Introduction to Metamorphic Petrology

Recommended Textbook: J.D. Winter (2001) An Introduction to Igneous and Metamorphic Petrology: Prentice Hall Pub.

Scope of Metamorphic petrology

Metamorphic petrology is the study of the subsolidus changes that a rock undergoes when exposed to physicochemical conditions different from those prevailing near the surface of the Earth.

Metamorphism produces changes in mineral assemblages and textures that reflect re-equilibration of the rock to the new physicochemical conditions, i.e., minimization of the energy of the system.

Metamorphism is commonly isochemical (except for volatile components, e.g., H2O, CO2). Where the system is open, the process is referred to as metasomatism.

Metamorphic Reactions

Dehydration

KAl3Si3O10(OH)2 + SiO2 = KAlSi3O8 + AlSi2O5 + H2O

Decarbonation

CaCO3 + SiO2 = CaSiO3 + CO2

Calcite Quartz Wollastonite

Muscovite Quartz K-Feldspar Sillimanite

Solid-Solid

NaAlSi3O8 = NaAlSi2O6 + SiO2

Albite Jadeite Quartz

Prograde and Retrograde Metamorphism

Prograde Path

Retrograde Path

Metamorphic Facies

A metamorphic facies is a domain of Pressure-Temperature Space

Metamorphic facies are defined by characteristic mineral assemblages specific to particular bulk-rock compositions

Conditions of Metamorphism and Metamorphic Facies

Contact or Thermal MetamorphismContact or Thermal Metamorphism Regional MetamorphismRegional Metamorphism

Orogenic MetamorphismOrogenic Metamorphism Burial MetamorphismBurial Metamorphism Ocean Floor MetamorphismOcean Floor Metamorphism

Hydrothermal Metamorphism Hydrothermal Metamorphism (Alteration)(Alteration)

ImpactImpact or or ShockShock MetamorphismMetamorphism

Types of Metamorphism

Contact or Thermal Metamorphism

Contact Metamorphism of Limestone

Diabase

Marble

Limestone

Marble

Limestone

Pyroxene

Plagioclase

Garnet

Thermally Metamorphosed Clastic Sediments

Orogenic Metamorphism

Orogenic Metamorphism

Orogenic Metamorphism and differential stressOrogenic Metamorphism and differential stress

11 > > 22 = = 3 3 foliation and no lineation foliation and no lineation

11 = = 22 > > 3 3 lineation and no foliation lineation and no foliation

11 > > 22 > > 3 3 both foliation and lineation both foliation and lineation

1

Foliation (or Cleavage) and Lineation

Cleavage

Bedding

Onset of Orogenic Metamorphism

Shale Slate

Bedding

Phyllite Schist

Progressive Orogenic Metamorphism

Progressive Orogenic Metamorphism

Gneiss

Anatexis

Anatexis or Partial Melting of Metasedimentary Rocks (Migmatites)

Burial Metamorphism

Burial Metamorphism

Subduction Metamorphism

Paired Metamorphic Belts

Blueschist Facies

Amphibolite Facies

Subduction Metamorphism

Ocean Floor Metamorphism

Ocean Floor Metamorphism

Metamorphic Isograd Mapping (Index Minerals)

Metamorphic Index Minerals

(Porphyroblasts)

Staurolite (Fe,Mg)2Al9Si4O23(OH) Garnet

(Fe,Mg)3Al2Si3O12

Cordierite(Mg,Fe)2Al4Si5O18

The Aluminosilicates Al2SiO5

Andalusite Kyanite

Sillimanite

Sillimanite

Metamorphic Isograds and P-T Paths

Barrow Zones Buchan Zones

Aluminosilcates as Indicators of Metamorphic Grade

Metamorphic reactions and metamorphic grade

Muscovite + Quartz = K-feldspar + sillimanite + H2O

SillimaniteQuartz

K-feldspar

Muscovite

Oslo:Oslo: K-Feldspar- Cordierite K-Feldspar- Cordierite Orijärvi:Orijärvi: Biotite-muscovite Biotite-muscovite

2 KMg2 KMg33AlSiAlSi33OO1010(OH)(OH)22 + 6 KAl + 6 KAl22AlSiAlSi33OO1010(OH)(OH)22 (Ms) + 15 SiO (Ms) + 15 SiO22

= 3 Mg= 3 Mg22AlAl44SiSi55OO1818 + 8 KAlSi + 8 KAlSi33OO88 + 8 H + 8 H22OO

Metamorphic Facies and IsogradsMetamorphic Facies and Isograds

Facies Series

Pressure-Temperature-Time Paths