ENVS 1050 Chapter 11: Geology Notes - week 11

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Thursday, July 10, 2014
Geology Notes - week 11
Structural Geology
Chapter 9 - All
Tectonic forces deform rocks in the crust
earth has a lot of rock layers that have been contorted, bent, overturned and with
fractures some occur along faults during major earthquakes, with spreading happening
for a long period of time and extension of the crust that elongate depressions form
ocean basins
Structural geologists study the crust and deformation of the architecture by studying the
orientation of the faults and folds deformed from the rocks and they can recreate some
servings with the help of tools.
Knowing this helps with economic well being, hydrothermal mineralization, work of
modern day life.
Deformation: general term that refers to all changes in the original form or size of a rock
body, location and orientation of rock. Most occurs along or near plate margins.
Force: a influence hat tends to put stationary objects in motion or change the motion of
moving bodies.
Stress: amount of force applied to a given area. magnitude is a part of the area where
the force acts.
Strain: visible result of that force.
Types of stress
1. differential: stress is applied unequally from different directions - this also causes
rocks to shear - similar to playing cards but happens in near surface environment by
close parallel surfaces of weakness ex; bedding planes, foliation and micro fault - by
contrast a great depth at temperatures and confining pressure are high shearing is
accomplished by solid state flow
2. compressional: differential stress that shortens a rock body. it is associated with
plate collisions and they tend to shorten and thicken the crust by folding and faulting.
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Thursday, July 10, 2014
3. tensional: stress elongate or pull apart a rock unit
How rocks deform
-bent
-fold
-fault
-* When stress is applied, rocks first apply by deforming elastically
Brittle/Failure
-rocks near the surface where the temperature and confining pressures are low and
tend to behave like solid and fracture once the strength is succeeded
Ductile
-depth temperatures and confining pressures are high rocks have this kind of
behaviour - similar to a penny getting flattened by a train
Rock type: crystalline have strong bonds that tend to fail of brittle fracture while
sedimentary rocks have weak spots and are subceptile to ductile flow - the weakest
natural occurring solid to exit ductile flow is glacial ice
time*
Mapping geologic structures: deformation generate features at different scales. for
example: mountain systems and bed rock. these are reffered too as rock structures.
-geologists can reconstruct the orientation and shape of existing structures and it is
mostly formed by sedimentary strata that is exposed since these are deposited in
horizontal layers. if they are still in this position it did not change and if the strata is
inclined, it indicates deformation.
-strike and dip determine the orientation and the attitude of a rock, layer, joint or fault
surface - measure in outcrops that are practical - then using the information they can
reconstruct
-strike: compass direction of the line produced by the intersection of an inclined rock
layer or fault with an horizontal plane
-dip:angle of inclination of the surface of a rock unit or fault measured from a
horizontal plane
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