Wise et al., 1984

What does deformation look like?

In the field: The Josephine Peridotite

Grain-size reductionCourse-grained

Cataclasite Frost et al., 2009

Partial Recrystallization of Quartz

Ultramylonite Mylonite

Crossed polars Uncrossed polars

SC-fabric C-surfaces: – Parallel to margin of shear surface S-surfaces: – Oblique to shear surface Foliation that makes an angle of <45˚ to shear plane (or shear zone boundary) is called S-foliation (from French word for schistosity, schistosité) C-bands are localized “mini” shear zones within the shear zone and shear the S-foliation (from French word for shear, cisaillement) – Usually long, straight, and parallel to shear zone boundary with the same sense of shear as the whole shear zone

SC-fabric

C-band S-band

More SC-fabric

Calcite twinning: Twin bands caused by deformation and accumulation of strain

Diffusion creep Herring, 1950

Dislocation creep

Deformation on the SEMP fault system

Possible directions 1.Go through questions on what deformation looks like. Hand samples and photos from the outcrops from the paper. 2.Discuss the paper in more depth, particularly thinking about the brittle-ductile transition zone and the differences between the two Klamms.

SEMP Fault Zone – Geologic Setting

SEMP Fault Zone - BDT Study Area

Kitzlochklamm (KK)Lichtensteinklamm (LK) DeformationMore ductile deformationMore brittle deformation StrainLow strain inferred from weak lattice preferred orientations (LPO) 70m-wide high strain fault core (50m-thick foliated gouge zone) Max. Temperature~400°C Grauwacken Zone (Slate/phylite) Well developed SC fabric Heavily twinned calcite veins Sweeping und. extinction in graphite schist Irregular to sweeping und. extinction in non-graphite schist Fractured feldspars Ground into clay (gouge) Foliated, but no SC fabric Riedel Shears in gouge Klammkalk (graphite rich marble tectonite) Weak SC fabric (lacks platy minerals) twins/mm (in calcite) Irregular und. extinction and regime 1 in quartz (low T, high strain rate) Limited weak SC (pervasive veining obscures comparison) twins/mm (in calcite) Irregular to sweeping und. extinction in quartz Grauwacken Zone/ Klammkalk Contact “Razor sharp” contact, juxtaposed along fault (pseudotachylite, mylonite, and gouge absent) Contact not exposed, Grauwacken gouged into a fine- grained clay

Grauwacken Deformation

Kitzlochklamm Klammkalk

KitzlochklammS-C fabric

S C

Kitzlochklamm Highly deformed zone adjacent to fault GRAUWACKEN KLAMMKALK ~1 m

KitzlochklammHighly deformed zone adjacent to fault

Liechtensteinklamm“phacoids”

Liechtensteinklammbrittle features Slickenlines?Fractured grauwacken outcrop (fault gouge zone just to the right of this photo). ~1 m

Liechtensteinklammbrittle features Fractured float (boulders deposited in river, not sure of origin)

Liechtensteinklammbrittle features Fractured klammkalk in river bed

Liechtensteinklammfault gouge zone ~1 m

Liechtensteinklammfoliated gouge on river bottom

Klammkalk quarryless deformed, have hand sample

Points for discussion Coseismic vs interseismic interpretation of fault deformation within the SEMP system – Hybrid behavior of fault over individual earthquake cycles? Thickness of BDT, and effects of neglecting BDT in models Juxtaposition of GWZ and Klammkalk in Kilzlochklamm – No observation of gouge, pseudotachylite, or mylonite zone

Mylonite – Sierra Nevada, CA

Passchier and Trouw (2005)