Final answer:
A high-grade metamorphic rock that has undergone partial melting is called a migmatite. Migmatites are characterized by the coexistence of igneous and metamorphic features due to the partial melting of the protolith under extreme metamorphic conditions.
Step-by-step explanation:
High-grade metamorphic rocks exhibit significant changes in texture and mineral composition due to intense temperature and pressure conditions. A high grade metamorphic rock that has undergone partial melting is known as a migmatite. This type of rock is distinguished by the presence of both igneous and metamorphic characteristics, indicative of the stage where partial melting begins. The original rock, or protolith, experiences such extreme conditions that it starts to partially melt, leading to the formation of migmatite, which showcases a combination of solid rock with portions that have melted and recrystallized.
Contrasting terms such as marble, which is metamorphosed limestone, and gneiss, another high-grade metamorphic rock known for its banded texture, highlight the variety in metamorphic rock types based on the protolith and the conditions of metamorphism. It is the mixture of melted and solid components in migmatites that sets them apart from other metamorphic rocks, demonstrating the intermediate process as rocks transition from a purely metamorphic to an igneous state.