Final answer:
A rock that has undergone partial melting is called migmatite, which shows characteristics of both metamorphic and igneous rocks, and indicates a high metamorphic grade.
Step-by-step explanation:
The rock that has undergone partial melting is known as migmatite. This rock represents a transitional stage between metamorphic and igneous rock and is formed when temperatures and pressures are high enough to initiate the melting of the protolith, the original unaltered rock, without completely transforming it into liquid magma. Migmatites often exhibit a mix of metamorphic and igneous features due to the presence of melted and recrystallized material alongside solid metamorphic textures. The process is governed by changes in temperature and pressure, or the addition of fluids such as water which can reduce the melting point of rocks. For identification purposes, migmatite is not only known for its visual appearance that shows bands or streaks of lighter, igneous-looking material alongside darker metamorphic material but also for what it indicates about the metamorphic grade of a rock, which is a term reflecting the intensity of heat and pressure the rock was subjected to during metamorphism.In conclusion, migmatite is a significant rock type because it helps geologists understand the transitional phases within the rock cycle that occur under specific temperature and pressure conditions deep within the Earth's crust.