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Metamorphic Rocks Francis, 2014
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paragoniteNaAl 2 (AlSi 3 O 10 (OH) 2 muscoviteKAl 2 (AlSi 3 O 10 (OH) 2 pyrophylliteAl 2 Si 4 O 10 (OH) 2 andalusiteAl 2 SiO 5 or Al 2 OSiO 4 kyaniteAl 2 SiO 5 or Al 2 OSiO 4 sillimaniteAl 2 SiO 5 or Al 2 OSiO 4 staurolite(Fe,Mg) 2 Al 9 O 6 (SiO 4 ) 4 (O,OH) 2 chloritoid(Fe,Mg) 2 Al 4 O 2 (SiO 4 ) 2 (OH) 4 cordierite(Fe,Mg) 2 Al 3 (Al,Si 5 )O 18.nH 2 O garnet(Fe,Mg) 3 Al 2 (SiO 4 ) 3 chlorite (Mg,Fe) 3 (Al,Si 3 )O 10 (OH) 2 (Mg,Fe) 3 (OH) 6 biotiteKFe 3 (AlSi 3 O 10 (OH) 2 zoisite - epidote Ca 2 (Fe,Al) 3 O(SiO 4 )(Si 2 O 7 )(OH) tremolite/ actinoliteCa 2 (FeMg) 5 Si 8 O 22 (OH) 2 Metamorphic Minerals AFM projection for Metapelites andalusite kyanite sillimanite staurolite
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Sillimanite Staurolite Cordierite / Pyrox Andalusite Kyanite Garnet /Biotite Actinolite Hornblende Chlorite Muscovite K-Spar
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Metamorphic Facies : A metamorphic facies is the set of mineral assemblages that are stable over a given range of P and T. The actual mineral assemblage within this set that a given rock exhibits is a function of its chemical composition. The delineation of the metamorphic facies commonly used today is a matter of historical development that predates actual experimental determination of pressures and temperatures. The division of the P-T metamorphic regime into the following metamorphic facies developed from field observations on the persistence of certain mineral assemblages for specific bulk compositions in geographic and thus P-T space: Zeolite - zeolites or clay minerals, calcite and/or quartz-filled amygdules Greenschist - green minerals: chlorite, actinolite, epidote Blueschist - blue amphibole, aragonite Amphibolite - dark amphibole (hornblende), garnet Granulite - absence of hydrous minerals and thus schistoscity, granular Eclogite - pyropic garnet & jadeiitic clinopyroxene – high pressure
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bedding Slate vs Shale Harder and cleavage at an angle to bedding Extremely fine-grained rock exhibiting a perfect planar cleavage defined by the alignment of sub-microscopic phyllosilicates grains. Distinguished from shale by its greater hardness and the fact that cleavage is generally at an angle to bedding.
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Phylites to Schists micaceous foliation with sheen or visible mica xyls garnet muscovite schist cordierite muscovite schist
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Schists
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Metapelites in the Amphibolite Facies kyanite staurolite schist garnet staurolite schist andalusite kyanite sillimanite No amphiboles because of the lack of Ca
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amphibolites basaltic bulk compositions Typically characterized amphibole-defined lineation, rather than mica-defined foliation Hornblende Plag garnet
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Amphibolites Hornblende garnet Plag
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Gneiss Gneissosity: Compositional layering produced by metamorphic (solid-state) segregation into alternating felsic (leucosomes) and mafic (melanosomes) layers.
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Gneiss
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granulite garnet-orthopyroxene-cordierite granulite garnet sillimanite gneiss andalusite kyanite sillimanite Feldspar is granular rather than lath-like.
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partial melting migmatites and diatextites
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diatexite, Hortavaer Complex, Norway partial melting migmatites and diatextites
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Metamorphosed Carbonates marble: crystalline metamorphosed limestone. skarn: calcium-rich contact-metasomatic rock – contains abundant calc-silicate minerals ± carbonate formed at the contacts between magmatic intrusions and dirty carbonate rocks. Gross DiopideCaMgSi 2 O 6 GrossulariteCa 3 Al 2 (SiO 4 ) 3 CalciteCaCO 3
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andalusite kyanite sillimanite High-pressure rock of basaltic composition dominated by pyropic garnet (Mg 3 Al 2 (SiO 4 ) 3 ) and jadeitic (NaAlSi 2 O 6 ) clinopyroxene kyanite (never sillimaniteassociated, with of diamonds. More mafic compositions of with similar mineralogy are termed garnet clinopyroxenites. Eclogite
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Mylonite / Tectonite Extremely fine-grained rock exhibiting fine parallel gneissic banding over extensive strike lengths, produced by extreme strain. Typically possess a pronounced mineral lineation parallel to the transport direction, commonly have rotated porphyroblasts
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Metapelites AFM Projections Shales are typically depleted in Ca and Na because they were lost to solution during the breakdown of tecto-, ino-, and orthosilicates to clay minerals during weathering. Furthermore, quartz and muscovite are typically ubiquitous phases in metapelites. As a result, we can project the compositions of metapelites into a simplified ternary system (end-members: Al 2 O 3 * (A), FeO (F), and MgO (M)), assuming that quartz and muscovite are always present. Components = 6: K 2 O, Al 2 O 3, SiO 2, FeO, MgO, H 2 O With excess quartz & water: C = 4 and F = 4 - P + 2 If muscovite is present, we can project the mineral assemblages onto the Al 2 O 3 – FeO – MgO plane, where: C = 3 and F = 3 - P + 2 thus F = 0 for P = 3, if Press & Temp are fixed
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andalusiteAl 2 SiO 5 or Al 2 OSiO 4 kyaniteAl 2 SiO 5 or Al 2 OSiO 4 sillimaniteAl 2 SiO 5 or Al 2 OSiO 4 pyrophylliteAl 2 Si 4 O 10 (OH) 2 paragoniteNaAl 2 (Al,Si 3 )O 10 (OH) 2 muscovite KAl 2 (Al,Si 3 )O 10 (OH) 2 staurolite(Fe,Mg) 2 Al 9 O 6 (SiO 4 ) 4 (O,OH) 2 chloritoid(Fe,Mg) 2 Al 4 O 2 (SiO4) 2 (OH) 4 cordierite(Fe,Mg) 2 Al 3 (Al,Si 5 )O 18.nH 2 O garnet(Fe,Mg) 3 Al 2 (SiO4) 3 chlorite (Mg,Fe) 3 (Al,Si 3 )O 10 (OH) 2 (Mg,Fe) 3 (OH) 6 biotiteK(Mg,Fe) 3 (Al,Si 3 )O 10 (OH) 2 K-feldsparKAlSi 3 O 8 Metapelite Minerals: quartz, muscovite, and :
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F = C - P
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