Thursday, July 10, 2014
Geology Notes - week 11
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
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
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.
Thursday, July 10, 2014
3. tensional: stress elongate or pull apart a rock unit
How rocks deform
-* When stress is applied, rocks ﬁrst apply by deforming elastically
-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
-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
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
-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