Geology 3120 Geology 3120 --A structural geology primerA structural geology primer

OutlineOutline

• Stress

• Lithology

• Strength

• Deformation styles

• Geologic time

• Deformation movements

• Attitudes

• Scaling Relationships

• Examples

StressStress

Stress = (Force / Area)

ShearTensileCompressive

y

x

LithologyLithology

GraniteDolomiteArkoseQuartz SandstoneGreywackeCoarse grained limestoneFine grained limestoneSiltstoneMarl, mudstoneShale AnhydriteHalite

Most stiff

Least stiff (fluid)

Strength of rockStrength of rock

Strength

••In addition to In addition to lithologylithology, , strength is a function of strength is a function of pressure, temperature, pressure, temperature, prepre--existing weakness, existing weakness, chemical reactions, time chemical reactions, time

Depth

Regarding Geologic Time…Regarding Geologic Time…

•• Page 36Page 36•• Required knowledge: Eras, Required knowledge: Eras, PeriodsPeriods•• Eras Eras -- Paleozoic (540Paleozoic (540--248 My)248 My)

Mesozoic (248Mesozoic (248--65 My) 65 My) Cenozoic (65Cenozoic (65--0 My)0 My)

•• Periods Periods -- COSDMPPCOSDMPPTJKTJKTQTQ

Deformation StylesDeformation Styles

NDuctile

Brittle

Deformation MovementsDeformation Movements

Rigid Body Translation

Rigid Body Rotation

Change in Shape

Change in Volume

BEFORE AFTER

AttitudesAttitudes

Planes

Faults

Bedding

Contacts

Lines

Slickenlines and grooves

Mineral growth

Piercing points

Scaling RelationshipsScaling Relationships

Thrust Earthquakes

MoineThrust

0 2 4 6 8 10-2

0

2

4

6

8

Log (L)Length of fault trace or rupture ( cm)

Log

(D)

Leng

th o

f di

spla

cem

ent

(cm

)

3a

3b

3c

D/ L=10

-1

D/ L=10

-5

D/ L=10

-4

D/ L=10

-3

D/ L=10

-2

Length (L)Dis

plac

emen

t (D

)

ExamplesExamples

• Faults

• Folds

• Joints

• Dikes

• Shear zones

• Extensional veins

FaultsFaults

Black Mountains, Death Valley

FaultsFaults

Black Mountains, Death Valley

FoldsFolds

Carboniferous limestones beds, Grenoble, France

FoldsFolds

Carboniferous limestones beds, Grenoble, France

Joints in the Sandstone, Moab regionJointsJoints

DikesDikes

Granite dikes, Dillon, CO

DikesDikes

Granite dikes, Dillon, CO

Shear zonesShear zones

San Gregario fault zone, California

Shear zonesShear zones

San Gregario fault zone, California

Extensional VeinsExtensional Veins

Calcite-filled veins, French Alps

Extensional VeinsExtensional Veins

Calcite-filled veins, French Alps