Classification and Facies Wikipedia Today Updates: Not today Lecture outline: - Rock classification - Facies Prograde Metamorphism • 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 Metamorphism Prograde Retrograde Retrograde Metamorphism Prograde Retrograde http://www.und.nodak.edu/instruct/mineral/ 320petrology/opticalmin/chlorite.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 Sillimanite Kyanite Staurolite Garnet Biotite Chlorite 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, CO2 5. Quartz - nearly pure SiO2. 6. Quartzo-feldspathic - high Si, Na, K, Al A Classification of Metamorphic Rocks A Classification of Metamorphic Rocks Compositional Classification Parent Clay-rich sediment Sand-rich sediment Clay-sand mix Quartz sand Marl (limy mud) Limestone Basalt Metamorphic rock pelite psammite semi-pelite quartzite metamarls-silicate/calcareous marble metabasite Pelite protolith: Foliated Metamorphic Rocks -- low grade a b Pelite protolith: Foliated Metamorphic Rocks --middle grade Pelite protolith: Foliated Metamorphic Rocks -- high grade Non-Foliated Rocks Specific Rock Types 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. Specific Rock Types http://z.about.com/d/geology/1/0/I/z/migmatite1_500.jpg http://www.earth.edu.waseda.ac.jp/photogeology/ 200504rocky/BigornMtS/1K_DSC_1687.jpg Specific Rock Types 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. http://z.about.com/d/geology/1/0/h/L/greenschist.jpg Specific Rock Types http://www.npolar.no/geonet/picture_atlas/SE02-1-25.jpg 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) http://www.dges.tohoku.ac.jp/museum/large/eclogite.jpg Metamorphic Facies Wikipedia Prograde Sequence and Facies Index minerals make zones, but COMPOSITION DEPENDENT Change in composition, means change in minerals occurring Chlorite zone. Chlorite Biotite zone. Biotite Garnet zone. Cordierite Staurolite zone. Andalusite Kyanite zone. Sillimanite Sillimanite zone. => Facies is better to compare different metamorphic rocks Prefix and mineral texture High Strain Rocks High Strain Rocks Why do we care about metamorphic rocks?