Tectonic deformation and geologic structures. Mountain building Anatomy of a convergent mountain...
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Transcript of Tectonic deformation and geologic structures. Mountain building Anatomy of a convergent mountain...
Tectonic deformation
and geologic structures
Mountain building
• Anatomy of a convergent mountain belt
Valley & ridge
Blue ridge
Mountain building
Continental rift; opening of an ocean basin?
• Extensional horsts and grabens
HorstGraben
Deformation
Deformation:1) translation2) rotation3) distortion (shape change)
Deformation results from stress,
Stress = force per unit area
Deformation - types of stress
Compressivestress
Tensionalstress
Lateral shearstress
Uniform pressure from all directions
Deformation - tectonic
Compression in a principal direction
Extension in a principal direction
Lateral shear
• Brittle: shallow crust; with increased stress little change until failure (breaks)
• Ductile: deeper crust; with increased stress gradual change (squishes)
Rock deformation: When does it fold and when does it fault?
depends on rock type, crustal depth, rate
Products of deformation
Faults
Folds
• Anticline: opens downward;
oldest rocks in center
• Syncline: opens upward;
youngest rocks in center
Types of folds
Strike and dip measurements along the limbs of a fold
Deformation - folds
dome basin
Types of folds
• fold appears to die out on ground surface
Plunging folds
http://www.fault-analysis-group.ucd.ie/papermodels/models/syncline_anticline_lowres.jpg
Types of faults
Thrust faults:• Compression• HW up• shallow dip
Normal faults:• Extension• HW down• steep dip
Types of faults
Strike-slip faults:• lateral shear• no vertical change• vertical dip
(map view)
Thrust, strike-slip or normal faults?
• Southern Appalachians - fold and thrust belt
• Cross-section through western Virginia
Interrelated Folds & faults
• imbricate thrusts
Wes
t V
irgin
ia
Virg
inia
Nor
th M
tn f
ault
Sta
unto
n fa
ult
Way
nesb
oro
Blu
e R
idge
Roc
kfis
h V
alle
y
Cha
rlott
esvi
lle
Gum
Spr
ing
10 km
Mountain building
Richmond Basin = continental rift; related to opening of the Atlantic ocean
• Extensional horsts and grabensR
ichm
ond Richmond Basin
Yor
ktow
n
Che
sape
ake
Bay
Gum
Spr
ing
Cap
e C
harle
s
10 km • Cross-section through eastern Virginia