Rock Structure and DeformationQuestionsSedimentary rocks, which make up most of the surface cover are:PowerPoint PresentationBut, we know that we observe much more than flat lying rocks…Rocks can obtain structure and deformation in various ways…Stress applied to rocks!Slide 8Type of structure also determined by:Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Types of structureSlide 18Slide 19Slide 20Non uniform vertical stressSlide 22Slide 23Slide 24Slide 25Slide 26Spatial orientation of Rock StructureStrike and DipSlide 29Slide 30StrikeFolds – ductile behavior Compressive stressParts of a foldFolds are named according to geometry of Limbs to AxisMonoclines – only one limbAnticlines and SynclinesSlide 37Folds may also be have a Horizontal Axis, or the Axis may PlungeFolds may be symmetric or they may be asymmetricSlide 40Slide 41Slide 42Slide 43Slide 44Folds also occur at a variety of scalesDomes and BasinsSlide 47Rock StructureRock Structureand Deformationand DeformationLecture #17Questions•What are the various rock structures and what types of forces cause each?•How can we describe the spatial orientation of various rock structures?•How does Plate tectonics play a role in orogenies (mountain building events)? What are other ways in which uplift can occur with rocks?Sedimentary rocks, which make up most of the surface cover are:•Originally deposited as horizontal layers–Oldest on bottom; youngest on top•Any alteration of this orientation = rock STRUCTURE•Any changes in shape = rock DEFORMATIONSediments and sedimentary rocksare originally formed as horizontal layersBut, we know that we observe much more than flat lying rocks…Rocks can obtain structure and deformation in various ways…•Tilted layers•Vertically uplifted rocks•Folding•Faulting•Combinations of movement.Why do rocks change orientation?Stress applied to rocks!•Stress may be vertical–Uniform stress or non-uniform stress•Stress may be compressive•Stress may be tensional•Stress may be shearingStress caused by Plate tectonic movement; magma bodies; crustal readjustmentType of structure also determined by:•The response of the rocks to the stress•BRITTLE v. DUCTILE behaviorDuctile rocks Bend (Folds)Plastic v. ElasticBrittle rocks Fracture (Faults)Ductile BehaviorBrittle BehaviorWhat determines Brittle v. Ductile behavior•Confining pressure•Temperature•Rock type•Nature and intensity of stress•FluidsConfining pressure > Ductile rocksDeeply buried rocks•Tend to behave as ductile material due to High Pressure, Temperature•But different rocks will respond differentially when subjected to equal forces–Fine-grained rocks usually ductile–Coarse-grained rocks may fractureShallow rocks will fractureTypes of structure1. Vertical Uplift–Uniform vertical stress uplifts rocks, evenlyUniform stress is appliedTypes of structure2. Tilting–Non-uniform vertical stress uplifts rocks, and raises one section higherNon uniform vertical stressTypes of structure3. FoldingCompressional stress plastically deforms rocksDUCTILE Behavior!FOLDS occur at all scalesTypes of structure4. Faulting–Tension, Compression or Shear stress!–Rocks break therefore:BRITTLE behaviorFAULTS occurAt all scalesSpatial orientation ofRock Structure•Measure the direction of rocks with respect to North–STRIKE•Measure the inclination of rocks–DIP–Geographic direction (DIP DIRECTION)–Divergence from the horizontal plane (DIP ANGLE)Strike and Dip•STRIKE – the intersection of the horizontal plane (ground surface) with an inclined plane (the inclined rocks)•Strike is measured and recorded in degrees from North•DIP – maximum angle of inclination from the horizontal (Dip direction is ALWAYS 90˚ from the Strike)STRIKESTRIKEDIP35Strike and DipStrike•The term Strike is used to describe:–The orientation of inclined rocks–The Orientation of folds (the Axis)–The orientation of a fault trace•Flat lying rocks have no Strike!Horizontal rocksymbolFolds – ductile behaviorCompressive stress•Parts of folds–Axis (Axial Plane)–Limbs–Core•Types of folds–Monoclines–Anticlines–Synclines–Domes and BasinsParts of a foldCOREFolds are named according to geometry of Limbs to Axis•Antiforms – Limbs dip away from axis IF the oldest Rock unit is in the core it is called an ANTICLINE•Synforms – Limbs dip towards axis IF the youngest rock is in the core it is called a SYNCLINEWhy a distinction between Antiform and Anticline and Synform and Syncline? Folds may be overturned!Monoclines – only one limbAnticlines and SynclinesFolds often occur in setsFolds may also be have a Horizontal Axis, or the Axis may PlungeFolds may be symmetricor they may be asymmetricClassification of folded rocksSymmetric axial plane is vertical, limbs dip in opposite directions at the same angle of dipAsymmetric axial plane at an angle, limbs dip in opposite directions at different angles of dipOverturned axial plane at an angle, limbs dip in the same direction but at different angles of dipRecumbent axial plane and limbs are horizontalFolds also occur at a variety of scalesDomes and Basins•Circular (more or less) features of upwarped or downwarped rock