geology 3120 - introduction to shear zonesgeode.colorado.edu/~structure/teaching_geol3120/... ·...
TRANSCRIPT
OutlineOutline
•• What’s Going On With Shear Zones?What’s Going On With Shear Zones?
•• Brittle Shear ZoneBrittle Shear Zone
•• Ductile Shear ZoneDuctile Shear Zone
•• SemiSemi--Brittle Shear ZoneBrittle Shear Zone
•• BrittleBrittle--Ductile Shear Zone Ductile Shear Zone
Formation of Shear ZonesFormation of Shear Zones
““All faults are shear zones but not all shear zones are faults”All faults are shear zones but not all shear zones are faults”
•• Brittle DeformationBrittle Deformation
•• Ductile DeformationDuctile Deformation
•• Zone of DeformationZone of Deformation
•• DiscontinuousDiscontinuous
•• ContinuousContinuous
••Brittle shear zones tend to form in the upper 5 Brittle shear zones tend to form in the upper 5 -- 10 km 10 km
••Ductile shear zones are located in the midDuctile shear zones are located in the mid--lower crust andlower crust and aesthenosphereaesthenosphere
Controlling FactorsControlling Factors
BrittleBrittle DuctileDuctile
TemperatureTemperature CoolerCooler HotterHotter
PressurePressure LowerLower HigherHigher
Strain RateStrain Rate HigherHigher LowerLower
Fluid Fluid PressurePressure
LowerLower HigherHigher
•• Also mineralogy and grain sizeAlso mineralogy and grain size
Semibrittle Semibrittle Shear ZonesShear Zones
V
E
F
ss11 -- axis of maximum instantaneous stretchingaxis of maximum instantaneous stretching
ss33 -- axis of maximum instantaneous shorteningaxis of maximum instantaneous shortening
Semibrittle Semibrittle Shear ZonesShear Zones
E
F
ss11 -- axis of maximum instantaneous stretchingaxis of maximum instantaneous stretching
ss33 -- axis of maximum instantaneous shorteningaxis of maximum instantaneous shortening
Semibrittle Semibrittle Shear ZonesShear Zones
F
ss11 -- axis of maximum instantaneous stretchingaxis of maximum instantaneous stretching
ss33 -- axis of maximum instantaneous shorteningaxis of maximum instantaneous shortening
Semibrittle Semibrittle Shear ZonesShear Zones
ss11 -- axis of maximum instantaneous stretchingaxis of maximum instantaneous stretching
ss33 -- axis of maximum instantaneous shorteningaxis of maximum instantaneous shortening
Example Example -- BrittleBrittle--Ductile Shear ZoneDuctile Shear Zone
•• Brittle deformation Brittle deformation -- feldspar crystalsfeldspar crystals
•• Ductile deformation Ductile deformation -- groundmassgroundmass
ReferencesReferences
Slide 1Slide 1
http://earth.leeds.ac.uk/http://earth.leeds.ac.uk/shearzonesshearzones/gallery/kohi2./gallery/kohi2.htmhtm
Slides 3, 5 Slides 3, 5 -- 8, 12 8, 12 -- 14, 16 14, 16 -- 19, 2119, 21Davis. G. H. and S. J. Reynolds, Structural Geology of Rocks andDavis. G. H. and S. J. Reynolds, Structural Geology of Rocks and Regions, 2nd ed., John Regions, 2nd ed., John Wiley & Sons, New York, 776 p., 1996.Wiley & Sons, New York, 776 p., 1996.
Slide 9Slide 9http://terraserver.homeadvisor.msn.com/image.http://terraserver.homeadvisor.msn.com/image.aspxaspx?t=1&s=14&x=116&y=1296&z=11&w=2?t=1&s=14&x=116&y=1296&z=11&w=2
Slide 15Slide 15http://earth.leeds.ac.uk/shearzones/gallery/laghetti.http://earth.leeds.ac.uk/shearzones/gallery/laghetti.htmhtm
Slide 20Slide 20http://earth.leeds.ac.uk/minor/tensiongash/index.http://earth.leeds.ac.uk/minor/tensiongash/index.htmhtm
Slide 22Slide 22www.www.brunelbrunel.ac.uk/.ac.uk/deptsdepts/geo//geo/iainsubiainsub// ShearKinShearKin//ShearKinShearKin.PPT.PPT