Chapter 4: Problem 6

How does oceanic crust form along a mid-ocean ridge? (E)

Short Answer

Expert verified

The oceanic crust forms along mid-ocean ridges due to the movement of tectonic plates and mantle convection. As oceanic plates diverge, hot mantle material rises to the surface, causing decompression melting and forming magma. The magma rises through the lithosphere, cools rapidly upon contact with seawater, and solidifies into dense basaltic rocks. This process continuously creates new oceanic crust while pushing older crust away from the mid-ocean ridge.

Step by step solution

Define mid-ocean ridge and oceanic crust

A mid-ocean ridge is an underwater mountain range formed by the tectonic movement of Earth's crust. This geologic feature marks the boundary between two oceanic plates that are moving away from each other. Oceanic crust is composed mainly of basalt, a dark-colored and dense igneous rock. It is formed from the cooling and solidification of magma that rises from the Earth's mantle to the surface.

Discuss tectonic plate movements

Tectonic plates are massive, irregularly shaped slabs of the Earth's lithosphere that move continuously atop the underlying, more fluid asthenosphere. Mid-ocean ridges are created along divergent plate boundaries, where two oceanic plates move away from each other. This movement is driven by mantle convection, which causes tectonic plates to be pulled apart.

Explain mantle convection and magma formation

Mantle convection is the slow movement of mantle material due to differences in temperature and pressure within the Earth. Hot, less dense mantle material rises towards the surface at the mid-ocean ridges, while cooler, denser mantle material sinks back into the Earth. As the hot mantle material rises, the pressure decreases, causing partial melting of the mantle rock (also called asthenosphere) to form magma. This process is known as decompression melting.

Describe the cooling and solidification of magma

Once the magma is formed, it rises through the cracks and fissures in the oceanic lithosphere. When it reaches the seafloor at the mid-ocean ridge, it rapidly cools and solidifies upon contact with the cold seawater. As the magma cools, it forms basaltic rocks such as pillow basalt and sheeted dikes. This creates new oceanic crust, which is continuously added to the edges of the diverging tectonic plates.

Summarize the formation of oceanic crust along mid-ocean ridges

The oceanic crust forms along mid-ocean ridges through the process of mantle convection and the movement of tectonic plates. As oceanic plates move apart, hot mantle material rises to the surface and causes decompression melting to form magma. This magma then rises through the lithosphere and cools rapidly upon contact with the seawater, forming dense basaltic rocks that create new oceanic crust. This process continues as the tectonic plates continue to diverge, gradually expanding the oceanic crust and pushing older crust away from the mid-ocean ridge.

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How does oceanic crust form along a mid-ocean ridge? (E)

Short Answer

Step by step solution

Define mid-ocean ridge and oceanic crust

Discuss tectonic plate movements

Explain mantle convection and magma formation

Describe the cooling and solidification of magma

Summarize the formation of oceanic crust along mid-ocean ridges

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