Download Plate C Plate D

OS 1 The Oceans
Fall 2007
Name: _______________________
Plate Tectonics
(you must turn Activities 1-2 in during Section)
Activity 1: Plate Boundaries
A “plate boundary” simply describes where two plates (either oceanic or continental
material) meet. There are only three types of plate boundaries Divergent (moving
away from each other), Convergent (moving towards each other), and Transform
(sliding past each other).
1. Cut out the triangle below, but keep the remaining sheet of paper in one piece.
a. Put the triangle back into the hole and move it in the direction of the
arrow on plate A.
b. On your paper, label the three sides of the triangle with the types of plate
boundaries (convergent, divergent, transform) created by the interaction
of plate A with plates B, C, and D.
Plate C
Plate D
2. Complete the following table to describe the characteristics of plate boundaries:
Name of Seafloor Feature
Divergent
Transform
N/A
Name of Tectonic Process
N/A
Volcanoes Present? (Y or N)
Earthquakes Present? (Y or N)
Plate tectonics- 1
Convergent
OS 1 The Oceans
Fall 2007
Activity 2: Seafloor Spreading
Use the map on page 3 for the following questions and be sure to show your work.
You will need a ruler and a calculator. If the line (upper left) is not 1 inch, you
should reprint your handout with scaling turned off.
Given that the distance between Points A and B is 4550 km, you should first
calculate the scale of this map. [For example, you could calculate how many miles
are represented by one centimeter.]
1. What is the map scale?
Select the third stripe to the east of the MAR. Record its age below and carefully
measure the distance it has moved from the mid-ocean ridge where it formed.
2. Sea floor age at selected stripe: __________million years (My)
3. Distance to the Mid-Atlantic Ridge (MAR) at selected stripe (in kilometers):
Using the age of the rock you have chosen and its distance from the MAR, calculate
the half-rate of sea floor spreading, the velocity at which one strip of this rock has
spread away from the MAR.
4. (distance/time) = km per My
Now calculate the total rate (velocity) that the two plates are moving away from
each other. This is considered, the rate of sea floor spreading.
5. (2 X half-rate = total spreading rate): ____________________km per My
Given that the total present day distance between North America and Africa
(between points A and B) is 4550 km, calculate the age of the North Atlantic
Ocean.
6. Age of North Atlantic Ocean: _____________________My
7. Convert the total sea floor spreading rate from #5 above to units that are easier
to "imagine" such as inches per year.
8. How much has the distance (in inches) between North America and Africa
increased since you were born (show your work)?
9. How much closer (in feet) were these two continents when Columbus made his
voyages in 1492? Columbus thought the Earth was 25% smaller than it is, because
he used the wrong map. In percent, how much smaller was the Atlantic in 1492
compared to today?
Plate tectonics- 2
OS 1 The Oceans
Fall 2007
Note: this line
should be 1
inch wide,
exactly
Plate tectonics- 3
OS 1 The Oceans
Fall 2007
Activity 3: Seafloor Profiles (you can do this at home)
In this activity we will think about how water depth of the ocean floor changes as it
ages and moves away from the mid-ocean ridge (rift valley).
1. Use the information in the table below to draw a simple profile of the sea floor
across a mid-ocean ridge on the graph below the table. First plot the points below
and then connect the dots with a continuous line.
Station
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Distance from Rift Valley (km)
5000 to west
3500 to west
2750 to west
1500 to west
750 to west
400 to west
100 to west
100 to east
400 to east
750 to east
1500 to east
2750 to east
3500 to east
5000 to east
Water Depth (m)
5250
4800
4500
4000
3500
3000
2800
2800
3000
3500
4000
4500
4800
5250
Rift Valley (located at 0 km)
West (km)
East (km)
5000 4000 3000 2000 1000 0 1000 2000 3000 4000 5000
0 m ---------------------------------------------------------------------------------------1000 m ----------------------------------------------------------------------------------2000 m ----------------------------------------------------------------------------------3000 m ----------------------------------------------------------------------------------4000 m ----------------------------------------------------------------------------------5000 m ----------------------------------------------------------------------------------6000 m ----------------------------------------------------------------------------------2. Explain why the water depth increases with distance from the rift valley of the
mid-ocean ridge as shown in your profile above.
Plate tectonics- 4
OS 1 The Oceans
Fall 2007
Activity 4: Ocean Depth and Age of Crust
We have seen that as ocean crust moves away from mid-ocean ridge it gets older
and deeper. We now can derive a relationship between water depth and age.
1. Make a plot of the Water Depth (D) vs. T 1/2 (where T = age of oceanic crust) on
the graph below. First complete the table below, then plot the data below the
table. (Note: T½ is the same as the square root of T)
Station
1
2
3
4
5
6
7
5500
5000
4500
4000
3500
3000
2500
2000
Water Depth (m)
2800
3000
3500
4000
4500
4800
5000
T (my)
2
4
10
20
32
40
42
T1/2 (You calculate missing values)
1.41
2.00
m-----------------------------------------------------------------------------------m-----------------------------------------------------------------------------------m-----------------------------------------------------------------------------------m-----------------------------------------------------------------------------------m-----------------------------------------------------------------------------------m-----------------------------------------------------------------------------------m-----------------------------------------------------------------------------------m____________________________________________________________
0
1
2
3
4
5
6
7
8
9
T 1/2 (Million Years)
Draw a straight line that connects the points on your graph above
2. How does the water depth of the sea floor change with increasing age of the
oceanic crust and lithosphere?
Based on the above plot, a relationship can be shown between the water depth to
the top of the oceanic crust (sea floor in this case) and the age of the crust at that
location. This relationship is:
D = 2500 + 350 T1/2, where D = depth in meters; T = age in million years
3. Predict the water depth of 7 million year-old oceanic crust.
4. Based on the age you calculated for the North Atlantic in Activity 2, how deep is
the oldest part of the North Atlantic basin?
5. Most of the Pacific Ocean basin is over 5000 meters deep. Estimate the age of
oceanic crust with a water depth of 5000 meters.
Plate tectonics- 5
OS 1 The Oceans
Fall 2007
Activity 5: Rate of plate movement
Another way to calculate plate movement is by looking at island chains that are
formed from hot spots. Dating of rocks from the Hawaiian Islands shows that the
ages of the volcanoes are progressively older to the northwest (upper left).
It appears that the active volcanoes on the "big island" of Hawaii overlie a very hot
region in the Earth's mantle. This hot region located deep with the earth, is known
as a “hot spot.” So as the Pacific plate moves slowly over the stationary “hot spot”
in the mantle, molten rock (called magma) rises to pierce a hole in the lithospheric
plate. A series of “burn marks” are left in the plate -- these “scars” are the
volcanic islands and underwater volcanoes that lie on the top of the plate -thereby creating a chain of seamounts and oceanic islands.
Ages of the volcanoes on the Hawaiian Islands.
Island
Age of Volcanoes
m.y.=million years
Distance From Center
of Hawaii (Big Island)
km = kilometers
Hawaii
Maui
Molokai
Oahu
Kauai
0 m.y.
1.1 m.y
1.6 m.y.
2.5 m.y.
4.0 m.y.
0 km
140 km
220 km
300 km
460 km
1. Draw an arrow on the following map to show the direction of the absolute
motion of the Pacific plate over the past 5 million years.
Plate tectonics- 6
OS 1 The Oceans
Fall 2007
2. Calculate the rate of absolute motion of the Pacific plate based on the data
shown above by first determining the rate of motion for each island and then
taking the average of these values. Don't forget to specify units.
3. Which ocean basin is experiencing the faster rate of spreading, the Atlantic
(Activity 2) or the Pacific (Activity 5)?
Plate tectonics- 7