1. Subduction: The oceanic plate, being denser than the continental plate, gets pushed down (subducted) beneath it.
2. Friction and Heat: The descending oceanic plate encounters immense friction against the continental plate. This friction generates significant heat.
3. Pressure: As the plate descends deeper into the Earth's mantle, the immense pressure also increases. This pressure, combined with the heat from friction, raises the melting point of the surrounding mantle rocks.
4. Water Content: The oceanic plate carries a considerable amount of water within its minerals. As the plate descends, this water is released, acting as a "flux" that further lowers the melting point of the surrounding mantle rock.
5. Partial Melting: This combination of heat, pressure, and water content leads to the partial melting of the surrounding mantle rock. This means that only a portion of the rock melts, creating a magma reservoir.
6. Magma Rise: The magma, being less dense than the surrounding solid rock, rises upwards through the mantle and crust. This magma can eventually erupt at the surface, forming volcanoes.
In summary:
* It's not just the descent of the plate that causes melting, but the combination of factors: friction, pressure, and water content.
* Partial melting: Not the entire rock melts, but a portion does, creating magma.
* Magma rise: The less dense magma rises to the surface, potentially leading to volcanic activity.
This process of subduction, friction, pressure, and water release is crucial for the creation of new crust and the formation of volcanic arcs along convergent plate boundaries.
