Homework for Plate Tectonics Review KEY
Structural Geology
Use these questions to test your knowledge of the Plate Tectonics Review
A. Short answer:
1.
An ophiolite suite is the sequence of rocks that makes up oceanic
lithosphere.
2. An aulocogen is the inactive arm of a three-branched fracture (Triple
Junction) that forms after the initial stages of continental rifting.
3.
Hot spots move
(lithosphere,plate).
much
more
slowly
than
the
overlying
4. The speed of tectonic plate movement varies from plate to plate in the
range of 1 to 10 centimeters per year.
5. The breakup of Pangaea occurred about 200 million years ago.
6. In the future, western California will move northwest along the San
Andreas fault.
7. A suture zone is the boundary between continents that have collided.
8. (Displaced, Exotic) terranes are fault-bounded rock bodies that originated
in one place and have been transported to a continental margin.
B. Match the Terms.
1. Suture zone__f__
a. accretionary wedge
2. Divergent zone quakes __i_ b. sediments, basalt, gabbro, peridotite
3. Mantle convection__h_
c. failed arm of a Triple Junction
4. Craton__g_
d. chimney structures mid-ocean ridge
5. Mélange __a_
e. seamount
6. Volcano caused by plume _e
f. two continents collided
7. Black smokers__d__
g. shield and platform
8. Aulocogen __c___
h. drives plate motion
9. Guyots ___j__
i. between offset ridge segments
10. Ophiolite __b__
j. flat-topped
C. True or False? Circle the correct answer.
1. The chimney-like structures around the mid-ocean “black smokers”
are encrusted with mineral precipitates rich in metals. True or False?
2. The speed of tectonic plate movement varies from plate to plate in the
range of 1 to 10 miles per year. True or False?
3. We can measure plate velocity with radiometric dating of seamount
chains, or the distance of a marine magnetic anomaly from a mid-ocean
ridge. True or False?
4. Marine magnetic anomalies (magnetic "stripes") are often symmetrical
about mid-ocean ridges. True or False?
5. The Hawaiian Islands and the Emperor Seamount chain were formed
because the Pacific plate is moving over a nearly stationary hot spot.
True or False?
6. Guyots are flat primarily because they have been planed off by
weathering, erosion, and ocean waves. True or False?
7. The youngest seamount will be the closest to the hot spot, and an
arrow from the youngest seamount to the next closest seamount indicates
the direction of plate movement. True or False?
8. Hot spots can be used as “fixed” reference points for determining plate
speed and direction because they move much more slowly than the
overlying plates. True or False?
9. The Red Sea contains active convergent margins. True or False?
10. The Great Rift valley of East Africa may be a failed arm (aulocogen)
of a three-branched rift (Triple Junction). True or False?
D. Multiple choice:
1) Unconsolidated sediments atop the oceanic lithosphere may include all
of the following EXCEPT:
(a) siliceous microscopic marine organisms.
(b) calcareous microscopic marine organisms.
(c) pillowed basaltic lavas. (not sediment)
(d) fine-grained, reddish brown clays.
2) The correct sequence of an ophiolite suite, from top to bottom, is:
(a) unconsolidated sediments, basalt layer, gabbro, peridotite.
(b) unconsolidated sediments, gabbro, peridotite, basalt layer.
(c) unconsolidated sediments, basalt layer, peridotite, gabbro.
(d) basalt layer, unconsolidated sediments, gabbro, peridotite.
3) At divergent zones, earthquakes commonly occur:
(a) between offset segments, where segments move in opposite
directions.
(b) at the ridge itself, where magma rises to the surface.
(c) at the ridge itself, where normal faulting occurs.
4) The correct sequence of subduction-zone features from land seaward
is:
(a) continent, forearc basin, accretionary wedge, volcanic arc, backarc
basin, trench.
(b) continent, accretionary wedge, backarc basin, trench, forearc basin,
trench, volcanic arc.
(c) continent, backarc basin, volcanic arc, forearc basin, accretionary
wedge, trench.
(d) continent, backarc basin, accretionary wedge, volcanic arc, forearc
basin, trench.
5) Which of the following tectonic features has been incorporated into the
Himalayan mountain belt?
(a) Accretionary wedges along the southern edge of the Asian plate.
(b) Volcanic arcs along the southern edge of the Asian plate.
(c) Batholiths intruded into the southern edge of the Asian plate.
(d) All of the above.
6) Which of the following statements concerning the basic components of
continents is TRUE?
(a) The continental platform is composed of continental shield covered
by a veneer of younger sedimentary rock.
(b) The edge of the craton is composed of coastal mountains, coastal
plains, and continental shelves.
(c) The continental shields are composed of exposed igneous and
metamorphic rocks.
(d) The shields and platforms are tectonically less active than the coastal
margins.
(e) All of the above.
7) Which of the following statements concerning displaced terranes is
TRUE?
(a) They are distinguished from surrounding rocks by their different
ages, structures, mineralogies, fossil assemblages, and magnetic
properties.
(b) They originated from somewhere other than their present locations.
(c) Many formed as isolated volcanic islands or as pieces broken off
from other continents.
(d) All of the above