GSCI 1051 Lecture Notes - Lecture 9: Overburden Pressure, Mica, Metamorphism
Document Summary
Process of metamorphism: recrystallization- changes grain size and shape without changing mineralogy, phase change- a mineral becomes another of the same composition but different crystal structure, neocrystalization- new minerals form as atoms move and/or dissolve and reprecipitate. Garnet and mica typically form in metamorphosed shale/mudstone: pressure solution-grains dissolve where they touch and ions precipitate elsewhere, plastic deformation- hot grains change shape without breaking under directed pressure. Causes of metamorphism: heat- atoms vibrate rapidly, breaking bonds and freeing them to form new ones. Upper limit is melting, which varies by rock type: pressure- atoms pack closer together, forming denser minerals. Rocks below ground experience lithostatic pressure, which is equal on all sides. Deeper rocks experience greater pressure and become more compact. Directed pressure is greater in one direction and aligns flat minerals such as micas (this preffered alignment is called foliation.
