zone?
Transform Boundary:
1. Imagine that we have a series of five GPS stations that monitor the motion of the Earth’s
surface in different places. We have drawn vectors to represent the motion of the ground in these
five locations. Which of the following would most likely create a transform boundary?
A
B
C
Explain your answers.
2. Why is volcanism not common at transform boundaries?
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D
E
Part IV: The Pacific Northwest
E
W
Olympic Mtns
ocean
Label the following features on the diagram above:
1. Juan de Fuca Ridge
2. Benioff zone
3. andesitic volcanism
4. basaltic volcanism
5. oceanic crust
6. “black smoker” vents
7. Juan de Fuca plate
8. continental crust
9. Pacific plate
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Cascade Mtns