Metamorphic rocks-Definition, Formation, Classification


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Metamorphic rocks-Definition, Formation, Classification

  1. 1. -J.Delince BSA-11-409
  2. 2. * *Metamorphism – A transformation *Those rocks which undergone various chemical and physical changes *They are formed from the parent material protolith *The protolith may be igneous , sedimentary , metamorphic *The minerals forming metamorphic rocks due to metamorphism is called as index minerals
  3. 3. * *Classification based on location of action by agents *Contact metamorphism – due to magma *Regional metamorphism –Due to heat and pressure *Most of the crust rocks are metamorphic *The metamorphic rocks also form important ores *It is the evolution of rock to suit the new environment
  4. 4. * *The actions of chemically active fluids, heat, pressure make the protolith to become destabilize and converted to metamorphic rocks. *Each element has own temperature to destabilize. *Using this property we can find the age of rocks *During the formation the igneous and sedimentary rocks get changed in composition, structure etc *If it occurs due to heat it is called as thermal metamorphism *If it is occurring due to both heat and pressure it is dynamo thermal metamorphism
  5. 5. * *Heat is dominant factor. *It increase with increase in depth and also the intruding of magma in the crystal layer of rocks *A contact metamorphosis *The gas emissions also reacts with rock and changes the property *There is addition of magmatic material
  6. 6. *In this case both the heat and the pressure acts. *Recrystallization of minerals occurs *Schist and gneiss *Here whole rock get metamorphosed – a regional metamorphosis *Granite to gneiss and on further to schist *The first conversion due to thermal metamorphism and second due to dynamo-thermal metamorphism
  7. 7. * Metamorphic rocks Foliated Non-foliated Granular
  8. 8. * *It is the rocks (parallel structures) contain micas and ferro magnesian minerals *It has four types Foliated Coarse grained -schists Medium grained Very fine grained Coarse grained- Gneiss
  9. 9. *Coarse grained- gneiss –they are formed from granite and contains quartz, mica, feldspars, amphiboles *Coarse grained –schist - they are granite ,basalt Having mica and silicates *Medium grained phyllite- from shale –micaceous – transition of schist to slate *Very fine grained- shale – micaceous with quartz- slate
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  14. 14. * *They are massive structures with quartz and feldspars *Fine grained peat , coal –anthracite , Amphibolite *They won’t create foliation even under pressure due to large sized particles
  15. 15. * *Formed from eqidimensional grains *Quartzite from sandstone –medium to coarse *Marble from dolomite and calcite –fine grained
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  17. 17. * *A text book of pedology- J.Sehgal * rocks.html
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