metamorphic rocks foliations, and lineations
Post on 23-Jan-2016
45 Views
Preview:
DESCRIPTION
TRANSCRIPT
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
Naming of Metamorphic Rocks
Slatey cleavage
Gneiss
Looks Like Bedding, but is it?
Metamorphic layering
Broosk Range, AK
Isoclinal Fold
Quartz-mica schist
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, AustraliaPhoto by E.L.Miller
Spaced cleavage
Cambrian Rocks, South Verkhoyansk foldbelt, Siberia
The beginning of Metamorphism:
Axial Planar Cleavage
Relationship o cleavage to folding
Axial-planar cleavage
Axial Planar cleavage
Processes of Cleavage Development
• Rotation of minerals
• Crenulation
• Pressure solution
• Recrystallization
SEM Image of Clays in Shale
Pressure solution in Clay-rich Limestone
Early pressure-solution cleavage in limestone
Small quartz vein cut by a spaced crenulation/solution cleavageDocumenting 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
Sandstone after compaction
Beginning of foliation
Crenulation Cleavage
Small scale kinks and pressure solution surfaces
Crenulation Cleavage Beginning
More Advanced Fabric
Coarse Sandstone-Strong Foliation
Two Foliations!
S2
S1
Spaced Pressure-Solution Cleavage
Shortening by folding vs. shortening by cleavage
top related