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UT - GEOS 401 - Study Guide

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UT - GEOS 401 - Study Guide

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background image Geology       Exam 2 Lecture 1 (Deformation) Why should we care? o Earthquakes
o Folded rocks are an important reservoir for oil and gas
Deformation forces 1. Tensional Forces
2. Compressive Forces
3. Shearing forces
Tensional is always going to lengthen the rocks Most Deformation will happen at plate boundaries Rocks responses to forces Brittle V Ductile behavior o Brittle breaks and ductile slowly bends
o *middle row of diagram is ductile the last one is brittle*
o At low temp the rocks are going to deform brittle and high temp 
you will get ductile behavior  o Low pressure is brittle and high pressure is ductile
o Shallow levels in the earth we would find brittle, but there are 
some exceptions o Pull it really fast means brittle/pulling slowly means ductile
o Igneous and metamorphic deforms brittle/sedimentary forms 
ductile o More water makes it behave more ductile and less is brittle
o EX: Starbursts
o Ice is brittle and ductile
Depends on where, how hot the rocks are, depth in the 
crust, etc.
o *high temp/pressure, strain rate and water content* Chapter 7 Notes Outcrops allow geologists to identify distinct formations: groups of 
rock layers that can be identified throughout a region by their physical 
Strike-compass direction of a rock layer where it intersects with a 
horizontal surface
Dip-measured at right angles of the strike is the amount of tilting—the 
angle at which the rock layer inclines from the horizontal
The strike and dip of a rock layer define its orientation at a particular 
background image Fault- a fracture that displaces the rock on either side of it o can be measured with strike and dip dip slip fault-one on which there has been relative movement of 
blocks of rocks up or down the dip of the fault plane
o caused by compressive and tensional forces o normal fault is when the hanging wall moves downward relative
to the foot wall, extending the structure horizontally
caused by tensional forces o reverse fault is when the hanging wall moves upward relative 
to the foot wall causing shortening 
caused by compressive forces strike-slip fault-a fault on which the movement of blocks has been 
horizontal, parallel to the strike of the fault plane
o caused by shearing  o is a left lateral fault if an observer sees that the block on the 
opposite side has moved to the left and vice versa for the right 
lateral fault
thrust fault-low angled reverse fault w/ one dip less than 45 degrees, 
so that the movement is more horizontal than vertical
o is a reverse fault w/ a shallow-dipping fault plane oblique slip faults-when faults show strike slip and dip slip motions Folds-occur when an originally planar structure, such as a sedimentary
rock is bent into a curved structure
o Bending can be gentle or severe depending on the magnitude of 
applied forces
o Anticlines- folds in which layered rocks are bent upward into 
o Synclines-folds that are bent downward into troughs Symmetrical folds-have limbs that dip symmetrically from the axial 
Asymmetrical-have one lip that dips more steeply than the other Overturned folds-have limbs that dip in the same direction, but 1 
limb has been tilted beyond the vertical
Deformation along plate boundaries usually results in linear fault, but 
some types of deformation are more vertical
background image o Basin- a synclinal structure, bowl shaped depression of rock 
layers in which the beds dip toward a central point
o Dome- an anticlinal structure, a broad circular or oval upward 
bulge of rock layers
Joint- second type of fracture in which a crack in a rock formation 
along which there has been no appreciable movement 
o Found in almost every outcrop and can be caused by tectonic 
Lecture 2 Where do these behaviors occur? o Shallow Crusts brittle o Deep Crusts Ductile Keywords/ Terms o Strike-the direction of the intersection of a rock layer w/ a horizontal surface o Dip- angle at which the bed inclines from the horizontal **strike and dip record the 3D orientation of a rock**
** dip will always be perpendicular to the strike**
o Fracture- is a break in the rock
o Joint- is a fracture w/ no offset
o Fault- a fracture w/ offset (relative motion on either side of the rock)
Sometimes there is no foot wall or hanging wall o Reverse (Thrust)-foot wall moves down and the hanging wall moves  up FDR- Footwall Down Reverse/ puts older rocks on top of 
younger rocks/ convergent boundary
Thrust- large lateral displacement  o Repeated sequences o Normal-footwall moved up and hanging wall moves down (FUN) Associated with divergent boundaries (found in rift zones) and
drops younger rocks down against older rocks
o Strike-slip faults- move from side to side Still can have footwall and hanging walls and does not have to
be vertical
o Right-lateral- if you are standing and both sides look as if they  moved to the right o Left Lateral- Vice versa
o Folds
Anticline- upside down U

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School: University of Texas at Austin
Department: Geoscience
Course: Understanding the Earth
Professor: Jaime Barnes
Term: Summer 2015
Name: The GEO 401 - Understanding the Earth - Study Guide - Geology Exam 2 Lecture 1 (Deformation)
Description: Geology Exam 2 Lecture 1 (Deformation)  Why should we care? o Earthquakes o Folded rocks are an important reservoir for oil and gas  Deformation forces 1
Uploaded: 04/05/2017
11 Pages 10 Views 8 Unlocks
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