Stuctural08spr x

X. Deformation and .
Mountain Building
A.
B.
C.
D.
E.

Plate Tectonics and Stress
Rock Deformation
Geologic Structures
Origin of Mountains
Continental Crust


Tectonic Stresses  Large Scale Strain
of the Crust i.e., Geologic Structures
Crust:
Rigid,
Thin








Inner core: Solid iron
Outer core: Liquid iron,
convecting (magnetic field)

Mantle (Asthenosphere) :
Solid iron-magnesium
silicate, plastic, convecting
Crust (Lithosphere): Rigid, thin
5-30km

Mantle:
Plastic,
Convecting


Tectonics and
Structural Geology
Tectonic Stresses
resulting from
Internal Energy
(heat driving convection)
Strains (deforms) the Mantle
and Crust
Bends

Rocks, i.e.,
ductile strain (Folds)
Breaks Rock, i.e.,
brittle strain (Joints) and
Moves large blocks along
Faults and
Releases energy 
Earthquakes

Fig. 10-CO, p. 216


Folds and Faults (Palmdale, Ca)

See Fig. 10-2a, p. 219


Eastern Pennsylvania

Northwestern
Africa


Stresses
at Plate
Boundaries


Divergent
(Tensional)
|



Convergent
(Compressional)



|
Transform
(Shear)

e.g., Pacific NW


Geologic
Structures


Different stresses result in
various forms of strain
(geologic structures)




Folds (compressive
stresses may cause ductile
strain)
Faults (Any type of stress
may cause brittle strain.
The type of fault depends
on the type of stress)


Stikes and Dips are used to
identify geologic structures

Strike and Dip


Define and map the orientation of
planar features








Bedding planes (sedimentary rocks)
Foliation
Joints
Faults
Dikes
Sills
Ore Veins
Fig. 10-4, p. 221


Strike and Dip




Strike: The line of
intersection between the
plane and a horizontal
surface
Dip: Angle that the plane
makes with that horizontal
plane

Strike and Dip
Map Symbol

Fig. 10-4, p. 221


Sipping Bedding Planes










Youngest (top)

P: Permian
P: Pennsylvanian
M: Mississippian

D: Devonian
S: Silurian
O: Ordovician
C: Cambrian


Oldest (bottom)

Sedimentary Rocks Dip in the
direction of younger rocks

D
S
O


Deciphering the Geology of Ohio
Using Dipping Bedding Planes




Beds Dip 2o, West
Younger rocks, West
Mirror image east of
Sandusky?
Sandstone

M 2o

Shale

2o

O

Limestone

2

o

D


Anticline (fold)


Anticline (fold)


Syncline (fold)



Plunging
Anticline


Fold Terminology

Axis






Axis
Axial Plane
Plunging
Age of rocks
and
outcrops

Axis


Plunging Anticline, Colorado


Eastern Pennsylvania


Folds and faults resulting from
compressive stresses





Anticlines (many plunging)
Synclines (many plunging)
Reverse faults
Thrust faults


Domes and Basins



Bedrock
Geology of the
Michigan Basin








During and after
the deposition of
Michigan’s
sedimentary rocks
The crust warped
downward
Exposing younger
rocks in the center
and

Older rocks on the
rim (e.g. Toledo)


Brittle Strain  Joints


When shallow crust is strained
rocks tend to exhibit brittle strain