Virtually all of the igneous rocks that we see on Earth are derived from magmas that formed from partial melting of existing rock, either in the upper mantle or the crust.
Partial melting is what happens when only some parts of a rock melt; it takes place because rocks are not pure materials.
Most rocks are made up of several minerals, each of which has a different melting temperature. The wax in a candle is a pure material. If instead you took a mixture of wax, plastic, aluminum, and glass and put it into the same warm oven, the wax would soon start to melt, but the plastic, aluminum, and glass would not melt Figure 3. Again this is partial melting.
As you can see from Figure 3. It is most likely that this is a very fine-grained mixture of solid wax and solid plastic, but it could also be some other substance that has formed from the combination of the two. In this example, we partially melted some pretend rock to create some pretend magma.
We then separated the magma from the source and allowed it to cool to make a new pretend rock with a composition quite different from the original material it lacks glass and aluminum. The main differences are that rocks are much more complex than the four-component system we used, and the mineral components of most rocks have more similar melting temperatures, so two or more minerals are likely to melt at the same time to varying degrees.
Another important difference is that when rocks melt, the process takes thousands to millions of years, not the 90 minutes it took in the pretend-rock example. Contrary to what one might expect, and contrary to what we did to make our pretend rock, most partial melting of real rock does not involve heating the rock up. The two main mechanisms through which rocks melt are decompression melting and flux melting.
Decompression melting takes place within Earth when a body of rock is held at approximately the same temperature but the pressure is reduced. This happens because the rock is being moved toward the surface, either at a mantle plume a. If a rock that is hot enough to be close to its melting point is moved toward the surface, the pressure is reduced, and the rock can pass to the liquid side of its melting curve.
At this point, partial melting starts to take place. Why do earthquakes happen in clusters? Where are earthquakes expected in the world, especially in Asia?
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