folds, faults, and mountain building chapter 9

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  • 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

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