GLS100 Lab: PLATE TECTONICS
Discovering Plate Boundaries Part 2
Physical Geology - Dr. Lindley S. Hanson
EXERCISE 1: QUIZ
Lab quiz - Identify the name of the plates on the blank map presented.
EXERCISE 2: PLATE BOUNDARY TYPES
Classifying Plate Boundaries: During the previous lab you used a variety of data to locate the
boundaries of the major tectonic plates. During this lab you will use the same data to classify these
boundaries, and to make additional interpretations.
Step 1: Learning the types of lithosphere and plate boundaries.
Tectonic plates, also call lithospheric plates, are conjoined pieces of the earth’s rigid outer-layer,
called the lithosphere. These plates float and slowly glide over the asthenosphere, a slowly
flowing (1-4 cm/year) plastic layer within the upper mantle. The two types of lithosphere are:

Oceanic Lithosphere: Typically less than 100 km thick. It contains the thin (2-7 km),
dense (~3 g/cm3) oceanic crust, and the upper congealed layer of the mantle.

Continental Lithosphere: Between 200 and 350 km in thickness. It contains the thicker
(10-30 km) and more buoyant (2.7 g/cm3) continental crust, and the upper congealed
layer of the upper mantle,
1. Geologists use two criteria to classify plate boundaries. According to table 1 what are
they?
______________________ and ___________________________
Table 1. TYPES OF PLATE BOUNDARIES
1. Convergent: Where plates collide
2. Divergent: Where plates pull apart
a. Continental-Oceanic
a. Oceanic-Oceanic
b. Oceanic-Oceanic
b. Continental-Continental
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c. Continental-Continental
3. Transform (conservative): Where
plates laterally slip past each other
Step 2: Learning the symbols
The map lines and symbols used delineate the three major types of plate boundaries are
shown in figure 1. At convergent boundaries one plate will dive beneath the other. The teeth
on this line point toward the over-riding plate.
Figure 1. Map line patterns and symbols use
to designate the three major types of plate
boundaries. The divergent boundary is a
double line indicating separation. The teeth
on the convergent boundary line point
towards the over-riding plate.
2. What do the arrows in figure 1 indicate?
Step 3: Divide into groups of two. Using the data from the previous lab classify the plate
boundaries on your map. Use the lines and symbols in figure 1. Place a question mark (?) where
the data are inconclusive.
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EXERCISE 3: INTERPRETING THE DATA
1. Convergent Boundaries involving oceanic crust
a. Describe the distribution of earthquakes and their hypocenters at convergent boundaries
where oceanic crust is involved.
b. On the next page draw a 2-D cross section across the Nazca and South American plates
that illustrates; (a) why earthquakes are shallow along convergent boundaries and deeper
farther away, and (b) how earthquakes indicates which are the subducting and over-riding
plates. Label and explain.
Explanation:
c. Is there any consistency to the composition of the descending (subducting) plate along these
boundaries? _______ Explain the observed pattern.
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d. List at least two prominent physiographic features typically developed along subduction
zones, and explain how they are created.
1. __________________________
2. __________________________
3. __________________________
e. Are volcanoes associated with these convergent boundaries? _______________ Why?
f. Make the above additions to your cross-section. Label and explain.
g. The tallest and broadest mountain belts such as the Himalayas, and in the past the
Appalachians, are produces when two continents collide. Explain why these mountain belts are
larger and broader than those formed along subduction zones.
2. Divergent Boundaries involving oceanic crust
a. Describe how divergent boundaries are indicated by the distribution and depth of
earthquakes.
b. Draw a cross section of the Mid-Atlantic Ridge from SA to Africa that illustrates and
explains (a) the distribution of earthquake, and (b) the distribution of seafloor ages across
the boundary and beyond. Label and explain.
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c. List the two major physiographic features associated with this type of divergent
boundary. _____________________ and _________________________
3. From table 1 you can see that there are no oceanic-continental divergent boundaries.
Develop a hypothesis that offers a possible explanation.
4. If you wanted to find the oldest rocks on the Earth why would you not look in the ocean
basins.
EXERCISE 4: HAITI
On January 12, 2010 a magnitude 7 earthquake hit Haiti, 25 km WSW of Port-au-Prince.
The depth was 18 km beneath the surface. The earthquake killed an estimated 200,000
and displaced millions.
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Figure 2. Map of Caribbean seismicity between 1990-2006.
1. The map in figure 2 shows the Caribbean Seismicity between 1990-2006. Interpret
the distribution of earthquakes and draw a line with the appropriate symbol(s)
indicating boundary type and relative motion. (Hint: a portion is occupied by a leftlateral fault)
2. How does the boundary around the NE end of the Caribbean Plate change in the
vicinity of Port-au-Prince.
Quiz: Below are questions and tasks you should be able to answer and complete.
1. Understand and be able to explain how plate boundaries are classified.
2. Be able to identify the type of plate boundary from the distribution of earthquakes, landforms
and other features located along it.
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3. Be able to explain which boundaries are subduction zones and why.
4. Be able to explain is the crust of the ocean floor so young.
5. Be able to identify the plates.
6. Be able to draw and label cross-sections across the different types of boundaries.
7. Explain how the pattern of earthquakes varies along different plate boundaries.
8. Explain why there area two levels of topography (ocean basins and continents) on the
earth’s surface.
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NOTES:
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