Transcript Geologic Structures

Structural Geology
Tectonic Stresses  Large Scale Strain
Crust:
of the Crust i.e., Geologic Structures
Rigid,
Thin
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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
Folds and Faults (Palmdale, Ca)
Eastern Pennsylvania
Northwestern
Africa
Northeastern
North America
Metamorphic
Grade
High
Low
Northwestern
Africa
Strike and Dip of Planar Feature
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Two methods of reporting planar orientation
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Quadrant: N15oE, 45oS (geologists)
Azmuthal: 195o/45o (engineers)
Stikes and Dips are used to
identify geologic structures
Brunton Pocket Transit
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Clinometer
Azimuthal Compass
Transit
Stresses
at Plate
Boundaries
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Divergent
(Tensional)
|
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Convergent
(Compressional)
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|
Transform
(Shear)
e.g., Pacific NW
Kehew, Fig. 1-20
Lab. Man., Fig. 21-2
Geologic
Structures
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Different stresses result in
various forms of strain
(geologic structures)
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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
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Folds and faults resulting from
compressive stresses
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Anticlines (many plunging)
Synclines (many plunging)
Reverse faults
Thrust faults
Domes and Basins
Bedrock
Geology of the
Michigan Basin
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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
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When shallow crust is strained
rocks tend to exhibit brittle strain
Sheet Joints
(due to Expansion and Exfoliation)
Fault:
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Movement occurring along a discontinuity
Brittle strain and subsequent movement as a
result of stress
Fault
terminology
Faults
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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
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Tensional Stresses cause brittle strain and
formation of sets of normal faults
i.e., Horsts and Grabens
Horsts and Grabens
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Older Rocks are exposed along the ridges
formed by the horsts
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Younger rocks lie beneath the grabens
Sediment fills in the linear valleys
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Nevada
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“Washboard
topography” is the
result of Horsts and
Grabens
A.k.a, Basin and
Range
Structural Oil Traps
Reverse and Thrust Faults
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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
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Intense folding and thrusting of
sedimentary rocks
Strike Slip Faults
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Physiographic Features
San Andreas Fault
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What type of fault is this?
What other features are
associated with the fault?