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-tectoniteL/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

Pressure solution in Clay-rich Limestone

Early pressure-solution cleavage in limestone

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

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