Rock DeformationRock Deformation

Chapter 11, Section 1Chapter 11, Section 1

Factors Affecting DeformationFactors Affecting DeformationDeformation – Deformation – all changes in the original shape all changes in the original shape and/or size of a rock bodyand/or size of a rock bodyStress – Stress – the force per unit area acting on a solidthe force per unit area acting on a solidWhen rocks are under stresses greater than their When rocks are under stresses greater than their own strength, they begin to deform, usually by own strength, they begin to deform, usually by folding, flowing, or fracturingfolding, flowing, or fracturingStrain – Strain – The change in shape or volume of a body The change in shape or volume of a body of rock as a result of stressof rock as a result of stressOnce the elastic limit or strength of a rock is Once the elastic limit or strength of a rock is surpassed, it either flows or fracturessurpassed, it either flows or fracturesThe factors that influence the strength of a rock and The factors that influence the strength of a rock and how it will deform include temperature, confining how it will deform include temperature, confining pressure, rock type, and timepressure, rock type, and time

Rocks deform permanently in two ways: Rocks deform permanently in two ways: brittle brittle deformationdeformation and and ductile deformationductile deformationRocks near the surface, where temperatures and Rocks near the surface, where temperatures and confining pressure are low, usually behave like brittle confining pressure are low, usually behave like brittle solids and fracture once their strength is exceeded – solids and fracture once their strength is exceeded – brittle deformationbrittle deformationDuctile deformationDuctile deformation is a type of solid-state flow that is a type of solid-state flow that produces a change in the size and shape of an object produces a change in the size and shape of an object without fracturing that objectwithout fracturing that objectThe mineral composition and texture of a rock will also The mineral composition and texture of a rock will also affect how it will deformaffect how it will deformForces that are unable to deform rock when first Forces that are unable to deform rock when first applied may cause rock to flow if the force is applied may cause rock to flow if the force is maintained over a long period of timemaintained over a long period of time

Factors Affecting DeformationFactors Affecting Deformation

DeformationDeformation

Concept CheckConcept Check

What is brittle deformation?What is brittle deformation?

The strength of a material is exceeded, The strength of a material is exceeded, and the material breaks or fractures.and the material breaks or fractures.

Types of StressTypes of Stress

The three types of stresses that rocks The three types of stresses that rocks commonly undergo are tensional stress, commonly undergo are tensional stress, compressional stress, and shear stresscompressional stress, and shear stress

When rocks are squeezed or shortened When rocks are squeezed or shortened the stress is compressional the stress is compressional

Tensional stress is caused by rocks being Tensional stress is caused by rocks being pulled in opposite directionspulled in opposite directions

Shear stress causes a body of rock to be Shear stress causes a body of rock to be distorteddistorted

Types of StressTypes of Stress

FoldsFoldsDuring mountain building, flat-lying sedimentary and During mountain building, flat-lying sedimentary and volcanic rocks are often bent into a series of wavelike volcanic rocks are often bent into a series of wavelike ripples called foldsripples called foldsThe three main types of folds are anticlines, synclines, The three main types of folds are anticlines, synclines, and monoclinesand monoclinesAnticline –Anticline – formed by the upfolding, or arching, of formed by the upfolding, or arching, of rock layersrock layersSyncline –Syncline – downfolds, or troughs, found in association downfolds, or troughs, found in association with anticlineswith anticlinesThe angle that a fold or fault makes with the horizontal The angle that a fold or fault makes with the horizontal is called the dip of the fold or faultis called the dip of the fold or faultMonocline –Monocline – large, step-like folds in otherwise large, step-like folds in otherwise horizontal sedimentary stratahorizontal sedimentary strataMonoclines seem to occur as sedimentary layers have Monoclines seem to occur as sedimentary layers have been folded over a large faulted block of underlying been folded over a large faulted block of underlying rockrock

Anticlines and SynclinesAnticlines and Synclines

Concept CheckConcept Check

What is a syncline?What is a syncline?

A down fold or troughA down fold or trough

FaultsFaultsFaults –Faults – fractures in the crust along which movement fractures in the crust along which movement has taken placehas taken placeThe major types of faults are normal faults, reverse The major types of faults are normal faults, reverse faults, thrust faults, and strike-slip faultsfaults, thrust faults, and strike-slip faultsNormal fault –Normal fault – occurs when the hanging wall block occurs when the hanging wall block moves down relative to the footwall block (result in the moves down relative to the footwall block (result in the lengthening of the crust)lengthening of the crust)Reverse fault –Reverse fault – the hanging wall block moves up the hanging wall block moves up relative to the footwall blockrelative to the footwall blockThrust faults –Thrust faults – reverse faults with dips less than 45 reverse faults with dips less than 45º º (results in the shortening of the rocks)(results in the shortening of the rocks)Strike-slip faults –Strike-slip faults – movement is horizontal and movement is horizontal and parallel to the trend, or strike of the fault surface parallel to the trend, or strike of the fault surface (caused by shear stress)(caused by shear stress)

Normal FaultNormal Fault

Reverse FaultReverse Fault

Thrust FaultThrust Fault

Strike-Slip FaultStrike-Slip Fault

Concept CheckConcept Check

What are the major types of faults?What are the major types of faults?

Normal, reverse, thrust, and strike-slipNormal, reverse, thrust, and strike-slip

AssignmentAssignment

Read Chapter 11, Section 1 (pg. 308-313)Read Chapter 11, Section 1 (pg. 308-313)

Do Section 11.1 Assessment #1-8 (pg. 313)Do Section 11.1 Assessment #1-8 (pg. 313)

Print out “Exploration Lab 11 - Investigating Print out “Exploration Lab 11 - Investigating Anticlines and Synclines”Anticlines and Synclines”