Geology 101 - Chapter 10
Match the ophiolite layers with the way in which they are created.
Gabbro layer -created when the magma chamber moves away from the rift and crystallizes. Pillow Basalt layer -created as magma erupts under water, creating elongated structures as the lava cools. Sheeted Dikes layer -created when pressure from new magma causes multiple factures through which magma travels up towards the surface.
Which of the following is a true statement regarding the Farallon Plate?
It was an oceanic plate that used to exist between the Pacific and North American Plates.
Which best explains the demise of the Farallon Plate?
It was subducting faster than it was being generated.
Why does oceanic lithosphere subduct even when the oceanic crust is less dense than the underlying asthenosphere?
Lithospheric mantle, which makes up roughly 80 percent of the subducting oceanic slab, is colder and denser than the asthenosphere. This density difference causes the oceanic slab to subduct even if the asthenosphere is very dense.
Match the features below with the locations indicated by letters on the diagram above. (You may use the same location more than once.)
Mid-Ocean Ridge -C Subduction Zone -B Divergent Plate Boundary -C Trench -B Passive Continental Margin -E Volcanic Ocean Island -D Continental Volcanic Arc -A
What happens as plates diverge at an oceanic ridge?
New oceanic crust and lithospheric mantle are generated by the cooling of molten rock upwelling from the mantle.
________ is (are) not part of an ophiolite complex.
Residual, unmelted, crustal lithosphere
What is the purpose of ARMS?
Scientist use ARMS, which is a small collection device, to collect thousands of specimens from the sea bed. - ARMS is placed on reefs so marine life can live in them.
Which one of the following types of plate boundaries is most commonly found along a coastline, where ocean and continent meet?
Convergent with subduction
Ocean trenches are associated with which one of the following plate boundary types?
Convergent with subduction.
What system hosts more biodiversity than any other ecosystem in the oceans?
Coral reefs are believed to have the highest biodiversity of any ecosystem in the oceans.
Which of the following is true regarding shallow subduction angles?
Sediment and seamounts are scraped from the downgoing plate to produce an accretionary wedge.
Young oceanic lithosphere typically experiences what type of subduction and at what angle?
Forced Subduction; shallow angle
Subduction can start in two ways: forced subduction and spontaneous subduction. For the figure above, does the angle of subduction indicate forced or spontaneous subduction?
Spontaneous subduction because the subduction angle is steep.
True or False: Submerged, flat-topped seamounts are known as guyots.
TRUE
True or False: When an ocean develops subduction along its margins, it is beginning the process of destruction and closing.
TRUE
Which of the following correctly describes the Atlantic and Pacific continental margins?
The Atlantic is a passive margin, and the Pacific is an active margin.
Which of the following accurately compares the Mid-Atlantic Ridge and East Pacific Rise?
The Mid-Atlantic Ridge is spreading at a much slower rate than the East Pacific Rise.
What happened to the Farallon Plate approximately 20 million years ago?
The San Andreas and Queen Charlotte Faults were established where it was subducted beneath the North American plate.
The world's oceans cover what percentage of Earth's surface?
The world's oceans cover almost 70 percent of earth's surface.
Passive continental margins develop:
Where one plate has broken into two, forming a divergent boundary.
Active continental margins develop:
Where one plate has subducted under another plate, forming a subduction zone.
What are the features associated with a divergent boundary that is spreading quickly?
a relatively smooth swell with gentle slopes
Strike-slip faulting of the Queen Charlotte and San Andreas fault systems shows __________.
a right lateral sense of motion
Where are deep-sea trenches found?
adjacent to active continental margins
Seamounts ________.
are volcanoes that form on the ocean floor
Where in the oceans are biological communities thriving without sunlight?
around seafloor, hot spring vents
Where are most modern divergent plate boundaries found?
at mid-ocean ridges
The timing of __________ and continental breakup strongly correlate.
flood basalt formation
What is the lowermost layer in an ophiolite complex?
gabbro
Passive continental margins
have developed from divergence.
The Gulf of Aden represents which part of the rifting sequence?
linear sea
Which of the following contains the entire ophiolite suite, in order from the mantle to the seafloor?
mantle peridotite, gabbro, sheeted dike complex, pillow lavas, deep-sea sediments
A slow-spreading ridge will generally have ________ compared to a faster spreading ridge.
more rugged topography
Which type of faulting is associated with the development of new ocean floor?
normal faulting
Which of the following is most likely to sink into the asthenosphere?
oceanic lithosphere that is more than 15 million years old
Which of the following is found in Layer 2 of the oceanic crust?
pillow lavas
What two layers of the ophiolite sequence are compositionally similar, but formed in different areas with respect to the crust?
pillow lavas and gabbro
Near which feature of plate tectonics is Mt. Kilimanjaro located?
rift valley
What feature connects the South American Paraná and African Entedeka flood basalts?
seamount chains
Compare continental margins and ocean basins of the Atlantic and Pacific oceans using the map below. Deep ocean trenches are delineated with red lines, which indicates the margin is active. Label these features correctly for margin type and ocean basin dynamics.
see image
Label the continental shelf, continental slope, continental rise, and abyssal plain by matching the following terms.
see image
Look at this illustration of the structure of the oceanic crust. Match the following terms to the appropriate part of the figure: pillow lavas, mantle peridotite and related rocks, sheeted dike complex, gabbro, deep-sea sediment.
see image
Review the accompanying topographic map of the eastern United States and the figure of a typical continental margin in this region. Label the different features shown.
see image
Review the graph and map. The graph points to latitude belts. Label each of these latitude belts with its correct description.
see image
Where do most divergent boundaries originate?
within continents
In the next 100 million years, the Red Sea will transition from a _______ to mature ocean, which will involve ______.
young narrow sea, spreading at a mid-ocean rift
Active vs. Passive Continental Margins
-Active continental margins are places where the edge of a continent is also the edge of a tectonic plate. -Passive continental margins are places where the edge of a continent is in the middle of a tectonic plate. These two types of plate margins are associated with very different geologic processes. At an active continental margin you will typically find a narrow continental shelf, a deep ocean trench, and volcanic and earthquake activity associated with subduction. At a passive continental margin, you will find a wide continental shelf, no volcanoes or earthquakes, with layers of sediment built up along the shelf.
Oceans cover approximately ________ of Earth's surface area?
70%
Pre-ocean is the youngest stage of an ocean's history. Post-ocean is the oldest stage in an ocean's history. List youngest to oldest.
A D B E C
Identify the following features found on the ocean floor (these are all features that are not associated with plate boundaries):
A -Abyssal Plain B -Guyot C -Volcanic Ocean Island D -Seamount
A) Find the Mid-Atlantic Ridge. This feature is a(n): B) The east coast of Australia has a(n):
A) Divergent Boundary B) Passive Continental Margin
A) When the angle of subduction is steep, the volcanic arc is ________ to the trench. B) When the angle of subduction is less steep (closer to horizontal), the trench and volcanic arc ___________.
A) close B) are farther apart
"Black smokers" are associated with ________.
Black smokers are associated with all of these: -metal-rich sulfide deposits -hot water -oceanic ridges
Which statement regarding Baja Mexico and the city of Los Angeles is correct?
Both are located on the Pacific Plate.
Various features (landforms) that we find on the ocean floor are associated with specific plate boundaries. Identify two landforms on the ocean floor that can be used to identify two different types of plate boundaries. For each of the two landforms you chose, identify the type of plate boundary that created it. (Format of your answer should be: "landform: created by plate boundary")
Deep-Ocean Trenches: created by convergent plate boundaries Mid-Ocean Ridge: created by divergent plate boundaries
Imagine you are an oceanographer using an echo sounder on a research vessel. Can you determine the water depth based on the amount of time it takes a sound pulse to travel to the ocean floor, reflect off the ocean bottom, and bounce back up to the recorder on the vessel? For this problem, the signal takes 6 seconds to strike the bottom and return to the recorder. Assume that the speed of sound waves in the water is 1500 meters per second. (distance = speed X time)
Depth of water can be determined when you know the wave travel speed and the amount of time it takes the wave to reach the seafloor. In this case, the water depth is 4500 meters.
When a plate boundary occurs in the middle of an ocean basin, what type of plate boundary is it most likely to be?
Divergent
A mid-ocean ridge is associated with which one of the following plate boundary types?
Divergent.
The ________ is an example of the earliest stage in the formation of a new ocean basin.
East African Rift
On Earth, we have oceans in each stage of maturity. So while we can not watch an individual ocean move through the stages, from creation to destruction, we can see what each stage looks like, and what geologic processes are associated with each stage. The map below identifies five locations that match the stages of ocean creation (pre-ocean) to ocean destruction (post ocean). List youngest to oldest.
East African Rift Red Sea Atlantic Ocean Pacific Ocean Himalayan Mountains
True or False: The Atlantic ocean is currently a mature ocean, so the next stage of ocean development will involve a continental rift.
FALSE
What is the goal of the Census of Marine Life?
The goal of the Census of Marine Life is to compile the most comprehensive list to date of all life in the oceans.
What is the primary reason for the elevated position of the oceanic ridge system?
The oceanic lithosphere at the ridge is hotter than the older lithosphere that is farther from the ridge. Because the hotter lithosphere at the ridge is less dense than the cooler lithosphere farther away, the lithosphere is more elevated at the ridge, sinking as it cools as it moves away from the ridge.
Choose the true statement regarding the continental shelf.
The shelf represents the flooded portions of continents.
Turbidity currents travel from the shelf through __________, creating deep sea fans.
canyons
A thick accumulation of sediment that has moved down from the continent and onto the deep ocean floor.
continental rise
Which of the following is a feature of a passive continental margin? Choose all that apply.
continental rise, wide continental shelf, deep-sea fans
Continental crust submerged under seawater.
continental shelf
Geologically, ________ are actually submerged parts of the continents.
continental shelves
A relatively steep structure that forms the boundary between continental crust and oceanic crust.
continental slope
The plate boundary in the U.S. Pacific Northwest is _____, while most of the California coast is characterized by a _____ plate boundary.
convergent; transform
Name the correct order of rifting events.
crustal upwarp, rift valley, linear sea, ocean
What causes melting of material under divergent plate boundaries?
decompression of rock
The features of active and passive continental margins and the characteristics of ocean basins are evidence for existence, or absence of a plate boundary. Read the sentences below, and fill in the blanks to make them complete and correct. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer.
see image; Subduction zones and mid-ocean ridges are responsible for many changes in the size of ocean basins. Oceanic crust spreads at mid-ocean ridges. Submarine canyons are deep valleys at passive continental boundaries. They are likely carved out by turbidity currents. Melt from the subducting plate rises to the surface and forms continental volcanic arcs on continents or volcanic island arcs in the ocean. The area surrounding the volcanoes in the Pacific Ocean is called the Ring of Fire. Contemplate how a change in water level would affect the land area at an active continental margin. The effect would be different at passive continental margins, which have gradual slopes. This thought experiment exemplifies the wide reaching impact of plate tectonics. Natural hazards, history, and resource exploration and extraction all informed by the study and application of this topic.
If the subduction angle is steep, the overriding plate may undergo __________.
subduction erosion
With which feature of plate tectonics is the Mariana Trench associated?
subduction zone
What is the source of magma for seafloor spreading?
the partial melting of peridotite into basaltic material from the mantle
Which of the following provides the best example of an active continental margin?
the west coast of South America
What sequence of rocks would you expect rift valley evolution to produce, from oldest to youngest?
volcanic rocks, clastic sedimentary rocks, deep sea sedimentary rocks
When do new oceans form?
when a continent is broken apart by a divergent boundary