Metamorphic facies

[1] The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure (See diagram in Figure 1).

[1] Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and places in the geological history of the area.

[1] The boundaries between facies (and corresponding areas on the temperature v. pressure graph) are wide because they are gradational and approximate.

A classic work of Turner's was the book he published in 1948 titled Mineralogical and Structural Evolution of Metamorphic Rocks.

[2] Turner continued to work in the field, refining the metamorphic facies classifications through the end of his career in the early 1970s.

Apart from the metamorphic facies of a rock, a whole terrane can be described by the abbreviations LT, MT, HT, LP, MP, HP (from low, medium or high; pressure or temperature).

The prehnite-pumpellyite is characterized by the mineral assemblages: In meta-igneous rocks and greywackes: In metapelites: The greenschist facies is at low pressure and temperature.

The facies is named for the typical schistose texture of the rocks and green colour of the minerals chlorite, epidote and actinolite.

It has the following mineral assemblages: In metabasites: In metapelites: In Si-dolostones: The granulite facies is the highest grade of metamorphism at medium pressure.

Hornfels is a rock formed by contact metamorphism, a process that characteristically involves high temperatures but low pressures/depths.