1. Heat:
* Source of Heat: Heat can come from a variety of sources, including:
* Magma intrusions: When molten rock (magma) pushes its way into existing rock, the surrounding rock is heated.
* Deep burial: As rocks are buried deeper within the Earth's crust, they are exposed to higher temperatures due to the Earth's internal heat.
* Regional metamorphism: Large-scale tectonic events like mountain building generate heat from friction and pressure.
* Effects of Heat:
* Recrystallization: The minerals within the igneous rock change their structure and sometimes their chemical composition. This leads to the formation of new minerals that are more stable at the higher temperatures.
* Grain growth: The individual crystals (grains) within the rock grow larger.
2. Pressure:
* Source of Pressure: Pressure can be caused by:
* Burial: Rocks are compressed under the weight of overlying rock layers.
* Tectonic forces: The movement of tectonic plates can exert immense pressure on rocks, causing them to fold and deform.
* Effects of Pressure:
* Mineral alignment: Pressure can cause the mineral grains within the rock to align themselves in a preferred direction, creating a layered or banded appearance.
* Density changes: Pressure can compact the rock, making it denser.
3. Fluids:
* Source of Fluids: Fluids, often rich in dissolved minerals, can be released from:
* Magma: Magma can release fluids as it cools and solidifies.
* Groundwater: Water percolating through the rocks can become heated and chemically active.
* Effects of Fluids:
* Chemical reactions: Fluids can react with the minerals in the igneous rock, changing their composition and forming new minerals.
* Migration of elements: Fluids can transport elements from one part of the rock to another, leading to the formation of distinctive mineral patterns.
Overall, the specific changes that occur during metamorphism depend on the intensity of heat, pressure, and the presence of fluids. The result is the formation of a metamorphic rock with a new mineral composition, texture, and often, a distinct banding or foliation.
