metamorphic rocks francis, 2014. paragonitenaal 2 (alsi 3 o 10 (oh) 2 muscovitekal 2 (alsi 3 o 10...
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Metamorphic RocksFrancis, 2014
paragonite NaAl2(AlSi3O10(OH)2
muscovite KAl2(AlSi3O10(OH)2
pyrophyllite Al2Si4O10(OH)2
andalusite Al2SiO5 or Al2OSiO4
kyanite Al2SiO5 or Al2OSiO4
sillimanite Al2SiO5 or Al2OSiO4
staurolite (Fe,Mg)2Al9O6(SiO4)4(O,OH)2
chloritoid (Fe,Mg)2Al4O2(SiO4)2(OH)4
cordierite (Fe,Mg)2Al3(Al,Si5)O18.nH2O
garnet (Fe,Mg)3Al2(SiO4)3
chlorite (Mg,Fe)3(Al,Si3)O10(OH)2(Mg,Fe)3(OH)6
biotite KFe3(AlSi3O10(OH)2
zoisite - epidote Ca2(Fe,Al)3O(SiO4)(Si2O7)(OH)tremolite/ actinolite Ca2(FeMg)5Si8O22(OH)2
Metamorphic Minerals
AFM projection for Metapelitesandalusite
kyanite
sillimanite
staurolite
SillimaniteStaurolite
Cordierite / Pyrox
Andalusite
Kyanite
Garnet /Biotite
Actinolite Hornblende
Chlorite
Muscovite K-Spar
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
bedding
bedding
bedd
ing
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.
Phylites to Schistsmicaceous foliation
with sheen or visible mica xyls
garnet muscovite schist
cordierite muscovite schist
Schists
Metapelites in the
Amphibolite Facies
kyanite staurolite schist
garnetstaurolite
schist
andalusite
kyanite
sillimanite
No amphiboles because
of the lack of Ca
amphibolites
basaltic bulk compositions
Typically characterized amphibole-defined lineation, rather than mica-defined foliation
HornblendePlag
garnet
Amphibolites
Hornblende
garnet
Plag
Gneiss
Gneissosity:
Compositional layering produced by metamorphic (solid-state) segregation into alternating felsic (leucosomes) and mafic (melanosomes) layers.
Gneiss
granulite
garnet-orthopyroxene-cordierite granulite
garnet sillimanite gneiss
andalusite
kyanite
sillimanite
Feldspar is granular rather than lath-like.
partial melting
migmatitesand
diatextites
diatexite, Hortavaer Complex, Norway
partial melting
migmatitesand
diatextites
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
Diopide CaMgSi2O6
Grossularite Ca3Al2(SiO4)3
Calcite CaCO3
andalusite
kyanite
sillimanite
High-pressure rock of basaltic composition dominated by pyropic garnet (Mg3Al2(SiO4)3) and jadeitic (NaAlSi2O6) clinopyroxene kyanite (never sillimaniteassociated, with of diamonds.
More mafic compositions of with similar mineralogy are termed garnet clinopyroxenites. Eclogite
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
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: Al2O3* (A), FeO (F), and MgO (M)), assuming that
quartz and muscovite are always present.
Components = 6:
K2O, Al2O3, SiO2, FeO, MgO, H2O
With excess quartz & water:
C = 4 and F = 4 - P + 2
If muscovite is present, we can project the mineral assemblages onto the Al2O3 – FeO – MgO plane, where:
C = 3 and F = 3 - P + 2
thus F = 0 for P = 3, if Press & Temp are fixed
andalusite Al2SiO5 or Al2OSiO4
kyanite Al2SiO5 or Al2OSiO4
sillimanite Al2SiO5 or Al2OSiO4
pyrophyllite Al2Si4O10(OH)2
paragonite NaAl2(Al,Si3)O10(OH)2
muscovite KAl2(Al,Si3)O10(OH)2
staurolite (Fe,Mg)2Al9O6(SiO4)4(O,OH)2
chloritoid (Fe,Mg)2Al4O2(SiO4)2(OH)4
cordierite (Fe,Mg)2Al3(Al,Si5)O18.nH2O
garnet (Fe,Mg)3Al2(SiO4)3
chlorite (Mg,Fe)3(Al,Si3)O10(OH)2(Mg,Fe)3(OH)6
biotite K(Mg,Fe)3(Al,Si3)O10(OH)2
K-feldspar KAlSi3O8
Metapelite Minerals: quartz, muscovite, and :
F = C - P
F = C - P