Скачать или смотреть The home of metamorphism (1): Glen Clova.

The geology of Glen Clova, and neighbouring Glen Esk, was seminal in developing our understanding of how metamorphism works. It was here in the 1890's that Barrow developed the concept of metamorphic zones and index minerals. The idea is that as pressure and temperature increase, for a given rock chemistry (ie a particular starting rock type) there wil be characteristic changes in stable minerals which will be dagnostic of the P-T conditions that rock went to. The index minerals of the "Barrovian zones" are useful for defining burial depths and temperatures and it is their first occurrance which defined their characteristic 'isograd'. The Barrovian index minerals are, in order of increasing severity of metamorphism:
Chlorite, Biotite, Garnet, Staurolite, Kyanite, Sillimanite;
and they are diagnostic of metapelites - rocks which were originally mudstones and shales. Watch the Glen Esk video for examples of each rock type.