Part 1. Overview of Metamorphism and Tectonics
Part 2. Introduction to Metamorphism
Part 3. Physical Processes of Metamorphism
Part 4. Introductory Phase Equilibria and Thermodynamics
Part 5. Ultramafic Rocks
Part 6. Mafic Rocks
Part 7. Pelitic Rocks
Part 8. Diffusion
Part 9. Thermobarometry
Part 10. Kinetics
Part 11. Interaction Between Metamorphism and Deformation
Part 12. Metamorphism and Geochronology
Part 13. Metamorphism and Tectonics I
Part 14. Metamorphism and Tectonics II
Thermodynamics Notes

Part 6. Mafic Rocks

Read Chapter 4 of An Introduction to Metamorphic Petrology by Bruce Yardley or Chapter 25 of Igneous and Metamorphic Petrology by John Winter or Chapter 16 of Igneous and Metamorphic Petrology by Philpotts

Solid Solutions and Exchange Vectors
Some minerals (e.g., quartz) have constant composition. However, most minerals are solid solutions that undergo compositional change in response to PTX (pressure, temperature, composition) changes. Garnet is an example of a relatively simple solid solution, with substitution occurring on only one site:

mineralend membersexchange vector
olivine forsterite Mg2SiO4 <—> fayalite Fe2SiO4 Fe2+ <—> Mg2+
plagioclase albite NaAlSi3O8 <—> anorthite CaAl2Si2O8 Na+ Si4+ <—> Ca2+ Al3+
amphibole tremolite Ca2Mg5Si8O22(OH)2 <—> tschermakite Ca2(Mg3Al2)(Al2Si6)O22(OH)2 VIMg2+ IVSi4+ <—>VIAl3+ IVAl3+ (tschermak exchange)
mica muscovite KAl2(AlSi3)O10(OH)2 <—> phengite KMgAlSi4O10(OH)2 VIAl3+ IVAl3+ <—> VIMg2+ IVSi4+(inverse tschermak exchange)

Metamorphic Facies
Metamorphic facies are defined for metamafic rocks.
It is a fact of the universe that the minerals in mafic rocks tend to have broad ranges in solid solution. This means that


faciesmineralsnotes
basalt and gabbro protoliths plagioclase NaAlSi3O8-CaAl2Si2O8 + pyroxene CaSiO3-MgSiO3-FeSiO3 .
zeolite facies common zeolites: laumontite, wairakite, analcime (Na,Ca)AlSiO(OH)x zeolites: channel structure makes them useful for engineering
common textures: in cracks, alteration of feldspar or glass
greenschist facies albite + epidote + actinolite + chlorite + quartz
albite NaAlSi3O8 takes up Na, Al, Si
epidote CaAlSiO(OH)x takes up Ca
actinolite Ca2(Fe,Mg)5Si8O22(OH)2 takes up Fe, Mg
chlorite (Mg,Fe)(AlSi)O(OH)x
.
albite-epidote amphibolite facies albite + epidote + hornblende + quartz

albite NaAlSi3O8 takes up Na, Al, Si
epidote CaAlSiO(OH)x takes up Ca
hornblende (K,Na)(Ca,Fe,Mg)(AlSi)O22(OH)2
modal proportion of albite decreases, Na enters amphibole
modal proportion of chlorite decreases, Fe + Mg enters amphibole
amphibolite facies plagioclase + hornblende + quartz epidote replaced by intermediate plagioclase
remainder of elements in hornblende
granulite facies orthopyroxene + clinopyroxene + plagioclase + quartz must have 2 pyroxenes; can also have hornblende or garnet
blueschist facies glaucophane Na2Mg3Al2Si8O22(OH)2
lawsonite or epidote CaAlSiO(OH)x
high P, low T
eclogite facies omphacite (Na,Al,Mg,Fe)Si2O6
garnet (Ca,Mg,Fe,Mn)3Al2Si3O12
high P, high T
coesite-eclogite facies coesite SiO2
diamond C
majorite Mg4Si4O12
pressures >2.5 GPa

Facies Series
A series of facies at low, medium, or high pressure. Metamorphic rocks formed by crustal extension are characterized by a low-pressure facies series. Metamorphic rocks formed during continental collision are characterized by a medium-pressure facies series. Subduction-zone metamorphic rocks are characterized by a high-pressure facies series.
facies seriestectonic settingminerals presentminerals absent
low P (Buchan) crustal extension andalusite, sillimanite, cordierite staurolite, kyanite
crustal thickening medium P (Barrovian) kyanite, sillimanite, staurolite cordierite
subduction high P (Franciscan) kyanite staurolite



Part 1. Overview of Metamorphism and Tectonics
Part 2. Introduction to Metamorphism
Part 3. Physical Processes of Metamorphism
Part 4. Introductory Phase Equilibria and Thermodynamics
Part 5. Ultramafic Rocks
Part 6. Mafic Rocks
Part 7. Pelitic Rocks
Part 8. Diffusion
Part 9. Thermobarometry
Part 10. Kinetics
Part 11. Interaction Between Metamorphism and Deformation
Part 12. Metamorphism and Geochronology
Part 13. Metamorphism and Tectonics I
Part 14. Metamorphism and Tectonics II
Thermodynamics Notes