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X Deformation and Mountain Building A B C D E Plate Tectonics and Stress Rock Deformation Geologic Structures Origin of Mountains Continental Crust 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 Tectonics and Structural Geology 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 Faults and Releases energy  Earthquakes Fig 10-CO, p 216 Folds and Faults (Palmdale, Ca) See Fig 10-2a, p 219 Eastern Pennsylvania Northwestern Africa Stresses at Plate Boundaries  Divergent (Tensional) |  Convergent (Compressional)  | Transform (Shear) e.g., Pacific NW 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) Stikes and Dips are used to identify geologic structures 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 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) Horst and Graben, Nevada Horst Graben Humboldt Range, Northern Nevada Fig 10-15b, p 233 Horst and Graben, Nevada Horst Graben Humboldt Range, Northern Nevada 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 Structures at a Passive Continental Margin   Resulting from continental breakup E.g., The Americas and Africa Salt Domes: e.g., Texas     Rising of less dense salt Stretches overlying crust Forming normal faults and Oil traps Structural Oil Traps Thrust Fault: Glacier NP, Montana Old Younger Structures at a Convergent Boundary Structures within Mountain Belts Compressional and Tensional Structures E.g., The Apls  Intense folding and thrusting of sedimentary rocks Strike Slip Faults  Physiographic Features San Andreas Fault   What type of fault is this? What other features are associated with the fault? [...]... rocks, West Mirror image east of Sandusky? Sandstone M 2o Shale 2o O Limestone 2 o D Anticline (fold) Anticline (fold) Syncline (fold) Plunging Anticline Fold Terminology Axis     Axis Axial Plane Plunging Age of rocks and outcrops Axis Plunging Anticline, Colorado Eastern Pennsylvania  Folds and faults resulting from compressive stresses     Anticlines (many plunging) Synclines (many plunging)... 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) Brittle Strain  Joints  When shallow crust is strained rocks tend to exhibit brittle strain Sheet Joints Defining Fault Orientation  Strike of fault plane parallels the    fault trace and fault... Horsts and Grabens Structures at Divergent Boundaries   Tensional Stresses cause brittle strain and formation of sets of normal faults i.e., Horsts and Grabens Horsts and Grabens  Older Rocks are exposed along the ridges formed by the horsts Horst   Graben Horst Graben Younger rocks lie beneath the grabens Sediment fills in the linear valleys Nevada     “Washboard topography” is the result
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