Chapter 6: Problem 14

Why does melting take place beneath the axis of a midocean ridge?

Short Answer

Expert verified

Melting occurs beneath the axis of a mid-ocean ridge due to the combination of decreasing pressure and relatively high temperature as the mantle material rises towards the Earth's surface. This causes the partial melting of the mantle, forming magma. The magma then rises through fractures in the lithosphere and solidifies on the ocean floor, ultimately leading to the formation of the mid-ocean ridge.

Step by step solution

Understanding mid-ocean ridges

Mid-ocean ridges are undersea mountain ranges caused by tectonic plate divergence, where two tectonic plates are moving away from each other. This process creates a rift at the boundary between the two plates, allowing magma to rise from the mantle and eventually cool to form new oceanic crust.

Role of mantle material

Beneath the mid-ocean ridges, the mantle material (a solid substance made mostly of iron, magnesium, and silicon) is subjected to extremely high pressures and temperatures. Due to the divergent movement of tectonic plates, mantle material from deeper down is forced upward, as the plates separate, filling the space created by the divergence.

Effect of decreasing pressure and temperature

As the mantle material moves closer to the Earth's surface, the pressure decreases, and its temperature just slightly decreases as well. The combination of lower pressure and relatively high temperature causes the mantle material, mainly the peridotite, to melt partially, forming magma.

Formation of magma and ridge

The partially molten mantle material, or magma, becomes less dense than its surroundings, and buoyancy forces it to rise. The magma finds its way through the fractures in the lithosphere (the solid outermost shell of the Earth) and emerges at the rift between the two diverging tectonic plates. As the magma reaches the surface of the ocean floor, it solidifies and creates new oceanic crust, adding to the mid-ocean ridge.

Summary

Melting takes place beneath the axis of a mid-ocean ridge because of the decreasing pressure on the upwelling mantle material and the relatively high temperature it maintains. This causes the partial melting of the mantle, forming magma that rises, cools, and solidifies on the ocean floor, ultimately leading to the formation of a mid-ocean ridge.

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Why does melting take place beneath the axis of a midocean ridge?

Short Answer

Step by step solution

Understanding mid-ocean ridges

Role of mantle material

Effect of decreasing pressure and temperature

Formation of magma and ridge

Summary

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