Classification and FaciesClassification and Facies

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Lecture outline:Lecture outline:- Rock classificationRock classification- Facies Facies

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

ProgradePrograde

RetrogradeRetrograde

Prograde MetamorphismPrograde Metamorphism

Retrograde MetamorphismRetrograde Metamorphism

ProgradePrograde

RetrogradeRetrogradehttp://www.und.nodak.edu/instruct/http://www.und.nodak.edu/instruct/mineral/320petrology/opticalmin/mineral/320petrology/opticalmin/chlorite.htmchlorite.htm

Common Prograde Sequence

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

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

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

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

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

Kyanite zone. Schists with kyanite, biotite, muscovite, quartz, plagioclase, 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 minerals

ChloriteChlorite

BiotiteBiotiteGarnetGarnet

StauroliteStaurolite

KyaniteKyanite

SillimaniteSillimanite

Types of ProtolithTypes of Protolith

Six chemically based-groups to start withSix chemically based-groups to start with

1. Ultramafic - very high Mg, Fe, Ni, Cr1. Ultramafic - very high Mg, Fe, Ni, Cr

2. Mafic - high Fe, Mg, and Ca2. Mafic - high Fe, Mg, and Ca

3. Shales (pelitic) - high Al, K, Si3. Shales (pelitic) - high Al, K, Si4. Carbonates- high Ca, Mg, CO4. Carbonates- high Ca, Mg, CO22

5. Quartz - nearly pure SiO5. Quartz - nearly pure SiO22..

6. Quartzo-feldspathic - high Si, Na, K, Al6. Quartzo-feldspathic - high Si, Na, K, Al

A Classification of Metamorphic RocksA Classification of Metamorphic Rocks

A Classification of Metamorphic RocksA Classification of Metamorphic Rocks

Compositional Classification

Parent Metamorphic rockClay-rich sediment peliteSand-rich sediment psammiteClay-sand mix semi-peliteQuartz sand quartziteMarl (limy mud) metamarls-silicate/calcareousLimestone marbleBasalt metabasite

aa

bb

Pelite protolith: Foliated Metamorphic RocksPelite protolith: Foliated Metamorphic Rocks-- low grade-- low grade

Pelite protolith: Foliated Metamorphic RocksPelite protolith: Foliated Metamorphic Rocks--middle grade--middle grade

Pelite protolith: Foliated Metamorphic RocksPelite protolith: Foliated Metamorphic Rocks-- high grade-- high grade

Non-Foliated RocksNon-Foliated Rocks

Specific Rock TypesSpecific Rock Types

Skarn: carbonate + contact Skarn: carbonate + contact metamorphism + Si added metamorphism + Si added (metasomatism). Minerals:(metasomatism). Minerals:grossular, epidote, tremolite, grossular, epidote, tremolite, wollastonite, diopsidewollastonite, diopside

Granulite: high-grade rock from pelitic, mafic, or Granulite: high-grade rock from pelitic, mafic, or quartzo-feldspathic protolith, quartzo-feldspathic protolith,

few OH-bearing minerals.few OH-bearing minerals.

Specific Rock Specific Rock TypesTypes

Specific Rock TypesSpecific Rock Types

http://z.about.com/d/geology/1/0/I/z/migmatite1_500.jpghttp://www.earth.edu.waseda.ac.jp/photogeology/200504rocky/BigornMtS/1K_DSC_1687.jpg

Protolith = mafic rock or Protolith = mafic rock or graywacke (dirty sst):graywacke (dirty sst):

Greenschist:Greenschist: low-grade, contains low-grade, contains chlorite, actinolite, epidote (all chlorite, actinolite, epidote (all green), and albite. green), and albite.

Amphibolite:Amphibolite: mid-grade, mid-grade, dominated by hornblende + dominated by hornblende + plagioclase. plagioclase.

Specific Rock TypesSpecific Rock Types http://z.about.com/d/geology/1/0/h/L/greenschist.jpg

Serpentinite:Serpentinite: ultramafic rock, ultramafic rock, low-grade metamorphosed.low-grade metamorphosed.

Blueschist:Blueschist: high-P, blue by high-P, blue by glaucophane--amphibole glaucophane--amphibole (mafic rock) or blue by (mafic rock) or blue by kyanite (pelite). kyanite (pelite).

EEccllooggiittee:: green + red due to green + red due to clinopyroxene and garnet clinopyroxene and garnet (omphacite + pyrope). (basalt) (omphacite + pyrope). (basalt)

Specific Rock TypesSpecific Rock Typeshttp://www.npolar.no/geonet/picture_atlas/SE02-1-25.jpg

http://www.dges.tohoku.ac.jp/museum/large/eclogite.jpg

Metamorphic FaciesMetamorphic Facies

Wikipedia

Prograde Sequence and FaciesPrograde Sequence and Facies

Index minerals make zones, but COMPOSITION DEPENDENTIndex minerals make zones, but COMPOSITION DEPENDENT

Change in composition, means change in minerals occurringChange in composition, means change in minerals occurring Chlorite zone. Chlorite zone. Biotite zone. Biotite zone. Garnet zone. Garnet zone. Staurolite zone. Staurolite zone. Kyanite zone. Kyanite zone. Sillimanite zone.

=> Facies is better to compare different metamorphic rocks

ChloriteChloriteBiotiteBiotiteCordieriteCordieriteAndalusiteAndalusiteSillimaniteSillimanite

Prefix and mineral texturePrefix and mineral texture

High Strain RocksHigh Strain Rocks

High Strain RocksHigh Strain Rocks

Why do we care about metamorphic Why do we care about metamorphic rocks?rocks?