Tectonic Phases in Metamorphic Rocks
In petrology, metamorphic phases can be distinguished by analysis of minerals and microstructures (petrography) in metamorphic rocks. By analysing the sequence in which the minerals and structures were formed, more than one phase can be found in most metamorphic rocks (this is called polymetamorphism). By radiometric dating the absolute age of the different phases of mineral growth can be determined, showing when the rock was under certain pressure-temperature conditions. The obtained age is not necessarily the age of a tectonic phase, but can show when the tectonic phase ended and crystallisation of new minerals occurred.
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