1. Heat:
* Source: Heat comes from the Earth's internal heat (from the core and mantle), magma intrusions, or friction caused by tectonic plate movement.
* Effect: Heat causes recrystallization, where existing minerals change their structure and/or composition. This leads to changes in texture, grain size, and even mineral types.
* Example: Shale (sedimentary rock) can be transformed into slate (metamorphic rock) due to heat.
2. Pressure:
* Source: Pressure arises from the weight of overlying rock layers or tectonic forces squeezing rocks together.
* Effect: Pressure causes compaction, where minerals are squeezed closer together, and deformation, where the rock structure is changed. This can lead to folding, banding, and other distinctive features.
* Example: Limestone (sedimentary rock) can be transformed into marble (metamorphic rock) due to pressure.
3. Chemically Active Fluids:
* Source: These fluids can be water, carbon dioxide, or other dissolved minerals circulating through the rock.
* Effect: These fluids can react with the minerals in the rock, altering their composition and leading to new minerals forming.
* Example: These fluids can cause the formation of mica, a common mineral in metamorphic rocks, through reactions with other minerals.
Key Points:
* The intensity and duration of these effects determine the type of metamorphic rock that is formed.
* High heat and pressure create rocks with large crystals and a more banded appearance, while low heat and pressure create rocks with smaller crystals and a more homogeneous appearance.
* Metamorphism can occur on a range of scales from localized changes around igneous intrusions to large-scale transformations associated with mountain building.
Understanding the effects of heat, pressure, and chemically active fluids is crucial for understanding the formation and properties of metamorphic rocks.
