They melt down to form molten magma.
Explanation
The Rock Cycle describes the continuous process through which rocks transform from one type (Igneous, Sedimentary, Metamorphic) to another due to geological forces such as weathering, heat, pressure, and melting.Analysis of Options:
- They break down into sediments. is incorrect: The breakdown of rocks into sediments occurs through exogenic processes such as weathering and erosion, not through the application of great heat and pressure.
- They melt down to form molten magma. is correct: Metamorphic rocks are formed under heat and pressure. However, if they are subjected to extreme heat and pressure that exceeds their melting point, the rock structure collapses and melts to form molten magma. This magma is the source material for igneous rocks.
- They turn into sedimentary rocks directly. is incorrect: Metamorphic rocks cannot transform directly into sedimentary rocks. They must first be weathered into sediments, transported, deposited, and lithified.
- They solidify into intrusive granite. is incorrect: Metamorphic rocks do not directly solidify into granite. They must first melt into magma. Granite is an intrusive igneous rock formed only when that magma subsequently cools and solidifies.
Key Takeaway: In the rock cycle, the transition from metamorphic rock to igneous rock occurs via the intermediate stage of melting into magma caused by extreme heat.