1. Heat:
* Source: Heat can come from:
* Magma intrusions: Hot, molten rock rising from deep within the Earth can bake surrounding rocks.
* Regional metamorphism: Heat generated from tectonic plate collisions or deep burial within the Earth's crust.
* Contact metamorphism: The heat from a nearby volcanic eruption can alter surrounding rocks.
* Temperature Range: The temperature needs to be high enough to cause recrystallization of minerals within the rock, but not so high that the rock melts completely (which would then create new igneous rocks). The typical range is roughly 200°C to 800°C (392°F to 1472°F).
2. Pressure:
* Source: Pressure can come from:
* Burial: Rocks buried deep within the Earth are subjected to immense pressure from the weight of the overlying rocks.
* Tectonic forces: Compression from colliding tectonic plates can create tremendous pressure.
* Effect: Pressure causes the minerals within the rock to rearrange and form new minerals that are denser and more stable under those conditions.
3. Fluids:
* Source: Water, dissolved gases, and other fluids can be present within the rock or released from surrounding rocks during metamorphism.
* Effect: Fluids act as catalysts, speeding up chemical reactions and facilitating the growth of new minerals. They can also transport minerals, leading to changes in the overall composition of the rock.
4. Time:
* Necessary Factor: Metamorphic processes occur over long periods of time, often millions of years. The changes happen gradually as the rock is subjected to the conditions described above.
In summary:
The transformation of an igneous rock into a metamorphic rock requires a combination of heat, pressure, and fluids, acting over geological time. The specific type of metamorphic rock that forms depends on the original igneous rock, the intensity and duration of the metamorphic conditions, and the presence of fluids.
