Structural Geology Tectonic Stresses Large Scale Strain Crust

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

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

Folds and Faults (Palmdale, Ca)

Eastern Pennsylvania Northwestern Africa

Northeastern North America Metamorphic Grade High Low Northwestern Africa

Strike and Dip of Planar Feature n Two methods of reporting planar orientation n n Quadrant: N 15 o. E, 45 o. S (geologists) Azmuthal: 195 o/45 o (engineers)

Stikes and Dips are used to identify geologic structures

Brunton Pocket Transit n n n Clinometer Azimuthal Compass Transit

Stresses at Plate Boundaries n Divergent (Tensional) | n Convergent (Compressional) n | Transform (Shear) e. g. , Pacific NW Kehew, Fig. 1 -20 Lab. Man. , Fig. 21 -2

Geologic Structures n Different stresses result in various forms of strain (geologic structures) n n 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)

Anticline (fold)

Syncline (fold)

Plunging Anticline

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

Domes and Basins

Bedrock Geology of the Michigan Basin n n 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 n When shallow crust is strained rocks tend to exhibit brittle strain

Sheet Joints (due to Expansion and Exfoliation)

Fault: Movement occurring along a discontinuity n Brittle strain and subsequent movement as a result of stress n Fault terminology n

Faults n n Fault: When movement occurs along a discontinuity Fault type depends on the type of stress

Normal Faults

Normal Faults, Horsts and Grabens

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

Horsts and Grabens n Older Rocks are exposed along the ridges formed by the horsts n Younger rocks lie beneath the grabens Sediment fills in the linear valleys n

Nevada n n “Washboard topography” is the result of Horsts and Grabens A. k. a, Basin and Range

Structural Oil Traps

Reverse and Thrust Faults n n 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

Thrust Fault: Glacier NP, Montana Old Younger

Structures at a Convergent Boundary

Structures within Mountain Belts

Compressional and Tensional Structures

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

Strike Slip Faults n Physiographic Features

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