A protolith is the original, unmetamorphosed rock from which a given metamorphic rock is formed, e. Monometamorphism is a metamorphism resulting from one metamorphic. The formations making up the earths crust is described by the term facies. The concept was first defined in 1914 by a finnish petrologist, pentti eelis eskola, as any rock of a.
Nowadays, differences in facies classification exist mainly in the transition from greenschist facies to amphibolite facies at higher pressure. The reply is given by the combining formula which indicates the number of possibili. A simple metamorphic classification pdf version for printing metamorphic rock classification textures of metamorphic rocks barrovian metamorphism. Furthermore, combining this with the knowledge of the stability fields. As metamorphic rocks change under heat and pressure, their ingredients recombine into new minerals that are suited to the conditions. The acquadolce subunit on the island of elba, italy, records blueschist. Metamorphic facies were first introduced by finnish geologist pentti eskola in 1920. Only a restricted number of new contact metamorphic rock names. The diagram below shows metamorphic facies in terms of pressure and temperature condiditons inside the earth.
Pdf petrogenesis of metamorphic rocks, 8th edition. A, b, c subdivision of facies according to pressure. To unravel ptt histories in the crust, it is necessary to combine results from field with. While these rocks will be exposed to the same range of pressure and temperatures conditions within that setting, the metamorphic rock that results will depend on the protolith. It is based on the assumption that metamorphic rocks represent a close approach to equilibrium. Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and. Metamorphic petrology 2 metamorphic facies heat flow and heat production in crust. Metamorphic grade increases eastward toward the core of the olympic uplift and passes, apparently gradationally, into the prehnitepumpellyite facies.
Restate how metamorphic rocks relate to the two other rock groups sedimentary and igneous. Review of the behavior of plagioclase under metamorphic. The granulite facies consists of very high grade metamorphic rocks like gneiss. Figures 5 and 6 show a simplified metamorphic facies classification after yardley 1989. Epidote in an epidoteamphibolite facies basaltic rock. Request pdf petrogenesis of metamorphic rocks metamorphic rocks make up.
The concept of metamorphic facies was established by eskola in 1915. If a low geothermal gradient was present, such the one labeled c in the diagram, then rocks would progress from zeolite facies to blueschist facies to eclogite facies. All the rocks that have reached chemical equilibrium under a particular set of physical conditions. Atlas of metamorphic minerals university of oxford. Barrovian metamorphism is widely found across time and space on all parts of the earth, and produces the most common metamorphic rocks. The map of metamorphic facies of the ussr using these facies and facies. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. Pentii eskola originally defined metamorphic facies on the basis of predictable mineral assemblages that develop in metamorphosed mafic rocks and occur worldwide. Here, in addition to the contact, buchan, and barrovian series, discussed above, are shown the facies series and metamorphic field gradients deduced for the franciscan rocks in california and the.
If the temperature of metamorphism is high enough for partial melting of the rock to occur, the changes would still be called metamorphism until the melt is separated from its. Metamorphic rocks home page james madison university. Zeolite facies metamorphism of sandstone in the western. The metamorphic facies of a rock is a more precise concept than its metamorphic grade. Metamorphic petrology 4 pelites the akfm system continuous and. Very low grade metamorphism of the taveyanne formation of. Petrology of metamorphic rocks associated with volcanogenic. Chapter 3 evaluation of metamorphic conditions the. Here are the typical minerals in rocks that are derived from sediments. Pyroxene hornfels facies is a highgrade 650 to 800 degrees celsius metamorphic facies associated with contact metamorphism at low pressures and high temperatures. A metamorphic reaction is an expression of how the minerals got to.
The changes in mineral assemblages are due to changes in the temperature and pressure conditions of metamorphism. Definition of metamorphic facies in the dictionary. The peak metamorphism of the garnet websterite was after. Progressive metamorphism culminated in granulite facies metamorphic conditions in an area near the atlantic coast of. Facies, index minerals, zones and the measure of metamorphic grade keys to metamorphic rock identification home page very basic classification key pdf version basic key including soapstone and. Information and translations of metamorphic facies in the most comprehensive dictionary definitions resource on the web. Metamorphic mineral assemblages for most metamorphicfacies units table 2 follow the detailed descriptions of the metamorphic units and are keyed to. C which is the average temperature at earths surface and 0. Most everyone is familiar with the meaning of igneous, metamorphic, and sedimentary facies. Garnet growth in mediumpressure granulite facies metapelites. Metamorphic facies are recognizable terranes or zones with an assemblage of key minerals that were in equilibrium under specific range of temperature and pressure during a metamorphic event. Changes occur in the solid state because melting doesn t occur. Chapter 1 subsurface macro structure rice university. The facies are named after the metamorphic rock formed under those facies conditions from basalt.
Learn vocabulary, terms, and more with flashcards, games, and other study tools. That mineral suite is taken as a sign of the pressure and temperature that made it. Alluvial fans may merge together to form an apronlike slope along the base of a mountain front. Demarcation must be made on empirical grounds based on petrographic observations, and checked against other independent evidence of facies transitions, such as reactions involved in the metamorphic process. The most common metamorphic facies in mountain belts are the greenschist and the highertemperature amphibolite facies. Rocks of the pyroxenehornfels facies are characteristically formed near larger granitic or gabbroic bodies at depths of a few kilometres or at pressures of a few hundred bars.
A rock or a rock complex may bear the effects of more than one metamorphic event e. The term was first used by coombs 1961 to describe a process of metamorphism that resulted in largescale recrystallization but with no strong penetrative deformation. Some of the pdf files are animations they contain more than one page that can be shown in sequence to see changes as temperature or some other variable changes. Permission is granted to copy, distribute andor modify this document under the terms of the gnu free documentation license, version 1. Thus, if we know the facies of metamorphic rocks in the region, we can determine what the geothermal gradient must have been like at the time the metamorphism occurred. Early miocene stages of continental collision in the northern apennines. Examples include the garnetcordierite, hypersthenesillimanite, staurolite, andalusite, sillimanite, and kyanite facies. These represent sequential changes in metamorphic facies, ranging from a lowgrade facies to a highgrade facies in any one area. Its products occur in large areas in new zealand, japan and elsewhere, and it defines the lowest stage of metamorphism. Granulite facies metamorphism and charnockite plutonism. A scheme of facies of regional metamorphism is proposed in which two pressure dependent facies series are recognized. A mixture of igneous and metamorphic rock produced by incomplete melting, typically badly deformed and contorted and penetrated by many veins, small pods, and lenses of melted rock.
Metamorphic field gradients as rocks are pushed deeper into the earth as a result of tectonism, they will encounter four stages during which temperature and pressure change in the rock in different ways. The mineralogical and structural adjustment of solid rocks to physical and chemical conditions that have been imposed at depths below the near surface zones of weathering and diagenesis and which differ from conditions under. Chapter 25 ans answers for chapter 25 metamorphic facies. Types and facies of metamorphism essay example graduateway. On the other hand, coals that sharply overlie nonrooted faciesparticularly higher energy sandstone and conglomerate facieswere eroded and transported from a nearby peatforming environment and are genetically related to underlying sediments mccabe, 1984. Barrovian metamorphism is the most commonly encountered. Facies concept developed by eskola norway, 1915 to compare metamorphic rocks from different areas.
A process of change 1 metamorphic rock forms from a preexisting rock or protolith. The concept of metamorphic facies is a systematic way to look at the mineral assemblages in rocks and determine a potential range of pressure and temperature pt conditions that were present when they formed. The amphibolite facies comprises relatively high metamorphic rocks like biotite schist and amphibole schist. Metamorphic facies represent specific pressure and temperature conditions. At the upper limit of the facies, migmatite formation may occur. Nov 11, 2012 zeolite facies lplt the zeolite facies is the metamorphic facies with the lowest metamorphic grade.
A metamorphic facies is a set of associated metamorphic rocks that formed under the same conditions. Metamorphic pt phase diagrams click on an image or the link in the caption, and a pdf file of the diagram will download to your computer. Layering parallell formed as a consequence of the alignment of mineral grains, or of compositional banding in metamorphic rock gneiss compositionally layered metamorphic rock, typically composed of alternating darkcolored and light colored layers that range in thickness usually feldspar, quartz, and mica very high temperatures and pressures. Individual facies are defined by specific mineralogical assemblages, which are consistent throughout a given facies. Jan 17, 2016 a metamorphic facies is a set of metamorphic mineral assemblages that were formed under similar pressures and temperatures. Metamorphic petrology 1 metamorphic processes, contact, regional, t and p variations. A more complete indication of this intensity or degree is provided with the concept of metamorphic facies in the barrovian sequence described by george barrow in zones of progressive metamorphism in scotland, metamorphic grades are also classified by mineral. Metamorphic grade is an informal indication of the amount or degree of metamorphism. Each metamorphic facies, therefore, contains all the possible mineral. Lecture notes metamorphism introduction metamorphism is a change of form that includes the growth of new minerals, typically in response to a rise in temperature and normally without the involvement of a magma.
This is an interpretative description that has many levels. This facies series is called the hornfels facies series or the contact facies series. Metamorphic rock metamorphic rock metamorphic facies. Burial metamorphism is here equated with depth or load metamorphism.
Earths surface conditions are near the top left corner of the graph at about 15. Monometamorphism is a metamorphism resulting from one metamorphic event fig. Metamorphic rocks, minerals, grade, and facies lucky sci. Miyashiro 1961, 1973 suggested that these changes in metamorphic facies should be designated metamorphic facies series, and he recognized four major facies series with two intermediate groups. 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. This will be the second last lecture on metamorphic rocks. They occur in belts of regional extent, from which the term regional metamorphism was originally derived. Metamorphic facies and metamorphosed mafic rocks 1.
The same metamorphic facies can contain different mineral assemblages as they are a direct product of different mineral and chemical composition of the original rock, i. During metamorphism, new minerals grow at the expense of old minerals, andor the shape, size, and arrangement of grains in the rock may change. In low grade metamorphic in this system, the reaction. As the chart below shows, certain facies are associated.
Is a process involving changes in the mineral contentcomposition andor microstructure of a rock, dominantly in the solid state. The major types of sedimentary rocks distribution of sediments on the earths surface. The book presents a general account of the metamorphic processes, with fundamental data on conditions of metamorphism, the principle of metamorphic facies, and the composition of metamorphic rocks. Interaction between metamorphic petrologists and geophysicists in the 1980s led to the realization that each metamorphic rock follows its own unique path through pressure depth temperature space during metamorphism and that these paths bear little or no resemblance to steadystate geotherms. These can range from textures similar to the original protolith at low grades of metamorphism, to textures that are purely produced during metamorphism and leave the rock with little resemblance to the original protolith. It occurs in intense tectonic conditions associated with volcanic arcs, and major mountain building. The blueschist metamorphic facies are characterized by the minerals jadeite, glaucophane, epidote, lawsonite, and garnet. Metamorphic rock metamorphic rock pressuretemperaturetime paths. The san andreas fault extends across california for nearly 800 miles between. Metamorphic facies defined and explained thoughtco. Metamorphic field gradients can also be used to define metamorphic facies series for specific metamorphic belts, as shown in the diagram below. The andesitic early oligocene taveyanne metagreywacke of the helvetic nappes of western switzerland shows an increase of metamorphic grade from zeolite facies through lower greenschist facies.
Each facies has several mineral assemblages unique to that facies. This process is mainly due to an adjustment of the rock to physical conditions that differ from those under which the rock originally formed and that also differ from the physical conditions normally occurring at the surface of the. Wikipedia has a good list of the minerals possible in each facies. Contact metamorphic rocks british geological survey. The map of metamorphic facies of the ussr using these facies and facies series. Metamorphic facies an overview sciencedirect topics. Metamorphic petrology 3 metamorphism of pelitic rocks minerals and isograds. Definition facies is a body of rock characterized by a particular combination of lithology, physical and biological structures that bestow an aspect that different from the bodies of rock above, below and laterally adjacent the facies concept refers to the sum of characteristics of a sedimentary unit, commonly at a fairly small cmm scale. Greenschists, as their name implies, tend to be green.
Metamorphic facies article about metamorphic facies by the. Types and facies of metamorphismmetamorphism is the process that engages the structural and compositional changes that took place during solid rock information as imposed by physical and chemical elements whereby the change is subjected at nearearths exterior zone of weathering and diagenesis 200oc, 300 mpa. In general, metamorphic rocks do not drastically change chemical composition during metamorphism, except in the special case where metasomatism is involved such as in the production of skarns, as discussed above. In any given metamorphic setting there can be a variety of protolith types exposed to metamorphism. Metamorphic facies are also designated according to the names of metamorphic minerals and the mineral sequences that are typical of the corresponding regions of thermodynamic stability. A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. It has parallel extinction relative to its usual long crystal dimension the b direction, but inclined excinction, looking down b relative to its. Sep 10, 2014 definition facies is a body of rock characterized by a particular combination of lithology, physical and biological structures that bestow an aspect that different from the bodies of rock above, below and laterally adjacent the facies concept refers to the sum of characteristics of a sedimentary unit, commonly at a fairly small cmm scale. Similar alteration reactions should be anticipated in other deeply buried clastic sequences in the oregon and washington coast ranges. A metamorphic facies is a set of metamorphic mineral assemblages that were formed under similar pressures and temperatures. The assemblage is typical of what is formed in conditions corresponding. Mar 27, 2017 as metamorphic rocks change under heat and pressure, their ingredients recombine into new minerals that are suited to the conditions. The metamorphic facies diagram shown in figure 1 differs in some details from that proposed by eskola, who named his metamorphic facies after metamorphosed mafic rocks.
To sum up, a metamorphic facies is the set of minerals found in a rock of a given composition. Metamorphic rocks and processes metamorphism comes from the greek words meta change morphe form metamorphic rocks form by solidstate no melting transformation of preexisting rock by processes that take place beneath earths surface. These are often foliated metamorphic rocks developed under medium to high temperatures. The book presents a general account of the metamorphic processes, with fundamental data on conditions of metamorphism, the principle of metamorphic facies, and the composition of metamorphic. The facies is named for zeolites, strongly hydrated tectosilicates it can have the following mineral assemblages.
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