Pdf constraints on granulite genesis from carbon isotope. Main types of metamorphism regional metamorphism is a type of metamorphism which occu rs over an area of wide extent, that is, affecting a large rock vo lume, and is associated with largescale tectonic processes, such. Evidence of reactioninduced microfracturing in granulite facies migmatites article in geology 284. The almost identical ages of the two types of core domains magmatic 791 9 ma and granulite facies metamorphic zircon 794 10 ma, and the triassic age 212 10 ma of eclogitic facies metamorphic overgrowth zircon rim are interpreted as indicating that the protolith of the eclogite is mafic granulite that originated from. Granulite facies is a highgrade metamorphic facies associated with orogenic regional metamorphism. Some veins display a boudinaged texture, possibly related to the d 2 deformation event in the ivrea. The middle crust is composed of rocks in the amphibolite facies and is intermediate in bulk composition, containing significant k, th, and u contents. In contrast to most granulite facies rocks, paragneisses containing borosilicate minerals in the larsemann hills, a coastal exposure on prydz bay, east antarctica, contain up to 2 wt. Both clinopyroxene and orthopyroxene may be present, and in fact, the coexistence of clino and orthopyroxene in a metabasite metamorphed basalt defines the granulite facies. The composition range of common mafic rocks is shaded. Granulite facies metamorphism occurs at temperatures of approximately 500 to 700 and pressures of 870 kbar. Rocks of other bulk compositions may retain some hydrous minerals, such as biotite and hornblende. The mineral composition is to be indicated by prefixing the major constituents.
In rocks of basaltic composition, the granulite facies is an anhydrous facies that results from progressive dehydration of amphibolites the minerals found in the rocks of the granulite facies include pyroxene, biotite, garnet, calcium plagioclase, and quartz or olivine. Norway are co 2rich, whereas those in the amphibolite facies rocks are h. The minerals found in the rocks of the granulite facies include pyroxene, biotite, garnet, calcium plagioclase, and quartz or olivine. Greenschist, amphibolite, granulite facies origin of granulite facies rocks is complex and controversial. The term facies was introduced by the swiss geologist amanz gressly in 1838 and was part of his significant contribution to the foundations of modern stratigraphy. Quick navtop about granulite classification subdivisions mineralogy references internet links mineral andor locality is an outreach project of the hudson institute of mineralogy, a 501c3 notforprofit organization.
Metamorphic facies is not obvious in a given field specimen. Granulite facies are documented by grtopxcpxplbearing mafic granulites and charnockitic gneisses, reporting p 0. Amphibolite facies includes calcite marbles, biotite schists and amphibolites. Nov 11, 2012 granulite facies mpht the granulite facies is the highest grade of metamorphism at medium pressure.
This metamorphism is attributed to crustal thickening related to overriding of the cabo delgado nappe. A highgrade metamorphic rock in which the silicates are dominantly waterfree, eg, feldspars, garnet, pyroxene. Metamorphic rock metamorphic rock metamorphic facies. Granulite gallery petrological features of granulites, charnockites and migmatites. Average continental crust is intermediate in composition and contains a significant proportion of the bulk silicate earths incompatible trace element budget 3555% of rb, ba, k, pb, th, and u. Amphibolitefaciestogranulitefacies reactions in experimentally deformedo unpowdered amphibolite bru. Metamorphic facies defined and explained thoughtco.
Anomalously low temperature orthopyroxene, spinel, and. Winter 2001 an introduction to igneous and metamorphic petrology. Granulitefacies metamorphism of the palaeoproterozoic. Metamorphism of pelitic rocks metapelites springerlink. This major textbook offers a new conceptual framework for metamorphic petrology, based on progress made over the past 20 years. Rocks of the granulite facies of metamorphism occupy a central role in discussions of petrogenesis of the crust. Marine and lacustrine sediments can be locally important. Most metamorphic terranes, especially in the internal parts of continents, are composed of greenschist, amphibolite, and granulite facies rocks, including migmatites at the high metamorphic grades. Fluids of granulite facies metamorphism springerlink. Bhattacharya a, sen sk 1986 granulite metamorphism, fluid buffering and dehydration melting in the madras charnockites and metapelites. Geochemistry of gneissgranulite transformation in the. Geology of the granulite and amphibolite facies gneisses of. In the archean dharwar craton of southern india ns trending belts of metabasic rocks are exposed which underwent regional metamorphism at about 2.
At the upper limit of the facies, migmatite formation may occur. If rocks are water saturated, they will, with a eutectic or eutectoid chemical composition near to granite, partially melt at. Fluid movements element transport and the composition of the deep crust. Bridgwater d ed fluid movementselement transport and the composition of the deep crust. Ansrucr reactions in mafic amphibolite marking the transition from amphibolite to granulite. A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. David bridgwater many geologists have an equivocal attitude to fluid movements within the crust and the associated changes in the chemical and physical properties of crustal rocks. The relatively lowtemperature metamorphism of the greenschist glaucophane schist, or zeolite facies is characteristic of the early preorogenic stages in the development of geosynclines. In rocks of basaltic composition, the granulite facies is an anhydrous facies that results from progressive dehydration of amphibolites at high temperature. Late paleoproterozoic granulitefacies metamorphism in the north.
Raith m, hoernes s, klatt e, stahle hj 1989 contrasting mechanisms of charnockite formation in the amphibolite to granulite grade transition zones of southern india. The trace element compositions of samples from exposed granulite facies terrains and 17 granulitic lower crustal xenoliths were determined using an inductively coupled plasma. Granulite facies mpht the granulite facies is the highest grade of metamorphism at medium pressure. Coutinho, university of sao paulo, sao paulo, brazil 2 l m university, munich, germany 3 f. A characteristic mineral for this facies and the pyroxenehornblende facies is orthopyroxene. Fluid movements element transport and the composition. Crustal structure and tectonics of the northern part of the southern granulite terrane, india v. During this period, the subject has undergone drastic changes, owing partly to the progress of thermodynamic investigations of metamorphic reactions and of the actual conditions of metamorphism under which such reactions occur, and partly to intensive field studies. The most common mineral assemblage of granulite facies consists of antiperthitic plagioclase, alkali feldspar containing up to 50% albite and al 2 o 3rich pyroxenes.
Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and. A sample of granulitefacies metamorphic rock of felsic composition, with garnet porphyroblasts. Crustal structure and tectonics of the northern part of the. The granulite facies is the highest grade of metamorphism at medium pressure. You may make use of these photographs for bona fide educational purposes. The names amphibolite and granulite have been used in geological literature for nearly 200 years. The granulite and hornfels facies were named after the textures of the rocks, with hornfels being the rocks commonly found in contact metamorphic aureoles high temperature, low pressure environments and granulites being coarse grained rocks with a granulitic texture and.
Magmas as a source of heat and fluids in granulite facies metamorphism. One might suppose that the middle crust in the sg3 area can be represented by rocks similar in age and composition of the protoliths to the sg3 archaean complex but metamorphosed under conditions of hightemperature amphibolite and granulite facies. Verbano zone and therefore related to the emplacement of the mafic underplating responsible for initiating granulite facies metamorphism. Metamorphic petrologists studying contact metamorphism early in the 20th century introduced the idea of metamorphic facies part of a rock or group of rocks that differs from the whole formation to correlate metamorphic events. The progressive changes in the assemblages and mineral chemistry of metabasites was studied in a ns traverse covering the chitradurga and nagamangala belts, the sargur area, and the nilgiri hills. The granulite facies is characterized by the following mineral assemblages. A common type of granulite found in highgrade metamorphic rocks of the continents contains pyroxene, plagioclase feldspar and accessory garnet, oxides and possibly amphiboles. The dominant soil associations are characterized by. Boron isotopic composition of tourmaline, prismatine, and. To sum up, a metamorphic facies is the set of minerals found in a rock of a given composition. Although brongniart described amphibolite as a rock composed of amphibole and plagioclase, in those early days the meaning of the term was variable. Such a facies series is related to a geothermal gradient of 2035. Due to the strong overprinting at subsequent granulite. Amphibolite and granulite recommendations by the iugs subcommission on the systematics of metamorphic rocks.
The concept was first defined in 1914 by a finnish petrologist, pentti eelis eskola, as any rock of a. Granulite news newspapers books scholar jstor march 2012 learn how and when to remove this template message. Franz, in reference module in earth systems and environmental sciences, 2015. Facies and mafic free download as powerpoint presentation.
Geochemistry of exposed granulite facies terrains and. As in all metamorphic rocks, the composition of the parent rock exerts a strong control on the particular mineralogy that is observed. Monometamorphism is a metamorphism resulting from one metamorphic event fig. The preservation of granulite facies mineral assemblages is an important feature in understanding highgrade processes in the middle to lower continental crust. A characteristic of this facies is the low content of water, which has been forced out of the rock by the high pressure and temperature. Changes in mineralogy depends very much on protolith, however, production of pyroxene, microcline and sapphirine are most characteristic. Progressive metamorphism of mafic rocks from greenschist to. The buchan facies series of regional metamorphism is characterized by the presence of andalusite, and sometimes cordierite, in intermediate grade mineral assemblages indicating that the conditions of metamorphism were at lower pressure and along a higher metamorphic field gradient than that recorded in barrovian facies series metamorphic rocks. The granulite and hornfels facies were named after the textures of the rocks, with hornfels being the rocks commonly found in contact metamorphic aureoles high temperature, low pressure environments and granulites being coarse grained rocks with a granulitic texture and being generally free of hydrous minerals. In general, facies are not defined for sedimentary rocks by features produced during weathering, metamorphism, or. Evidence of reactioninduced microfracturing in granulite. This enhancement is compatible with the reported compositional contrasts between granulite and amphibolite facies rock, but requires large fluid volumes. Greenschist, amphibolite, granulite facies 2 granulites are dry rocks dont melt due to lack of available water granulite facies terranes represent deeply buried and dehydrated roots of the continental crust fluid inclusions in granulite facies rocks of s.
Examples of granulite facies rocks and mineral assemblages. Granulite facies, one of the major divisions of the mineral facies classification of metamorphic rocks, the rocks of which formed under the most intense temperaturepressure conditions usually found in regional metamorphism. That mineral suite is taken as a sign of the pressure and temperature that made it. The major protolith of the soils in this portion of coastal maine is glacial till. Progressive metamorphism of mafic rocks from greenschist. The diagrams presented here show that melt loss at a given temperature has a significant influence on both uptemperature and downtemperature stable mineral assemblages. There seems now to be a broader recognition of the variety of pt paths and tectonic settings to be found in granulitefacies terrains. In various memoirs and books turner used the doubtful sound pyroxene assemblages as examples of his almandinediopsidehornblende subfacies 1948, hornblendegranulite facies 1958, and amphibolite granulite transition facies 1968. In this case, the ages of granulite facies reequilibration of the former hpuhp rocks. Although granulite facies rocks are present in zones of orogenesis ranging in age from 300 to 3,000 m. Polymetamorphism is a metamorphism resulting from more than one metamorphic event fig. Examples of granulitefacies rocks and mineral assemblages.
Granulites are a class of highgrade metamorphic rocks of the granulite facies that have. Geology of the granulite and amphibolite facies gneisses. When the temperature or pressure in a rock body change, the rock can cross into a different facies and some minerals become stable while others become unstable or metastable. A relatively coarse, granular rock formed at high pressures and temperatures, which may exhibit a crude gneissic structure due to the parallelism of flat lenses of quartz. Consistent with the paleogeographic reconstructions matte, 1986. The term facies is widely used in connection with sedimentary rock bodies, but is not restricted to them. The amphibolite to granulite facies rocks overlying the mct occupies a vast expanse of. The compositional ranges of minerals are generally similar to those of granulite facies metapelites, but moderately elevated contents of mn in garnet from the garnetites, and zn in spinel from the aluminous gneisses, are consistent with hydrothermal addition of these elements to the protolith. Crustal structure and tectonics of the northern part of. Whether minerals really react depends on the reaction kinetics, the activation energy of the reaction and how.
Mar 27, 2017 metamorphic facies is not obvious in a given field specimen. The different metamorphic facies are defined by the mineralogical composition of a rock. Sassi, department of mineralogy and petrography, university of padova, italy. Metamorphic facies academic dictionaries and encyclopedias. Canadian journal of earth sciences canadian science publishing. In the later orogenic stages, rocks undergo hightemperature metamorphism, primarily of the amphibolite and granulite facies.
Granulite article about granulite by the free dictionary. Pressure granulite facies overprinting during the exhumation. Almost all wellstudied examples are precambrian, which has suggested to many workers that metamorphic temperature regimes operating in the remote geological past were higher than are characteristic of more recent metamorphism. Apr, 2016 granulite facies are documented by grtopxcpxplbearing mafic granulites and charnockitic gneisses, reporting p 0. The compositional ranges of minerals are generally similar to those of granulitefacies metapelites, but moderately elevated contents of mn in garnet from the garnetites, and zn in spinel from the aluminous gneisses, are consistent with hydrothermal addition of these elements to the protolith. Facies, metamorphic an ensemble of metamorphic rocks of varying composition that correspond to specific conditions of formation relative to the primary factors of metamorphism, namely, temperature, geostatic pressure, and the partial pressures of the volatile components in the fluids involved in metamorphic reactions among minerals seemetamorphism. Evidence for pttime paths of hightemperature metamorphism. Amphiboles and micas both disappear in granulite facies rocks, hornblende dehydrates to form pyroxene and plagioclase. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs.