Remetamorphism

Remetamorphism refers to the process where existing metamorphic rocks are subjected to a new set of metamorphic conditions. This results in the alteration or recrystallization of minerals and textures that were formed during a previous metamorphic event. Essentially, it's a second (or subsequent) metamorphism that overprints the original metamorphic fabric.

The new conditions can involve changes in temperature, pressure, or the presence of different chemically active fluids. For instance, a rock that was previously metamorphosed under low-grade conditions might be heated to higher temperatures, leading to the formation of new minerals stable at those higher temperatures. Similarly, an increase in pressure could cause minerals to transform into denser polymorphs or to develop new preferred orientations. The degree of remetamorphism depends on the intensity and duration of the new metamorphic event, as well as the mineralogical and textural characteristics of the pre-existing rock.

Recognizing remetamorphism in rocks often involves identifying relict textures or minerals from the earlier metamorphic stage alongside newly formed minerals and textures indicative of the later event. The study of remetamorphism is crucial for understanding the complex geological histories of many regions and for reconstructing the thermal and pressure regimes that rocks have experienced over geological time. It highlights that metamorphism is not always a single event but can be a protracted process involving multiple stages of transformation.