1. Metapelites Francis, 2013 qtz muscovite muscovite qtz qtz qtz garnet

2. Solid - Solid Reactions: One Component
andalusite sillimanite
Al2Si Al2Si05
From the phase rule, we know that this is reaction is univariant and thus can be represented by a line in P-T space:
F = C - P = 1
At equilibrium:
G (P,T) = Ho(1bar,T) T So(1bar,T) (P-1) V = 0
dG (P,T) = 0 = - So dT + VdP
S, V, and H vary little with T and P for solid - solid reactions because the changes in the reactants with T and P tend to parallel
those in the products. Thus the above equation approximates that of a straight line in P - T space with a slope of:
dP/dT = S/ V = bar / K
V = Joules / bar mol
S = Joules / mol K

3. F = C – P + 2 F = 2 – 3 + 2 F = 1, if C = 3 univariant
Solid - Solid Reactions: Two Component
albite jadeite quartz
NaAlSi3O NaAlSi2O SiO2
dP/dT = S/ V = bar / oK
V = Joules / bar mol
S = Joules / mol K
Most solid - solid reactions have positive slopes in P - T space because the higher temperature side of the reaction typically has both
higher entropy and volume.
F = C – P + 2
F = 2 – 3 + 2
F = 1, if C = univariant Jd Ab
Qtz Jd
Qtz Jd Ab
Qtz

4. F = 3 - P + 2 F = 2, if P =3 F = 1, if P = 4, univariant Temperature
Three Component Systems:
F = P
F = 2, if P =3
F = 1, if P = 4, univariant
Tie-line switching (2D) or
piercing plane (nD) reactions
Temperature
B + D
A + E
Pressure

5. F = 3 - P + 2 F = 2, if P =3 F = 1, if P = 4, univariant Temperature
Terminal reactions at which phases appear or disappear
B + C = A appearance
D = A + B + C disappearance
F = P
F = 2, if P =3
F = 1, if P = 4, univariant
Temperature
A + B + C D
Pressure

6. Metapelites: ~ 4 component system
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. Their bulk compositions can be approximated in a 6 component system
Components C = 6:
K2O, Al2O3, SiO2, FeO, MgO, H2O
With excess quartz & water:
C = 4
~ 4 component system
With excess water and quartz

7. Metapelites C = 3 and F = 3 - P + 2 AFM Projections
J.B. Thompson, 1957
If muscovite is present:
we can project the mineral assemblages
onto the Al2O3* – FeO – MgO plane, where:
C = 3 and F = 3 - P + 2
Muscovite is typically a ubiquitous
phase in metapelites.

8. MgO / (MgO + FeO) 1.0 0.5 Al2O3* Al2O3* + MgO +FeO 0.0 -0.5
Al2O3* = Al2O3 - 3×K2O
MgO / (MgO + FeO)

9. Phase Rule:
if P and T are held Constant
F = C - P
F = 3 - P

10. F = 3 - P

12. Lower Greenschist Facies montmorillonite chlorite + water
green mica - in
montmorillonite chlorite + water
(Al1-X(Mg,Fe)X)2Si3O10(OH)2 + XNa+.nH2O (Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH)6
white mica - in
kaolinite + qtz muscovite + water
Al2Si2O5(OH) KAl2(Al,Si3)O10(OH)2

13. Lower Greenschist Facies
biotite - in
K-spar + chlorite biotite + muscovite + qtz + water
KAlSi3O8 + (Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH)6 K(Mg,Fe)3(Al,Si3)O10(OH) KAl2(Al,Si3)O10(OH)2
kyanite or andalusite - in
pyrophyllite Al-silicate qtz + water
Al2Si4O10(OH) Al2Si SiO2

14. Biotite - in
The temperature of the first appearance of biotite depends on the Mg/Fe ratio of the whole rock composition.

15. Upper Greenschist Facies
garnet – in (Fe-rich systems)
Fe-chlorite + muscovite + qtz garnet biotite + water
(Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH)6 (Fe,Mg)3Al2(SiO4)3 + (Mg,Fe)3(Al,Si3)O10(OH)2
+ KAl2(Al,Si3)O10(OH)2 + SiO2

16. Upper Greenschist Facies – con’t
staurolite - in
garnet + chlorite staurolite + biotite + water
(Fe,Mg)3Al2(SiO4)3 + K(Mg,Fe)3(Al,Si3)O10(OH) Fe2Al9O6(SiO4)4(O,OH)2 +
K(Mg,Fe)3(Al,Si3)O10(OH)2

17. Lower Amphibolite Facies
The transition from greenschist facies to the amphibolite facies in metapelites corresponds to the discontinuous reaction:
(Mg,Fe)7Al4Si4O15(OH) KAl2AlSi3O10(OH) Fe2Al9O6(SiO4)4(O,OH)2
chlorite muscovite staurolite
K(Mg,Fe)3AlSi3O10(OH)2 + Al2SiO water
biotite kyanite
Temp

19. Lower Amphibolite Facies
chlorite-out
chlorite biotite + Al-silicate + cordierite + water
(Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH)6 K(Mg,Fe)3(Al,Si3)O10(OH)2 + Al2Si05
1st cordierite-in (Fe,Mg)2Al3(Al,Si5)O18.nH2O + H2O

20. Upper Amphibolite Facies
staurolite-out
garnet-in
staurolite garnet biotite Al-silicate + water
Fe2Al9O6(SiO4)4(O,OH) (Fe,Mg)3Al2(SiO4)3 + K(Mg,Fe)3(Al,Si3)O10(OH) Al2Si05
garnet sillimante schist
muscovite qtz muscovite - out K-spar Al-silicate + water
KAl2(Al,Si3)O10(OH) SiO2 KAlSi3O Al2Si05

21. Granulite Facies 2nd cordierite-in
muscovite muscovite - out K-spar corundum + water
KAl2(Al,Si3)O10(OH) KAlSi3O Al2O3
2nd cordierite-in
biotite Al-silicate K-spar cordierite garnet
K(Mg,Fe)3(Al,Si3O10(OH) Al2SiO KAlSi3O8 + (Fe,Mg)2Al3(Al,Si5)O18.nH2O + Fe3Al2(SiO4)3

23. Partial Melting of Metapelites:
In the presence of a vapor phase, the partial melting of metapelite lithologies is controlled by the intersection of the breakdown curve for muscovite with the wet solidus curve for granite. In more mafic systems, the breakdown curve for biotite may be the controlling factor.
XH2O=0.7
muscovite breakdown:
musc + qtz Al-sil + K-spar + H2O
Go = - RTlnXH2O (+)
wet melting:
H2O + metapelite granite melt
Go = - RTln(1/XH2O) (-)
migmatite