folds, faults, and mountain building chapter 9

Folds, Faults, and Mountain BuildingChapter 9

Stress!!!Stressa force exerted on an objectRocks react to stress by Deforming plasticallyDeforming elasticallyBreaking by brittle fractureQuestion of the hour (#1)How will a particular rock react to a particular stress?

Its all in the NatureRock compositionEx: Hitting a chunk of concrete with a sledgehammer VS. hitting a giant rubber tire with a sledgehammer

I Cant Take the Pressure!!Pressure and Temp. increase with depthTemp vs. pressureBurial promotes plastic deformation

If you cant stand the heatHigher temperatures favor plastic deformationEx. Bending a steel nailNeed to be super strongOr just heat the thing up

Its About TimeStress applied slowly favors plastic behaviorStress applied suddenly favors brittle behavior

May the Tectonic Force be With You.Plate tectonic forcesTensionalStretch and pull formations apartCompressiveSqueeze and shorten rock formationsShearingTwo sides of a formation are pushed in opposite directions (sliding past one another)

Geologic StructuresPlate tectonicsprimary stressor3 main types of structuresFoldsductile deformation (primarily)Faultsbrittle deformationJointsbrittle deformation

FoldsA fold is a bend in the rockPlastic deformationThree characteristicsUsually results from compressionFolding always shortens the horizontal distances in rockA fold usually occurs as part of a group of folds

Anticline Vs. Syncline

Plunging Folds

Overturned and Asymmetric

Circular FeaturesDomesCircular anticlinal structure (both pics)Beds dip away from centerBasinCircular synclinal structureBeds dip towards center

All My Faults are Stress Related!!!Brittle deformationFaultsCracks in rock along which motion has occurredMovement may be gradual or sudden (earthquake)Usually associated with other faults in a fault zoneQuestion of the hour (#2): Why do rocks move repeatedly along faults and fault zones?

Nature is LazyRock moves repeatedly along faults and fault zones becauseTectonic forces often affect one location for a long timeIts easierThree types of faultsDepend on tectonic forces

Normal Faulting

Reverse Fault (part 1)

Reverse Fault (part 2)

Strike-slip Fault

Ah, How My Joints AcheA joint is a fracture in rock along which no motion has occurredPlanes of weaknesslike mineral cleavageGood for mining

Styles of Continental DeformationRelating Small Structures to Big Picture

Question of the Hour (#3)Where do mountains come from?In a subducting zoneMagmas/lavasstall/eruptHigh temprocks expand when heatedContinent/continent collisionunderthrustingCrust is shoved under other crustCompression squeezes crustthickness increases

Tensional TectonicsPlates can split apartRift valleys long narrow troughs formed by a block that has dropped down between two big normal faults

Rifting and Normal Faulting

Compressive TectonicsFold and thrust belts:When two continental plates collide, crust compressedCrust thickened by underthrustingthicken crust 2x

Transverse Margins