metamorphic rocks

Metamorphic rocksMetamorphic rocks

TodayTodayUpdates:Updates:

MidtermMidterm

Lecture outline:Lecture outline:

- Types of metamorphismTypes of metamorphism

- Prograde and retrogradePrograde and retrograde

Types of MetamorphismTypes of Metamorphism

Different approaches to classificationDifferent approaches to classification

1. Based on 1. Based on pressure/stress and temperaturepressure/stress and temperature:: Dynamic Metamorphism: deviatoric stressDynamic Metamorphism: deviatoric stress Thermal Metamorphism: increase in TThermal Metamorphism: increase in T Dynamo-thermal Metamorphism: P+T changeDynamo-thermal Metamorphism: P+T change

Types of MetamorphismTypes of Metamorphism

2. Based on 2. Based on settingsetting Contact MetamorphismContact Metamorphism Regional MetamorphismRegional Metamorphism Hydrothermal MetamorphismHydrothermal Metamorphism Fault-Zone Metamorphism Fault-Zone Metamorphism Impact or Shock MetamorphismImpact or Shock Metamorphism

Contact MetamorphismContact Metamorphism

The size and shape of an aureole is controlled by:The size and shape of an aureole is controlled by:

Pluton:Pluton:

Country rocks:Country rocks:

Size Shape Orientation

Temperature Composition

CompositionComposition Depth and metamorphic grade prior to intrusionDepth and metamorphic grade prior to intrusion Permeability Permeability

Contact Metamorphism 2Contact Metamorphism 2

Contact -- rock typesContact -- rock types

Contact -- rock types 2Contact -- rock types 2

Regional MetamorphismRegional Metamorphism

Regional/Orogenic MetamorphismRegional/Orogenic Metamorphism

Regional/Orogenic Metamorphism 2Regional/Orogenic Metamorphism 2

Regional/Orogenic Metamorphism 3 Regional/Orogenic Metamorphism 3

Regional/Orogenic Metamorphism 4 Regional/Orogenic Metamorphism 4

http://193.232.116.228/personal/vsz/autoref/fig2ce.GIF

Regional: burial metamorphismRegional: burial metamorphism

Hydrothermal MetamorphismHydrothermal Metamorphism

Basalt

Serpentinite

Water

Fault zone and impactFault zone and impact

www.lpi.usra.edu/meetings/gap2007/gapII-logo.jpg

Progressive Nature of MetamorphismProgressive Nature of Metamorphism

Prograde

Retrograde

Prograde MetamorphismPrograde Metamorphism

• Normally progress through series of mineral Normally progress through series of mineral assemblages, for example:assemblages, for example:

1.1. epidote, chlorite, andalusite, muscovite, quartz, epidote, chlorite, andalusite, muscovite, quartz, k-spar, and albitek-spar, and albite

2.2. sillimanite, plagioclase, cordierite, muscovite, sillimanite, plagioclase, cordierite, muscovite, quartz and k-sparquartz and k-spar

3.3. sillimanite, plagioclase, cordierite, quartz, and sillimanite, plagioclase, cordierite, quartz, and k-spark-spar

Prograde

Retrograde

Prograde MetamorphismPrograde Metamorphism

Retrograde MetamorphismRetrograde Metamorphism

Prograde

Retrogradehttp://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/chlorite.htm

Common Prograde SequenceCommon Prograde Sequence

Index minerals make zones:Index minerals make zones: Chlorite zone. Pelitic rocks are slates or phyllites and typically Chlorite zone. Pelitic rocks are slates or phyllites and typically

contain chlorite, muscovite, quartz and albitecontain chlorite, muscovite, quartz and albite Biotite zone. Slates give way to phyllites and schists, with biotite, Biotite zone. Slates give way to phyllites and schists, with biotite,

chlorite, muscovite, quartz, and albitechlorite, muscovite, quartz, and albite Garnet zone. Schists with conspicuous red almandine garnet, Garnet zone. Schists with conspicuous red almandine garnet,

usually with biotite, chlorite, muscovite, quartz, and albite or usually with biotite, chlorite, muscovite, quartz, and albite or oligoclaseoligoclase

Staurolite zone. Schists with staurolite, biotite, muscovite, quartz, Staurolite zone. Schists with staurolite, biotite, muscovite, quartz, garnet, and plagioclase. Some chlorite may persistgarnet, and plagioclase. Some chlorite may persist

Kyanite zone. Schists with kyanite, biotite, muscovite, quartz, Kyanite zone. Schists with kyanite, biotite, muscovite, quartz, plagioclase, and usually garnet and stauroliteplagioclase, and usually garnet and staurolite

Sillimanite zone. Schists and gneisses with sillimanite, biotite, muscovite, quartz, plagioclase, garnet, and perhaps staurolite. Some kyanite may also be present (although kyanite and sillimanite are both polymorphs of Al2SiO5)

Sequence of indicator mineralsSequence of indicator minerals

Chlorite

BiotiteGarnet

Staurolite

Kyanite

Sillimanite