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Topic: Blueschist Facies

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Thomas Will This allows a tight constraint of the peak metamorphic conditions and shows that the blueschist- and eclogite-facies mineral assemblages in the Tianshan HP-LT belt were overprinted by epidote-amphibolite-facies mineral assemblages following a decompressional PT path with slight heating similar to "Alpine-type" subduction zones. This intimate interlayering of blueschist- and eclogite-facies rocks as well as new geothermobarometrical evidence indicate unequivocally that they shared a common peak and post-peak metamorphic history. The late Paleozoic western Tianshan high-pressure metamorphic belt in NW China consists of eclogite-, blueschist- and greenschist-facies rocks, including meta-pillow lavas and meta-sedimentary gneisses, as well as minor Late Silurian marble lenses and ultramafic bands. www.uni-wuerzburg.de /mineralogie/will.html

McGraw-Hill AccessScience: Blueschist The name "blueschist" derives from the fact that at this metamorphic grade, rocks of ordinary basaltic composition are often bluish because they contain the sodium-bearing blue amphiboles glaucophane or crossite rather than the calcium-bearing green or black amphiboles actinolite or hornblende, which are developed in the more common greenschist- or amphibolite-facies metamorphism. More recently the term "blueschist facies" has been preferred because glaucophane is not always developed in many important rock types, for example, graywacke sandstones, which may contain other minerals that are characteristic of high pressure and low temperature such as aragonite, lawsonite, and jadeite+ quartz. Metamorphic rocks of the relatively uncommon blueschist facies contain assemblages of minerals that record these high pressures and low temperatures. dx.doi.org /10.1036/1097-8542.088400

Olympus Microscopy Resource Center: Polarized Light Microscopy Gallery - Glaucophane Schist 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. 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. www.olympusmicro.com /galleries/polarizedlight/pages/glaucophaneschistlarge.html

PSIgate - Physical Sciences Information Gateway: Search/Browse Results This site provides an introduction to regional metamorphism, including the Buchan facies series, the Barrovian facies series and the Blueschist facies series. A total of 11 figures illustrate this lecture text. The site is provided by Dave Jessey and Don Tarman, California State Polytechnic University Geological Sciences Department, Pomona, CA, USA. www.psigate.ac.uk /roads/cgi-bin/psisearch.pl?term1=blueschist&limit=0&subject=All

gv-fr juxt Moving westward from the CRT, the FRA degrades metamorphically from blueschist to prehnite,pumpellyite to zeolite facies. After being subducted, the blueschist rocks were tectonically thrust eastward and upward (by the interaction of the continental margin and a more westerly subduction zone) onto the Klamath-Sierran basement. These changes indicate an isothermal decrease in external pressure from one facies to the next, an observation explained by increasing lateral distances away from a subduction zone. seis.natsci.csulb.edu /rmorris/gvs-fra.htm

IngentaConnect Blueschist-Greenschist Transition in the Mt. Hibernia Schist, Uni... 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). api.ingentaconnect.com /content/bell/igr/2003/00000045/00000001/art00001

Catalogo Articoli The Osayama blueschists indicate that the 'cold' subduction type (Franciscan type) metamorphism to reach eclogite-facies and subsequent quick exhumat;ion took place in the northwestern Pacific margin in Carboniferous time, like some other circum-Pacific orogenic belts (western USA and eastern Australia), where such subduction metamorphism already started as early as the Ordovician. The mineralogic and paragenetic features of the Osayama bluesehists are compatible with a hypothesis that they were derived from a coherent blueschist-facies metamorphic sequence, formed in a subduction zone with a low geothermal gradient (similar to 10 degrees C/km). Gabbroic blocks derived from the Oeyama ophiolite are also enclosed as tectonic blocks in the serpentinite matrix and have experienced a blueschist metamorphism together with the other blueschist blocks. serials.cib.unibo.it /cgi-ser/start/it/spogli/df-s.tcl?prog_art=1838081&language=ITALIANO&view=articoli

DGGS Publications Sainsbury, C.L., Coleman, R.G., and Kachadoorian, Reuben, 1970, Blueschist and related greenschist facies rocks of the Seward Peninsula, Alaska, in U.S. Geological Survey Staff, Geological Survey research 1970, Chapter B: U.S. Geological Survey Professional Paper 700-B, p. Title: Blueschist and related greenschist facies rocks of the Seward Peninsula, Alaska www.dggs.dnr.state.ak.us /pubs/pubs?reqtype=citation&ID=4203

Lawsonite-Omphacite-Bearing Metabasites of the Pam Peninsula, NE New Caledonia: Evidence for Disrupted Blueschist- to Eclogite-Facies Conditions -- FITZHERBERT et al. 44 (10): 1805 -- Journal of Petrology Lawsonite-Omphacite-Bearing Metabasites of the Pam Peninsula, NE New Caledonia: Evidence for Disrupted Blueschist- to Eclogite-Facies Conditions -- FITZHERBERT et al. Lawsonite–Omphacite-Bearing Metabasites of the Pam Peninsula, NE New Caledonia: Evidence for Disrupted Blueschist- to Eclogite-Facies Conditions petrology.oupjournals.org /cgi/content/abstract/44/10/1805

Blueschist Photograph of a handsample representing the blueschist facies. www.eos.ubc.ca /courses/eosc221/meta/mfacies/m136.html

Subduction zone metamorphism Blueschists are normally gradational into eclogite facies rocks, which are characteristic of pressure greater than that of normal crustal thicknesses (shown on Blueschists contain a number of diagnostic minerals, which only form at high pressures and low temperatures. This process of subduction is not so efficient that we never see examples of blueschist metamorphism exposed at the Earth's surface. gemoc.anu.edu.au /course/geol1002/theory/rock/hardrock/19/index.htm

Discovery of Blueschists in the Medvednica Mountain (Northern Croatia) and Their Significance for the Interpretation of the Geotectonic Evolution of the Area, Geologia Croatica, 51/1, 27-32, Zagreb, 1998 These mineral associations indicate metamorphic conditions which are transitional between blueschist and eclogite facies, i.e. Blueschists were discovered in the metamorphic rocks of the Medvednica mountain. Two varieties of blueschists are recognised, one with garnets and another with omphacite. www.geologia-croatica.hr /abstract/gc-51-1-05.html

All about Facies - RecipeLand.com Reference library For example, you might refer to a "tan, cross-bedded oolitic limestone facies" or a " blueschist facies". The characteristics of the rock unit come from the depositional environment. www.recipeland.com /encyclopaedia/index.php/Facies

Blueschist preservation in a retrograded, high-pressure, low-temperature metamorphic terrane, Tinos, Greece: Implications for fluid flow paths in subduction zones Digital mapping reveals that while most HP-LT rocks in the outcrop were pervasively retrograded to greenschist facies, the marble-blueschist contact zone underwent an even more intense retrogression. 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. Blueschist preservation in a retrograded, high-pressure, low-temperature metamorphic terrane, Tinos, Greece: Implications for fluid flow paths in subduction zones www.agu.org /pubs/crossref/2003/2002GC000380.shtml

Metamorphic rocks - Metamorphic Facies Turner (1981) also distinguishes a pumpellyite-actinolite facies and a lawsonite-albite facies, transitional between the prehnite-pumpellyite, blueschist and greenschist facies, but Yardley considers these subdivisions too small to be of general practical use. In many metamorphic belts, the diagnostic assemblages of the zeolite and prehnite-pumpellyite facies are not seen, and the lowest grade rocks can be allocated to the greenschist facies. as enclaves or tectonically-incorporated blocks in blueschists or medium to high grade gneisses, or as nodules brought up in kimberlite pipes. teachserv.earth.ox.ac.uk /courses/es2-metrock/1metfac.html

Glaucophane - Wikipedia, the free encyclopedia - TESTVERSION It is glaucophane's color that gives the blueschist facies its name. This material has undergone intense pressure and moderate heat as it was subducted downward toward the mantle. Glaucophane is also found in eclogites that have undergone retrograde metamorphism. www.wissen-im-web.net /wiki/Glaucophane

IngentaConnect Blueschist blocks at Mochimaru in the Tari-Misaka ultramafic comp... After their capture by serpentinites and before the emplacement of the serpentinites into the present geological position, the tectonic blocks were subjected to high P/T metamorphism around the boundary between the blueschist and pumpellyite–actinolite facies. Blueschist tectonic blocks occur in serpentinites at Mochimaru, Hiroshima Prefecture, Southwest Japan. Blueschist blocks at Mochimaru in the Tari-Misaka ultramafic complex: Their petrologic characteristics and significance www.ingentaconnect.com /content/bsc/iar/1999/00000008/00000002/art00228

GEOCHEMISTRY AND METAMORPHISM OF BLUESCHIST/ECLOGITE FACIES ROCKS ON THE ISLAND OF SYROS, CYCLADES, GREECE In general, the mafic rocks have a variety of textures and modes, but most are either fine-grained, blueschists with a well-developed fabric (S approx.=L) or coarse-grained (>1 cm), massive omphacite- or Glau-rich rocks. Syros is part of the Attic-Cycladic blueschist belt. Based on textures, mineralogy and field relations, previous workers (Dixon and Ridley, 1987) have interpreted the mafic rocks as meta-basalt and metagabbros. gsa.confex.com /gsa/2001AM/finalprogram/abstract_27040.htm

SCICHINA Online But there were at least two stages of blueschist facies retrograde metamorphism overprinted during their uplift. The metamorphic PT path of Western Tianshan eclogites is characterized by clockwise ITD resulting from the subduction of Tarim plate northward to Yili-Central Tianshan plate followed by fast uplift to the surface. www.scienceinchina.com /yk/yd/0101/yd0085.stm

IngentaConnect The age of blueschist metamorphism in Anglesey, North Wales: evid... The ‘Penmynydd’ schists of SE Anglesey include several high P /low T lithologies including: (1) metasedimentary quartz–phengite schist; and (2) mafic blueschist with barroisite/crossite assemblages that appear to have developed from an earlier actinolitic greenschist facies protolith. Ar ages suggest multiple metamorphism of oceanic crust before the arrival of the blueschist terrane and its accretion to the late Precambrian basement of southern Britain immediately prior to development of the Welsh Basin. IngentaConnect The age of blueschist metamorphism in Anglesey, North Wales: evid... api.ingentaconnect.com /content/geol/jgs/1987/00000144/00000006/14460843

metamorphic rocks Blueschist facies is a low grade type of regional metamorphism specially in mountain building areas. Lower temperatures to higher temperatures produce other types of minerals. www.msnucleus.org /membership/html/jh/earth/metamorphic/lesson4/metamorphic4d.html

Blueschist Facies These lecture notes describe blueschist facies rocks, including their distribution, mineral assemblages and textures. The notes also discuss two models for the preservation and uplift of blueschist facies rocks. Three petrogenetic models are presented, the metasomatic recrystallization hypotheses, the tectonic overpressure model, and the burial metamorphism hypothesis. www.dlesecommunity.carleton.edu /resources/311.html

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