Why are rocks not melting deep in the earth’s crust?

Magma is generated within Earth's mantle, the thick layer between Earth's crust and outer core. Rock found deep within the crust is extremely hot, soft, and pliable, but rock does not become liquid until much deeper in the upper mantle. Pockets, or chambers of magma, can originate at various depths within the earth. The composition of the magma varies and indicates the source materials and depth from which they originated. Silicon dioxide (SiO2) is the predominant ingredient in magma. Other ingredients include aluminum oxide, iron, magnesium, calcium, sodium, potassium, titanium, manganese, phosphorus, and water.

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