A Metamorphic grade is a general term for describing the relative temperature and pressure conditions under which metamorphic rocks form. McGrawHill. Metamorphic Facies. 25-3. The mineralogy of the a metamorphic rock is not the only line of evidence to determine its history. Prentice Hall. There is, however, a sample of eclogite in your GY 111L metamorphic rock tray just to keep you on your toes. METAMORPHIC FACIES: Metamorphic rocks are often classified on the basis of metamorphic facies. Metamorphic Petrology: Mineralogical, Field, and Tectonic Aspects. This type of metamorphic rock is the name of highest-grade metamorphic facies. The eclogite facies is an extremely high grade region of the plot and comprises metamorphic rocks that are a bit beyond our level in GY 111. ... PowerPoint Presentation Author: Owner Created Date: The granulite facies consists of very high grade metamorphic rocks like gneiss. Metamorphic Facies. 7.25 • Metamorphism can occur at divergent and convergent boundaries. After Turner (1981). The fabric of a metamorphic rock also tells of its history. 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: Chart of metamorphic facies showing mineral reactions and indicators for impure limestone, pelitic and mafic igneous protoliths (modified from Brownlow, 1979). 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 … Each facies has several mineral assemblages unique to that facies; the assemblage depends on the parent rock (shale vs. basalt). 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. They are said to belong to the same metamorphic facies. Barrovian metamorphic sequences. 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). 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. Metamorphic rocks form by the alteration of pre-existing rocks in the solid state by heat, pressure, and chemically active fluids. • A metamorphic facies is a set of associated metamorphic rocks that formed under the same conditions. Wikipedia has a good list of the minerals possible in each facies. Fig. Fig. Temperaturepressure diagram showing the three major types of metamorphic facies series proposed by Miyashiro (1973, 1994). 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