Metamorphic series

Metamorphic series include the Barrovian and Buchan series of metamorphic rocks. George Barrow was a geologist in Scotland who discovered the Barrovian series. . These are also called metamorphic facies series. A metamorphic facies series is a sequence of metamorphic facies which plot in a temperature-pressure diagram along a line, and this line represents a certain geothermal gradient. They are not the same as metamorphic zones, as these are defined as a region on a geological map where the pressure-temperature conditions for an index mineral (a mineral that indicates the approximate metamorphic grade of a rock), were appropriate for these minerals to form..

In the figure above, one can study different metamorphic series for different rocks. Note, however, that the names Buchan and Barrovian facies series are often used in another context, i.e. for the kyanite-andalusite-sillimanite polymorphs. However, Buchan facies series plot along line 3 and Barrovian at somewhat higher pressure and with the appearance of kyanite.The facies series have connections to plate tectonics. Facies series 1 is typical of contact metamorphism, but also found in regional metamorphosed rocks. Facies series 2 correlates with volcanic arc environments, and so on: 3. Collisional mountain belts, regional metamorphism 4. Stable continents and 5. Accretionary prisms. Original image: Woudloper.

The Buchan and Barrovian facies series relate to this diagram of Al₂SiO₅ polymorphs (also called a petrogenetic grid), with increasing temperature along the x-axis and increasing pressure along the y-axis. See Metamorphism#Regional

• Buchan metamorphism has the facies series greenschist-amphibolite-granulite
• Barrovian metamorphism has the same facies series but has approximately 1 kbar more pressure so these rocks form kyanite