• A metamorphic facies is a set of associated metamorphic rocks that formed under the same conditions. METAMORPHIC FACIES: Metamorphic rocks are often classified on the basis of metamorphic facies. Metamorphic facies represent specific pressure and temperature conditions. Chart of metamorphic facies showing mineral reactions and indicators for impure limestone, pelitic and mafic igneous protoliths (modified from Brownlow, 1979). After Turner (1981). They are said to belong to the same metamorphic facies. The mineralogy of the a metamorphic rock is not the only line of evidence to determine its history. Metamorphic rocks form by the alteration of pre-existing rocks in the solid state by heat, pressure, and chemically active fluids. Metamorphic grade is a general term for describing the relative temperature and pressure conditions under which metamorphic rocks form. Thermodynamics and Gibbs free energy • Reactions take place in a direction that lowers Gibbs free energy • Equilibrium is achieved only when Gibbs ... PowerPoint Presentation Author: Temperaturepressure diagram showing the three major types of metamorphic facies series proposed by Miyashiro (1973, 1994). Metamorphic Facies Best, Chapter 10 Metamorphic Grade Controlled by the temperature of metamorphism Low-grade rocks contain hydrated and carbonated phases High-grade rocks are dehydrated and decarbonized Metamorphic Zones Mappable metamorphic units of similar grade in a rock of distinct composition Isograds are lines marking the first appearance of key minerals Zones of … Parent rocks of different compositions, if metamorphosed under the same pressure-temperature conditions, will characteristically contain the same set of definite minerals. This eclogite specimen from Jenner, California, consists of high-magnesium pyrope garnet , green omphacite (a high-sodium/aluminum pyroxene) and deep-blue glaucophane (a sodium-rich amphibole). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Fig. 25-3. Metamorphic Zones and Facies. Metamorphic Facies. Granulite facies (Fig.1) was introduced by Eskola (1939) to define the highest grade of regional metamorphic rocks that contain pyroxene in place of normal hydrous ferromagnesian minerals. Wikipedia has a good list of the minerals possible in each facies. Metamorphic Petrology: Mineralogical, Field, and Tectonic Aspects. Fig. Metamorphic facies • We know that the chemical composition of metamorphosed rocks does not change • Metamorphism is isochemical • Elements are redistributed but not lost • Consequently any changes are the result of temperature and pressure • This has led to the concept of metamorphic facies A There is, however, a sample of eclogite in your GY 111L metamorphic rock tray just to keep you on your toes. Metamorphic Facies. McGrawHill. GRADE OF METAMORPHISM Low-grade metamorphism It takes place at temperatures between about 200 to 320oC, and relatively low pressure.Low grade metamorphic rocks are characterized by an abundance of hydrous minerals. 7.25 • Metamorphism can occur at divergent and convergent boundaries. Barrovian metamorphic sequences. This type of metamorphic rock is the name of highest-grade metamorphic facies. ... PowerPoint Presentation Author: Owner Created Date: Prentice Hall. The fabric of a metamorphic rock also tells of its history. 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