Answer:
Hydrothermal solutions
Step-by-step explanation:
Metamorphism is a set of geological processes leading to the formation of metamorphic rocks.
The metamorphic process can occur in a closed system, where the recrystallized and neocrystallized minerals are formed from the available matter from the composition of the protolith. On the other hand, in the case of an open system, hydrothermal solutions percolate the original rock, modifying its composition in order to generate a product (rock) with new composition.