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 Muscovite Quartz K-Feldspar Sillimanite Decarbonation CaCO3 + SiO2 = CaSiO3 + CO2 Calcite Quartz Wollastonite Solid-Solid NaAlSi3O8 = NaAlSi2O6 + SiO2 Albite Jadeite Quartz

Prograde and Retrograde Metamorphism Retrograde Path Prograde 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

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

Contact or Thermal Metamorphism

Contact Metamorphism of Limestone Marble Diabase Marble Limestone

Thermally Metamorphosed Clastic Sediments Plagioclase Pyroxene Garnet

Orogenic Metamorphism

Orogenic Metamorphism

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

Onset of Orogenic Metamorphism Shale Slate Bedding Cleavage Bedding

Progressive Orogenic Metamorphism Phyllite Schist

Progressive Orogenic Metamorphism Gneiss

Anatexis

Anatexis or Partial Melting of Metasedimentary Rocks (Migmatites)

Burial Metamorphism

Burial Metamorphism

Subduction Metamorphism

Paired Metamorphic Belts Amphibolite Facies Blueschist Facies

Subduction Metamorphism

Ocean Floor Metamorphism

Ocean Floor Metamorphism

Metamorphic Isograd Mapping (Index Minerals)

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

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 Muscovite Quartz Sillimanite K-feldspar

Metamorphic Facies and Isograds Oslo: K-Feldspar- Cordierite Orijärvi: Biotite-muscovite 2 KMg3AlSi3O10(OH)2 + 6 KAl2AlSi3O10(OH)2 (Ms) + 15 SiO2 = 3 Mg2Al4Si5O18 + 8 KAlSi3O8 + 8 H2O

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

Pressure-Temperature-Time Paths