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Unformatted text preview: Geology 1001
Chapter 7 Crustal Deformation: Folding and Faulting Deformation: misshape, or change the natural form of something. Alter the shape of by pressure or stress Pressure = stress = force/area Deformation = strain = result of stress Stress 3 types Tensional or pull-a-part stress pullCompressional or push-together stress pushLateral or horizontal shear stress 1 Strain = breaks or fracture Strain = bends or folding How does a rock respond to stress? Depends: Rate (fast vs. slow) of deformation Temperature Rapid deformation, low temperature = Rock breaks Slow deformation, high temperatures = Rock bends 2 Brittle Deformation: Fracture Deformation: Represents deformation in the shallow crust Brittle deformation Fault: Break in a rock Fault: Normal fault
TENS ION Fault plane Exten sion 3 Reverse fault
COMPR ESSIO N Comp ressio n Thrust fault COM PRES SION Com pr e s sion Strike-Slip Faults StrikeLeft-lateral strike-slip fault
SH EA R 4 Strike-Slip Faults StrikeRight-lateral strike-slip fault
SH EA R Oblique-Slip Faults ObliqueOblique-slip faulting is caused by a combination of forces. TENS SH Ductile Deformation: Flow like a liquid Deformation: Represents deformation in the deep crust EA R I ON 5 Ductile Deformation Fold: Bend in a rock Fold: Folds Folds 6 Folds Anticlines: rocks dip away from the center Syncline: rocks dip towards the center Symmetrical Folds: axis is perpendicular Zagros MTN's, Iran MTN' Photo by J. T. Daniels http://disc.gsfc.nasa.gov/geomorphology/GEO_2/GEO_PLATE_T-42.shtml 7 Asymmetrical Folds: axis is tilted Overturned Folds: older beds above younger beds 8 Where does the crust deform? Swiss Alps 9 Convergent Margins: compressional stress 10 Convergent Plate Boundaries: The Appalachians Big Mountains Thrust Faults Fold belts Thick crust Divergent Margins: tensional stress 11 Style of Deformation: Tensional
Sinai Egypt RED SEA Saudi Arabia Rift valley Styles of Deformation: Tensional East African Rift Valley 12 Structures and Tectonic Settings Divergent Plate Boundary: Red Sea, East Africa Rifts and rift valleys Normal faults Thin crust = volcanic activity Transform Margins: Horizontal shear stress 13 Styles of Deformation: Shearing Styles of Deformation: Shearing Transform Boundaries: San Andreas Fault System Complex deformation: can be extensional and/or compressional. compressional. Strike-slip faults Strike- 14 ...
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- Spring '07