Petrogenetic grid

Experimentally determined mineral or mineral-assemblage stability ranges are plotted as metamorphic reaction boundaries in a pressure–temperature cartesian coordinate system to produce a petrogenetic grid for a particular rock composition.

[3][4][5][6] Figure 1 is an example of a complex petrogenetic grid for metamorphosed pelitic rocks.

This assumes the rock has a KFMASH (K2O–FeO–MgO–Al2O3–SiO2–H2O) composition because that is what the experimental data was created with.

[7] At the time, he envisioned geologists eventually determining every possible metamorphic reaction and assemblage in nature, but realized that the magnitude of undertaking the necessary experiments was a huge task that would not be finished for a very long time.

Depending on the level of precision and characterization needed, a petrogenetic grid may be simple, or it may be an extremely large system consisting of a hundred or more reactions.

Figure 1. Petrogenetic grid for metapelites (several authors). [ 1 ] [ 2 ] Metamorphic facies included are: BS = Blueschist facies , EC = Eclogite facies , PP = Prehnite-Pumpellyite facies , GS = Granulite facies , EA = Epidote-Amphibolite facies , AM = Amphibolite facies , GRA = Granulite facies , UHT = Ultra-High Temperature facies , HAE = Hornfels-Albite-Epidote facies , Hbl = Hornblende-Hornfels facies , HPX = Hornfels-Pyroxene Facies , San = Sanidinite facies