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


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, Australia
Photo 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