1. Burial and Pressure:
* Sedimentary rocks form at the Earth's surface, but tectonic forces can cause these layers to be buried deeper and deeper.
* The weight of overlying layers creates immense pressure on the sedimentary rock.
2. Heat:
* As the rock is buried deeper, it gets closer to the Earth's hot interior.
* The geothermal gradient (the increase in temperature with depth) causes the rock to heat up significantly.
3. Recrystallization:
* The combined effects of heat and pressure cause the minerals in the sedimentary rock to become unstable.
* These minerals will re-crystallize into new, more stable forms. This process is called metamorphism.
4. New Textures and Structures:
* The recrystallization process can also change the rock's texture. For example, grains can become larger and more tightly packed.
* The pressure can also cause the rock to become folded or sheared, creating new structural features.
Examples:
* Sandstone (sedimentary) can be transformed into quartzite (metamorphic)
* Limestone (sedimentary) can be transformed into marble (metamorphic)
* Shale (sedimentary) can be transformed into slate, schist, or gneiss (metamorphic)
Factors Influencing Metamorphism:
* Temperature: Higher temperatures lead to more significant changes in mineral composition and texture.
* Pressure: Pressure can cause minerals to align in a specific direction, creating foliation (layers).
* Time: Metamorphism is a slow process that can take millions of years.
* Fluids: Water and other fluids can facilitate chemical reactions during metamorphism.
In essence, sedimentary rock transforms into metamorphic rock when it is exposed to extreme heat and pressure within the Earth's crust, causing its minerals to recrystallize and its texture to change.
