At what temperature and depth does a metamorphic rock begin to melt?

Metamorphic rocks begin to melt at varying temperatures and depths because their melting points are influenced by several factors, such as the rock's composition, the presence of volatiles (like water), and pressure conditions. However, melting typically starts at temperatures above 650°C to 800°C, under high-pressure conditions within the Earth's crust. As for depth, this generally occurs at depths of roughly 15 to 50 kilometers or more, where the pressure is around 0.5 to 2 GPa (gigapascals). The exact conditions depend on the specific rock type and the tectonic setting.

The transition from solid rock to melt is not always abrupt. Before complete melting, rocks often go through a stage of partial melting, where some minerals melt while others remain solid. The presence of water can lower the melting temperature and cause melting at lower temperatures than in dry conditions.