3 Stress!!! Stress—a force exerted on an object Rocks react to stress by Deforming plasticallyDeforming elasticallyBreaking by brittle fractureQuestion of the hour (#1)How will a particular rock react to a particular stress?
4 It’s all in the Nature… Rock composition Ex: Hitting a chunk of concrete with a sledgehammer VS. hitting a giant rubber tire with a sledgehammer
5 I Can’t Take the Pressure!! Pressure and Temp. increase with depthTemp vs. pressureBurial promotes plastic deformation
6 If you can’t stand the heat… Higher temperatures favor plastic deformationEx. Bending a steel nailNeed to be super strongOr just heat the thing up…
8 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)
9 Geologic Structures Plate tectonics—primary stressor 3 main types of structuresFolds—ductile deformation (primarily)Faults—brittle deformationJoints—brittle deformation
10 Folds A fold is a bend in the rock Three characteristics Plastic deformationThree characteristicsUsually results from compressionFolding always shortens the horizontal distances in rockA fold usually occurs as part of a group of folds
14 Circular Features Domes Basin Circular anticlinal structure (both pics)Beds dip away from centerBasinCircular synclinal structureBeds dip towards center
15 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?
16 Nature is LazyRock moves repeatedly along faults and fault zones becauseTectonic forces often affect one location for a long timeIt’s easierThree types of faultsDepend on tectonic forces
21 Ah, How My Joints Ache…A joint is a fracture in rock along which no motion has occurredPlanes of weakness—like mineral cleavageGood for mining
22 Styles of Continental Deformation Relating Small Structures to Big Picture
23 Question of the Hour (#3) Where do mountains come from?In a subducting zoneMagmas/lavas—stall/eruptHigh temp—rocks expand when heatedContinent/continent collision—underthrustingCrust is shoved under other crustCompression squeezes crust—thickness increases
24 Tensional Tectonics Plates can split apart Rift valleys – long narrow troughs formed by a block that has dropped down between two big normal faults