What chemical changes occur during the process of metamorphism that turn sedimentary rocks into metamorphic rocks?
During the process of metamorphism, several chemical changes occur that transform sedimentary rocks into metamorphic rocks. These changes are mainly driven by the combination of heat, pressure, and the presence of fluids.
To understand the specific chemical changes involved, we need to explore the processes that occur during metamorphism:
1. Heat: Increased temperature is a significant driving force in metamorphism. It leads to the breaking and reforming of chemical bonds within minerals, causing them to undergo chemical changes. The heat also helps facilitate the movement of atoms and ions, allowing new mineral growth to occur.
2. Pressure: Metamorphism occurs under high-pressure conditions, typically generated by the overlying weight of rocks above or from tectonic forces. The pressure causes some minerals to recrystallize, align, or grow in a preferred direction. Additionally, pressure can cause minerals to undergo phase transformations, converting them into new minerals stable under these conditions.
3. Fluids: Fluids, including water or hydrothermal solutions, play a crucial role in metamorphism. They assist in transporting and exchanging chemical elements between minerals. Fluids can dissolve minerals from the original sedimentary rock and precipitate new minerals, leading to the formation of metamorphic minerals. Chemical reactions can occur more rapidly in the presence of fluids.
As a result of these processes, a variety of chemical changes can occur during metamorphism, including:
1. Recrystallization: Existing minerals within the sedimentary rock can break down and reform as new minerals with different chemical compositions. For example, under heat and pressure, clay minerals may recrystallize and transform into mica or chlorite.
2. Metamorphic reactions: Chemical reactions between minerals can lead to the formation of new minerals with different compositions. For instance, the reaction between calcite and silica can produce the mineral wollastonite during metamorphism.
3. Mineral growth: Metamorphism can also facilitate the growth of new minerals, especially in the presence of fluids. This growth can occur as mineral crystals nucleate and grow within the rock matrix. For example, the growth of garnet crystals within a metamorphic rock is a common occurrence.
Overall, the combination of heat, pressure, and fluids during metamorphism brings about various chemical changes that result in the alteration and formation of new minerals, ultimately transforming sedimentary rocks into metamorphic rocks.