GEOL LAB 2
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CUNY College of Staten Island *
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Course
100
Subject
Geology
Date
Apr 3, 2024
Type
Pages
13
Uploaded by ChancellorBoar4201
Introduction:
To understand plate tectonics, one must be familiar with the lithosphere, Earth’s solid outermost
layer consisting of the crust and the uppermost part of the upper mantle. The lithosphere is
divided into plates that move relative to each other and interactions along their boundary zones
produce earthquakes, volcanoes, mountain ranges, mid-ocean ridges, and trenches. In divergent
plate boundaries, plates are moving away from each other resulting in the partial melting of the
asthenosphere, seafloor spreading, or new crust to be added to both sides of the boundary.
Furthermore, there are convergent plate boundaries, where two plates move towards one another;
this can potentially cause the subduction of oceanic lithosphere and earthquakes along this
subduction zone. Lastly, with transform plate boundaries, plates move in the same direction
along fracture zones; however, they move in opposite directions between ridge segments and
transform faults. Four major factors influence the behavior of Earth’s materials: strength, gravity
and buoyancy, and heat flow. Strength refers to the amount of stress a material can withstand,
which is directly influenced by its mineral composition, grain size, temperature, and pressure.
Additionally, when a mass of greater density is surrounded by a fluid of lesser density, the mass
with the greater density will move downward; however, if a mass with lesser density is
surrounded by a fluid of greater density, such as magma, the less dense mass will be pushed
upwards. Finally, heat flows within the solid Earth by conduction in the lithosphere and
convection in the mantle.
Activity 2.2: Plate Motion and the San Andreas Fault
A) Displacement Along the San Andreas
1.
The distance between Neenach and Pinnacles along the San Andreas Fault is
approximately three inches or approximately 75 millimeters. Given that each millimeter
on the map represents 4km on Earth’s surface,
the approximate distance from Neenach
to Pinnacles is 300 km.
2.
Estimated average rate of displacement since 19 Myr: 15.789 km/Myr
Displacement =
?𝑖??????
?𝑖??
Displacement =
300 ??
19 ?𝑦?
3.
Estimated age of faulting: 14.151 Myr
Age =
?𝑖??????
????
Age =
300 ??
21.2 ??
Age = 14.151 Myr
B)Motion of the Crust in a Plate Boundary Zone
1.
2 cm = 50 mm/yr, 1 cm = 25 mm/yr
Atlantic Plate:
a)
1.1 cm = 27.5 mm/yr
b)
1.2 cm = 30 mm/yr
c)
1.3 mm = 32.5 mm/yr
d)
1.4 cm = 35 mm/yr
Average = 31.25 mm/yr
North American Plate:
a)
0.3 cm = 7.5 mm/yr
b)
0.4 cm = 10 mm/yr
c)
0.5 cm = 12.5 mm/yr
d)
0.6 cm = 15 mm/yr
Average = 11.25 mm/yr
Based on the average of four vectors for each plate boundary, the Pacific Plate is
moving faster by an estimated 20 mm/yr.
2.
Add half-arrows along the San Andreas Fault to show the sense of motion across the
fault.
Figure A2.2.2.
C) The crust along the Big Bend might be affected by this difference in motion compared to the
northwest and southwest because the northwest and southwest sectors move in a parallel motion
to each other and the transform fault plane; therefore, in this location, the plates are more likely
to slide past each other. However, at the Big Bend, the GPS velocity vectors show a change in
motion direction, hence, the slower velocity of the northern portion of the plane against the faster
velocity of the southern portion of the plane makes it subject to a collision. This location
experiences more compression and stress given they move at different rates and in slightly
different directions now. Such characteristics can produce thrust faulting, or rocks being pushed
against one another, and as a result, there is a potential for increased seismic activity.
Activity 2.4: Hotspots and Plate Motions
1.) If the Emperor and Hawaiian Islands Chains developed as a result of the same mantle
hotspot, the change in direction of the hotspot trail at ~42 Myr can be a result of the
change in direction or velocity of the Pacific Plate. Specifically, when the Pacific Plate
was moving over a hotspot, magma would rise to the surface and create volcanic islands;
however, the trajectory of this plate could have been affected by mantle convection
patterns, collision of tectonic plates, or if a new ocean crust is formed.
2.) The rate of Pacific Plate motion relative to the Hawaiian hotspot as it was developing the
2,300 km-long Emperor Seamount Chain from 65 Myr to 42 Myr was
100 mm per year
.
By studying the age and location of volcanic features, the Pacific Plate was moving in a
north-northwest direction
relative to the hotspot during this time interval.
Work:
Rate of motion =
?𝑖??????
?𝑖??
Rate of motion =
=
2,300 ??
65 ?𝑦? − 42 ?𝑦?
2,300,000 ?
23,000,000 𝑦?
Rate of motion =
0.1 ??????
1 𝑦???
Rate of motion =
100 ??
1 𝑦???
3.) The rate of Pacific Plate motion relative to the Hawaiian hotspot from 5.1 to 0.8 Myr was
93 mm/yr.
Work:
Rate of motion =
?𝑖??????
?𝑖??
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Rate of motion =
=
400 ??
5.1 ?𝑦? − 0.8 ?𝑦?
400,000 ?
4,300,000 𝑦?
Rate of motion =
0.093 ??????
1 𝑦???
Rate of motion =
93 ??
1 𝑦???
4.) The rate of Pacific Plate motion relative to the Hawaiian hotspot, Lo’ihi Seamount, from
0.8 Myr to today is
287.5 mm/year.
Work:
Rate of motion =
?𝑖??????
?𝑖??
Rate of motion =
=
230 ??
0.8 ?𝑦? − 0
230,000 ?
800,000 𝑦?
Rate of motion =
0.2875 ??????
1 𝑦???
Rate of motion =
287.5 ??
1 𝑦???
5a.) The current motion of HNLC on Oahu compared to the direction of Pacific Plate motion
relative to the Hawaiian hotspot over the past 42 million years is
northwest.
5b.) Rate of movement of North = 34.607
mm/yr
± 0. 038
Rate of movement of West = 62.814
mm/yr
±
0. 041
Pythagorean Theorem =
=
?
2
+
?
2
?
2
Pythagorean Theorem =
34. 607
2
+ 62. 814
2
=
?
2
Pythagorean Theorem = 1197.644 + 3945.598 = 5143.243
=
?
2
5143. 243
c = 71.716 mm/year
The current speed of the Pacific Plate at Oahu relative to the NNR reference frame
without considering the 0.038 mm/yr and 0.041 mm/yr error is 71.716 mm/year.
6.) Reflect and Discuss: Based on the above work, the directions, and rate of the Pacific Plate
over the past ~70 million years have been mostly moving in the north, and eventually, the
northwestern direction at an estimated average of 10 centimeters or 100 millimeters per year.
This is subject to change based on its location or interaction with other plate boundaries.
1.) The progressive chain of volcanic centers indicates that the Yellowstone hotspot has
continually moved across the North American plate for millions of years. Since
Yellowstone is still an active hotspot it means that the North American plate is still
moving over it, which can allow the hotspot to melt the crust and create new volcanoes.
Up to this point, there has been a pattern of southwest direction.
2.) The average speed and direction of the North American Plate motion at Yellowstone
relative to the hotspot since 13.8 Myr is
45.4 mm/yr southwest.
Work:
Speed =
?𝑖??????
?𝑖??
Speed =
=
600 ??
13.8 ?𝑦? − 0.6 ?𝑦?
600,000 ?
13,200,000 𝑦?
Speed =
0.0454 ??????
1 𝑦???
Speed =
45.4 ??
1 𝑦???
3a.) The current speed of the North American Plate at P717 relative to the NNR reference
frame is
16.99 or approximately 17 mm/yr.
Moving south at 8.155
±
0. 123 ??/𝑦?
Moving west at 14.905
±
0. 094 ??/𝑦?
Pythagorean Theorem =
=
?
2
+
?
2
?
2
Pythagorean Theorem =
8. 155
2
+ 14. 905
2
=
?
2
Pythagorean Theorem = 66.504 + 222.159 = 288.663
=
?
2
288. 663
c = 16.99 mm/yr
3b.) The present-day direction and speed of P717 relative to the NNR Reference frame is
headed southwest at a speed of 17 mm/yr. While the direction of the North American Plate
relative to the hotspot during the past 13.8 Myr has been southwest, it was moving at a speed
of 45.4 mm/yr, which is slightly faster than that of the P717.
C) Reflect and Discuss
Hotspots help scientists understand plate tectonic processes and rates because these hotspot
locations release heat, lava, on the Earth’s surface that results in the formation of volcanoes. The
hotspots themselves aren’t moving; however, it is the movement of the plate that explains the
chains of volcanic mountains. Depending on the time required and the distance between these
formations, scientists can analyze the rate at which the tectonic plates are moving. Additionally,
hotspots can provide information about the composition of Earth’s mantle as hotspot volcanism
is associated with mantle plumes or columns of hot material deep in the Earth.
Activity 2.6: Paleomagnetic Stripes and Seafloor Spreading
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1.
Draw a line on the seafloor to show where the new ocean crust and lithosphere are
forming now. Label the segments of your line that are Juan de Fuca Ridge and Gorda
Ridge. Label the segments of your pencil line that are transform fault plate boundaries.
Add a half arrow to show the motion of the two plates relative to the transform fault.
2.
The average rate and direction of seafloor spread in mm per year west of the Juan
de Fuca Ridge from B to A was 31.25 mm/yr.
Rate =
=
* 100 km/cm
?𝑖?????? ???? ? ?? ? 𝑖? ????𝑖??????
??
2.5 ??
??
Average rate (km/yr) = 250 kilometers
Average rate (mm/yr) = 250,000,000 mm/yr
Time @ A = 8 million years
Time @ B = 0 million years
Average rate =
=
31.25 mm/yr
250,000,000 ??
8,000,000 𝑦????
3.
The average rate and direction of seafloor spread in mm per year west of the Juan
de Fuca Ridge from B to C was 29.375 mm/yr.
Rate =
=
* 100 km/cm
?𝑖?????? ???? ? ?? ? 𝑖? ????𝑖??????
??
2.35 ??
??
Average rate (km/yr) = 235 kilometers
Average rate (mm/yr) = 235,000,000 mm/yr
Time @ C = 8 million years
Time @ B = 0 million years
Average rate =
=
29.375 mm/yr
235,000,000 ??
8,000,000 𝑦????
4.
The rocks older than 11 million years are present west of the Juan de Fuca Ridge but not
east of the ridge because the seafloor rocks along line segment C-D would be in a
subduction zone, meaning the Juan de Fuca Plate, an oceanic plate, is being forced
beneath the North American Plate. As it moves eastward towards the North American
plate, the oceanic crust is carried downward into Earth’s mantle, which melts and
eventually becomes part of the mantle (removing it from the seafloor).
5a.) If you were to take a submarine to view the sea floor along the black curve with
triangular barbs east of point C, you could oceanic trenches, which are depressions in the
ocean floor formed at subduction zones. As explained above, the Juan de Fuca plate would
be pushed beneath the North American Plate. Also, there could be a potential formation of
volcanoes as magma rises to the surface around subduction zones or one could spot
seamounts forming as the two plates collide.
5b.) Based on Fig. 2.1, the North American Plate is the lithospheric plate, a convergent plate
boundary located east of the barbed curve.
5c.) Based on Fig 2.1, the Juan de Fuca Plate is the lithospheric plate located west of the
barbed curve. Traveling further west would be the Pacific Plate.
6.) Reflect and Discuss
The formation of the Cascade Range volcanoes is caused by the subduction of the Juan
de Fuca plate beneath the North American Plate because as the Juan de Fuca plate sinks,
it transforms into magma. Given it is less dense than solid rock, it rises through weaker
points in Earth’s crust, and eventually with enough build-up, the magma is forced to the
surface through volcanic fissures; hence, it creates a zone of volcanic and seismic
activity.
Activity 2.7: Atlantic Seafloor Spreading
1.) The average speed that
drifted away from the ridge at A during the past 67.7
?
??
Myr is 19.76 mm/yr.
?𝑣????? ????? = ????? ?𝑖??????
?𝑖??
Average speed =
1338 ?? * 10
6
??
67.7 ?𝑦? * 10
6 𝑦???
Average speed = 19.76 mm/yr
The average speed that
drifted away from the ridge at A during the past 67.7
?
?𝐹
Myr is 19.49 mm/yr.
?𝑣????? ????? = ????? ?𝑖??????
?𝑖??
Average speed =
1320 ?? * 10
6
??
67.7 ?𝑦? * 10
6 𝑦???
Average speed = 19.49 mm/yr
The
Plate moved faster relative to the ridge over the past 67.7 Myr.
?
??
2.) The average speed at which new lithosphere was added to the North American plate
along
to
is 15.365 mm/yr.
?
??
?
??
?𝑣????? ????? = ????? ?𝑖??????
?𝑖??
Average speed =
=
1354 ?? * 10
6
??
(154.3 − 67.7) * 10
6 𝑦???
1354000000 ??
86600000 𝑦?
Average speed = 15.365 mm/yr
The average speed at which new lithosphere was added to the African plate along
to
is 14.769 mm/yr.
?
?𝐹
?
?𝐹
?𝑣????? ????? = ????? ?𝑖??????
?𝑖??
Average speed =
=
1279 ?? * 10
6
??
(154.3 − 67.7) * 10
6 𝑦???
1279000000 ??
86600000 𝑦?
Average speed = 14.769 mm/yr
The North American plate moved faster relative to the ridge between 154.3 and 67.7
Myr.
B) Based on the answers in part A, the North Atlantic Ocean Basin developed by the lithosphere
being added more rapidly to one side than the other. Specifically, the
portions
?
??
??? ?
??
moved faster.
C)
The coastlines of North America and Africa touched approximately 314.712 - 335.12
million years ago.
Time = Distance/Rate
CNA-BNA: 1354 km/ 15.365 mm/yr = 88.12 Myr + 247 Myr = 335.12 Myr
BNA-A: 1338 km/ 19.76 mm/yr = 67.712 Myr + 247 Myr = 314.712 Myr
A-BAF: 1320 km/19.49mm/yr = 67.72 Myr + 247 Myr = 314.72 Myr
BAF-CAF: 1279/14.769 mm/yr = 86.6 Myr + 247 Myr = 333.6 Myr
D)
Number of meters that Africa and North America have moved apart since the US was
formed: 9.69475
Time = 2023 - 1776 (247 years)
Rate for BNA to A = (19.76 mm/yr)247 = 4880.72 mm, 4.88072 m
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Rate for BAF to A =(19.49 mm/yr)247 = 4814.03 mm, 4.81403 m
4.88072 + 4.81403 =
9.69475 meters
There are uncertainties in the time variances and the distances between different points from the
coast. To address the uncertainty, one could add and subtract the time variances to calculate the
difference in calculations in time. One could also use the average of these results. Another way
to limit uncertainty is to round one's calculations at the very end of the calculations to reduce any
changes to precision.
Activity 2.8: Using Earthquakes to Identify Plate Boundaries
A) Outline the location of all plate boundaries on the map. Label the East Pacific Ridge,
Galapagos Ridge, Chile Ridge, and all of the plates.
1.
A convergent plate boundary is shown in the cross-section, explaining the subduction
zone.
2.
Refer to the above image for the interpretation of where the top surface of the subducting
plate is located.
3.
Refer to the above image for where earthquakes are present in the subducting slab, the
earthquakes in the South American Plate above the subducting Nazca Plate.
4.
Magma probably originates at a depth of 100-120 km as this is where the Nazca Plate is
subducting and therefore the formation of magma and its rise to the surface creates
volcanoes.
5.
Reflect and Discuss: The deepest earthquake plotted on the cross-section is located at a
depth of 620 km. There is a higher chance of earthquakes occurring at this depth in a
subduction zone but not elsewhere in the mantle at the same depth because as one
tectonic plate is being pushed under another into the Earth’s mantle, there is a significant
increase in temperature and pressure. This makes the rocks prone to deformation or
fracture, which is responsible for earthquakes. Essentially, it is the pressure and stress at
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this location as opposed to any other of the same depth that permits this process to take
place.
Conclusion:
From this lab, I gained a better understanding of how tectonic plates interact and
influence the Earth’s surface by considering plate motions, seafloor spreading, and the
identification of the type of plate boundaries, such as convergent, divergent, and transform
plates. Plate boundary interactions are very important in sculpting our land as the pressure,
stress, and temperature changes allow for the creation of mountain ranges, trenches, and
volcanoes. Additionally, I became better informed on hotspots and the active role they play in the
development of volcanoes, such as those in Hawaii. Moreover, the provided images in the lab
included several scales; in having to use distance for certain analyses, I became more familiar
with measuring distances and converting between units. There were also time scales, typically
representing millions of years, which really added to my understanding of how long these
geological processes take place.