Geology Chapter on Seafloor Spreading

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Questions and Answers

What is the primary characteristic of oceanic ridges?

They are mostly submerged under land.

They are typically located on continental plates.

They generate new ocean floor. (correct)

They exist only in polar regions.

How long is the global oceanic ridge system?

Around 100,000 kilometers

Approximately 70,000 kilometers (correct)

Over 50,000 kilometers

Typically 30,000 kilometers

What geological process primarily occurs at divergent plate boundaries?

Formation of mountains

Seafloor spreading (correct)

Converging tectonic plates

Subduction of plates

What feature is commonly found along the crest of some segments of oceanic ridges?

Rift valleys (D) Signup and view all the answers

What average rate does seafloor spreading occur?

5 centimeters per year (D) Signup and view all the answers

Which of these regions features slow seafloor spreading of about 2 centimeters per year?

Mid-Atlantic Ridge (D) Signup and view all the answers

Which statement about oceanic ridges is false?

They are located only in oceanic regions. (A) Signup and view all the answers

What main force is associated with the formation of rift valleys along oceanic ridges?

Tension (C) Signup and view all the answers

What is the primary process responsible for generating new oceanic crust?

Seafloor spreading (B) Signup and view all the answers

What feature primarily characterizes divergent plate boundaries?

Spreading centers (A) Signup and view all the answers

As oceanic lithosphere ages, what happens to its thickness?

It increases due to cooling and contraction (A) Signup and view all the answers

What is a consequence of the cooling of the upper asthenosphere as it moves away from the zone of upwelling?

It becomes part of oceanic lithosphere (B) Signup and view all the answers

How long does it take for the temperature of oceanic lithosphere to stabilize?

80 million years (D) Signup and view all the answers

What causes the ocean depth to increase away from the ridge crest?

Contraction and increased density of lithosphere (D) Signup and view all the answers

How is the newly formed oceanic crust affected by contact with cold ocean water?

It maintains its thickness (C) Signup and view all the answers

What is the approximate maximum thickness of oceanic lithosphere?

100 kilometers (60 miles) (D) Signup and view all the answers

Study Notes

Divergent Plate Boundaries

Most divergent plate boundaries are found at oceanic ridges, functioning as constructive plate margins generating new ocean floor.
Oceanic ridges are characterized by high heat flow, volcanism, and form the longest topographic feature on Earth, over 70,000 kilometers (43,000 miles) long.
Major segments of the global ridge system include the Mid-Atlantic Ridge, East Pacific Rise, and Mid-Indian Ridge, covering 20% of Earth’s surface.
The average elevation of oceanic ridges is 2 to 3 kilometers (1 to 2 miles) above adjacent ocean basins, despite varying widths from 1,000 kilometers (600 miles) to over 4,000 kilometers (2,500 miles).
Ridges often feature rift valleys, evidence of tensional forces pulling apart the ocean crust.

Seafloor Spreading

Seafloor spreading is the process generating new oceanic crust at divergent boundaries, averaging about 5 centimeters (2 inches) per year.
Slow spreading rates of approximately 2 centimeters (1 inch) per year occur at the Mid-Atlantic Ridge, while faster rates over 15 centimeters (6 inches) have been observed at the East Pacific Rise.
All of Earth’s oceanic lithosphere has been produced in the last 200 million years through this process.
The mechanism involves the movement of two adjacent plates away from each other, creating fractures in the ocean crust that allow magma from the mantle to rise and solidify.

Aging of Oceanic Lithosphere

The lithospheric mantle under newly formed crust is thin due to the high temperatures of the upwelling mantle.
Newly formed oceanic crust cools quickly in contact with ocean water, maintaining a thickness of about 7 kilometers (4 miles).
As the oceanic crust moves away from the hot upwelling zone, it cools, thickens, and becomes denser over time, stabilizing around 80 million years after formation.
The maximum thickness of the oceanic lithosphere can reach about 100 kilometers (60 miles) as it ages.
The increase in lithospheric density and thickness contributes to the greater ocean depth observed away from the ridge crest.

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Description

This quiz explores the concept of seafloor spreading and the geological processes that occur at divergent plate boundaries. It covers the formation of oceanic crust and the role of mantle rocks in generating magma. Test your knowledge on this fundamental aspect of plate tectonics and ocean geology.