Transcript Rock Deformation

Rock Deformation
Chapter 11, Section 1
Factors Affecting Deformation
Deformation – all changes in the original shape
and/or size of a rock body
Stress – the force per unit area acting on a solid
When rocks are under stresses greater than their
own strength, they begin to deform, usually by
folding, flowing, or fracturing
Strain – The change in shape or volume of a body
of rock as a result of stress
Once the elastic limit or strength of a rock is
surpassed, it either flows or fractures
The factors that influence the strength of a rock and
how it will deform include temperature, confining
pressure, rock type, and time
Factors Affecting Deformation
Rocks deform permanently in two ways: brittle
deformation and ductile deformation
Rocks near the surface, where temperatures and
confining pressure are low, usually behave like brittle
solids and fracture once their strength is exceeded –
brittle deformation
Ductile deformation is a type of solid-state flow that
produces a change in the size and shape of an object
without fracturing that object
The mineral composition and texture of a rock will also
affect how it will deform
Forces that are unable to deform rock when first
applied may cause rock to flow if the force is
maintained over a long period of time
Deformation
Concept Check
What is brittle deformation?
The strength of a material is exceeded,
and the material breaks or fractures.
Types of Stress
The three types of stresses that rocks
commonly undergo are tensional stress,
compressional stress, and shear stress
When rocks are squeezed or shortened
the stress is compressional
Tensional stress is caused by rocks being
pulled in opposite directions
Shear stress causes a body of rock to be
distorted
Types of Stress
Folds
During mountain building, flat-lying sedimentary and
volcanic rocks are often bent into a series of wavelike
ripples called folds
The three main types of folds are anticlines, synclines,
and monoclines
Anticline – formed by the upfolding, or arching, of
rock layers
Syncline – downfolds, or troughs, found in association
with anticlines
The angle that a fold or fault makes with the horizontal
is called the dip of the fold or fault
Monocline – large, step-like folds in otherwise
horizontal sedimentary strata
Monoclines seem to occur as sedimentary layers have
been folded over a large faulted block of underlying
rock
Anticlines and Synclines
Concept Check
What is a syncline?
A down fold or trough
Faults
Faults – fractures in the crust along which movement
has taken place
The major types of faults are normal faults, reverse
faults, thrust faults, and strike-slip faults
Normal fault – occurs when the hanging wall block
moves down relative to the footwall block (result in the
lengthening of the crust)
Reverse fault – the hanging wall block moves up
relative to the footwall block
Thrust faults – reverse faults with dips less than 45º
(results in the shortening of the rocks)
Strike-slip faults – movement is horizontal and
parallel to the trend, or strike of the fault surface
(caused by shear stress)
Normal Fault
Reverse Fault
Thrust Fault
Strike-Slip Fault
Concept Check
What are the major types of faults?
Normal, reverse, thrust, and strike-slip
Assignment
Read Chapter 11, Section 1 (pg. 308-313)
Do Chapter 11 Assessment #1-36 (pg. 329330)
For Section 1: Do #’s 1, 2, 4-6, 8, 10-13, 1618, 24, 25, 27, 29, & 31-34