Mastering Geology: Chapter 13 Ocean floor

How does an accretionary wedge form?

An accretionary wedge forms at an active continental margin when the subducting oceanic slab scrapes pieces of itself onto the more buoyant continental slab.

Select the correct description of a passive continental margin and the correct description of an active continental margin. SELECT ONE FOR EACH.

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 features a continental shelf, a continental slope, and a continental rise (from land toward the sea).

How do oceanic ridges differ from continental mountain ranges?

Most mountain ranges form through the collisions of two continents, whereas oceanic ridges form when material upwells from the mantle and generates new oceanic crust.

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.

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.

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.

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 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.

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.

What are the features associated with a divergent boundary that is spreading quickly?

a relatively smooth swell with gentle slopes

Where are most modern divergent plate boundaries found?

at mid-ocean ridges

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

normal faulting

What is a black smoker?

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

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

What features on the ocean floor most resemble flood basalt provinces on the continents?

oceanic plateaus

What two layers of the ophiolite sequence are compositionally similar, but formed in different areas with respect to the crust?

pillow lavas and gabbro

Where do most divergent boundaries originate?

within continents

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

- deep-ocean basins - continental margins - oceanic ridges

How are deep-ocean trenches related to plate boundaries?

Deep-ocean trenches are sites of plate convergence where an oceanic plate subducts under another plate.

Part complete 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.

What causes melting of material under divergent plate boundaries?

decompression of rock

What is bathymetry?

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

When do new oceans form?

when a continent is broken apart by a divergent boundary

The oceanic ridge system _____. SELECT ALL THAT APPLY.

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

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.