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Geol 2312 Igneous and Metamorphic Petrology

Geol 2312 Igneous and Metamorphic Petrology. Lecture 27 Metamorphism of Pelitic Sediments. April 10, 2009. Metamorphic Zones vs. Metamorphic Facies Pelitic Sediments - Mafic Igneous Rocks. Pelitic Sedimentary Rocks Mudstone, Shale, Graywacke.

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Geol 2312 Igneous and Metamorphic Petrology

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  1. Geol 2312 Igneous and Metamorphic Petrology Lecture 27 Metamorphism of Pelitic Sediments April 10, 2009

  2. Metamorphic Zones vs. Metamorphic FaciesPelitic Sediments - Mafic Igneous Rocks

  3. Pelitic Sedimentary RocksMudstone, Shale, Graywacke Pelitic sediments are composed of predominantly Al-K-rich clays and micas (>50%), with quartz, feldspar, and other minerals. Because clays are very sensitive to variations in temperature and pressure, they undergo extensive changes in mineralogy during progressive metamorphism Shale Basalt 49.0 1.5 15.0 9.0 11.0 0.4 10.0 2.5 0.9 0.5 Graywacke

  4. Chemographic Diagrams for MetapelitesAKF and AFM Pelitic Rocks Mafic Rocks

  5. Petrogenetic Grids for Metapelites“KFMASH” - K2O-FeO-MgO-Al2O3-SiO2-H2O Purple: Mg Orange: Fe

  6. Orogenic MetamorphismChlorite-Biotite Zone Biotite-in Isograd Tie-line Flip Chl + Kfs = Bt + Ms (+ Qtz + H2O)

  7. Orogenic MetamorphismBiotite Zone Progressive Metamorphism through the Biotite Zone Muscovite diminishes relative to Biotite and Al-rich Chlorite

  8. Orogenic MetamorphismBiotite-Garnet Zone Garnet-in Isograd Lower Biotite Zone Garnet Zone Upper Biotite Zone Tie-line Flip Chloritoid + Biotite (+ Qtz) = Garnet + Fe-Chlorite (+ H2O) Occurs at lower T for Fe-rich compositions

  9. Orogenic MetamorphismGarnet-Staurolite Zone Staurolite-in Isograd Cld+Ky = St + Chl (+ Qtz + H2O) Cld (+Qtz) = Grt + Chl + St (+ Qtz + H2O) Grt + Chl (+ Ms) = St + Bt (+ Qtz + H2O) Retreat of Chl SS

  10. Orogenic MetamorphismStaurolite Zone Importance of Composition A) Gt+Chl+Bt Gt+Bt+St B) Gt+Chl+St  Gt+Bt+St C) Gt+Chl+St Chl+Bt+St D) Gt+Chl+Bt  Chl+Bt+St Staurolite Stability Field

  11. Orogenic MetamorphismStaurolite-Kyanite-Sillimanite Zone Kyanite-in Isograd Sillimanite-in Isograd

  12. Thermal Metamorphism of Metapelites Albite-Epidote hornfels facies Hornblende hornfels facies Pyroxene hornfels facies

  13. High Pressure Metamorphismof Pelitic Sediments

  14. Partial Melting of Pelitic Sediments Na

  15. Migmatites a. Breccia structure in agmatite. b. Net-like structure. c. Raft-like structure. d. Vein structure. e. Stromatic, or layered, structure. f. Dilation structure in a boudinaged layer. g. Schleiren structure. h. Nebulitic structure. From Mehnert (1968) Migmatites and the Origin of Granitic Rocks. Elsevier.

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