Rock metamorphism is always associated with processes and changes. Metamorphism reworks rocks in the earth’s crust and mantle. Typical effects of rock metamorphism include: Minerals and mineral assemblages originally not present in the rock may form; the new mineral assemblages form at the expense of old ones, consequently older minerals may disappear (e.g., a metamorphic rock may originally contain Grt + Qtz + Sil; a metamorphic event transforms this rock into one that contains Crd (cordierite) in addition to the minerals previously present in the rock).The relative abundance of minerals in a rock may systematically change and the new rock may have a different modal composition (metamorphism may increase the amount of Crd present in the rock and decrease the volume proportion of Grt + Qtz + Sil).Metamorphic minerals may systematically change their composition (e.g., the XFe of Grt and Crd may simultaneously increase during metamorphism).The structure of rocks in crust and mantle may be modified (e.g., randomly oriented sillimanite needles may be aligned parallel after the process)The composition of the bulk rock may be altered during metamorphism by adding or removing components to or from the rock from a source/sink outside the volume of the rock considered (e.g., adding K2O dissolved in an aqueous solution to a Grt + Crd + Sill + Qtz rock may result in the formation of biotite).
Weitere Kapitel dieses Buchs durch Wischen aufrufen
- Metamorphic Processes
Professor Dr. Kurt Bucher
Professor Dr. Martin Frey
- Springer Berlin Heidelberg
- Chapter 3
Fallstudie Überschwemmungskarten/© Thaut Images | Fotolia