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X. Deformation and . Mountain Building

X. Deformation and . Mountain Building. Plate Tectonics and Stress Rock Deformation Geologic Structures Origin of Mountains Continental Crust. Tectonic Stresses  Large Scale S train of the Crust i.e., Geologic Structures. Crust : Rigid, Thin. Inner core: Solid iron

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X. Deformation and . Mountain Building

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  1. X. Deformation and . Mountain Building Plate Tectonics and Stress Rock Deformation Geologic Structures Origin of Mountains Continental Crust

  2. Tectonic Stresses Large Scale Strain of the Crust i.e., Geologic Structures Crust: Rigid, Thin • Inner core: Solid iron • Outer core: Liquid iron, convecting (magnetic field) • Mantle(Asthenosphere): Solid iron-magnesium silicate, plastic, convecting • Crust(Lithosphere):Rigid, thin 5-30km Mantle: Plastic, Convecting

  3. Tectonic Stresses resulting from Internal Energy (heat driving convection) Strains (deforms) the Mantle and Crust Bends Rocks, i.e., ductile strain (Folds) Breaks Rock, i.e., brittle strain (Joints) and Moves large blocks along Faultsand Releases energy  Earthquakes Tectonics and Structural Geology

  4. Fig. 10-CO, p. 216

  5. Folds and Faults (Palmdale, Ca) See Fig. 10-2a, p. 219

  6. Eastern Pennsylvania Northwestern Africa

  7. Stresses at Plate Boundaries • Divergent (Tensional) | • Convergent (Compressional) | • Transform (Shear) e.g., Pacific NW

  8. Geologic Structures • Different stresses result in various forms of strain (geologic structures) • Folds (compressive stresses may cause ductile strain) • Faults (Any type of stress may cause brittle strain. The type of fault depends on the type of stress)

  9. Stikes and Dips are used to identify geologic structures

  10. Strike and Dip • Define and map the orientation of planar features • Bedding planes (sedimentary rocks) • Foliation • Joints • Faults • Dikes • Sills • Ore Veins Fig. 10-4, p. 221

  11. Strike and Dip Strike and Dip Map Symbol • Strike: The line of intersection between the plane and a horizontal surface • Dip: Angle that the plane makes with that horizontal plane Fig. 10-4, p. 221

  12. Sipping Bedding Planes Sedimentary Rocks Dip in the direction of younger rocks • Youngest (top) • P: Permian • P: Pennsylvanian • M: Mississippian • D: Devonian • S: Silurian • O: Ordovician • C: Cambrian • Oldest (bottom) D S O

  13. Deciphering the Geology of OhioUsing Dipping Bedding Planes • Beds Dip 2o, West • Younger rocks, West • Mirror image east of Sandusky? Sandstone Shale Limestone MOD 2o 2o 2o

  14. Anticline (fold)

  15. Anticline (fold)

  16. Syncline (fold)

  17. Plunging Anticline

  18. Fold Terminology Axis Axis • Axis • Axial Plane • Plunging • Age of rocks and outcrops

  19. Plunging Anticline, Colorado

  20. Eastern Pennsylvania • Folds and faults resulting from compressive stresses • Anticlines (many plunging) • Synclines (many plunging) • Reverse faults • Thrust faults

  21. Domes and Basins

  22. Bedrock Geology of the Michigan Basin • During and after the deposition of Michigan’s sedimentary rocks • The crust warped downward • Exposing younger rocks in the center and • Older rocks on the rim (e.g. Toledo)

  23. Brittle Strain  Joints • When shallow crust is strained rocks tend to exhibit brittle strain

  24. Sheet Joints

  25. Fig. 10-11a, p. 227 Defining Fault Orientation • Strike of fault plane parallels the • fault trace and • fault scarp • Direction of Dip of the fault plane indicates the Hanging wall block

  26. Fault: • Movement occurring along a discontinuity • Brittle strain and subsequent movement as a result of stress • Fault terminology

  27. Faults • Fault: When movement occurs along a discontinuity • Fault type depends on the type of stress

  28. Normal Faults

  29. Normal Faults, Horsts and Grabens

  30. Structures at Divergent Boundaries • Tensional Stresses cause brittle strain and formation of sets of normal faults • i.e., Horsts and Grabens

  31. Horsts and Grabens • Older Rocks are exposed along the ridges formed by the horsts • Younger rocks lie beneath the grabens • Sediment fills in the linear valleys Horst Horst Graben Graben

  32. Nevada • “Washboard topography” is the result of Horsts and Grabens • A.k.a, Basin and Range • E.g., Humbolt Range • E.g., Death Valley (Graben)

  33. Horst and Graben, Nevada Horst Graben Humboldt Range, Northern Nevada Fig. 10-15b, p. 233

  34. Horst and Graben, Nevada Horst Graben Humboldt Range, Northern Nevada

  35. Reverse and Thrust Faults • Compressive stress causes the hanging wall to move upward relative to the foot wall  Reverse Fault • At convergent plate boundaries ancient rocks can be thrust over younger rocks  Thrust Fault

  36. Structures at a Passive Continental Margin • Resulting from continental breakup • E.g., The Americas and Africa

  37. Salt Domes: e.g., Texas • Rising of less dense salt • Stretches overlying crust • Forming normal faults and • Oil traps

  38. Structural Oil Traps

  39. Thrust Fault: Glacier NP, Montana Old Younger

  40. Structures at a Convergent Boundary

  41. Structures within Mountain Belts

  42. Compressional and TensionalStructures

  43. E.g., The Apls • Intense folding and thrusting of sedimentary rocks

  44. Strike Slip Faults • Physiographic Features

  45. San Andreas Fault • What type of fault is this? • What other features are associated with the fault?

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