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GEOL 1101 LAB #6 PLATE TECTONICS
1. List at least 5 lines of evidence that Wegener and other early workers (pre-1960) used to support the theory
of “continental drift”.
2. Below are pictures of different types of plate boundaries. Name each type shown and give an example.
TYPES OF PLATE BOUNDARIES ARE: ocean-ocean divergent (Mid Ocean Ridge);
continent-continent divergent (continental rift);
ocean-ocean convergent (island arc subduction); oceancontinent convergent (continental volcanic arc subduction);
continent-continent convergent (continental collision);
transform
A.
A. =
EXAMPLE:
B.
B. =
EXAMPLE:
C.
C. =
EXAMPLE:
D.
D=
EXAMPLE:
E.
E=
EXAMPLE:
F.
F=
EXAMPLE:
3. At which of the 6 types of plate boundaries listed in question 2 will sea floor spreading occur?
4. New oceanic crust is created due to sea floor spreading. Why then don’t the ocean basins on Earth keep
getting larger and larger (an expanding Earth, which DOESN’T happen, but why)?
5. On the world map at the end of this lab, draw and label the following features: the Mid Atlantic Ridge; the
East Pacific Rise; the continental shelves of North America; the Nazca trench; the Cascadia trench; the Japan
trench; the Middle America trench; the Puerto Rico trench; the Himalayas; the San Andreas Fault; the Andes;
the Cascades; the Alps; the Río Grande Rift; the East African Rift; the Appalachian Mountains; the Gulf of
Mexico, the Atlantic Ocean, the Pacific Ocean, the Indian Ocean, the Mediterranean Sea.
PLATE VELOCITIES
Velocity = distance ÷ time
We can determine how fast plates are moving (plate velocities) in 2 ways. A RELATIVE plate velocity can be
determined looking at the ages of the oceanic crust and its distance from the mid ocean ridge. We call this
“relative motion” because both plates on either side of the mid ocean ridge are moving.
For example: 3 million year old oceanic crust is 250 km from the mid ocean ridge where it was erupted, so the
relative velocity of that plate is 250 km in 3 million years.
BUT – we report plate velocities in centimeters per year, so you must convert kilometers to cm and millions of
years (m.y.) to years.
1 km = 100,000 cm; 1 million years (1 m.y.) = 1,000,000 years
In the example above, the plate velocity is then:
250 km/3 m.y. = 25000000 cm / 3000000 years = 8.3 cm/ year
Relative velocities are usually reported as a graph, so many measurements are taken. By reading the
coordinates of the line, we can get the relative velocity (see the Lecture Notes on Plate Tectonics for full details).
6. The graph below shows the relative velocities of 2 mid ocean ridges, the Mid Atlantic Ridge at Iceland, and
the East Pacific Rise. Using the method described in the Lecture Notes on Plate Tectonics, determine the
velocity of each ridge in centimeters per year (cm/yr)
6A. Plate Velocity for Mid Atlantic Ridge at Iceland =_____________________ cm/yr
6B. Plate Velocity for East Pacific Rise = _____________ cm/yr
Absolute Plate Velocities use a fixed reference point. A good way to determine absolute velocities is using
hotspot data from a fixed hotspot, like the Hawaiian hotspot. Since the active volcano at Kilauea is currently
over the hotspot, it is 0 years old. Use the map scale in the lower left corner and determine the plate velocity
in cm/yr from Kilauea to Kauai (use a straight line distance).
Remember 1 m.y. is 1,000,000 years, so if the age has a decimal, that counts as a place value!
For example, 2.3 m.y = 2,300,000 years
7. 7A. distance from Kilauea to Kauai = ______________km = ____________________cm
7B.
age = _____________________ years
7C. plate velocity of the Pacific plate over the Hawaiian hotspot = ______________ cm/yr
8. The 4 major tectonic features in western North America we see today are the San Andreas Fault, the
Cascades, the Basin and Range Province, and the Rio Grande Rift. Name the type of stress that is responsible
for each of these tectonic features.
San Andreas :
Rio Grande Rift :
Basin and Range Province:
Cascades:
9. If the Rio Grande Rift continues, what could this area look like in 20 – 30 million years?
Name a present day example of this situation.
10. Label the letters A – G on the sketch below (continental crust, oceanic crust, asthenosphere, lithosphere,
Moho, trench, volcanic arc)
A=
B=
C=
D=
E=
F=
G=
EXTRA CREDIT: For up to 4 points extra credit on the next Lab Exam, go to the following website EXPLORING
THE BASIN AND RANGE to answer questions 11: http://ds.iris.edu/aed2/index.phtml?code=BASIN
11. Click on Plate Tectonics. You can move your mouse over each of the topics below the map to answer the
following:
How many square km does the Basin and Range cover?
Approximately how many mountain ranges are in the Basin and Range?
Approximately what is the maximum uplift between the top of these mountains and the down
dropped valley?
What 3 metals (barite is not a metal) are mined in the Basin and Range? Why are there so
mines in this region?
many
Click on the “NEXT” button (several times!) to answer the following:
Why is the Basin and Range crust thin?
Why is the Basin and Range Province at a high elevation?
How much are the Basin and Range mountains rising each year?
How much is the Basin and Range Province extending each year?
Look at the map with arrows showing plate velocity and movement. In general, which direction
Nevada (NV) moving?
In general, which direction is Oregon (OR) moving?
Which state on this map has the fastest plate motion (shown by the longest arrows)?
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