metamorphic rocks francis, 2014. paragonitenaal 2 (alsi 3 o 10 (oh) 2 muscovitekal 2 (alsi 3 o 10...

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