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Metamorphic Rocks Foliations, and Lineations

Metamorphic Rocks Foliations, and Lineations. Topics. Fabrics Foliation, cleavage, lineation Cleavage and Folds Geometry Strain significance Origin of Cleavage Pressure solution Passive rotation Recrystallization Shear zones. Geothermal Gradient and Metamorphism.

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Metamorphic Rocks Foliations, and Lineations

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  1. Metamorphic Rocks Foliations, and Lineations

  2. Topics • Fabrics • Foliation, cleavage, lineation • Cleavage and Folds • Geometry • Strain significance • Origin of Cleavage • Pressure solution • Passive rotation • Recrystallization • Shear zones

  3. Geothermal Gradient and Metamorphism

  4. Naming of Metamorphic Rocks

  5. Slatey cleavage

  6. Gneiss

  7. Looks Like Bedding, but is it?

  8. Metamorphic layering Broosk Range, AK

  9. Isoclinal Fold

  10. Quartz-mica schist

  11. Fabric Elements • Bedding • Compositional layering • Mineral grains • Fold Hinges • Axial planes • Planes of parting or fracture • etc

  12. Metamorphic Fabrics • Foliation • Cleavage • Schistosity • Lineation S-tectonite L-tectonite L/S-tectonite

  13. Random fabric Foliation Lineation

  14. Penetrative Fabric Spaced Fabric

  15. Cleavage • A kind of foliation • Deformation Fabric • Rock splits along preferred planes Lachlan fold belt, Australia Photo by E.L.Miller

  16. Spaced cleavage Cambrian Rocks, South Verkhoyansk foldbelt, Siberia

  17. The beginning of Metamorphism: The beginning of Metamorphism: Axial Planar Cleavage

  18. Relationship o cleavage to folding Axial-planar cleavage

  19. Axial Planar cleavage

  20. Processes of Cleavage Development • Rotation of minerals • Crenulation • Pressure solution • Recrystallization

  21. SEM Image of Clays in Shale

  22. Pressure solution in Clay-rich Limestone

  23. Early pressure-solution cleavage in limestone

  24. Small quartz vein cut by a spaced crenulation/solution cleavage Documenting the extent of material removal along these surfaces. Photo from David Gray, Monash University, Australia

  25. Sequential diagram of % shortening by folding (initially by buckling), cleavage development and dissolution. Courtesy of David Gray, Monash University, Australia

  26. Sandstone after compaction

  27. Beginning of foliation

  28. Crenulation Cleavage Small scale kinks and pressure solution surfaces

  29. Crenulation Cleavage Beginning

  30. More Advanced Fabric

  31. Coarse Sandstone-Strong Foliation

  32. Two Foliations! S2 S1

  33. Spaced Pressure-Solution Cleavage

  34. Shortening by folding vs. shortening by cleavage

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