Ch10 structural geology_fall2007
-
Upload
- -
Category
Technology
-
view
857 -
download
0
Transcript of Ch10 structural geology_fall2007
![Page 1: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/1.jpg)
CRUSTAL DEFORMATION and Geologic Structures
![Page 2: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/2.jpg)
Deformation
• Deformation involves:– Stress – the amount of force applied to
a given area.
– Types of Stress:– Confining Stress – stress applied
equally in all directions.– Differential Stress – stress applied
unequally in different directions.
![Page 3: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/3.jpg)
Deformational Stress• Types of Differential Stress:
(1) Compressional Stress – shortens and thickens a rock body (associated with convergent plate boundaries).
(2) Tensional Stress – tends to elongate and thin or pull apart a rock unit (associated with divergent plate boundaries).
(3) Shear Stress – produces a motion similar to slippage that occurs between individual playing cards when the top of the stack is moved relative to the bottom (associated with transform plate boundaries).
![Page 4: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/4.jpg)
Deformation of the Earth’s Crust Caused by Tectonic Forces and Associated Differential
Stresses
![Page 5: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/5.jpg)
Deformation
• Differential stress applied to rocks during tectonic activity causes rocks to respond via deformation.
• Strain – changes in the shape or size of a rock body caused by stress.
• Strained rock bodies do not retain their original configuration during deformation.
![Page 6: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/6.jpg)
How Do Rocks Deform?• Rocks subjected to stresses greater than
their own strength begin to deform usually by folding, flowing, or fracturing.
– General Characteristics of Rock Deformation:
• Elastic deformation – the rock returns to nearly its original size and shape when the stress is removed.
• Once the elastic limit (strength) of a rock is surpassed, it either flows (ductile deformation) or fractures (brittle deformation).
![Page 7: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/7.jpg)
• Factors that influence the strength of a rock and how it will deform:
• Depth• Temperature• Confining Pressure• Rock Type• Availability of Fluids• Time
How Do Rocks Deform?
![Page 8: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/8.jpg)
• Rocks near the surface, where confining pressures and temperatures are low, will behave as a brittle solid and fracture once their strength is exceeded.
• Rocks at depth, where confining pressures and temperatures are high, will exhibit ductile behavior or solid-state flow, in which changes occur without fracturing.
How Do Rocks Deform?
![Page 9: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/9.jpg)
Crustal Structures• Folds – During crustal deformation rocks
are often bent into a series of wave-like undulations. – Anticlines and Synclines– Domes and Basins– Monoclines
• Characteristics of Folds:• Most folds result from compressional
stresses which shorten and thicken the crust.• Most of them occur in a series.
![Page 10: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/10.jpg)
Anatomy of a Fold• Limbs – Refers to the two sides of a fold.
• Axis (or Hinge) – A line drawn down the points of maximum curvature of each layer.
• Axial Plane – An imaginary surface that divides a fold symmetrically.
• Plunge – In complex folding, the axis is often inclined at an angle called plunge.
![Page 11: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/11.jpg)
(A) Horizontal Anticline
and(B) Plunging
Anticline
![Page 12: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/12.jpg)
Common Types of Folds
• Anticline – upfolded or arched rock layers.
• Syncline – downfolds or troughs of rock layers.
Photo courtesy of J. T. Daniels http://disc.gsfc.nasa.gov/geomorphology/GEO_2/GEO_PLATE_T-42.shtml
Photo courtesy of Brennan T. Jordan, Department of Earth Sciences, University of South Dakota http://www.usd.edu/~Brennan.Jordan/
![Page 13: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/13.jpg)
Common Types of Folds• Depending on their orientation, anticlines and
synclines can be described as…• Symmetrical, asymmetrical, overturned, recumbent
(a type of overturned fold – “lying on its side”), or plunging.
![Page 14: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/14.jpg)
Formationof Folds
Insert Animation #30:
Folds
![Page 15: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/15.jpg)
Name the Folds Below
![Page 16: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/16.jpg)
Plunging Anticlines
and Synclines
(Note: the outcrop pattern of an
anticline points in the direction it is
plunging, whereas the opposite is
true for a syncline)
![Page 17: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/17.jpg)
Sheep Mountain, A Plunging Anticline
![Page 18: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/18.jpg)
Formationof Folds
Insert Animation #30:
Plunging Folds
![Page 19: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/19.jpg)
Other Types of Folds• Monoclines
• Large, step-like folds in otherwise horizontal sedimentary strata. • Closely associated with faulting.
![Page 20: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/20.jpg)
Other Types of Folds• Dome
• Upwarped displacement of rocks.
• Circular or slightly elongated structure.
• Oldest rocks in center, younger rocks on the flanks.
![Page 21: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/21.jpg)
Other Types of Folds• Basin
• Circular or slightly elongated structure.
• Downwarped displacement of rocks.
• Youngest rocks are found near the center, oldest rocks on the flanks.
![Page 22: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/22.jpg)
Crustal Structures• Faults – Fractures in rocks along which appreciable
displacement has taken place.• Fault Zone – Displacements along multiple interconnected
faults.• Sudden movements along faults are the cause of most
earthquakes.
![Page 23: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/23.jpg)
Types of Faults• Classified by their relative movement
which can be Horizontal, Vertical, or Oblique.
![Page 24: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/24.jpg)
Summary of Fault Types
• Dip-Slip Faults:• Normal (gravity) – associated with divergent plate
boundaries.
• Reverse and Thrust – associated with convergent plate boundaries.
• Strike-Slip Faults:• Lateral (right and left) – associated with transform
plate boundaries.
![Page 25: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/25.jpg)
Dip-Slip Faults
• Movement is mainly parallel to the dip of the fault surface.
• Parts of a dip-slip fault include the hanging wall (rock surface above the fault) and the footwall (rock surface below the fault).
![Page 26: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/26.jpg)
Dip-Slip Faults• Normal Fault (gravity)
Dip-Slip Faults– Hanging wall block moves
down relative to the footwall block.
– Tensional stress– Accommodate lengthening or
extension and thinning of the crust.
– Associated with divergent plate boundaries.
– Most are small with displacements of a meter or so.
– Larger scale normal faults are associated with structures called fault-block mountains (Teton Range in Wyoming, Basin and Range Province in Nevada).
![Page 27: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/27.jpg)
Formationof Normal
Faults
Insert Animation #29:
Faults – Normal
![Page 28: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/28.jpg)
Normal Faulting – Fault Block Mountains• Fault-Block Mountains – Basin and Range Province
in Nevada – topography generated by a system of roughly north to south trending normal faults.
• Movements along these faults have produced alternating uplifted blocks called horsts (form elevated ranges) and down-dropped blocks called grabens (form basins).
• Half-Grabens – a tilted fault block in which the higher side forms mountainous topography and the lower side forms a basin that fills with sediment.
• Detachment Fault – nearly horizontal fault extending up to hundreds of kilometers into the subsurface. Smaller faults are connected to this larger fault. Boundary between ductile and brittle deformation.
![Page 29: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/29.jpg)
Dip-Slip Faults• Reverse and Thrust Dip-Slip Faults
– Hanging wall block moves up relative to the footwall block.
– Reverse faults have dips greater than 45o
– Thrust faults have dips less than 45o.
• Strong compressional stress.
• Accommodate shortening and thickening of the crust.
• Associated with convergent plate boundaries.
![Page 30: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/30.jpg)
Formationof Reverse
Faults
Insert Animation #29:
Faults – Reverse
![Page 31: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/31.jpg)
Idealized Development of Lewis Overthrust Fault near Glacier National Park
![Page 32: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/32.jpg)
Strike-Slip Faults
• Dominant displacement is horizontal and parallel to the strike of the fault.
• May produce broad zones of roughly parallel fractures up too several kilometers in width.
• Shear stress.
• Associated with transform plate boundaries.
![Page 33: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/33.jpg)
Formationof Strike-Slip
Faults
Insert Animation #29:
Faults – Strike-Slip
![Page 34: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/34.jpg)
Types of Strike-Slip Faults• Right-Lateral – as you face the fault, the
opposite side of the fault moves to the right.• Left-Lateral – as you face the fault, the
opposite side of the fault moves to the left.
http://www.pbs.org/wnet/savageearth/animations/
Animations:
Right-Lateral Strike-Slip Fault
![Page 35: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/35.jpg)
Types of Strike-Slip Faults
• Transform Fault– Large strike-slip
fault that cuts through accommodates motion between two large crustal plates.
– Example: San Andreas Fault System
![Page 36: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/36.jpg)
Name the Type of Fault Below
![Page 37: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/37.jpg)
Name the Type of Fault Below
![Page 38: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/38.jpg)
Name the Type of Fault Below
Insert Animation #28: Exposing Metamorphic Rock
![Page 39: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/39.jpg)
Name the Type of Fault Below
![Page 40: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/40.jpg)
Name the Type of Fault Below
![Page 41: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/41.jpg)
Name the Structure
![Page 42: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/42.jpg)
Name the Structure
![Page 43: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/43.jpg)
Mapping Geologic Structures
• Geologists measure the orientation or attitude of a rock layers or fault/fracture surfaces in order to describe and map geologic structures that result from deformation.
![Page 44: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/44.jpg)
Mapping Geologic Structures– Strike (Trend)
• The compass direction of the line produced by the intersection of an inclined rock layer or fault with a horizontal plane.
• Generally expressed an an angle relative to north.
• Example: N10ºE
![Page 45: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/45.jpg)
Mapping Geologic Structures– Dip (Inclination)
• The angle of inclination of the surface of a rock unit or fault measured from a horizontal plane.
• Includes both an inclination and a direction toward which the rock is inclined.
• Example: 30ºSE
![Page 46: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/46.jpg)
A Geologic Map Showing Strike and Dip of Structures
By knowing the strike and dip, geologists can predict the nature of rock structures hidden beneath the surface.
![Page 47: Ch10 structural geology_fall2007](https://reader035.fdocuments.us/reader035/viewer/2022070319/557c8288d8b42a9f578b4c33/html5/thumbnails/47.jpg)
Geologist Measuring the Dip of Strata in a Roadcut