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Introduction to Metamorphic Petrology

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

2 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.

3 Metamorphic Reactions
Dehydration KAl3Si3O10(OH)2 + SiO2 = KAlSi3O8 + AlSi2O5 + H2O Muscovite Quartz K-Feldspar Sillimanite Decarbonation CaCO3 + SiO2 = CaSiO3 + CO2 Calcite Quartz Wollastonite Solid-Solid NaAlSi3O8 = NaAlSi2O6 + SiO2 Albite Jadeite Quartz

4 Prograde and Retrograde Metamorphism
Retrograde Path Prograde Path

5 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

6 Conditions of Metamorphism and Metamorphic Facies

7 Types of Metamorphism Contact or Thermal Metamorphism
Regional Metamorphism Orogenic Metamorphism Burial Metamorphism Ocean Floor Metamorphism Hydrothermal Metamorphism (Alteration) Impact or Shock Metamorphism

8 Contact or Thermal Metamorphism

9 Contact Metamorphism of Limestone
Marble Diabase Marble Limestone

10 Thermally Metamorphosed Clastic Sediments
Plagioclase Pyroxene Garnet

11 Orogenic Metamorphism

12 Orogenic Metamorphism

13 Orogenic Metamorphism and differential stress
Foliation (or Cleavage) and Lineation s1 s1 > s2 = s3  foliation and no lineation s1 = s2 > s3  lineation and no foliation s1 > s2 > s3  both foliation and lineation

14 Onset of Orogenic Metamorphism
Shale Slate Bedding Cleavage Bedding

15 Progressive Orogenic Metamorphism
Phyllite Schist

16 Progressive Orogenic Metamorphism

17 Anatexis

18 Anatexis or Partial Melting of Metasedimentary Rocks (Migmatites)

19 Burial Metamorphism

20 Burial Metamorphism

21 Subduction Metamorphism

22 Paired Metamorphic Belts
Amphibolite Facies Blueschist Facies

23 Subduction Metamorphism

24 Ocean Floor Metamorphism

25 Ocean Floor Metamorphism

26 Metamorphic Isograd Mapping (Index Minerals)

27 Metamorphic Index Minerals
(Porphyroblasts) Cordierite (Mg,Fe)2Al4Si5O18 Staurolite (Fe,Mg)2Al9Si4O23(OH) Garnet (Fe,Mg)3Al2Si3O12

28 The Aluminosilicates Al2SiO5
Andalusite Kyanite Sillimanite Sillimanite

29 Metamorphic Isograds and P-T Paths
Barrow Zones Buchan Zones

30 Aluminosilcates as Indicators of Metamorphic Grade

31 Metamorphic reactions and metamorphic grade
Muscovite + Quartz = K-feldspar + sillimanite + H2O Muscovite Quartz Sillimanite K-feldspar

32 Metamorphic Facies and Isograds
Oslo: K-Feldspar- Cordierite Orijärvi: Biotite-muscovite 2 KMg3AlSi3O10(OH)2 + 6 KAl2AlSi3O10(OH)2 (Ms) + 15 SiO2 = 3 Mg2Al4Si5O KAlSi3O8 + 8 H2O

33 Facies Series The high P/T series, for example, typically occurs in subduction zones where “normal” isotherms are depressed by the subduction of cool lithosphere faster than it can equilibrate thermally The facies sequence here is (zeolite facies) - (prehnite- pumpellyite facies) - blueschist facies - eclogite facies. The medium P/T series is characteristic of common orogenic belts (Barrovian type) The sequence is (zeolite facies) - (prehnite-pumpellyite facies) - greenschist facies -amphibolite facies - (granulite facies) Crustal melting under water-saturated conditions occurs in the upper amphibolite facies (the solidus is indicated in Fig. 25-2) The granulite facies, therefore, occurs only in water-deficient rocks, either dehydrated lower crust, or areas with high XCO2 in the fluid The low P/T series is characteristic of high-heat-flow orogenic belts (Buchan or Ryoke-Abukuma type), rift areas, or contact metamorphism The sequence of facies may be a low-pressure version of the medium P/T series described above (but with cordierite and/or andalusite), or the sequence (zeolite facies) - albite-epidote hornfels facies - hornblende hornfels facies - pyroxene hornfels facies Sanidinite facies rocks are rare, requiring the transport of great heat to shallow levels

34 Pressure-Temperature-Time Paths

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