The story of Tucson extensional geology

Undeformed granite

Mylonite

Low strain

High strain

Normal faults throughout - cut foliation and other ductile structures

Normal fault

Foliation- not sedimentary layering

Measurable like bedding-good first indication of direction of ductile deformation

MylonitesPorphyroclasts

Gneissic banding

Rotated crystals

Fractured fold - top to the south

S

C

Top to the south sense of shear

Ductile first

Brittle later

X-cutting dike - seals all the ductile deformation- an absolute age on this basaltic material would constrain the end of ductile deformation

Ductile deformation top to the south is given by foliation (direction), sense of shear indicators (folding, S-Cs) and lineation

Brittle is overprinted- low angle normal faults cutting the old foliation

Sequence of events:

The strength versus depth issue