PLATE TECTONICS 2023 (1)
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Dec 6, 2023
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PLATE TECTONICS
Answer the following questions.
If you need help please let me know.
1.
List 5 lines of evidence that Wegener and other early workers (
pre-1960
) used to support the
theory of “continental drift”.
1.
The fit of the continents
2.
Locations of past glaciations
3.
The distribution of climate belts
4.
The distribution of fossils
5.
Matching geologic units
2.
New oceanic crust is created due to sea floor spreading. Why don’t the ocean basins on Earth keep
getting larger and larger? Why isn’t there an ever-expanding Earth?
Since it is being pushed away at plate velocities, we can see it happens over a long amount of time to
have the earth or the ocean basins expand.
PLATE VELOCITIES (
Velocity = distance ÷ time)
We can determine how fast plates are moving (plate velocities) in 2 ways: relative and absolute plate
velocity.
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:
Distance /Time
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 or can be taken.
By
reading the coordinates of the line, we can get the relative velocity.
The graph below shows the relative velocities of 2 mid ocean ridges, the Mid Atlantic Ridge at Iceland,
and the East Pacific Rise.
3.
Determine the velocity of each ridge in centimeters per year (cm/yr)
A
.
Plate Velocity for Mid Atlantic Ridge at Iceland =____200,000_________________ cm/yr
B.
Plate Velocity for East Pacific Rise =
_______6,000,000______ 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.
For Question 4 below - 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
4a
. Distance from Kilauea to Kauai = __450____________km =
_________45,000,000___________cm
4b
.
Age = __________4,700,000___________ years
4c.
Plate velocity of the Pacific plate over the Hawaiian hotspot = ______9.57________ cm/yr
5.
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 :
Shear stress
Rio Grande Rift :
Tensional stress
Basin and Range Province:
extensional stress/ tension stress
Cascades:
Compressional stress
6
.
If the Rio Grande Rift continues, what could this area look like in 20 – 30 million years?
Name a
present-day example of the above situation.
If the Rio Grande Rift continues for another 20-30 million years, the rift’s area will resemble the sea
floor spreading where the water has entered in some ways.
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A present-day example of the above situation is the Great Rift Valley of the East African rift. Due to
the extension of the lithosphere, there has been sea floor spreading; leading to the formation of the Red
Sea.
Using
https://www.iris.edu/hq/files/interactives/BR_PlateTectonic.html
answer the following
questions.
You can move your mouse over each of the topics below the map to answer the following:
7.
How many square km does the Basin and Range cover?
800,000km
8.
Approximately how many mountain ranges are in the Basin and Range?
100 or so mountain ranges in the basin and range
9.
Approximately what is the maximum uplift between the top of these mountains and the down
dropped valley?
10,000feet
10.
What earthquake vulnerability does the El Paso area have for the next 50 years? (tell me
the color)
The vulnerability would be in the lower range; in the green
11
. What 3 metals (barite is not a metal) are mined in the Basin and Range?
Why are there so
many mines in this region?
Copper, gold, and silver are the 3 metals that are mined in the Basin and Range.
These precious metals are formed in deep depths; hence why there are so many mines in the region.
12
. How many national parks are located within the Basin and Range?
15 national parks are located within the basin and range.
Using
http://ds.iris.edu/aed2/c/basin/tectonics/Imgw_Basin_Tectonics_P2.html
Answer the following questions:
13.
Why is the Basin and Range crust thin?
The Basin and range crust are thin because the faults are leveled out with depth.
14.
How much does the Basin and Range expand each year?
The Basin and Range province is expanding at an average rate of 5 millimeters (0.2 inches) per year.
15.
How thick is the NA late under the Basin and Range?
The tectonic plate in the Basin and Range Province is about 60 km thick.
16.
Is this normal?
Why or why not?
No, it's not normal because typically these plates are 200 km thick.
Using
http://ds.iris.edu/aed2/c/basin/tectonics/Imgw_Basin_Tectonics_P3.html
answer the following:
17.
If the Basin and Range is an extensional area why are there high mountains?
There are high mountains because when this area was created, it was stretched, causing the
surface to fracture into high and low terrain.