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Geology 101: Crustal Deformation - Stress Types, Deformation, Mapping, Folds, Exams of Earth Sciences
An introduction to geology, focusing on crustal deformation. Topics include types of stress, brittle and ductile deformation, mapping geologic structures, and fold types. Students are encouraged to study the document for exams, which cover the same format as exam 1 and contribute 15% to the final grade.
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Download Geology 101: Crustal Deformation - Stress Types, Deformation, Mapping, Folds and more Exams Earth Sciences in PDF only on Docsity!
Introduction
to Geology
GEO-101-004Class 14: Crustal
Deformation
- Exam
- •March 8 (1.5+ weeks from now)•15% of final grade•Same format as Exam
From http://serc.carleton.edu/introgeo
Last Question of the Day
What is this a picture of?Write down your observations
In the News
From http://news.bbc.co.uk/2/hi/in_pictures/4293419.stm
Question of the Day
Relative Dating
Examine the geologic cross section above•Which feature is the youngest?•Which feature is the oldest?
Structural geology
•
Structural geologists study the architectureand processes responsible for deformationof Earth’s crust
•
A working knowledge of rock structures isessential to our modern way of life. Why??
Deformation
•
Deformation is a general term that refers to allchanges in the original form and/or size of arock body
•
Most crustal deformation occurs along platemargins
•
Deformation involves
•
Force – that which tends to put stationary objectsin motion or changes the motions of movingobjects
Stress - force applied to a given area
Deformation
•
Types of stress
•
Compressional stress – shortens a rock body
Deformation
•
Types of stress
•
Tensional stress – tends to elongate or pull aparta rock unit
Deformation
•
Types of stress
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Shear stress – produces a motion similar to slippagethat occurs between individual playing cards whenthe top of the stack is moved relative to the bottom
Deformation
•
Strain – changes in the shape or size of a rock body causedby stress
Deformation
•
How rocks deform
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Rocks subjected to stresses greater than their ownstrength begin to deform usually by folding, flowing,or fracturing
Deformation
•
How rocks deform
•
Rocks subjected to stresses greater than their ownstrength begin to deform usually by folding, flowing,or fracturing
Deformation
•
How rocks deform
•
General characteristics of rock deformation
–
Elastic deformation – the rock returns to nearlyits original size and shape when the stress isremoved – like a rubber band
Once the elastic limit (strength) of a rock issurpassed, it either flows (ductile deformation) orfractures (brittle deformation) - Temperature, confining pressure, rock type, andtime will determine how the rock deforms
Brittle deformation causes rocks to be transported on faultsand folds, whereas ductile deformation involves elastic andrecoverable strain only.
Brittle deformation is very similar to ductile deformationexcept for the elastic strain energy found in rocks that haveundergone brittle deformation.
Brittle deformation occurs in rocks that are hotter, whereasbrittle deformation occurs at low temperature where energy islower.
Brittle deformation occurs in rocks that are colder, whereasductile deformation occurs at high temperature where energyis higher.
How is “brittle” deformation different from “ductile”deformation, and why?
Mapping geologic structures
•
When conducting a study of a region, ageologist identifies and describes thedominant rock structures
•
At many different scales – mineraldeformation to an entire mountain belt
•
A geologist identifies and describes thedominant structures
–
May be concealed by vegetation, sedimentation
Only a few sites may be available - May be aided by satellite and aerial imagery
Strike and dip of a rock layer
Figure 10.
A geologic map showing strike
and dip of structures
Figure 10.
Folds
•
During crustaldeformation (compression)rocks are often bent into aseries of wave-likeundulations called foldsCharacteristics of folds
–
Parts of a fold
•
Limbs – refers to thetwo sides of a fold
Hinge line – a linedrawn down thepoints of maximumcurvature of eachlayer - Axial plane – animaginary surfacethat divides a foldsymmetrically
Folds
•
Common types of folds
•
Anticline – upfolded or arched rock layers (oldestrocks exposed in the center)
Syncline – downfolds or troughs of rock layers(youngest rocks exposed in the center) - Can be symmetrical or asymmetrical - Overturned (can be recumbent)
Syncline (left) and
anticline (right)
Figure 10.11
Folds
•
Common types of folds
•
Monoclines – large, step-like folds in otherwisehorizontal sedimentary strata
Often the result of folding above a buried fault
Folds
•
Other types of folds
–
Dome
•
Upwarped displacement ofrocks
Circular or slightlyelongated structure - Oldest rocks in center,younger rocks on the flanks
Folds
•
Other types of folds
–
Basin
•
Circular or slightlyelongated structure
Downwarpeddisplacement of rocks - Youngest rocks are foundnear the center, oldestrocks on the flanks