II. Tectonic
Evolution of the Ocean Basins (50 Points). The following section concerns the northern North
Atlantic, Norwegian Sea, & the Arctic Ocean (Figure 1) & the North
Atlantic Ocean (Figure 2). A
time scale is also provided at the back of the test. The light dashed line is the shelf edge.
A. Spreading
Rates. Calculate the following
spreading rates. Show your
calculations. Remember: 1 degree of latitude equals ~110 km. (13 pts.)
1. What
is the current full spreading rate for the Mid-Ocean Ridge (MAR) between the
Lomonosov Ridge & the Siberian margin?
2. What
is the current full spreading rate for the MAR between northern Greenland &
Norway?
3. What
is the current full spreading rate for the MAR between southern Greenland &
Rockall Plateau?
4. What
is the current full spreading rate for the MAR between the Grand Banks &
Iberia?
5. What
is the current full spreading rate for the MAR between Dakar & Savannah?
6. Why
do the spreading rates vary among the five MAR ridge segments for which you
have calculated spreading rates? (3 pts.)
B. Answer
& do the following. (37 pts.)
1. Indicate
on Figure 2 the location of the oldest seafloor in the North Atlantic Ocean
using shading. (3 pts.)
1.a. Where
is the oldest seafloor in the North Atlantic Ocean?
b. How old is this seafloor (age and
geologic period)?
c. How do you know this?
2. a. When did Laurasia begin
to separate from Gondwana (anomaly #, age & geologic period)?
b. How
do you know this?
3. a. When did Laurasia begin
to break up (anomaly #, age & geologic period)?
b. How
do you know this?
c. What
do the bights formed by anomaly 34 off the Grand Banks & Iberia imply about
Iberia during the initial Laurasian breakup? (3 pts.)
4. a. How old is the oldest
seafloor adjacent to the margins of Greenland (anomaly #, age & geologic
period)?
b. How
do you know this?
c. When
did Greenland & Eurasia begin to separate (anomaly #, age & geologic
period)?
d. What
do the bights formed by anomalies 24-20 south of Greenland & off the
Rockall Plateau imply about Greenland during this time period? (3 pts.)
e. When
did Greenland become part of North America (anomaly #, age & geologic
period)?
b. How do you know this?
VII. Tectonic Evolution of the Ocean Basins (25
Points). Answer the following questions
concerning the North Atlantic Ocean. Refer to figure 1 and the time scale at the back of this
test. The light dashed line is the
shelf break.
7. How
many hotspots are there in this part of the Atlantic? Name them.
3. a. When did North America begin to
separate from Eurasia (age and geologic period)?
b. How do you know this?
VIII.
Tectonic Evolution of the Ocean Basins (20 Points). Answer the following questions
concerning the northern North Atlantic, Norwegian Sea, and the Arctic Ocean. Refer to figure 1 on the last page of
this test. The light dashed line
is the shelf break.
10. a. What is the probable
origin of the Lomonosov Ridge?
b. How
do you know this?
1.a.)
How old is the basin between the Lomonosov Ridge and the continental
margin between Siberia and Spitbergen?
b.) How
do you know this?
2.a.)
How would you determine the age of the other two basins in the Arctic
Ocean?
b.) Are
they probably older than the basin east of the Lomonosov Ridge?
c.) Why?
6. What
kind of plate boundary trends between Spitzbergen and northern Greenland?
8. Briefly
describe the tectonic history of the seafloor between southern Norway &
central Greenland (north of Iceland & the Faeroe Islands). Include in your description the origin
of Jan Mayen Ridge & timing of events. (3 pts.)
9. Briefly
describe the origin of Iceland, the Faeroe Islands & the Iceland-Faeroe
Ridge. (3 pts.)
7. What
kind of crust probably underlies the Rockall Plateau?
7.a.)
What kind of crust probably underlies the Rockall, Voring and Chukchi
Plateaus?
b.)
Briefly explain why you think this. (2 pts.)
II. Tectonic
Evolution of the South Atlantic
- Answer the following questions concerning the South Atlantic Ocean. Refer to figure 1 and the time scale at
the back of this test. The light
dashed line is the shelf break.
(50 Points).
1.a. Where
is the oldest seafloor in the South Atlantic Ocean?
b. How
old is this seafloor (age & geologic period)?
c. What
specific data allows you to answer the questions above?
2.a. How
fast (cm/yr) did South America separate from the southern tip of Africa during
the Early Cretaceous? Remember -
show you calculations!
b. How
fast (cm/yr) did South America separated from Africa during the Late
Cretaceous?
c. How
fast (cm/yr) did South America separate from Africa during the Paleocene,
Eocene & Oligocene?
d. How
fast (cm/yr) did South America separate from Africa during the Miocene,
Pliocene & Quaternary?
e. Why
did the paleomagnetists at Lamont choose the magnetic anomaly lineations in the
South Atlantic as the basis for extending the paleomagnetic reversal time scale
from the Gilbert Epoch to anomaly 32?
3.a. What
evidence is there for mid-ocean ridge jumps in the South Atlantic Ocean?
b. When
did this (these) ridge jumps occur (age & geologic period)?
4.a. What
are the Walvis Ridge & the Rio Grande Rise called?
b. How
did they form?
c. Were
they ever one feature?
d. If
so, when did they become separate features (age & geologic period)?
e. Why
is the Walvis Ridge longer in a North-South direction than the Rio Grande Rise?
f. What
does the Tristan hotspot have to do with these features?
5.a. When
did the Islas Orcadas & Randy Rises form (age & geologic period)?
b. When
did they separate (age & geologic period)?
6.a. What
kind of crust underlies the Falkland Plateau & Mozambique Ridge?
b. What
evidence can you cite to support your answer above?
7.a. What
age is the seafloor in the triangular area immediately to the west of the
Mozambique Ridge (age & geologic period)?
b. What
evidence supports your answer above?
8. Where
in the South Atlantic would you expect to find INTERMEDIATE & DEEP
earthquakes?
9. What
is the significance of the magnetic bight formed by anomalies 32-34 due south
of Africa? Use a sketch if you
wish.
10. How
did the line of seamounts off Brazil lying at ~20 degrees S latitude between 28
degrees W & 38 degrees W probably form?
III.
Tectonic Evolution of the Ocean Basins (35 Points). Answer the following questions
concerning the Pacific Ocean.
Refer to the map and magnetic polarity time scale at the end of this
test. Questions 1,2 and 5 are
worth 5 points each and questions 3 and 4 are worth 10 points each.
(9 pts.)
1.a. Where is the oldest
seafloor in the Pacific located?
b. How
old is this seafloor?
c. How
do you know this?
(10 pts.) 2.
The Mesozoic sequence in the western Pacific shows two bights. In the space below, sketch a cartoon
showing the implications of this in terms of: 1) plate boundary types, 2) number of plate boundaries, and
3) number of plates. Label all
plates.
(10 pts.) 3.
Why do magnetic anomaly #'s increase to the south away from the Aleutian
Trench? Use sketches to illustrate
the sequence of events leading to the present situation.
(9 pts.)
4.a. Why did the East
Pacific Rise change oriention?
b. How
do we know that it changed orientation?
c. When
did it change orientation?
(2 pts.)
5. Why is there a bend in
the Hawaiian-Emperor Seamount Chain?
V. Tectonic
Evolution of the Ocean Basins (50
Points). The following section concerns the
tectonic evolution of the Indian
Ocean (Figure 1 at the back of the test). A time scale is also provided at the back of the test. The light dashed line is the shelf
edge.
A. Spreading Rates. Calculate the following spreading
rates. Show your calculations and
indicate on Figure 1 where you have made your measurements. Remember: 1 degree of latitude equals ~110 km. (10 pts.)
1. What
is the current full spreading rate for the Mid-Ocean Ridge (MOR) between India
and Madagascar?
2. What
is the current full spreading rate for the MOR between Kerguelen Plateau and
Broken Ridge?
3. What
is the current full spreading rate for the MOR south of Australia (at 50 degrees
S and 125 degrees E)?
4. How
fast did West & East Gondwana separate during the Late Jurassic (~160-145
m.y. ago)?
5. How
fast did India separate from Antarctica/Australia between the Late Cretaceous
(~80 m.y. ago) and the Early Eocene (~50 m.y. ago)?
B. Answer
and do the following. (40 pts.)
1. a. Indicate on Figure 1
the location of the oldest seafloor in the Indian Ocean using shading.
1.a.
Where is the oldest seafloor in the Indian Ocean?
b. How
old is this seafloor (age and geologic period)?
c. How
do you know this?
b. When did Gondwana begin to
break up (anomaly #, age and geologic period)?
c. How do you know that
Madagascar separated from Kenya and not from Mozambique?
7.a. Did
Madagascar separate from Kenya or Mozambique?
b. How
do you know this?
d. Using the drawing provided in
Figure 2, sketch the fragments into which Gondwana broke up and label them.[In
this an all subsequent sketches, indicate how each of the modern Gondwana
fragments - South America, Africa, Arabian Peninsula, India, Madagascar,
Antarctic, Australia, and Sunda Peninsula - related to each other, that is how
did they change from being 1 plate to the present 6 plates (S. Am., African,
Arab., Indo-Aust., Ant. & Eurasian).] (3 pts.)
2. a. What do the M-sequence
anomalies (give their anomaly #'s, age and geologic period) off western
Australia indicate about the continued disintegration of Gondwana during the
Early Cretaceous?
2.a.
When did India begin to separate from Gondwana?
b. How
do you know this?
b. Sketch and label the
fragments into which Gondwana has broken by this time. (3 pts.)
3.a.
When did Africa begin to separate from Gondwana?
b. How
do you know this?
3. a. What evidence is there
for Cretaceous spreading ridge reorientations in the eastern Indian Ocean?
b. When did reorientation take
place (anomaly #, age and geologic period)?
c. Is there any difficulty
determining when reorientation occurred?
d. What other tectonic events
occurred in the Indian Ocean about this time? [Hint: What is
happening with India?]
e. Sketch and label the
fragments into which Gondwana has broken by this time. (3 pts.)
4. a. Why are the 90East and
Chagos-Laccadive Ridges and the eastern Mascarene Plateau so linear?
b. Why are the Chagos-Laccadive
Ridge & Mascarene Plateau and Broken Ridge and Kerguelen Plateau separate
features?
5. When
was the majority of seafloor between India & Arabia formed (age &
geologic period)?
5. a. When did Australia and
Antarctica begin to separate (anomaly #, age and geologic period)?
b. Sketch and label the
fragments into which Gondwana has broken by this time. (3 pts.)
6. a. When did the MOR in the
Indian Ocean attain its current orientation (anomaly #, age and geologic
period)?
b. What probably caused the MOR
to reorient from its Late Cretaceous and Early Tertiary orientation to its
current orientation?
8. a. When
did India collide with Asia (age and geologic period)?
b. How
do you know this?
7. What
has been the most recent (within the last 10 m.y. or so) event in the breakup
of Gondwana?
8. How
is the subduction of seafloor in the Java Trench similar to that in the
Aleutian Trench? Use sketches if
you wish.
V. Tectonic
Evolution of the Ocean Basins (15
Points). Answer the following:
1. Briefly
discuss the reason that it is pure coincidence that the oldest seafloor in both
the Atlantic & Pacific Oceans is ~190 my old. Use sketches if you wish. (5 pts.)
2. How
is the subduction of seafloor in the Java Trench similar to that in the
Aleutian Trench? Use sketches if
you wish. (5 pts.)
3. What
two major events in the tectonic history of the ocean basins contributed to the
profound cooling of deep ocean waters characterizing the Cenozoic, & when
did they occur. (5 pts.)