1. Heat and Pressure (Regional Metamorphism):
* How it works: This is the most common type of metamorphism. Large-scale geological processes like the collision of tectonic plates (mountain building) generate immense heat and pressure. These forces act upon existing rocks, causing changes in their mineral composition and texture.
* Example: Shale (sedimentary rock) can be metamorphosed into slate, then schist, and ultimately gneiss under increasing heat and pressure. Similarly, granite (igneous rock) can be transformed into a variety of metamorphic rocks like gneiss and migmatite.
2. Contact Metamorphism:
* How it works: When magma (molten rock) intrudes into existing rocks, the intense heat from the magma cooks the surrounding rock. This localized heating alters the minerals and texture of the existing rock, turning it into a metamorphic rock.
* Example: Limestone (sedimentary rock) can be metamorphosed into marble by contact metamorphism. Similarly, basalt (igneous rock) can be changed into hornfels.
Key Takeaway: Both heat and pressure are essential for the formation of metamorphic rocks. Regional metamorphism involves widespread heat and pressure, while contact metamorphism is more localized, occurring near intruding magma.
