Chapter 13 Ocean Floor

The continental shelf is composed of which material(s)?

Granitic crust covered with sedimentary rocks

Which ship was involved in the first global, comprehensive study of the Earth's oceans starting in 1872?

H.M.S. Challenger

How do researchers today routinely determine the depth of the water to the seafloor?

High-resolution multibeam instruments

What happened when the spreading center that generated the Farallon plate collided with the North American plate?

The spreading center ultimately subducted beneath the coast of California. This event destroyed this spreading center and replaced it with a transform fault system.

submerged, flat-topped seamount.

guyot

Which seafloor mapping method can map the largest extent of seafloor in the shortest amount of time?

satellites with radar altimeter

Volcanic island arcs are found near which features on the seafloor?

Deep-ocean trenches

narrow creases in the seafloor that result from subduction

Submarine trench

The oceanic crust is composed almost entirely of ________ rocks that are underlain by ________ rocks, which makes up the lithospheric mantle.

mafic; ultramafic

Which type of faulting is associated with the development of new ocean floor?

normal faulting

Submarine volcanoes, called ________ may rise hundreds of meters above the surrounding seafloor.

seamounts

What is bathymetry?

the topography of the ocean floor and the measurement of ocean depths

A ________ forms when a rising mantle plume causes the overlying crust to dome and separate into three rifts.

triple junction

What is the source of flood basalts associated with oceanic plateaus?

The melting of the head of a mantle plume

Why does the East Pacific Rise lack a rift valley?

The rate of seafloor spreading at the East Pacific Rise is very fast.

How can satellites orbiting Earth determine features on the seafloor without being able to directly observe them beneath several kilometers of seawater?

The satellite measures the variation in the sea-surface elevation by bouncing microwaves off of the water's surface, which mimics the shape of the seafloor.

Although many areas of the continental shelves are relatively featureless, there are some locations on the shelves that have received extensive glacial deposits and significant dissection by streams. How would this have been possible?

The sea level dropped during the last glacial episode because water was stored in large ice sheets, exposing the shelves.

What rock would you expect to find associated with a mid-ocean ridge?

What rock would you expect to find associated with a mid-ocean ridge?

What role do mineral phase changes play in plate subduction?

When an oceanic slab reaches 400 km within the mantle, the mineral olivine changes to its more dense spinel structure. This increase in density helps pull the slab farther down into the mantle.

flat seafloor in the deep ocean

abyssal plain

A(n) ________ forms when sediments from the ocean floor and pieces of oceanic crust are scraped from a subducting oceanic plate and adhere to an overriding tectonic plate.

accretionary wedge

Where are most modern divergent plate boundaries found?

at mid-ocean ridges

The measurement of ocean depth and the topography of the ocean floor are known as ________.

bathymetry

What are the four layers of oceanic crust from top to bottom?

deep-sea sediment, pillow lavas, sheeted dike complex, gabbro

Because massive submarine structures such as seamounts and ridges exert stronger than average gravitational attraction, they produce depressed areas on the ocean's surface.

false

Volcanic islands such as the Hawaiian islands form as a result of ________.

mantle plumes

Where do most divergent boundaries originate?

within continents

What are the four stages of the evolution of an ocean basin from first to last?

(1) The upper crust is broken along normal faults while the lower crust is deformed by ductile stretching; (2) tension pulls apart the crusts and crust slab sink in the middle, forming a rift valley; (3) continued spreading creates a narrow sea; (4) after continued spreading, an ocean and ridge system are created.

What submarine oceanic features are circled in this image?

Seamounts

What is the definition of subduction erosion?

Sediment and rock are scraped off the bottom of an overriding plate and transported into the mantle by a descending plate. Submit

What feature is present in this image? [weird yellow things pointing up]

black smocker

Thermal springs known as ________ are often associated with oceanic ridges, where hot water containing dissolved minerals gushes from the seafloor.

black smokers

gently sloping, submerged extension of the continent

continental shelf

a steep incline that marks the boundary between the continental crust and the oceanic crust.

continental slope

What causes melting of material under divergent plate boundaries?

decompression of rock

Select the correct description of a passive continental margin and the correct description of an active continental margin. Where is each type found?

-An active continental margin is located along a convergent plate boundary, has a deep-ocean trench where subduction takes place, and may have evidence of an accretionary wedge or of subduction erosion. -A passive continental margin is tectonically inactive and far from plate boundaries and features a continental shelf, a continental slope, and a continental rise (from land toward the sea).

What of the below is true for oceanic ridges?

-Oceanic ridge is transected along its length by transform faults at irregular intervals. -Oceanic ridge winds through all of the major oceans on Earth.

How are a slow spreading center such as the Mid-Atlantic Ridge and a fast spreading center such as the East Pacific Rise different from each other?

-Slow spreading centers have prominent ridges and rugged topography; fast spreading centers have rather smooth topographies. -Slow spreading centers tend to have developed rift valleys; fast spreading centers often lack rift valleys. Submit

What are three major features of a passive continental margin?

-continental slope -continental rise -continental shelf

What are the three major topographic provinces of the ocean floor?

-ocean ridges -continental margins -deep-ocean basins

What is the average thickness of the oceanic crust?

7 Km

What happened when the spreading center that generated the Farallon plate collided with the North American plate?

A transform boundary was created.

On the HMS Challenger what was used to measure ocean depths?

A weighted overline

What feature in this image is indicated with arrow X? (Note: it is made of sediments.) [yellowish part by coninetental crust]

Accretionary wedge

How are active continental margins related to plate tectonics?

Active continental margins are located along convergent plate boundaries, where oceanic lithosphere subducts beneath the edge of the continent.

Which of the following is not a possible mechanism contributing to continental rifting?

Changes in gravitational attraction of the moon

Which of the following groups contains all three major topographic provinces oceanographers use to define the seafloor?

Continental margins, mid-ocean ridges, and deep-ocean basins

Which of the following locations displays a triple junction that resulted from a rising mantle plume?

Eastern Africa/Arabian Peninsula

______ play a role in the break-up of supercontinents, like Pangaea.

Mantle plumes Submit

The steepest angle of subduction of oceanic plates can be found at _______.

Mariana Trench

How does a sheeted dike complex form?

New dikes intrude older dikes, which are still warm and weak.

Which of the following is associated with a passive continental margin?

No tectonic boundaries nearby

How does a guyot form?

Over time, guyots lose their original shapes and sizes through the process of weathering, after moving away from their original locations over hot spots. Submit

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, lithosphere is more elevated at the ridge, sinking as it cools while moving away from the ridge.

What is a black smoker?

a particle-filled cloud resulting from metallic-rich solutions gushing form the seafloor into the ocean water

When do new oceans form?

when a continent is broken apart by a divergent boundary

Which part of a passive continental margin is built up by repeated deposition from turbidity currents?

Continental rise

Along which tectonic boundary are deep-ocean trenches found?

Convergent

Which of the following is associated with an active continental margin?

Convergent boundaries

Which process, common near black smokers, uses hot water circulating through the crust to alter olivine and pyroxene into chlorite and serpentine?

Hydrothermal metamorphism

How does hydrothermal metamorphism alter saltwater and the basaltic rocks that make up the seafloor?

Hydrothermal metamorphism causes the minerals olivine and pyroxene in basalt to form new minerals, such as chlorite and serpentine. It also dissolves various ions in the hot seawater, which eventually rise along fractures and spew out on the ocean floor.

Contrast spontaneous subduction with forced subduction.

Spontaneous subduction, which occurs at Mariana-type subduction zones, takes place when old, dense lithosphere subducts beneath the other plate at a very steep angle. In contrast, forced subduction, which occurs at Peru-Chile-type subduction zones, takes place when hot, low-density lithosphere subducts beneath the other plate at a shallow angle because of compressive forces. Submit