The story of Tucson extensional geology
Jan 20, 2016
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