Geology: Mid-Oceanic Ridges

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Questions and Answers

What is the primary morphological difference between fast-spreading and slow-spreading ridges?

Fast-spreading ridges have a rugged rift mountain structure.

Slow-spreading ridges are dominated by volcanism.

Fast-spreading ridges have a narrow summit graben. (correct)

Slow-spreading ridges have a smooth volcanic summit.

Which mid-ocean ridge is characterized by a rift valley similar to the Grand Canyon?

East Pacific Rise

Mid-Atlantic Ridge (correct)

Gakkel Ridge

Southwest Indian Ridge

What is the typical spreading rate of the East Pacific Rise?

Less than 20 mm per year

0.8 to 2 inches per year

2 to 5 centimeters per year

3 to 6 inches per year (correct)

What is the primary function of mid oceanic ridges in tectonic activity?

To serve as divergent tectonic boundaries Signup and view all the answers

What is the characteristic crustal thickness at ultraslow-spreading ridges?

1 to 4 km Signup and view all the answers

What unique feature is present in ultraslow-spreading ridges?

Amagmatic rifts exposing mantle peridotite Signup and view all the answers

How thick is the lithosphere, which includes the crust and uppermost mantle?

About 70–100 km Signup and view all the answers

What type of geological features primarily bound tectonic plates?

Mid oceanic ridges, subduction zones, and transform faults Signup and view all the answers

Which factor does NOT contribute to the changeover from slow- to ultraslow-spreading characteristics?

Spreading rate Signup and view all the answers

Which statement is true regarding the morphology of slow-spreading ridges?

They are dominated by tectonics. Signup and view all the answers

What is the rate of seafloor spreading at the fastest mid oceanic ridges?

Up to 200 mm/year Signup and view all the answers

What is typically associated with fast-spreading ridges regarding volcanic activity?

Volcanism is a dominant feature. Signup and view all the answers

Which mid oceanic ridge is noted as the slowest spreading ridge?

Gakkel mid oceanic ridge Signup and view all the answers

How many primary tectonic plates are currently recognized?

Eight Signup and view all the answers

What geological process occurs simultaneously with the formation of new crust at mid oceanic ridges?

Subduction of oceanic plate Signup and view all the answers

Which of the following best describes the nature of the motion of tectonic plates?

Continuous at a speed of a few centimeters per year Signup and view all the answers

What is the maximum rate of magma generation at the East Pacific Rise?

200 mm/year Signup and view all the answers

How does the seafloor morphology differ between fast and slow spreading ridges?

Slow spreading ridges exhibit rugged topography. Signup and view all the answers

What feature is typically present on slow spreading ridges?

Axial valley Signup and view all the answers

What happens to most of the magma generated beneath a mid oceanic ridge?

It freezes within the crust without erupting. Signup and view all the answers

What are dikes in the context of mid oceanic ridges?

Magma-filled cracks that transport magma to the surface. Signup and view all the answers

How thick is the average oceanic crust, and how much of it is formed by eruption processes?

7 km thick, with 1 to 3 km from eruptions. Signup and view all the answers

What rate defines a 'slow' ridge in terms of lava generation?

Less than 60 mm/year Signup and view all the answers

Which of the following is a characteristic of the East Pacific Rise?

It has a smooth volcanic summit. Signup and view all the answers

Study Notes

Introduction to Mid Oceanic Ridges

The lithosphere, which includes the Earth’s crust and upper mantle, is approximately 70-100 km thick and divided into tectonic plates.
There are around eight primary tectonic plates, along with seven secondary plates and several tertiary plates.
Tectonic plate boundaries include mid oceanic ridges, subduction zones, and transform faults, all associated with seismic activity.
Plates move at speeds of a few centimeters per year, creating new crust at mid oceanic ridges and recycling old lithosphere at subduction zones.

Morphology of Mid Oceanic Ridges

Mid oceanic ridges are underwater linear features that demarcate divergent tectonic boundaries between lithospheric plates.
These ridges extend approximately 65,000 km globally, creating significant seafloor spreading through volcanic activity.
Seafloor spreading rates range from 6 to 200 mm/year, categorizing ridges into slow, intermediate, and fast spreading types.
The Gakkel Ridge (Arctic) is the slowest, spreading at about 6 mm/year, while the East Pacific Rise is the fastest, with rates of up to 200 mm/year.
Fast spreading ridges exhibit smooth seafloor surfaces, while slow spreading ridges characterize rough topography and are marked by axial valleys or rifts.

Internal Structure of Mid Oceanic Ridges

Beneath a mid oceanic ridge, mantle material partially melts due to decreased pressure, forming magma that pools below the seafloor before erupting.
The average thickness of oceanic crust is around 7 km; however, only 1 to 3 km forms through eruptions.
Eruptions occur when magma pressure forces it to the surface, creating "dikes"—magma-filled cracks facilitating the flow to the seafloor.
Magma eruption rates can vary, with typical new lava coating the seafloor at rates of about 60 mm/year for "fast" and less than 60 mm/year for "slow" spreading.

Comparison of Ridge Types

Fast-spreading ridges often have a narrow axial rise and smoother features dominated by volcanic activity.
Slow-spreading ridges are characterized by broad axial valleys, rugged topography, and tectonic features evident in their formation.
The Mid-Atlantic Ridge (2-5 cm/year) forms a noticeable rift valley, while the East Pacific Rise (6-16 cm/year) features a smooth summit without a prominent rift.

Ultraslow-Spreading Ridges

Ultraslow-spreading ridges (<20 mm/year) exhibit unique characteristics, such as thinner seismic crust (~1-4 km) and amagmatic rifts exposing mantle material at the seafloor.
These ridges differ from standard ridges by featuring mantle peridotite exposed due to minimal basaltic activity.

Key Locations

Mid-Atlantic Ridge: Central in the Atlantic Ocean, forming a significant rift valley.
East Pacific Rise: Fast spreading with a smooth summit and no prominent rift valley.
Gakkel Ridge: The slowest spreading ridge, located between Greenland and Siberia.

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Description

Explore the fascinating world of mid-oceanic ridges and the tectonic plates that shape our planet's surface. This quiz dives into the lithosphere and examines the major and secondary tectonic plates, their boundaries, and their geological significance. Test your knowledge on Earth’s dynamic systems and processes.