The dominant soil associations are characterized by. Use these facies if clearly associated with a pluton. Examples of granulite facies rocks and mineral assemblages. Although granulite facies rocks are present in zones of orogenesis ranging in age from 300 to 3,000 m. The content of amphibole and plagioclase together is mostly higher than 90%, and may be as low as 75%. Metamorphism of mafic rocks first evident in the greenschist facies, which correlates with the chlorite and biotite zones of associated pelitic rocks. The amphibolite to granulite facies rocks overlying the mct occupies a vast expanse of. Grew and manton 1986 reported 2507 and 2520 ma age from the study of allanite in pegmatoid veins cutting across amphibolite in the kabbaldurga charnockite. Fluids of granulite facies metamorphism springerlink.
The word granite comes from the latin granum, a grain, in reference to the coarsegrained structure of such a completely crystalline rock. Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and. Crustal structure and tectonics of the northern part of the southern granulite terrane, india v. The major change in fluid composition between upperamphibolite facies gneisses and granulites. 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.
Pdf constraints on granulite genesis from carbon isotope. Granulite facies synonyms, granulite facies pronunciation, granulite facies translation, english dictionary definition of granulite facies. Sassi, department of mineralogy and petrography, university of padova, italy. Granulite facies definition of granulite facies by the.
The modal compositions of amphibolites show that most of them contain more than 50% of amphibole, but those with 50 to 30% are not unusual. Granulite article about granulite by the free dictionary. Norway are co 2rich, whereas those in the amphibolite facies rocks are h. The composition of any fluid phase that was present during metamorphism. Grenvillian metamorphic grade in the grenville province is generally high, in the upper amphibolite and granulite facies. 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. These relationships offer the possibility of constraining the amount of. A sample of granulitefacies metamorphic rock of felsic composition, with garnet porphyroblasts. Granulite facies mpht the granulite facies is the highest grade of metamorphism at medium pressure. During late deformation, a series of mylonitic shear surfaces developed, one of which intersected and broke this garnet, offsetting the two sides by about 0. Metamorphic facies is not obvious in a given field specimen. It is believed that the granulite facies, introduced by eskola 1939, originates through a further rise in temperature after the field of the highesttemperature subfacies of the almandineamphibolite facies has been traversed. Whereas felsic to mafic granulites with an average intermediate major element composition are typically observed in old exposed lower crustal. Lithologic and geochemical comparison of supracrustal.
Granulites are a class of highgrade metamorphic rocks of the granulite facies that have experienced hightemperature and moderatepressure metamorphism. Granulite news newspapers books scholar jstor march 2012 learn how and when to remove this template message. Metamorphic conditions which create typical greenschist facies assemblages are called the barrovian facies. Greenschist facies is determined by the particular temperature and pressure conditions required to metamorphose basalt to form the typical greenschist facies minerals chlorite, actinolite, and albite. In general, facies are not defined for sedimentary rocks by features produced during weathering, metamorphism, or. A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. Thus, one can refer to a greenschist facies pelitic schist, an amphibolite facies calcsilicate rock, or a. 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. It was equivalent to the now littleused latinderived. Based on the mass balance equation, eclogitization of the granulite shows a reduction of volume of c. A characteristic mineral for this facies and the pyroxenehornblende facies is orthopyroxene. That mineral suite is taken as a sign of the pressure and temperature that made it.
Melt loss and the preservation of granulite facies mineral. Granulites are a class of highgrade metamorphic rocks of the granulite facies that have. The composition and geochemical behaviour of fluids which emanate from or pass through terrains undergoing granulite facies metamorphism viz. A metamorphic rock consisting of similarly sized, interlocking minerals, especially feldspar, quartz, and garnet, and lacking the layering and foliation. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. They are medium to coarsegrained and mainly composed of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure. The granulite facies is the highest grade of metamorphism at medium pressure. Trap falls formation may be equivalent in part to golden hill schist gray to silvery, partly rusty weathering, mediumgrained generally well layered schist, composed of quartz, sodic plagioclase, biotite, muscovite, and garnet, locally with sillimanite or kyanite, interlayered with twomica gneiss and granulite and with amphibolite. Franz, in reference module in earth systems and environmental sciences, 2015. Amphiboles and micas both disappear in granulite facies rocks, hornblende dehydrates to form pyroxene and plagioclase. Outcrops of eclogitefacies rocks showing a granulitefacies overprint are.
Late paleoproterozoic granulitefacies metamorphism in the north. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. This is a biotitecordieritesillimanitegarnet gneiss, metamorphosed in the lower granulite facies. 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. During hydration and metamorphism, the density changes from c. We report new petrological data for granulites from the central zone of the limpopo complex, southern africa, and construct a prograde pt. Accessory phases are zoned and vary markedly in abundance and composition between the palaeosome and neosome of migmatites. Multi stage late archaean granulite facies metamorphism in northern labrador, canada. If rocks are water saturated, they will, with a eutectic or eutectoid chemical composition near to granite, partially melt at. The mineral composition is to be indicated by prefixing the major constituents.
Granulite facies article about granulite facies by the. A pelitic or calcareous rock will develop very different mineral assemblages from a metabasalt, yet the same facies names apply. 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. 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. Geochemistry of exposed granulite facies terrains and. Changes in mineralogy depends very much on protolith, however, production of pyroxene, microcline and sapphirine are most characteristic. Pdf trace element partitioning in the granulite facies. Granulite facies mineral assemblages are preserved due to substantial melt loss white and powell, 2002. 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. As minerals often form from a liquid or aqueous medium, tiny blebs of that liquid can become trapped within the crystal, or along healed crystal fractures. The mode proportion of hornblende increased to more than 40% when.
Granulitefacies rocks metamorphosed at very high temperatures were identified in the early 1980s, although it took another decade for the geoscience community to recognize uht metamorphism as a common regional phenomenon. Pressure granulite facies overprinting during the exhumation. The trace element compositions of samples from exposed granulite facies terrains and 17 granulitic lower crustal xenoliths were determined using an inductively coupled plasma. The ages of granulite facies metamorphism in the southern part of the dharwar protocontinent range between 2500 50 and 2540 17 ma hansen et al. 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.
Metamorphic events also vary spatially and temporally, and have been dated at 1190 to 1160 ma, 1080 to 1020 ma and 1010 to 990 ma in different parts of the province e. Typical minerals include chlorite, albite, actinolite, epidote, quartz, and possibly calcite, biotite, or stilpnomelane. The term was earlier used by geologists to describe a clayrich, finegrained clastic sediment or sedimentary rock, i. Rocks of the granulite facies of metamorphism occupy a central role in discussions of petrogenesis of the crust. 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. Granulite facies is a highgrade metamorphic facies associated with orogenic regional metamorphism.
The term facies is widely used in connection with sedimentary rock bodies, but is not restricted to them. Goldschmidt 1911, 1912a, contact metamorphosed pelitic, calcareous, and psammitic hornfelses in the oslo region. There seems now to be a broader recognition of the variety of pt paths and tectonic settings to be found in granulitefacies terrains. The potential role of fluids during regional granulitefacies.
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. The granulitefacies, metabasite layers tonalitic composition are orthopyroxene bearing whereas the metapelite layers represent sillimanitebearing restites. Most xenoliths found are pyroxeneplagioclase orthogneisses, although quartzo. The major change in fluid composition between upperamphibolite facies gne isses and granulites. 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. Greenschist facies results from low temperature, moderate pressure metamorphism. Granulitefacies rocks in the whatley mill gneiss, pine. Marine and lacustrine sediments can be locally important. A model for the granulitemigmatite association in the archean basement of southwestern montana. To sum up, a metamorphic facies is the set of minerals found in a rock of a given composition.
A characteristic mineral for this facies and the pyroxene hornblende facies is orthopyroxene. Consequently, a reinvestigation of the temperature and pressure conditions during regional metamorphism was undertaken. Evidence for pttime paths of hightemperature metamorphism. Granulitefacies overprint in garnet peridotites and kyanite. For example, the presence of chlorite in amphibolite and granulite facies rocks would be indicative that the chlorite is a retrograde mineral or mineral produced during weathering, and thus would not be considered in the application of the phase rule. As in all metamorphic rocks, the composition of the parent rock exerts a strong control on the particular mineralogy that is observed. Highpressure and ultrahightemperature granulitefacies. 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. A fluid inclusion is a microscopic bubble of liquid and gas that is trapped within a crystal.
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