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Lecture SIX Metamorphic Grade and Facies

Lecture SIX Metamorphic Grade and Facies. Metamorphic grade and Facies.

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Lecture SIX Metamorphic Grade and Facies

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  1. Lecture SIXMetamorphic Grade and Facies

  2. Metamorphic grade and Facies Systematic spatial distribution in mineral assemblages that formed during metamorphism in metamorphic terrains allow to delineate mineral zonation, using index minerals (e.g. chlorite, biotite, garnet, staurolite, cordierite, sillimanite, andalusite, wollastonite, diopside… etc.) • - Mineral zone: Zones in the field, which mark the first appearance of an index mineral, such as chlorite zone, garnet zone. • Mineral isograde: boundary marked between two mineral zones, which include: • Mineral-in: first app • Mineral-out: the last appearance of

  3. Example: Wadi Tweiba (S. Sinai) mineral zones

  4. Gabal Yelleq (Sinai) contact aureole mineral zones

  5. Metapelites metamorphic zones (Scotland)

  6. Distribution of minerals within metamorphic zones

  7. Metamorphic grades Metamorphic grades is a general term for describing the relative P-T conditions under which the metamorphic rocks form. The grades could subdivided into: • Very low grade • Low grade • Medium grade • High grade • Very high grade The boundaries between the grades are chosen to correspond to important discontinuous reactions (could recognized as major isograde), and they correlate with the scheme of metamorphic facies.

  8. Metamorphic facies Metamorphic facies is defined as a set of metamorphic mineral assemblage, repeatedly associated in space and time.

  9. Metamorphic grades and facies

  10. Metamorphic grades and facies

  11. Metamorphic series

  12. Graphical representation of metamorphic mineral assemblage 1- ACF and AKF diagrams: Suitable for mafic rocks and calc-silicates. 2- AFM diagram: Useful for pelitic rocks. 3- CAS (CaO - Al2O3 - SiO2) diagram: Useful for marly rocks (calcareous mudstones). 4- MCS (MgO - CaO - SiO2) diagram: Useful for ultramafic rocks.

  13. ACF diagram

  14. AKF diagram

  15. Plotting of mineral assemblage and rock categories in ACF and AKF

  16. AFM plotting

  17. AFM diagram

  18. SCM diagram

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