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Deformation Standards: Introduction, Mapping, and Plate Tectonics

This article provides an introduction to deformation standards in geology, including the composition and structure of Earth's materials, geologic mapping techniques, and the role of plate tectonics in deformation. It covers topics such as geologic maps, strike and dip, geologic cross sections, plate boundaries, plate tectonic forces, brittle vs. ductile behavior, and basic deformation structures like faults and folds.

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Deformation Standards: Introduction, Mapping, and Plate Tectonics

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  1. Structure An Introduction to Deformation

  2. Standards • Describe the composition and structure of Earth’s materials

  3. A Brief Intro to Mapping • Geologic maps – represent the rock formations exposed at Earth’s surface. • Maps have special symbols to indicate strike and dip of rock formations, and lines to mark faults

  4. Geologic Map of New Mexico

  5. Strike and Dip • Strike – the compass direction of a rock layer as it intersects with a horizontal surface • Dip – is measured at right angles to strike and is the amount of tilting of the formation (angle at which the bed is inclined from the horizontal)

  6. Geologic Cross Sections • Diagrams that show the features that would be visible if vertical slices were made through part of the crust • Shows the rocks and structures under the surface

  7. Plate Tectonics • Steady motion between plates causes deformation at plate boundaries. • Rocks are deformed by faulting and folding. • Layers of rock can be pushed into folds. • Or, rock formations can break and slip on both sides of a fracture, forming a fault.

  8. Review Types of Plate Boundaries • Convergent • Plates push together • Divergent • Plates pull apart • Transform • Plates slide horizontally past each other

  9. Types of Plate Tectonic Force • Tensional forces – stretch and pull formations apart. • Dominate at divergent boundaries. • Compressive forces – squeeze and shorten rock formations. • Dominate at convergent boundaries. • Shearing forces – push two sides of a formation in opposite directions. • Dominate at transform boundaries.

  10. Ductile vs. Brittle • Brittle material – a material that undergoes little deformation under increasing force until it suddenly breaks • Ductile material – a material that undergoes smooth and continuous plastic deformation under increasing force and does not spring back to its original shape when the force is removed.

  11. Brittle & Ductile Behavior in the Crust • Some rocks are brittle and others ductile. • The same rock can be brittle at shallow depths and ductiledeep in the crust • A rock formation that would flow as a ductile material if deformed slowly may break as a brittle material if deformed more rapidly. • Exs: silly putty and gak (in-class & video) • Rocks break more easily under tension than compression

  12. Basic Deformation Structures • Faults • Folds • Circular Structures • Joints

  13. Fault • Surface across which rock formations have been displaced • Offset can be centimeters to hundreds of kilometers • Faults are classified by their slip direction. 2 Main types: • Dip-slip fault • Strike-slip fault

  14. Dip-Slip Fault • There has been relative movement of the blocks (rock to either side of the fault) up or down the dip of the fault plane. • Dip = tilt of the fault • Caused by compressive or tensional forces.

  15. Dip-Slip Fault • 3 types: • Normal fault • Reverse fault • Thrust fault

  16. Fault Parts • Fault – plane along which rocks have been displaced • Hanging wall – rocks above fault plane • Foot wall – rocks below fault plane Draw & label this diagram in your notes Cross-Section View Fault Plane Hanging Wall Foot Wall

  17. Normal Fault • Dip-slip fault formed when rocks above the fault plane (on the top side of the dip) move down relative to rocks below the fault plane. • This extends the structure horizontally. • Formed by tensional forces

  18. Photo: http://www.southalabama.edu/geography/allison/gy480tour.htm

  19. Photo: http://www.webpages.uidaho.edu/~simkat/geol345_files/2010lecture12.html

  20. Reverse Fault • Rocks above fault plane move upward in relation to the rocks below. • Causes shortening of the structure. • Formed by compressive forces

  21. Photo: http://www.corbisimages.com/Enlargement/ IH011691.html

  22. http://www.flickr.com/photos/51870389@N05/4778443130/

  23. Thrust Fault • Low-angle reverse fault – the angle of the fault plane is less than 45 • This causes the overlying block to move horizontally

  24. Photo: http://www.geology.wisc.edu/courses/g112/rock_deformation.html

  25. Strike Slip Fault • Movement is horizontal (just like movement at transform boundaries) • Caused by shearing forces • Two types: • Right-lateral fault • Left-lateral fault

  26. Right-Lateral Fault • An observer on one side of the fault sees the block on the opposite side move to the right.

  27. Fence along San Andreas Fault Photo: http://www-class.unl.edu/geol101i/images/structure%20images/fence.gif

  28. Photo: http://www.uoregon.edu/~millerm/LVSS.jpeg

  29. Left-Lateral Fault • The block on the opposite side of the fault moves to the left.

  30. Recognizing Faults in the Field • Faults may form a small cliff called a scarp

  31. Recognizing Faults in the Field • Formations that have large offsets (like on the San Andreas) differ in age and rock type • Small amounts of offset can be observed and measured

  32. Folds • A bend in rocks • Are often observed in layered rocks • Have a range of sizes • Two types: • Anticlines • Synclines Photo: http://www.science.smith.edu/~rburger/ Images/Many%20chev%20folds%20crop.jpg

  33. Photo: http://gse.umr.edu/images/folds-7.jpg

  34. Anticline • Layered rocks that fold upward into arches • Oldest rocks are in center of fold

  35. Photo: J. T. Daniels. http://www.teachingboxes.org/mountainBuilding/lessons/ foldImages/index.html

  36. Syncline • Layered rocks that fold downward into troughs. • Youngest rocks are in center of fold • Synclines look like Smiles

  37. Photo: http://geology.about.com/library/bl/images/blsyncline.htm

  38. Photo: http://gsc.nrcan.gc.ca/natmap/ cf/images/syncline440.gif

  39. Parts of Folds • Anticlines and synclines have limbs and an axial plane: • Limbs – the two sides of the fold • Axial plane – an imaginary surface that divides a fold as symmetrically as possible, with one limb on either side of the plane

  40. Photo: http://ess.nrcan.gc.ca/esic/gallery/images/180345.jpg

  41. Overturned Fold • Forms when deformation is intense and one limb has been tilted beyond the vertical. • Both limbs dip in the same direction, but the order of layers in the bottom limb is the reverse of their original sequence – that is, older rocks are on top of younger rocks

  42. Photo: http://bio-geo-terms.blogspot.com/2007/02/overturned-and-recumbent.html

  43. Photo:http://visualsunlimited.photoshelter.com/image/I00000omOQcPh5PYPhoto:http://visualsunlimited.photoshelter.com/image/I00000omOQcPh5PY

  44. Circular Structures • In many cases, these form from upward force of rising material or downward force of sinking material • Two types: • Dome • Basin

  45. Domes • Broad, circular or oval upward bulge of rock layers • Type of anticline

  46. Basins • Bowl-shaped depression of rock layers • Type of syncline Photo: http://www.ysnet.org.my/Maliau/ public/images/maliau/satellite_image2.jpg

  47. Joints • A type of fracture, or crack, along which there has been no movement. • Found in almost every outcrop • Formed by: • Tectonic forces • Expansion & contraction of rocks

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