Which deformation and stresses cause theses structures ? - PowerPoint PPT Presentation

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Which deformation and stresses cause theses structures ?

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Which deformation and stresses cause theses structures ?
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Which deformation and stresses cause theses structures ?

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  1. FOLDS and thrust Whichdeformationand stresses cause theses structures ? Folding of Shale-Sandstone sequence, Kings Canyon, California

  2. … Compression…Shortening

  3. The fold is like a Thrust defined by its orientation Parts of a fold: • axial plane • limbs • “hinge” Hinge

  4. Types of Folds • Anticline = arch • Syncline = trough • Monocline = stair step • Dome or Basin Chevron Fold, Laurel Mt., CA

  5. Syncline Youngest rocks in middle syncline, Israel

  6. Anticline Oldest rocks in middle Virgin anticline, southern Utah

  7. Domes & Basins Chernicoff and Whitney Think of an Egg Carton!

  8. Map from Topozone.com Grenville Dome: Sinclair, WY

  9. Syncline- Anticline Pairs + Domes: Zagros Mts, Iran NASA “Earth as Art” web page

  10. Monocline

  11. Fold Classification

  12. Fold in Glacier, Antarctica

  13. Folds axis are perpendicular to the main direction of compression

  14. Domes are not produced by horizontal but vertical compression Little Shuteye, Sierra Nevada, CA David Rogers Casey Moore, UCSC

  15. Minor Folds and Foliation Are Clues to Much Larger Structures

  16. Pressure Foliation • pressure flattens and/or aligns minerals in a rock • platy or sheet-like structure reflects the direction in which pressure was applied • Slate, schist, and gneiss foliated 1 mm Microscope Image of Foliated Garnet Schist, VT

  17. Foliation In every case, the foliation is: In the direction of least resistance at right angles to the direction of greatest compression.

  18. Fold And Foliation

  19. Folds and Foliation

  20. How Geologists Use These Clues • Here's an outcrop that might be seen in the field.

  21. Minor Folds and foliations can be used to determine the axe of the fold

  22. Pay attentionit migth look like folds • K = Cretaceous • J = Jurassic • Tr = triassic • At X, we have younger rocks surrounded by older rock

  23. But it is produced by differential errosion on a thrust • Dark green is older rock, thrust over the younger yellow rock • The Klippe (K) • W is a Fenster or Window

  24. Folds and and Thrust are often associated The overturned fold in the upper diagram may break, yielding an overthrust fold or thrust fault

  25. Folds and thrust have the sameorigin

  26. ReverseFault Small thrust fault, Las Vegas, NV, Source: M. Miller, U. of Oregon

  27. Thrust Faults in Snow

  28. Folds and thrust are both responsible for the orogens fold-thrust complex developed in Upper Jurassic limestones in the Haut Giffre area of the Subalpine thrust belt (Morcles nappe in France) R.W.H. Butler

  29. Folded Appalachians Near Harrisburg, PA, Source: NASA

  30. Folding in Malaspina Glacier, AK, 1969

  31. Oil and Gas Concentrate in Domes Chernicoff and Whitney

  32. Growth of Minerals

  33. Small Scale Structures Mimic Large Scale Structures!! Bohlen et al., 1987 Folded Amphibolite in Marble, Warrensburg (K. Hollocher, NYSGA field photo)

  34. Foliation Macroscopic and Microscopic Feldspar (strong) Quartz (weak) Foliated Slate, Shelburne, VT, UVM Mulwaree fault zone, Australia Mulwaree fault zone, Australia, Tullis et al. Foliated Gneiss, Nunavut,S. Tella Photo.

  35. Pressure Cararra MarbleDeformationExperiments Brittle Ductile K. Hamblin A. Kronenberg

  36. Continental Extension Chernicoff and Whitney

  37. Basin and Range Nevada Bureau of Mines and Geology

  38. Extension • Crust Thins Ductile • Faulting Brittle

  39. Shearing • lateral slip creates faults • common at transform boundaries

  40. Faults Hanging Wall • result from brittle deformation • rocks offset across fault • Sides referred to as “hanging wall” and “footwall” • 3 types of fault Footwall

  41. Strike & Dip • Describe fault orientation • Direction of slip determines kind of fault: “dip-slip” or “strike-slip” Chernicoff and Whitney

  42. NormalFault Normal Fault, Lamb Canyon, CA

  43. Strike-SlipFault Strike-slip fault near Las Vegas, NV, Source: M. Miller, U. of Oregon

  44. Strike-slip fault displacement in orchard

  45. Joints • Brittle “cracks” in rocks • Form near surface • Regular spatial distribution • No offset

  46. Preferential weathering of joints in Sandstone; Calcite veins in joints of marble, Laurel Mt., CA