CEE 1030 1st Edition Lecture 10Structural geology  Structural geology- study type of rocks and their geometry: deformation? Folds, faults, joints…Important to society? YES- examples: stability of ground for building, groundwater flow, tracing surface coal and ore deposits, gas and oil traps, construction sites Mapping geological structures- critical to know structure and type of rock units- field observations by geologists: describe and map orientations and lithology of rock unites- often limited number of outcrops  sites were bedrock is exposed at surfaceWork is aided by advances in: Ariel photographySatellite imageryGlobal positioning systems (GPS) Strike (trend)- compass direction of line produced by intersection of an inclined rock layer or fault with horizontal plane  Dip (inclination)- angle of inclination of the surface of a rock unit or fault measured from a horizontal plane Investigating the shallow earth  Drilling- expensive, information from one spot  Seismic reflection- sound waves into ground get reflected from boundaries of different rock types Structural geology- deformation Deformation- general term for all changes in the original form or size of a rock unit These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. most common forms of deformation are: folding and faulting  Stress- force applied to a given area Strain- changes in the shape or size of a rock unit caused by stress Elastic deformation- the rock returns to nearly its original size and shape when the stress is removed- one elastic limit (strength) of rock is exceeded, it either: flows (ductile or plastic deformation) or fractures (brittle deformation) - ex. brittle deformation occurs when you drop a plate and it shatters, fractures - ex. ductile deformation occurs when you squash a ball of dough, flows Style of rock deformation What controls brittle vs. ductile deformation?- factors that influence the strength of a rock and how it will deform, include:  temperature confining pressure  rock minerals  time - rapid deformation= brittle- slow deformation= ductile Brittle deformation - two types of rock fracture:  joints- no appreciable movement across crack  faults- relative movement of rocks on either side of fracture - joints very common rock structures significance of joints: concentrates effects of chemical weathering  controls location of many ore mineral deposits highly jointed rocks often represent a risk to construction projects (weakens rock, fluid path) Faults- sudden movement along fault generates earthquake - types of faults: dip-slip and strike- slip  dip- slip: movement if mainly parallel to the dip of the fault surface  hanging wall- rock surface above the fault footwall- rock surface below the fault- different types of faults are found in different types of environments where the stresses are different Dip- slip faults: Normal - normal faults accommodate lengthening or extension of crust Dip- slip: reverse and thrust - reverse faults have dips greater than 45o- thrust faults have dips less than 45o Strike- slip faults- dominant displacement is horizontal and parallel to the strike of the fault - left- lateral: as you face the fault, the opposite side of the fault moves to the leftDuctile deformation: folds- during crustal deformation rocks are often bent into a series of wave-like undulations called folds as compressional stresses shorten and thicken the crust - Anticline: upfolded in arch, makes an arch shape, like shape of an A- Syncline: downfolded into trough  Monoclines- large, step-like folds in otherwise horizontal sedimentary strata, often the result of aburied fault -ex. San Rafael monocline, UtahDomes and Basins - broad gentle warping of sedimentary strata dome- anticlinal structure: oldest rocks in centre basin- synclinal structure: youngest rocks in centre ex: Black Hills, South Dakota, a domeex. Michigan, a