Download Part 1 – Plate Boundaries

Name ________________________
Earth Systems Science
Lab 8 - Plate Tectonics
Introduction:
An important reason why Earth is so unique is that it is geologically alive. Our planet’s internal heat
engine drives the motion of its surface, creating a planet that is constantly changing. The theory of plate
tectonics unifies and clarifies what were once thought to be unrelated Earth processes such as
earthquakes, volcanic activity, and the distribution of continents, oceans, and natural resources. This lab
will help you explore several concepts related to plate tectonics to gain a deeper understanding of this
cornerstone of earth science.
Equipment:
Labtop, tablet computer, or networked lab computer
Part 1 – Plate Boundaries
In this section, you will investigate various aspects of plate boundaries using the website Jules Verne
Voyager Jr. ( http://jules.unavco.org/VoyagerJr/Earth)
1.1 – Sketch each type of plate boundary in the spaces below using a block diagram format. Use the
textbooks provide for help.
Divergent Boundary
Convergent (Subduction)
Transform Boundary
Convergent (Collision)
1.2 – Experiment with ways to navigate around the world map on Jules Verne Voyager Jr.
• To see an area in more detail, click once on that area.
• To zoom out, click the “zoom out” box in the upper left part of the window.
• To go straight back to the world map, click the “World Map” box.
Experiment with different base maps by clicking on a new base map (such as “Color Topography”) and
clicking the “Make changes” box.
Experiment with adding other features in the “Add feature(s)” menu. To add more than one feature, hold
down the “Ctrl” key while selecting. Click the “Make changes” box to see the changes.
The key to each map is located in a pop-up window (so make sure you’re enabled pop-up windows). Use
the key to help you interpret each of the features on the map.
After you have experimented a bit, select the “Ocean Floor Age” map and add the “Tectonic Plates”
feature. Use the key to help you fill out the following table. (Ask your instructor or lab assistant for help if
you don’t know how to find any of the locations.)
Location
Type of plate boundary
Age of ocean floor (millions of
years)
Mid-Atlantic Ridge
East Pacific Rise
Marianas Trench
Peru-Chile Trend (at the bend in
the west coast of South America)
1.3 - Generalize: what is the age of oceanic crust at mid-ocean ridges?
1.4 – What happens at mid-ocean ridges to cause oceanic crust to be that age? Use a sketch to illustrate
your answer.
1.5 - What generalizations are possible about the age of oceanic crust at trenches?
1.6 - What is the age (in millions of years) of the oldest oceanic crust on the map?
1.7 - Where is the oldest oceanic crust found (specific geographic location, not generalization)?
Part 2: Plate Tectonics, Volcanic Activity, and Earthquakes
This portion of the lab will challenge you to synthesize information about the distribution of plate
boundary types, volcanic activity, earthquakes, and global topography. The goal is for you to gain a
deeper understanding about the relationships between plate tectonics and other earth processes.
2.1 – Switch your base map to one of the options that shows topography. (Face of the Earth & Relief,
Color Topography, or Gray Topography can all work.) Leave “Tectonic Plates” as the only feature added.
Examine your map of plate boundaries and the Earth’s topography. Consider where different boundary
types are located in relation to mountain ranges, continental boundaries, oceanic trenches, and ocean
basins.
Type of plate boundary
Divergent
Topographic observations
Convergent – subduction
Convergent – collision
Transform
2.2 – Select a base map that allows you to see topography (Gray Topography is pretty good). Then add
both “Tectonic Plates” and “Volcanoes” from the “Add feature(s)” menu. Make the changes. Then fill out
the following table comparing the location of volcanoes with plate boundaries. Zoom in to some plate
boundaries to see the exact location of the volcanoes compared to the plate boundaries.
Type of plate boundary
Example
Volcanoes (not present, on boundary,
or near boundary)
Divergent
Convergent – subduction
Convergent – collision
Transform
In next week’s lab, you will work more with the types of igneous rocks formed by volcanoes at the
various types of plate boundaries.
2.3 – Change your features so that you can see “Tectonic Plates” and “Earthquakes.” Select a base map
that allows you to see the colors representing the different earthquakes. Scroll to the bottom of the pop-up
window that shows the key, so you can see what the different colored dots represent.
Fill out the following table
Type of plate boundary
Divergent
Are earthquakes present?
Depth of earthquakes
Convergent – subduction
Convergent – collision
Transform
2.4 – Zoom in to an example of a subduction zone (Japan, Sumatra, or the west coast of South America
are good examples). Describe the pattern of earthquake depths compared to the location of the plate
boundary. (You may want to switch back and forth from showing earthquakes to only showing the plate
boundary.)
2.5 – Explain why the earthquake depths form that pattern near subduction zones. Use a sketch to
illustrate your answer.
2.6 – Are there any earthquakes within plates (not on plate boundaries)? Suggest at least two possible
explanations for their existence.
Part 3 –Plate Velocities
In this part of the lab, you will look at velocities of plates (based on the ages of the ocean floor and other
geologic scale data, and observed by high-precision GPS measurements in the last 20 years).
3.1 – Select a base map that allows you to see topography (Gray Topography is good). Add “Tectonic
Plates.” In the “Add velocities” menu, click “No-Net-Rotation” and the “Model” radio button. Make
changes.
The “No-Net-Rotation” velocities are the closest we have to absolute plate velocities. “Model” velocities
are based on long-term (millions of years) geologic data, put together into a global model.
Zoom into each of the following plate boundaries. For each one,
a) Sketch the geometry of the boundary and the orientation of the arrows.
b) Use two pieces of scrap paper to represent the plates. Move the two pieces in the directions indicated
by the arrows. Describe what happens to the space between the pieces of paper in each case.
Boundary
East Pacific Rise
(Pacific/Nazca
boundary)
Japan Trench
(northern Japan)
Sketch
What happens in space
between pieces of paper?
3.2 – In some cases, the “No-Net-Rotation” model is more difficult to visualize. In that case, you can look
at the velocity compared to one of the two plates by selecting a plate name from the list in the “Add
velocities” menu.
As an example, zoom in to California and look at plate velocities across the San Andreas Fault. Select
“No-Net-Rotation” and “Model”, and sketch the orientation of the arrows on either side of the plate
boundary. Then change the velocity to “N. America” and sketch the arrows on either side of the boundary.
Finally, change the velocity to “Pacific” and sketch the arrows on either side of the boundary.
Velocities compared to:
No-Net-Rotation
Sketch of velocities
N. America
Pacific
With a partner, move two pieces of scrap paper in the directions shown in each of your sketches. Try to
form a transform plate boundary (with all motion parallel to the boundary) in each case. It should be
possible to move the paper so that no paper overlaps and no gap opens up in each case.
3.4 – The length of the velocity arrows on the maps tells you how fast the plates are moving. To figure out
the approximate plate velocity, compare the length to the length of the “50 mm/yr” arrow at the top of the
map.
Select the velocity compared to North America. How fast is the Pacific Plate moving compared to North
America along the San Andreas Fault?
Part 4 – Plate Motion and the Hawaiian-Emperor Seamount Chain
In this section, you will piece together the history of the motion of the Pacific Plate based on the geometry
and ages of the Hawaii-Emperor Seamount Chain. The following map and data are from USGS
Professional Paper 1350, and the exercises are modified from the Laboratory Manual for Physical
Geology, by Jones and Jones.
In 1963 one of the great plate tectonics pioneers, J. Tuzo Wilson, proposed that all of the volcanic islands
in the Hawaii-Emperor chain formed above the same hot spot, or thermal plume. If this hypothesis is
true, then volcanoes should be older farther away from the hot spot, and a distance-age relationship can be
used to measure the rate of motion for the Pacific Plate.
Figure 4.1 - Map of Hawaiian-Emperor chain, shown with 1- and 2-km bathymetric contours.
4.1 – On the map on the previous page, indicate where the hot spot is currently located relative to the
islands and seamounts in the chain. Hint: The “Big Island” of Hawaii has several active volcanoes. The
other islands are extinct volcanoes.
4.2 – If hot spots are stationary mantle plumes, why is there a chain of islands instead of just one huge
volcanic island?
Table 4.1 – Data for selected volcanoes of the Hawaiian-Emperor Chain.
4.3 – Plot the data from Table 4.1 into the graph below, labeling each point with the name of its
corresponding volcano. All of the distances are relative to Kilauea, a currently active volcano on the
island of Hawaii.
4.4 – Draw three best fit line segments: (1) between Kilauea and Laysan, (2) between Laysan and
Daikakuji, (3) between Daikakuji and Suiko Central. How do these line segments differ?
4.5 – Calculate the rate of plate motion in millimeters per year for segment 1: divide the distance
between islands by the time interval difference between islands, then convert to mm/yr. Show your
work!
4.6 – Go back to the website http://jules.unavco.org/VoyagerJr/Earth. Select a base map that’s easy to
read, add “Tectonic Plates,” and add the “No-Net-Rotation” velocities (“Both”). Zoom in to Hawaii. The
length of the arrows is proportional to the velocity in mm/year, using the scale at the top of the map.
Approximately how fast is Hawaii observed to be moving, according to high-precision GPS
measurements? Compare that answer to the value that you calculated.
Part 5 – Summary
5.1 – The original theory of plate tectonics, developed in the 1960s, explained many of the patterns that
you have looked at today. The age of the ocean floor, the distribution and depth of earthquakes, and the
age of volcanoes in the Hawaiian-Emperor seamounts were all new information to geologists in the years
after World War II.
Summarize how the plate tectonic model (rigid plates moving over a weak asthenosphere) explains:
a) the pattern of ages on the ocean floor
b) the global distribution of earthquakes and earthquake depths
5.2 - What was the most surprising thing in lab today?