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Metamorphic Facies Metamorphic Facies ERSC 3P21 Metamorphic Petrology II 24/08/2011 Metamorphic Facies • Facies – ____________________________ ____________________________________ ____________________________________ • There is a predictable and common correspondence between the __________ of each rock and its ______________________ • Mineral _____________ that define the metamorphic _______ indicate that a state of stable _________ has been ________ over a restricted T and P condition. ERSC 3P21 - Brock University Greg Finn Metamorphic Facies • Several different facies have been formally recognized and have been named according to distinct aspects of the facies – eg. greenschist = characterized by schists in which green chlorite, talc, serpentine, epidote and actinolite are predominant • Examine the mineralogical characteristics in metamorphosed mafic (basic) rocks subjected to prograde metamorphism ERSC 3P21 - Brock University Greg Finn Metamorphic Grade Calculated 14 Geothermal Water Gradient saturated 40 granite 12 solidus Diagenesis 10 30 Liquid 8 VERY LOW or+ab+q HIGH GRADE 20 GRADE Depth (km) 6 Pressure (kbar) LOW 4 GRADE MEDIUM 10 GRADE mu + q 2 or+Al2SiO5+H2O 100 200 300 400 500 600 700 800 900 1000 Temperature (C) ERSC 3P21 - Brock University Greg Finn 1 ERSC 3P21 Metamorphic Petrology II 24/08/2011 Metamorphic Facies Calculated 14 Geothermal Water Gradient saturated 40 Eclogite granite 12 solidus Diagenesis Glaucophane 30 10 Lawsonite 8 Granulite 20 Amphibolite Depth (km) 6 Prehnite Pressure (kbar) Greenschist Pumpellyite 4 10 Zeolite 2 Px Hornfels Hornfels Sanidinite 100 200 300 400 500 600 700 800 900 1000 Temperature (C) ERSC 3P21 - Brock University Greg Finn Zeolite Facies • Zeolites are a group of white to colourless _______ ________ silicates, analogous in 2005/gold2005/images/zeolite.jpg composition to __________ • Common Zeolites are: http://www.the-conference.com/ • Laumontite - Ca(Al2Si4)O12·4H2O • Heulandite – (Ca,Na)2(Al2Si7)O18·6H2O • Analcime – NaAlSi2O6·H2O • Assemblage qtz + heulandite + chlorite is diagnostic http://www.curiogrove.com/Zeolite/gfx/ze002.jpg ERSC 3P21 - Brock University Greg Finn Prehnite - Pumpellyite Facies • Prehnite and pumpellyite, along with the zeolites, commonly occur as _________ fillings in originally vesicular samples • Minerals present are: • Prehnite – Ca2Al2Si3O10(OH)2 • Pumpellyite – http://www.dsuper.net/~marcouet/images/prehnite.jpg Ca2MgAl2(SiO4)(Si2O7)(OH)2·H2O • Assemblage qtz + Prehnite + Pumpellyite is diagnostic http://www.asahi-net.or.jp/~ug7s-ktu/e_pumpel.htm ERSC 3P21 - Brock University Greg Finn 2 ERSC 3P21 Metamorphic Petrology II 24/08/2011 Glaucophane - Lawsonite Facies • AKA - ___________________ • Minerals present are blue in colour • Glaucophane - Na2MgAl2Si8O22(OH)2 • Lawsonite - CaAl2Si2O7(OH)2H2O • Jadeite – NaAlSi2O6 • Characteristic of regions of ______ and _________ metamorphism, near _____________ zones • Assemblage jadeite + qtz + aragonite is diagnostic ERSC 3P21 - Brock University Greg Finn http://geosciences.geol.u-psud.fr/ObjectifTerre/Mineralogie/mineropolarisant/Glaucophane/GlauLP.jpg http://ic.ucsc.edu/~rocks/eart005/Metamorphic/Green_Blue.htm http://www.tulane.edu/~sanelson/images/fransican.gif ERSC 3P21 - Brock University Greg Finn • Formation of Blueschists http://www.uwgb.edu/dutchs/graphic0/platetec/metzone.gif ERSC 3P21 - Brock University Greg Finn From: http://www.uwgb.edu/dutchs/platetec/orogeny.htm 3 ERSC 3P21 Metamorphic Petrology II 24/08/2011 Metamorphic Facies Calculated 14 Geothermal Water Gradient saturated 40 granite 12 solidus Diagenesis Glaucophane 10 30 Lawsonite 8 20 Depth (km) 6 Prehnite Pressure (kbar) Pumpellyite 4 10 Zeolite 2 100 200 300 400 500 600 700 800 900 1000 Temperature (C) ERSC 3P21 - Brock University Greg Finn Greenschist Facies • A _______ schist developed through the metamorphism of a ______-rich rock – basalt • Common minerals are: 3+ • Epidote – Ca2Fe Al2OSi2O7(SiO4)(OH) 2+ • Actinolite – Ca2(Mg,Fe )5Si8O22(OH)2 • Chlorite – (Mg,Al,Fe)3(Si,Al)4O10(OH)2·(Mg,Al,Fe)3(OH)6 • Albite + Epidote + Actinolite + Chlorite + Calcite in mafic rocks • Pyrophyllite in pelitic rocks ERSC 3P21 - Brock University Greg Finn ERSC 3P21 - Brock University Greg Finn 4 ERSC 3P21 Metamorphic Petrology II 24/08/2011 Amphibolite Facies • Abundant _____ and little ____, as such they do not produce quartz and micas • Named for abundant ____________ • Common minerals are: • Hornblende – Ca2(Mg,Fe,Al)5Si8O22(OH)2 • Plagioclase – (Ca,Na)2(Al,Si)AlSi2)O8 »>An20 2+ 3+ • Garnet – (Ca,Mg,Fe ,Mn)3(Al,Fe ,Cr)2(SiO4)3 • Kyanite (Al2SiO5) in pelites • Assemblage hornblende + plagioclase is diagnostic ERSC 3P21 - Brock University Greg Finn ERSC 3P21 - Brock University Greg Finn hb hb cpx cpx hb hb p p cpx cpx op p op p p p a b Sample 99-3 - Amphibolite (metamorphosed gabbro) under (a) plane light and (b) crossed polars. Minerals present include plagioclase (p), clinopyroxene (cpx) (note the variable colour (pleochroism) of the cpx brown and green), hornblende (hb) and opaques (op). (FOV = 8.5mm) ERSC 3P21 - Brock University Greg Finn 5 ERSC 3P21 Metamorphic Petrology II 24/08/2011 Metamorphic Facies Calculated 14 Geothermal Water Gradient saturated 40 granite 12 solidus Diagenesis Glaucophane 30 10 Lawsonite 8 20 Amphibolite Depth (km) 6 Prehnite Pressure (kbar) Greenschist Pumpellyite 4 10 Zeolite 2 100 200 300 400 500 600 700 800 900 1000 Temperature (C) ERSC 3P21 - Brock University Greg Finn Granulite Facies • Characteristic of _____________ • Cpx + Opx + Pl + (Fe,Mg) Garnet ERSC 3P21 - Brock University Greg Finn Eclogite Facies • Lower _____ or upper ______ (deepest material sampled on a regular basis) • Feldspar-free assemblage, • Jadeite + pyrope (Mg garnet) is diagnostic ERSC 3P21 - Brock University Greg Finn 6 ERSC 3P21 Metamorphic Petrology II 24/08/2011 cpx cpx clinopyroxene clinopyroxene garnet garnet gt gt cpx cpx garnet garnet cpx cpx cpx cpx 2.0 mm cpx 2.0 mm cpx Sample PT-279: Eclogite. This sample is equivalent to the basalt, gabbro and amphibolite, except that it has been metamorphosed to a higher degree (~500-700°C and >10 kbars). This sample consists of medium to coarse grained clinopyroxene (cpx) which exhibits a weak green pleochroism and garnet (gt), an isotropic mineral. Hornblende, light green to dark green pleochroism, is present in this sample (not visible in this view). Minor amounts of plagioclase and quartz make up the fine grained matrix. ERSC 3P21 - Brock University Greg Finn Metamorphic Facies Calculated 14 Geothermal Water Gradient saturated 40 Eclogitegranite 12 solidus Diagenesis Glaucophane 30 10 Lawsonite 8 Granulite 20 Amphibolite Depth (km) 6 Prehnite Pressure (kbar) Greenschist Pumpellyite 4 10 Zeolite 2 Px Hornfels Hornfels Sanidinite 100 200 300 400 500 600 700 800 900 1000 Temperature (C) ERSC 3P21 - Brock University Greg Finn Characteristics of regionally metamorphsed mudstones Grade Rock Name Grain Size Key Minerals Features Protolith Mudstone Very fine grained, Clays, quartz Fissile, shale, bedding or clay sized massive, mudstone particles texture Very Low Slate Very Fine, Clays, chlorite, Bedding, slaty cleavage recrystallized quartz, Fe-oxides particles Low Phyllite Fine Micas, chlorite, Bedding, phyllitic foliation quartz, Fe-oxides Medium Schist Fine to medium, Micas, chlorite, Schistosity, with random quartz, plag, garnet, porphyroblasts, rare isolated large staurolite, kyanite, bedding porphyrobalsts Fe-Ti oxides High Schist/gneiss Medium to Biotite, quartz, plag., Schistosity or coarse garnet, cordierite, gneissosity, segregation sillimanite, Fe-Ti layering, porphyroblasts oxides Very Gneiss Medium to Biotite, quartz,plag., Gneissosity, segregation, coarse orthoclase, layering, porphyroblasts, High sillimanite, garnet, migmatitic layering cordierite, Fe-Ti ox. ERSC 3P21 - Brock University Greg Finn 7.
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