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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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Topics • Fabrics • Foliation, cleavage, lineation • Cleavage and Folds • Geometry • Strain significance • Origin of Cleavage • Pressure solution • Passive rotation • Recrystallization • Shear zones
Metamorphic layering Broosk Range, AK
Fabric Elements • Bedding • Compositional layering • Mineral grains • Fold Hinges • Axial planes • Planes of parting or fracture • etc
Metamorphic Fabrics • Foliation • Cleavage • Schistosity • Lineation S-tectonite L-tectonite L/S-tectonite
Random fabric Foliation Lineation
Penetrative Fabric Spaced Fabric
Cleavage • A kind of foliation • Deformation Fabric • Rock splits along preferred planes Lachlan fold belt, Australia Photo by E.L.Miller
Spaced cleavage Cambrian Rocks, South Verkhoyansk foldbelt, Siberia
The beginning of Metamorphism: The beginning of Metamorphism: Axial Planar Cleavage
Relationship o cleavage to folding Axial-planar cleavage
Processes of Cleavage Development • Rotation of minerals • Crenulation • Pressure solution • Recrystallization
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
Sequential diagram of % shortening by folding (initially by buckling), cleavage development and dissolution. Courtesy of David Gray, Monash University, Australia
Crenulation Cleavage Small scale kinks and pressure solution surfaces
Two Foliations! S2 S1