Magma originates from melting of rocks deep within Earth's interior, primarily in the mantle and, to a lesser extent, the crust. It forms when rocks are heated, undergo decompression, or experience changes in composition (for example, addition of volatiles like water), allowing minerals to melt and create a mobile silicate melt that can pool in magma chambers and feed volcanic eruptions. Key points

• Where magma forms: mainly in the mantle; partial melting also occurs in the crust under appropriate conditions. This is driven by heat, pressure changes, or volatile-assisted melting.

• How melting happens: three broad mechanisms drive melting:
  • Temperature increase, raising rocks to their solidus/liq uus transition.

* Decompression melting, where pressure drops as rocks ascend, common at mid-ocean ridges and rifts.

* Addition of volatiles (notably water), which lowers melting temperatures and promotes melting in subduction zones.

• Path to the surface: magma tends to accumulate in chambers or mush zones and can rise through the crust via conduits, potentially erupting as lava or explosively if gas pressure builds.

If you’d like, I can pull concise, up-to-date sources or create a short illustrated summary with a diagram-style explanation of the processes (melting mechanisms, mantle vs crust sources, and typical tectonic settings).