1. Metabasites / Metacarbonates
garnet
Hornblende
Plag
garnet
garnet
Metabasites / Metacarbonates
Francis, 2014

2. Metabasites:
Mafic volcanics such as basalts and andesites have more complicated and variable compositions than shales, containing significant quantities of Ca and Na, in addition to Si, Al, Mg Fe, K, and H2O. At least 8 components are necessary to describe such systems, and it is no longer possible to construct a simple projection scheme that is thermodynamically rigorous. The metamorphic mineral assemblages of mafic volcanic rocks are commonly portrayed in an ACF projection, but it should be remembered that, unlike the metapelite AFM diagram, 3 phase regions in the ACF diagram are not strictly invariant and crossing tie lines are not uncommon.

4. Zeolite Facies W = Na, Ca, K, (Ba, Sr,…) T = Si, Al
The beginning of metamorphism in volcanic rocks and volcanogenic sediments is marked by the development of zeolites in vesicles and fractures under conditions of shallow burial. In consequence, volcanic rocks change from being vesicular to amygdular. Apart from the filling of vesicules and void spaces with these secondary minerals, rocks in the zeolite facies look essentially unmetamorphosed, although they often appear somewhat weathered in hand specimen: dirty, brownish, and oxidized because the processes of weathering have continued into the zeolite facies. Massive samples may still be quite pristine, however, retaining their original igneous mineralogy, especially if they have been isolated from extensive weathering and are relatively dry.
General Zeolite formula: WnTmO2m.sH2O
W = Na, Ca, K, (Ba, Sr,…)
T = Si, Al
Ca Zeolites Na Zeolites
Low T Chabazite Phillipsite
CaAl2Si4O12.6H2O Na3Al3Si5O16.6H2O
Stilbite
CaAl2Si7O18.7H2O
Heulandite Analcime CaAl2Si7O18.6H2O NaAlSi2O6.H2O
Laumontite Natrolite
CaAl2Si4O12.4H2O Na4Al4Si6O20.4H2O
High T Wairakite Albite - Feldspar
CaAl2Si4O12.2H2O NaAlSi3O8

5. Zeolites in
volcanic amygdules

6. Laumontite + CO2 Calcite + Kaolinite + Quartz + Water
Zeolite assemblages are stable only at relatively low PCO2. Even at relatively modest levels of CO2, zeolite mineral assemblages are commonly replaced by carbonate and clay minerals.
Laumontite CO Calcite + Kaolinite + Quartz + Water
CaAl2Si4O12.4H2O + CO CaCO3 + Al2Si2O5(OH)4 + 2SiO2 + 2H2O
(XCO2 > 0.01)

7. Prehnite - Pumpellyite sub-Facies of the Greenschist Facies
The development of prehnite and pumpellyite in the both the groundmass and void spaces marks the beginning of the prehnite - pumpellyite sub-facies in metavolcanic and metavolcanogenic sedimentary rocks. Volcanic rocks in this metamorphic facies begin to take on a greenish colour, although they typically are relatively unstrained and unrecrystallized, and commonly appear little metamorphosed in hand specimen, except for the development of a greenish colour. The presence of prehnite and pumpellyite are best recognized in thin section.
Prehnite Ca2Al(AlSi3)O10(OH)2
brittle mica
Pumpellyite W4X(OH,O)Y5O(OH)3(TO4)2(T2O7)2.2H2O
sorosilicate
T = Si, Al
Y = Al, Fe3+, Ti4+
X = Mn, Fe2+, Mg, Al, Fe3+
W = Ca, K, Na
meta-pillow
basalt

8. Greenschist Facies
epidote & actinolite - in
prehnite + qtz + chlorite zoisite actinolite + water
Ca2Al(AlSi3)O10(OH)2 + SiO Ca2(Fe,Al)3O(SiO4)(Si2O7)(OH) + Ca2(Mg,Fe)5Si8O22(OH)2
(Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH)6
pumpellyite + qtz + chlorite zoisite actinolite + water
Ca4(Mg,Fe)(Al,Fe3+)5O(OH)3(Si2O7)2(SiO4)2.2H2O Ca2(Fe,Al)3O(SiO4)(Si2O7)(OH) + Ca2(Mg,Fe)5Si8O22(OH)
+ SiO2 + (Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH)6

9. Ca-plag - in chlorite + zoisite + qtz actinolite + plagioclase + water
(Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH) Ca2(Mg,Fe)5Si8O22(OH) + (Ca,Na)(Al,Si)4O8
+ Ca2(Fe,Al)3O(SiO4)(Si2O7)(OH) + SiO2

10. Amphibolite Facies actinolite hornblende
Hornblende - in
actinolite hornblende
Ca2(Mg,Fe)5(Si8O22)(OH)2 NaCa2(Mg,Fe,Al)5(Al2Si6O22)(OH)2
Garnet & Hb - in
epidote + chlorite hornblende + garnet + water
Ca2(Fe,Al)3O(SiO4)(Si2O7)(OH) NaCa2(Mg,Fe,Al)5(Al2Si6O22(OH)2 +
(Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH)6 (Ca,Fe,Mg)3(Al,Fe3+)2(SiO4)3

11. Upper Amphibolite Facies
Cpx - in
hornblende + epidote clinopyroxene + plagioclase + water
NaCa2(Mg,Fe,Al)5(Al2Si6O22(OH) Ca(Mg,Fe)Si2O (Ca,Na)(Al,Si)4O8
Ca2(Fe,Al)3O(SiO4)(Si2O7)(OH)
hornblende can no longer coexist with epidote
Opx - in
hornblende + garnet orthopyroxene + plagioclase + water
NaCa2(Mg,Fe,Al)5(Al2Si6O22(OH) (Mg,Fe)2Si2O (Ca,Na)(Al,Si)4O8
(Ca,Fe,Mg)3(Al,Fe3+)2(SiO4)3
hornblende can no longer coexist with garnet

12. Granulite Facies Hornblende - out
hornblende clinopyroxene + plagioclase + opx + water
NaCa2(Mg,Fe,Al)5(Al2Si6O22(OH)2 Ca(Mg,Fe)Si2O6 + (Ca,Na)(Al,Si)4O (MgFe)SiO3

13. Garnet - in
anorthite orthopyroxene garnet clinopyroxene
CaAl2Si2O (Fe,Mg)SiO (Fe,Mg)3Al2(SiO4) Ca(Mg,Fe)2Si2O6

14. brownish blackish greenish hydrous partial melt bluish
Summary of Metabasic Volcanic Rocks
granular
gneissic
brownish
weathered
blackish
Crystalline
gneissic
greenish
fine-grain
schitose if deformed
hydrous
partial
melt
bluish
un-equilibrated
phyllites

15. Plag Oliv Oliv Eclogite Oliv Oliv Plag Oliv + Plag
Opx + Cpx + Spin / Garn
Garnet
Pyroxenite
Plag
Oliv
Oliv
Eclogite
Oliv
Oliv
Plag

16. The Granulite - Eclogite Transition: appearance of Garnet:
The complete transition from granulite to eclogite facies occurs over a 5 kb pressure range, beginning with the:
appearance of Garnet:
Pyroxene Granulite Garnet Granulite
and ending with:
disappearance of Plagioclase:
Garnet Granulite Eclogite
The
Granulite - Eclogite
Transition:
increasing pressure
The exact position of these reactions is sensitive to bulk composition. The official Eclogite field is defined for quartz-normative bulk compositions. More Fe-rich and alkaline basalts will convert to a garnet pyroxenite mineralogy at lower pressures in the garnet granulite field. Most petrologists refer to such rocks as garnet pyroxenite rather than eclogite.

17. Meta-Plutonic Rocks
mafic
magma

18. Metamorphic Coronas Plag Oliv Oliv Plag
Oliv + Plag Opx + Cpx + Spin or
Garn
Oliv
Plag

19. calcite
calcite
grossularite
diopside
Meta-carbonates / Skarns

20. Skarns are rocks rich in calc-silicate minerals that are produced by the contact metamorphism of limestones and dolomites. The silica required for the prograde metamorphic reactions may come from detrital quartz and/or silica sponge spicules, etc. in the original carbonate sediment, but may also be introduced metasomatically by fluids emanating from the igneous intrusion responsible for the contact metamorphism.
Metacarbonates
Skarns are typically named on the basis of their most characteristic mineral assemblage,
eg.: olivine-diopside skarn

22. Prograde Metacarbonate Reactions
Greenwood
Classification
Talc - in
3CaMg(CO3)2 + 4SiO2 + H2O Mg3Si4O10(OH)2 + 3CaCO3 + 3CO #6
Dolomite Qtz Talc Calcite
Tremolite - in
5CaMg(CO3)2 + 8SiO2 + H2O Ca2Mg5Si8O22(OH)2 + 3CaCO3 +7CO #6
Dolomite Qtz Tremolite Calcite
Diopside - in
Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 2SiO CaMgSi2O6 + 3CO2 + H2O #4
Tremolite Calcite Diopside
Olivine - in
Ca2Mg5Si8O22(OH)2 + 11CaMg(CO3) Mg2SiO4 + 13CaCO3 + 9CO2 + H2O #4
Tremolite Dolomite Olivine Calcite
Tremolite-out
Ca2Mg5Si8O22(OH)2 + CaCO Mg2SiO4 + 3CaMgSi2O6 + CO2 + H2O #4
Tremolite Calcite Olivine Diopside
Wollastonite-in
CaCO3 + SiO CaSiO3 + CO #3
Calcite Qtz Wollastonite