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Structural Geology
Appalachian MountainsPennsylvania
It has long been evident to geologists that great forces operate in Earth’s crust
These forces apparently involve bending, breaking, and overturning rock layers
Differential t
Stress is a force acting upon a solid.Strain is a change in shape or volumeof a solid as a result of stress
stress
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Solid rock may respond to stress in two ways:
Ductile Behavior (bending, stretching)( g g)
Brittle Behavior (breaking)
Behavior determined by several factors:
Rate of strain, confining pressure, rock composition, temperature, presence of water
Joints
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Faulting
H i ll d f t llHanging-wall and footwall
Types of Faults
Normal Fault Reverse Fault
Strike-Slip Fault
Normal Fault
Strike-Slip Fault
Reverse Fault
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Horst and Graben Da Basics• Tensional stress = normal fault• Compressive stress = reverse faultp• Shear stress = strike slip fault
Geometry of a foldGeometry of a fold
AnticlineAnticline
SynclineSyncline
Plunging AnticlinePlunging Anticline
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Open (symmetrical)
I li lIsoclinal
Asymmetrical
Overturned
Recumbent
Evolution of a fold into a
reverse fault
Age relationships of folded beds
An eroded anticline will have older beds in the middleAn eroded anticline will have older beds in the middleAn eroded syncline will have younger beds in middle
Strike and Dip
How do geologistsmap complex 3-Dstructures with only surface data?
Strike and DipMaking a Geologic Map
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Measuringorientation ofrock outcrops
What are the age relationshipsof these rocks?
Erosion removes portions of a fold
Strike and Dip symbols on maps
Plunging folds revealed by topography
“Law of V’s” - Plunging anticline points in direction of plungePlunging syncline opens in direction of plunge
GeologicMap
Pay attention to age relationships andstrike and dip symbols
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Describe the structures and stress
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Draw the geologic map Three General Types of Mountains
• Fold and Thrust Belts• Fault Block Mountains
• Volcanic Mountains
Fold and Thrust Mountains
Fault Block
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Volcanic Mountains
So…how would you figure out the Appalachians? A Low-Angle Reverse Fault - Thrust Fault
Fig. 15.16
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Keystone Thrust west of Las Vegas
Fig. 15.17B
What is the geologic structure of Michigan?
Geologic Map of U.S.
Ordovician Late Carboniferous
U.S. Orogenies Western U.S. Eastern U.S.Permian
Cretaceous
TaconicOrdovician
AcadianDevonian
AlleghenianPennsylvanian
LaramideTertiary
SevierCretaceous
NevadanJurassic
GrenvilleProterozoic
SonomanTriassic
AntlerLate Devonian
KenoranArchean
time
PangeaBreakup
RodiniaAssembly
RodiniaBreakup
PangeaAssembly
Precambrian
Paleozoic
Mesozoic
Cenozoic
HudsonianProterozoic
AppalachiansIsostatic rise
Rocky Mts, CO. Plat.,Sierra Mts. – Tectonic Rise
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Mountain BuildingIsostasy - equilibrium Appalachian Fold and Thrust Belt