structural geology tectonic stresses large scale strain of the crust i.e., geologic structures...
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Structural GeologyTectonic Stresses Large Scale Strain of the Crust i.e., Geologic Structures
Inner core: Solid iron Outer core: Liquid iron,
convecting (magnetic field)
Mantle (Asthenosphere) : Solid iron-magnesium silicate, plastic, convecting
Crust (Lithosphere): Rigid, thin5-30km
Crust: Rigid, Thin
Mantle: Plastic, Convecting
Tectonics and Structural Geology
Tectonic Stresses resulting fromInternal 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 andReleases energy Earthquakes
Folds and Faults (Palmdale, Ca)
Eastern PennsylvaniaEastern Pennsylvania
NorthwesternAfrica
MetamorphicGrade
High
Low
NortheasternNorth America
NorthwesternAfrica
Strike and Dip of Planar Feature
Two methods of reporting planar orientation Quadrant: N15oE, 45oS (geologists) Azmuthal: 195o/45o (engineers)
Stikes and Dips are used to identify geologic structures
Brunton Pocket Transit
Clinometer Azimuthal Compass Transit
Stresses at Plate
Boundaries Divergent (Tensional)
| Convergent (Compressional) | Transform (Shear)
e.g., Pacific NWKehew, Fig. 1-20Lab. Man., Fig. 21-2
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)
Anticline (fold)
Syncline (fold)
Plunging Anticline
Eastern PennsylvaniaEastern Pennsylvania Folds and faults resulting from
compressive stresses Anticlines (many plunging) Synclines (many plunging) Reverse faults Thrust faults
Domes and Basins
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)
When shallow crust is strained rocks tend to exhibit brittle strain
Brittle Strain Joints
Sheet Joints (due to Expansion and Exfoliation)
Fault: Movement occurring along a discontinuity Brittle strain and subsequent movement as a
result of stress Fault
terminology
Faults
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
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
Younger rocks lie beneath the grabens Sediment fills in the linear valleys
Nevada
“Washboard topography” is the result of Horsts and Grabens
A.k.a, Basin and Range
Structural Oil Traps
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
Thrust Fault: Glacier NP, Montana
Old
Younger
Structures at a Convergent Boundary
Structures within Mountain Belts
Compressional and TensionalStructures
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?
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