Pathway 1: Direct Metamorphism
1. Igneous Rock Formation: Magma cools and solidifies, forming an igneous rock.
2. Burial and Heat/Pressure: The igneous rock is buried deep within the Earth's crust. The intense heat and pressure from overlying rock layers cause changes in the rock's mineral composition and texture.
3. Metamorphic Rock Formation: The intense heat and pressure transform the igneous rock into a metamorphic rock. This process is called contact metamorphism if the heat is primarily from nearby magma and regional metamorphism if the heat and pressure are due to tectonic forces.
Pathway 2: Erosion, Sedimentation, and Metamorphism
1. Igneous Rock Formation: Magma cools and solidifies, forming an igneous rock.
2. Weathering and Erosion: The igneous rock is exposed to the surface and broken down by weathering (rain, wind, ice) and erosion (wind, water, ice).
3. Sedimentation: The eroded fragments of the igneous rock are transported and deposited in a new location, forming sediment layers.
4. Lithification: The sediment layers are buried and compacted, eventually forming sedimentary rock.
5. Burial and Heat/Pressure: The sedimentary rock is buried deeper within the Earth's crust, where it is subjected to intense heat and pressure.
6. Metamorphic Rock Formation: The sedimentary rock containing fragments of the original igneous rock is transformed into metamorphic rock.
Important Note: In both pathways, the key factor in the transformation of igneous to metamorphic rock is the application of heat and pressure.
