Documentation of textures, modes and compositions of minerals in metamorphosed basalts across two greenschist tolower amphibolite facies sequences flin flon, manitoba and rossland, british columbia was combined with a compilation of the literature data to assess equilibrium and disequilibrium processes across this important transition zone. This metaophiolite contains blueschist units, lawsonite eclogites and completely serpentinized ultramafic rocks, and is characterized by high pressure low temperature metamorphism. Metamorphic facies 4 facies of very low grade q q best developed during burial and hydrotheral mor metamorphism but rocks often fail to fully recrystallize at very low grades and equilibrium not always attained so zeolite and prehnitepumpellyite facies not always represented and greenschist facies is the lowest grade found in many regional. Experimental fluidmediated alteration of zircon under lower. Metamorphic facies the concept of metamorphic facies. The name comes from commonly having an abundance of green minerals such as chlorite, serpentine, and epidote, and platy minerals. Many of these rocks partly retain their primary structures and textures despite the intense deformation and metamorphic overprints in almost all supracrustal belts. In the greenschist facies phyllites, detrital and metamorphic allanite is present, whereas monazite is absent. Winter 2001 an introduction to igneous and metamorphic petrology. The lower greenschist facies in the scottish highlands. The facies is named for the typical schistose texture of the rocks and green colour of the minerals. The hp event blueschist facies was dated at 358365 ma with the 40 ar 39 ar phengite and rbsr whole rock, phengite, and epidote methods, while a younger age of 345353 ma was determined for the greenschist metamorphic event using the same methods bosse et al.
Tectonic exhumation during the formation of the southern canadian rocky mountains produced a domainal subgreenschist facies. The blueschist unit contains metagraywacke, metashale, metaconglomerate, greenstone, quartz schist, blueschist, and eclogite blocks in a finegrained, schistose matrix which probably recrystallized from a mixture of ultramafic and clayrich, quartzose detritus. The timeaveraged flux rate for a co 2bearing hydrous fluid during greenschist facies regional metamorphism was estimated to be 10 10. Equilibrium and disequilibrium processes across the. Greenschist facies article about greenschist facies by. Greenschists form by regional metamorphism of mafic igneous rocks, usually basaltic rocks, under greenschist facies metamorphism usually produced by regional metamorphism, typically 300450 c and 14 kilobars. Decreasing temperature is reflected by amphiboles that evolved from pargasitic to actinolitic compositions.
Note, however that blueschist facies is commonly used as a synonym for the glaucophaneschist facies and that the epidoteamphibolite facies is. A high, intermediate, ar lowpressure facies series is indicated by an h, i, or l in place of the final letter in the symbol used for the previously mentioned facies groups. Oceanic gabbro from leg 153 records retrograde metamorphism caused by progressive unroofing in the footwall of a brittleductile normal fault. Greenschistfacies metamorphism of the burgess shale and. 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. The greenschist facies represents the lower temperature part of this facies series. Greenschistamphibolite transition equilibria at low. Request pdf experimental fluidmediated alteration of zircon under lower greenschist facies conditions the application of zircon for the dating of geological processes and tectonic events has. Seismic facies analysis is the description and interpretation of seismic reflection parameters, such as configuration, continuity, amplitude, and frequency, within the stratigraphic framework of a depositional sequence. Citeseerx document details isaac councill, lee giles, pradeep teregowda. This study provides petrologic context for recently identified low.
At flin flon and rossland, the greenschist amphibolite facies transition occurs over a narrow spatial interval marked by hornblendein, oligoclasein and actinoliteout isograds. Pdf greenschist facies hydrothermal alteration of oceanic gabbros. Kisters, in earths oldest rocks second edition, 2019. Highest degrees of waterrock interaction are associated with. 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. Greenschists form by metamorphism of basic igneous rocks, the chlorite component being derived from the ferromagnesium minerals present in the original rock. Greenschist facies definition of greenschist facies by. In contrast, apatite from a variscan granitoid yields variscan u. Petrologic and geochemical comparison of the blueschist and.
As is the case in the buchan facies series, the greenschist amphibolite facies boundary is a broad zone. Blueschist facies an overview sciencedirect topics. Pdf oxygen isotope composition and geothermometry of. In detail, the behaviour of mn associated with secondary magnetite alteration is complex and curious. Metamorphic facies is not obvious in a given field specimen. Greenschist facies, one of the major divisions of the mineral facies classification of metamorphic rocks, the rocks of which formed under the lowest temperature and pressure conditions usually produced by regional metamorphism. 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. Gold mineralization in the greenschist facies deposits of the shebafairview and agnesprinceton mine complexes is structurally controlled by eastwest trending shear zones that are situated in, or in close proximity to, major d 2 structures. Sedimentary facies free download as powerpoint presentation. Petrologic and geochemical comparison of the blueschist. Mar 27, 2017 metamorphic facies is not obvious in a given field specimen.
You can make the connection more directly between the metamorphic facies and the types of metamorphism discussed in the previous section by matching up the letters a through e in figure 10. Figure 17 shows data from a suite of samples from the low greenschist facies, serpentinized mt keith complex, including grains such as the one illustrated in fig. Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures. Greenschist facies synonyms, greenschist facies pronunciation, greenschist facies translation, english dictionary definition of greenschist facies. A schist whose greenish colour is due to the presence of minerals such as actinolite, chlorite and epidote. Paragenetic relations of greenschistamphibolite minerals including plagioclases, epidote, chlorite, caamphiboles and quartz in the model system na 2 oca0mg0al 2 0 3 sio 2 h 2 o are delineated. The supracrustal rocks are generally metamorphosed to amphibolite facies, less commonly to granulite facies, and rarely to greenschist facies.
Greenschist facies metamorphic zircon overgrowths as a. The concept of facies, that is a body of rock with specified characteristics, has been used by geologists ever. At the upper limit of the facies, migmatite formation may occur. Most parts of the central block is built up of amphibolite facies rocks. Metamorphic conditions which create typical greenschist facies assemblages are called the barrovian facies sequence, and. Albite veins occur in greenschist facies metabasites gr 20d, groa 49, 50. Thickness, from the upper contact to the first appearance of relict sedimentary structure, ranges approximately 1 to 20 feet 0. Pdf greenschist facies regional and contact metamorphism. Ppt ch 25 metamorphic facies powerpoint presentation free. Greenschist facies hydrothermal alteration of oceanic gabbros.
Sediments greenschist facies biotite zone akf biotite in isograd tie line flip from geol 3041 at louisiana state university. Named for equivalent mafic rock type at those conditions. Convection occurs if the lower part of a fluid body is hotter than the upper part, hot fluid rises away from the heat source bringing heat to. Media in category greenschist the following 6 files are in this category, out of 6 total. Reading, department of earth sciences, parks road, oxford ox1 3pr, uk.
The composition range of common mafic rocks is shaded. Metamorphosed silty mudstones of the burgess shale and stephen shale formations record a poly metamorphic history. The behaviour of monazite from greenschist facies phyllites to. Types of schist used in buildings of minoan crete pdf. Inclusions of supracrustal rocks, metamorphosed at upper greenschist to amphibolite facies, are widespread in the rhodesdale granitoidgneiss terrain and have been assigned to the sebakwian group macgregor, 1951. Greenschist facies definition of greenschist facies by the. Oxygen isotope composition and geothermometry of granulite to greenschist facies metamorphic rocks.
Pdf the conditions of two separate greenschist facies metamorphic events have been reconstructed at the syngenetic thalanga. A lithium isotopic study of sub greenschist to greenschist facies metamorphism in an accretionary prism, new zealand. The names of eskolas facies are based on mineral assemblages found in metabasic basic rocks. Thus, since basic rocks metamorphosed to the greenschist facies contain the green minerals, chlorite and actinolite, along with other minerals like plagioclase, biotite, and garnet, the rocks were called greenschists. Metamorphic conditions which create typical greenschist facies assemblages are called the barrovian facies. Pdf greenschist amphiboles from haast river, new zealand. Albiteepidote hornfels facies z likely to be recognized only in the outermost parts of thermal aureoles in country rocks originally of very low metamorphic grade. Paragenetic relations of greenschist amphibolite minerals including plagioclases, epidote, chlorite, caamphiboles and quartz in the model system na 2 oca0mg0al 2 0 3 sio 2 h 2 o are delineated. The sodic amphibole ranges in composition from glaucophane to. Greenschistfacies metamorphism of the burgess shale and its. Amphibolite facies includes calcite marbles, biotite schists and amphibolites.
Rocks of the greenschist facies in eastern otago, new zealand, have been investigated in an area some thirteen to sixteen kilometers wide and sixtyfive kilometers long extending northeastwards approximately normal to the boundary of the schist with lower grade rocks. We investigated the crystal and structural behavior of several crbearing spinels from the archean chromitites of amsaga mauritania. In rocks with an initially low proportion of carbonate minerals, the greenschist to amphibolite facies transition is the primary period of. In can be easily distinguished from the higher temperature almandineamphibolite facies when the following critical minerals, characteristic solely of the greenschist facies, are. Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and.
This file is licensed under the creative commons attributionshare alike 3. Reaction softening by dissolutionprecipitation creep in a. Metamorphic conditions which create typical greenschist facies assemblages are called the barrovian facies sequence, and the lowerpressure abukuma facies series. Types, grade and facies of metamorphism recommendations by the iugs subcommission on th e systematics of metamorphic rocks. The elekdag metaophiolite is located in the central part of the pontides orogenic belt in northern anatolia, turkey. Textures are interpreted as recording an initial, nearstatic greenschist recrystallisation of a basic plutonic igneous rock, followed by deformation during continuing metamorphism at greenschist, then blueschist, grades. Temperatures of approximately 400 to 500 c 750 to 930 f and depths of about 8 to 50 kilometres. 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. Greenschist facies results from low temperature, moderate pressure metamorphism.
Unlimited viewing of the articlechapter pdf and any associated supplements and figures. Following the amphibolite to greenschist metamorphic path. Seismic facies are mappable, three dimensional seismic units composed of groups of reflections whose parameters differ from those of adjacent facies units. Sedimentary facies, process and environmental facies models, sequence stratigraphy.
The transformation from blueschist to greenschist facies forms a major part of the alpine regional geodynamic evolution of. Conduction is the transfer of heat vibration from one molecule to the adjacent atommolecule dominant form of heat transfer in solids. That mineral suite is taken as a sign of the pressure and temperature that made it. Greenschist amphibolite facies transition involves two major mineralogical changes. A greenish schist that forms under conditions of low temperature and low pressure and often contains the mineral chlorite, epidote, or actinolite. Within the greenschist facies and the hornblendeactinolite zone, albite is the only plagioclase present and has an average modal proportion of 43% in the greenschist facies decreasing to 30% in. Tectonic exhumation during the formation of the southern canadian rocky mountains produced a domainal subgreenschist facies retrograde overprint in which a highangle crenulation cleavage s 2 was developed. Pb ages with mafic igneous trace element signatures is also sporadically preserved in the greenschist. A greenschist protolith for blueschist in anglesey, u. The greenschist facies in part of eastern otago, new zealand. The results subdivide the transition zone into a highpressure albiteepidote amphibolite facies and a lowerpressure actinolitecalcic plagioclase hornfels. Flux rates for water and carbon during greenschist facies. To sum up, a metamorphic facies is the set of minerals found in a rock of a given composition.
Transformation of blueschist to greenschist facies rocks as a. The deformation mechanism here was thus one of dissolutionprecipitation creep, activated at considerably lower stresses than might be predicted in quartzofeldspathic rocks at the same lower greenschist facies conditions. 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. The facies is named for the typical schistose texture of the rocks and green colour of the minerals chlorite, epidote and actinolite. Pdf greenschist facies regional and contact metamorphism of the. Jan 01, 2003 an early greenschist facies event associated with burial by paleozoic strata produced a nearly ubiquitous beddingparallel cleavage s 1. Chrome spinel geochemistry of ultramafic rocks from the. Types, grade and facies of metamorphism british geological survey. Pdf amphibolite and blueschistgreenschist facies metamorphism. 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. Sediments greenschist facies biotite zone akf biotite in. In the catalina schist terrane, a nappe of blueschist facies melange is overlain by one of isoclinallyfolded greenschist facies rocks. Greenschist facies article about greenschist facies by the. Greenschist contains clots and lenses of blue quartz and abundant sulfide.
The results subdivide the transition zone into a highpressure albiteepidote amphibolite facies and a lowerpressure actinolite. Sassi 5, rolf schmid6 1 institute of geological sciences, polish academy of sciences, warsaw, poland 2 cnrs. Sedimentary environments is one of the most distinguished and influential textbooks in the earth sciences published in the last 20 years. Chan2 1california institute of technology, pasadena, ca, usa 2academia sinica, taipei, taiwan now at. This is the lowpressure equivalent of the greenschist facies, and the assemblages are very similar. An early greenschist facies event associated with burial by paleozoic strata produced a nearly ubiquitous beddingparallel cleavage s 1. Nonessential minerals these minerals are common, sometimes major components, but are not always present. Greenschist facies an overview sciencedirect topics. If burial continues along barrovian sequence metamorphic trajectories, greenschist facies gives rise to amphibolite facies assemblages, dominated by.
Devolatilization of metabasic rocks during greenschist. Axel hofmann, godfrey chagondah, in earths oldest rocks second edition, 2019. The more common minerals found in such rocks include quartz. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures.
These were formed during a first metamorphic event m1a which is characterized by a. Application of titaniuminquartz thermobarometry to. This process constitutes both reaction and microstructural softening. Download fulltext pdf greenschist facies regional and contact metamorphism of the thalanga volcanichosted massive sulfide deposit northern queensland, australia.
As the pt conditions increase, greenschist facies assemblages with new minerals form. Examples include the garnetcordierite, hypersthenesillimanite, staurolite, andalusite, sillimanite, and kyanite facies. The multiple greenschist and blueschist facies metamorphic events have been particularly difficult to resolve. Greenschist facies mpmt 11112012the greenschist facies is at medium pressure and temperature. Manganese in chromite in greenschist facies serpentinites. Under more typical conditions, this is the greenschist facies, and in a subduction zone it is the blueschist facies. Sedimentary facies sedimentary rock stratigraphy free. Unit does not crop out and is known only from subsurface borings and artificial exposures.
Amphibolite and blueschistgreenschist facies metamorphism. Temperatures between 300 and 450 c 570 and 840 f and pressures of 1 to 4 kilobars are typical. The greenschist facies is at low pressure and temperature. Since the publication of the last edition, the study of sedimentary environments and facies has made great strides, with major advances in facies modelling. Amphibolite and blueschistgreenschist facies metamorphism, blue mountain inlier, eastern jamaica. Facies represent specific temperature pressure regimes. Interpreted to be late proterozoic by volkert and drake 1993 on the basis of geochemical similarity to late proterozoic metadiabase dikes in new jersey highlands. Quartzofeldspathic schists predominate but greenschists and metacherts occur sporadically throughout the area. Metamorphic facies article about metamorphic facies by the.
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