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Topic: Blueschist


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 Blueschist - Wikipedia, the free encyclopedia
Blueschists may appear blue, fl, gray, or blue-green in outcrop.
When lawsonite occurs in blueschists, it appears as white tabular crystals.
Blueschist mineralogy varies by rock composition, but the classic equilibrium assemblages of blueschist facies are:
en.wikipedia.org /wiki/Blueschist   (532 words)

  
 Geological setting
The maximum thickness of the wedge during its deposition was calculated to be between 40 and 65 km, dependent on pressure estimates used for the blueschists (Schwartz et al.
The Monviso ophiolitic massif, 35 km NS and 35 km EW, forms the structural base of the unit (Figure 3) and is separated from the blueschistSchistes Lustrés’ by a ductile normal fault within the western serpentinite unit (Traversetta unit) (Ballèvre et al.
The exhumation rate of the unit was estimated by Schwartz et al (2000) as fast at the beginning (1 cm.yr-1) and slower at the blueschist to greenschist-facies transition (1 mm.yr-1).
www.virtualexplorer.com.au /journal/2004/16/guillot/setting.html   (1150 words)

  
 Blueschist preservation in a retrograded, high-pressure, low-temperature metamorphic terrane, Tinos, Greece: ...
Blueschist preservation in a retrograded, high-pressure, low-temperature metamorphic terrane, Tinos, Greece: Implications for fluid flow paths in subduction zones
The preservation of high-pressure, low-temperature (HP-LT) mineral assemblages adjacent to marble unit contacts on the Cycladic island of Tinos in Greece was investigated using a new type of digital outcrop mapping and numerical modeling of metamorphic fluid infiltration.
Mineral assemblage distributions in a large blueschist outcrop, adjacent to the basal contact of a 150-meter thick marble horizon, were mapped at centimeter-scale resolution onto digital photographs using a belt-worn computer and graphics editing software.
www.agu.org /pubs/crossref/2003/2002GC000380.shtml   (360 words)

  
 Metamorphic Facies & Metamorphism and Plate Tectonics
Under a normal to high geothermal gradient, such as "B", rocks would progress from zeolite facies to greenschist, amphibolite, and eclogite facies as the grade of metamorphism (or depth of burial) increased.
Basic rocks metamorphosed to the blueschist facies contain the blue sodic amphibole, gluacophane (along with garnet and lawsonite) are thus blueschists.
In 1961, Miyashiro noted that in the Cicumpacific region, belts of high pressure, low temperature metamorphism on the oceanic side were associated with belts of high pressure, high temperature metamorphism on the continent side.
www.tulane.edu /~sanelson/eens211/metamorphic_facies.htm   (1407 words)

  
 Singular Equilibria in Paragonite Blueschists, Amphibolites and Eclogites
As mafic schists metamorphosed at blueschist, amphibolite and eclogite facies conditions are commonly saturated in quartz, epidote and paragonite (Guidotti, 1987), we will show in the next section that chemographic relationships can be analysed in a condensed ternary model system.
The interpretation of the transformations from blueschist to eclogite facies and from eclogite to amphibolite facies still relies upon a poor knowledge of the thermodynamic properties of amphibole solid solutions.
Ridley, J. Evidence of a temperature-dependent `blueschist' to `eclogite' transformation in high-pressure metamorphism of metabasic rock.
library.iem.ac.ru /j-petr/7-3998/html/egb051_gml.html   (8856 words)

  
 ESS 301 - Lecture Key Points
The Shuksan Blueschist provides geologists with insight into the timing of collisional events.
The blueschist formed at a depth of roughly 30 km (20 miles) at 120 million years ago.
Thus, the ocean-floor rocks were down in a trench and the upper portion of the subduction zone.
faculty.washington.edu /sechern/ess301/key/050425.html   (382 words)

  
 Fluid backflow
The predominant basic composition of the descending plate is transformed into mineral assemblages of the blueschist facies and in the following of the eclogite facies with several dehydrating reactions.
Although the rocks are mostly blueschists, some show relics of omphacite and garnets indicating eclogitic facies.
Inclusions of epidote, quartz, barroisite or glaucophane and pseudomorphs of epidote, mica and quartz from lawsonite in the core of garnet describe the mineral assemblage during the prograde blueschist facies metamorphism.
min.uni-kiel.de /petrographie/schenk/projekte/fluide/fluidbackflow.html   (550 words)

  
 Orogeny
Greenschist and amphibolite metamorphism in the core of the range, blueschist metamorphism along its outer edge.
The two sides of the orogenic belt are separated by a suture marked by blueschist metamorphism, melange, ophiolites and major faults.
The rising magma from the descending plate heats the crust, resulting in greenschist and amphibolite metamorphism in the igneous arc.
www.uwgb.edu /dutchs/platetec/orogeny.htm   (1334 words)

  
 ORIGIN OF BLUESCHIST BRECCIA, SYROS, GREECE   (Site not responding. Last check: 2007-11-03)
The first and second episodes, late Cretaceous and Eocene high-pressure blueschist facies metamorphisms, are associated with subduction zone metamorphism.
The matrix of the breccia is strongly metamorphosed at the blueschist grade and contains glaucophane + garnet + zoisite +/- omphacite +/- chlorite +/- epidote.
The breccia is in contact with a coarse-grained metagabbro to the south and pelitic schist and marble to the north.
gsa.confex.com /gsa/2001NE/finalprogram/abstract_2785.htm   (437 words)

  
 How to resist subduction: Evidence for large-scale out-of-sequence thrusting during Eocene collision in western Turkey ...
Structural analysis reveals that the Anatolide belt in western Turkey formed under greenschist facies metamorphic conditions in the Eocene when a high-pressure metamorphic fragment of the Adriatic plate (the Cycladic blueschist unit) was thrust onto the imbricated mid-crustal units of the Anatolian microcontinent (the Menderes nappes).
Structure and geodynamic evolution of the Anatolide belt are in striking contrast to the neighbouring Aegean and contradict the model of a laterally continuous orogenic zone, in which the Anatolide microcontinent is interpreted as an eastern extension of the Adriatic plate.
It will be shown that the tectonometamorphic differences of both units and the geometry of their thrust contact have significant implications on the timing of collision and exhumation processes, and on the palaeogeography of the eastern Mediterranean.
www.findarticles.com /p/articles/mi_qa3721/is_200109/ai_n8995742   (960 words)

  
 Metamorphic geology research in Turkey
blueschist facies metasedimentary and metavolcanic rocks (some containing eclogite pods) record prograde and retrograde metamorphism.
These rocks are extremely interesting because the blueschists are adjacent to quartzites that contain andalusite + kyanite + sillimanite + staurolite ± garnet, and schists that contain chloritoid ± staurolite ± garnet.
We are trying to relate the metamorphic history of these rocks (blueschists, eclogites, and Al2SiO5-bearing rocks) to the subduction and exhumation processes, as well as other important events in the region (emplacement of ophiolites; magmatism).
www.geo.umn.edu /orgs/whitney/turkey2.html   (867 words)

  
 [No title]
The blueschist event in the Eastern Alps is not well constraint in respect to age dating.
In the LEW mostly the deeper parts (North Penninic metasediments) are metamorphosed in blueschist facies In the RWG the ophiolites indicate clearly the blueschist event, the metasediments below and above the ophiolites are not well investigated.
Therefore, the question whether the blueschist event is synchronous throughout the Penninic realm in the Eastern Alps and its range is an unsolved problem.
homepages.uni-tuebingen.de /alpshop/TGAvol/-037.html   (1149 words)

  
 Blueschist and Ring Mountain, TSAW Project   (Site not responding. Last check: 2007-11-03)
Simplistically, what is called blueschist metamorphism describes a form of mineral changes that occur under conditions of extremely high pressures and relatively low temperatures (i.e., deep burial inside the Earth...without being heated to the temperatures expected at such depths).
This photo (with text) shows two of the blueschist blocks near the crest of the Ring Mountain area.
These blueschists are found in numerous places within the Franciscan rocks of California and some of the 'highest pressurized' ones reported are found in the melange of Baker Beach in San Francisco.
www.marin.cc.ca.us /~jim/ring/blue.html   (216 words)

  
 Olympus Microscopy Resource Center: Polarized Light Microscopy Gallery - Glaucophane Schist
Glaucophane only occurs in certain rocks, such as schist, marble, and eclogite, and is generally formed in a highly metamorphic zone known to geologists by the term blueschist facies.
The typical location of blueschist facies is along continental margins affected by shifting of oceanic plates and in areas of high volcanic and seismic activity.
Some of the best-known examples of blueschist facies in the world are found in Japan, California, the Mediterranean, and the Alps.
www.olympusmicro.com /galleries/polarizedlight/pages/glaucophaneschistsmall.html   (216 words)

  
 Blueschists   (Site not responding. Last check: 2007-11-03)
Blueschist is an unusual metamorphic rock that is produced by subduction of oceanic crust.
The occurrence of blueschist prior to the Mesozoic is rare so it's possible that the Precambrian Anglesey blueschists are perhaps the oldest recorded blueschists in the world.
The presence of blue glaucophanic amphibole is usually associated with rocks subducted at ocean trenches where high pressures and low temperatures are the norm.
www.kabrna.com /cpgs/anglesey/blueschist.htm   (265 words)

  
 Regional Metamorphism
The Blueschist Facies develops in terranes in which the geothermal gradient is low or the overall P/T is moderate to high.
Three hypotheses for the origin of Blueschist Facies Series rocks are advocated by various geologists.
In particular, the presence of Blueschist Facies Series rocks in paired metamorphic belts suggests that subduction and associated accretion of subducted rocks, are generally responsible for Blueschist Facies and related rocks.
geology.csupomona.edu /alert/metamorphic/regional.htm   (2511 words)

  
 Talc - The real meaning from Timesharetalk wikipedia   (Site not responding. Last check: 2007-11-03)
In this reaction, the ratio of talc and kyanite is dependant on aluminium content with more aluminous rocks favoring production of kyanite.
This is typically associated with high-pressure, low-temperature minerals such as phengite, garnet, glaucophane within the lower blueschist facies.
Talc is a very common metamorphic mineral in metamorphic belts which contain ultramafic rocks and within whiteschist and blueschist metamorphic terranes.
www.timesharetalk.co.uk /wiki.asp?k=Talc   (726 words)

  
 Spear Graduate Funding
This proposal seeks funds to study the metamorphic evolution of blueschists and eclogites from the islands of Syros and Sifnos in the Cyclades Blueschist belt, Greece.
The Cycladic islands contain high-pressure metamorphic rocks that are believed to be the dismembered roots of the mountain belt formed during Eurasia-Africa subduction and fragmented during the continental extension that followed collapse in the Aegean area.
The major goal of this project is to determine the fine structure of the P-T-t history in blueschists, eclogites, and greenschists of different tectonic units in order to constrain the burial and uplift history of the blueschist/eclogite belt.
ees2.geo.rpi.edu /spear/SpearGraduateFunding.html   (1148 words)

  
 Zircon   (Site not responding. Last check: 2007-11-03)
Blocks of eclogite, garnet hornblendite, and garnet blueschist are found within the (meta)sedimentary Franciscan Complex of central and northern California.
Zircon was reported within a garnet blueschist block from the Franciscan as early as 1894 by Palache, but no attempt has been made to use this mineral to study these rocks since that time.
The ages of these zircons are young (~140 Ma) for Franciscan eclogite and hornblendite (~150-160 Ma), but similar in age to garnet blueschists (Anczkiewcz et al., 2004).
web.mac.com /sandlerpage/iWeb/Zeb/Zircon.html   (306 words)

  
 IngentaConnect Blueschist-Greenschist Transition in the Mt. Hibernia Schist, Uni...   (Site not responding. Last check: 2007-11-03)
The metamorphism reflects a Sanbagawa facies series, wherein two facies, blueschist and greenschist, and transitional schist are recognized.
P-T conditions for the blueschist and transitional schist were estimated by multiple equilibria analysis involving mineral components in NCMASH.
The highest P-T conditions are represented by the blueschist assemblage, Gln + Pmp + Act + Chl + Qtz + Alb + (relict Cpx).
www.ingentaconnect.com /content/bell/igr/2003/00000045/00000001/art00001   (380 words)

  
 Geoscience - The Earth - Shaping the Earth - Metamorphism and metamorphic rocks
Blueschist (17 cm x 11 cm) Clear Creek, New Idria District, California, USA.
These rocks are commonly schistose, may have a characteristic blue colour, and are termed blueschists.
The New England Fold Belt contains small amounts of blueschists and eclogites that formed in the collision zones of subducting slabs.
www.amonline.net.au /geoscience/earth/metamorphism.htm   (2757 words)

  
 Blueschist Facies   (Site not responding. Last check: 2007-11-03)
These lecture notes describe blueschist facies rocks, including their distribution, mineral assemblages and textures.
Three petrogenetic models are presented, the metasomatic recrystallization hypotheses, the tectonic overpressure model, and the burial metamorphism hypothesis.
The notes also discuss two models for the preservation and uplift of blueschist facies rocks.
serc.carleton.edu /resources/311.html   (98 words)

  
 IngentaConnect Petrogenesis of lawsonite and epidote eclogite and blueschist, Si...   (Site not responding. Last check: 2007-11-03)
Petrogenesis of lawsonite and epidote eclogite and blueschist, Sivrihisar Massif, Turkey
The Sivrihisar Massif, Turkey, is comprised of blueschist and eclogite facies metasedimentary and metabasaltic rocks.
Abundant metre- to centimetre-scale eclogite pods occur in blueschist facies metabasalt, marble and quartz-rich rocks.
www.ingentaconnect.com /content/bsc/jmg/2006/00000024/00000009/art00003   (221 words)

  
 Kinds of Metamorphism
Note also the diagonal red arrow, the geothermal gradient, the average increase in temperature with depth.
There is much to explore to understand these rocks and so we will deal with them at another page.
Blueschist metamorphism occurs at convergent plate boundaries in subduction zones, either under volcanic arcs, or under continents (cordilleran type).
csmres.jmu.edu /geollab/Fichter/MetaRx/MetaKind.html   (879 words)

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