Final answer:
Long-buried igneous rock, when subjected to high temperatures and pressures, can undergo metamorphism to become metamorphic rock through a process of melting and recrystallization without fully melting.
Step-by-step explanation:
If exposed to high enough temperatures and pressures, long-buried igneous rock could melting and recrystallize. The process through which a rock's physical and chemical conditions change, making it stable under new conditions, is known as metamorphism. The original igneous rock, when subjected to increased heat and pressure beneath Earth's surface, can transform into metamorphic rock. This transformation occurs under subsolidus conditions, which are elevated temperatures sufficient for recrystallization without causing the rock to melt. During metamorphism, the texture, mineral content, and crystal size of the rock can change, indicating the conditions it has gone through.