Classification and Facies Wikipedia

Today Updates: Not today Lecture outline: - Rock classification - Facies

Prograde Metamorphism Normally progress through series of mineral assemblages, for example:Normally progress through series of mineral assemblages, for example: 1.epidote, chlorite, andalusite, muscovite, quartz, k-spar, and albite 2.sillimanite, plagioclase, cordierite, muscovite, quartz and k-spar 3.sillimanite, plagioclase, cordierite, quartz, and k-spar

Prograde Retrograde Prograde Metamorphism

Retrograde Metamorphism Prograde Retrograde 320petrology/opticalmin/chlorite.htm

Common Prograde Sequence Index minerals make zones: s s Chlorite zone. Pelitic rocks are slates or phyllites and typically contain chlorite, muscovite, quartz and albite s s Biotite zone. Slates give way to phyllites and schists, with biotite, chlorite, muscovite, quartz, and albite s s Garnet zone. Schists with conspicuous red almandine garnet, usually with biotite, chlorite, muscovite, quartz, and albite or oligoclase s s Staurolite zone. Schists with staurolite, biotite, muscovite, quartz, garnet, and plagioclase. Some chlorite may persist s s Kyanite zone. Schists with kyanite, biotite, muscovite, quartz, plagioclase, and usually garnet and staurolite s s 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 Al 2 SiO 5 )

Sequence of indicator mineralsChlorite Biotite Garnet Staurolite Kyanite Sillimanite

Types of Protolith Six chemically based-groups to start with 1. Ultramafic - very high Mg, Fe, Ni, Cr 2. Mafic - high Fe, Mg, and Ca 3. Shales (pelitic) - high Al, K, Si 4. Carbonates- high Ca, Mg, CO 2 5. Quartz - nearly pure SiO Quartzo-feldspathic - high Si, Na, K, Al

A Classification of Metamorphic Rocks

Compositional Classification ParentMetamorphic rock Clay-rich sedimentpelite Sand-rich sedimentpsammite Clay-sand mixsemi-pelite Quartz sandquartzite Marl (limy mud)metamarls-silicate/calcareous Limestonemarble Basaltmetabasite

a b Pelite protolith: Foliated Metamorphic Rocks -- low grade

Pelite protolith: Foliated Metamorphic Rocks --middle grade

Pelite protolith: Foliated Metamorphic Rocks -- high grade

Non-Foliated Rocks

Specific Rock Types

Skarn: carbonate + contact metamorphism + Si added (metasomatism). Minerals: grossular, epidote, tremolite, wollastonite, diopside Granulite: high-grade rock from pelitic, mafic, or quartzo-feldspathic protolith, few OH-bearing minerals. few OH-bearing minerals. Specific Rock Types

rocky/BigornMtS/1K_DSC_1687.jpg

Protolith = mafic rock or graywacke (dirty sst): Greenschist: low-grade, contains chlorite, actinolite, epidote (all green), and albite. Amphibolite: mid-grade, dominated by hornblende + plagioclase. Specific Rock Types

Serpentinite: ultramafic rock, low-grade metamorphosed. Blueschist: high-P, blue by glaucophane--amphibole (mafic rock) or blue by kyanite (pelite). Eclogite: green + red due to clinopyroxene and garnet (omphacite + pyrope). (basalt) Specific Rock Types

Metamorphic Facies Wikipedia

Prograde Sequence and Facies Index minerals make zones, but COMPOSITION DEPENDENT Change in composition, means change in minerals occurring s Chlorite zone. s Biotite zone. s Garnet zone. s Staurolite zone. s Kyanite zone. s s Sillimanite zone. => Facies is better to compare different metamorphic rocks F Chlorite F Biotite F Cordierite F Andalusite F Sillimanite

Prefix and mineral texture

High Strain Rocks

Why do we care about metamorphic rocks?