GLG 101 - Physical GeologyGLG 101 - Physical Geology Bob LeightyBob Leighty

Geologic StructuresGeologic Structures

These lecture notes are very similar to the ones I use in my traditional classes. You’ll find they are loaded with imagery and streamlined text that highlight the most essential terms and concepts. The notes provide a framework for learning and, by themselves, are not meant to be a comprehensive source of information.To take advantage of the global knowledge base known as the Internet, I have included numerous hyperlinks to external web sites (like the Wikipedia, USGS, NASA, etc.). Follow the links and scan them for relevant info. The information from linked web sites is meant to supplement and reinforce the lecture notes – you won’t be responsible for knowing everything contained in them.

As a distance learning student, you need to explore and understand the content more independently than in a traditional class. As always, I will help guide you through this learning adventure. Remember, email Dr. Bob if you have any questions about today’s lecture (rleighty@mail.mc.maricopa.edu).Leave no questions behind!Explore and have fun!Explore and have fun!

These notes and web links are your primary “lecture” content in this class. Additionally, various articles are assigned each week to supplement this “lecture” information. I believe you’ll have enough information to reference without having to purchase a costly textbook.

If rocks are subjected to stress, they may be deformed (& show strain)

undeformed rocks deformed rocks (strain)

(stress)compression

Stress & StrainStress & StrainStructuralStructuralGeologyGeology

Types of StressTypes of StressStress & StrainStress & StrainStructuralStructural

GeologyGeology

higher T (deeper)lower T (shallow)stronger rocks weaker rocks

Brittle Ductile(faulting) (folding)

fast strain rate slow strain rate

Types of StrainTypes of StrainStress & StrainStress & StrainStructuralStructural

GeologyGeology

Form under brittle conditions by any stress

Fractures with differential offset (vertical and/or horizontal)

FW

How to ID a fault with vertical offset

HW 1) Find matching features on either side of the faultHangingwall (HW): rocks above the fault plane

Footwall (FW): rocks below the fault plane

2) Which way does the HW move?

FaultsFaultsStructuralStructuralGeologyGeology

Normal faults – Tensional stress causes HW

HW

Reverse faults – Compressional stress causes HW

HW

Transform faults – Shear stress causes horizontal movement

FaultsFaultsStructuralStructuralGeologyGeology

FaultsFaultsStructuralStructuralGeologyGeology

Unnamed fault on AZ87(a high-angle normal fault) HW

FW

South Mountain detachment fault(a low-angle normal fault)

Thrust faults = low-angle (dip <45º) reverse faults

HWFW

FaultsFaultsStructuralStructuralGeologyGeology

The San Andreas transform fault (mostly horizontal movement)

FaultsFaultsStructuralStructuralGeologyGeology

Joint: a fracture where no offset has occurred

JointsJointsStructuralStructuralGeologyGeology

Form under ductile conditions by compressional stresses

FoldsFoldsStructuralStructuralGeologyGeology

Axial plane - splits the fold into two limbs

FoldsFoldsStructuralStructuralGeologyGeology

FoldsFoldsStructuralStructuralGeologyGeology

Strike & dip – describes orientation of bedding

dip

measuring strike & dip with a compass

strike dip

strik

e

FoldsFoldsStructuralStructuralGeologyGeology

limbs dip in toward axial plane

youngest beds in center of the fold

“point” downSynclinesSynclines

FoldsFoldsStructuralStructuralGeologyGeology

“point” up limbs dip away from axial plane oldest beds in center of the fold

AnticlinesAnticlinesFoldsFoldsStructuralStructural

GeologyGeology

Folds “plunge” when the fold axis is not horizontal

Form curving outcrop patterns

Plunging FoldsPlunging FoldsFoldsFoldsStructuralStructural

GeologyGeology

A one-limbed fold with horizontal beds on the top & bottom

MonoclinesMonoclinesFoldsFoldsStructuralStructural

GeologyGeology

Dome – A circular upwarp (a circular anticline)

Black Hills, SD

Structural DomesStructural DomesFoldsFoldsStructuralStructural

GeologyGeology

Basin – A circular downwarp (a circular syncline)

Michigan

Structural BasinsStructural BasinsFoldsFoldsStructuralStructural

GeologyGeology

WWW Links in this LectureWWW Links in this Lecture> Stress - http://en.wikipedia.org/wiki/Stress_%28physics%29> Strain - http://en.wikipedia.org/wiki/Strain_%28materials_science%29> Faults - http://en.wikipedia.org/wiki/Faults> Dip-slip fault - http://en.wikipedia.org/wiki/Geologic_fault#Dip-slip_faults> Strike-slip fault - http://en.wikipedia.org/wiki/Geologic_fault#Strike-slip_faults> Detachment fault - http://en.wikipedia.org/wiki/Detachment_fault> Thrust fault - http://en.wikipedia.org/wiki/Thrust_fault> San Andreas transform fault - http://en.wikipedia.org/wiki/San_Andreas_Fault> Joint - http://en.wikipedia.org/wiki/Joint_%28geology%29> Folds - http://en.wikipedia.org/wiki/Fold_%28geology%29> Strike and dip - http://en.wikipedia.org/wiki/Strike_and_dip> Syncline - http://en.wikipedia.org/wiki/Syncline> Anticline - http://en.wikipedia.org/wiki/Anticline> Dome - http://en.wikipedia.org/wiki/Dome_%28geology%29> Basin - http://en.wikipedia.org/wiki/Basin_%28geology%29

StructuralStructuralGeologyGeology