CEE 1030 1st Edition Lecture 9 Structural 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 surface Work is aided by advances in Ariel photography Satellite imagery Global 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 left Ductile 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 a buried fault ex San Rafael monocline Utah Domes 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 dome ex Michigan a basin