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Stress & Strain

Stress & Strain. Structural geology & Plate tectonics. Stress & Strain. Applied force & deformation. Increasing strain with increasing stress. Rock deformation. Key factors: Composition Temperature Stress duration Stress rate. Plate choctonics. Joints (tectonic).

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Stress & Strain

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  1. Stress & Strain Structural geology & Plate tectonics

  2. Stress & Strain Applied force & deformation

  3. Increasing strain with increasing stress

  4. Rock deformation Key factors: Composition Temperature Stress duration Stress rate

  5. Plate choctonics

  6. Joints (tectonic) Brittle fracturing with little displacement

  7. Joints (igneous) Contraction during cooling

  8. Faults Brittle deformation with displacement Extension = 'normal' faults

  9. Faults Compression = 'reverse' faults

  10. Strike-slip faults Lateral movement San Andreas Fault, western USA

  11. Ductile (plastic) deformation King Oscar Fjord, Greenland = Folding Mainly at depths >10 km, and T >300° C

  12. Low-grade strain ‘Delabole butterflies’, Cornwall Tyne & Wear Museums University of Exeter Fossil rich mudstone strained into slate

  13. High-grade strain Gneiss, Aguanish, Quebec

  14. Mapping out the structures

  15. Old Lost Seas The Theory of Plate Tectonics

  16. Earth Puzzles * Fossil distributions * Continental margins * Volcanoes and earthquakes * Compositions

  17. W is for Walcott

  18. W is for Wegener * Continental drift * Gondwanaland & Pangaea = “near-universal and near-perpetual ridicule”

  19. W is for Wilson • Geophysicist • Hotspots • 'Proto-Atlantic’ • Wilson Cycles

  20. Plate tectonics

  21. Earth interior

  22. Terms • Crust (chemical) = mafic-felsic rocks overlying ultramafic mantle • (0-70 km thick) • Lithosphere (mechanical) = brittle upper layers (crust + upper mantle) • (0-300 km thick) • Aesthenosphere (mechanical) = ductile part of upper mantle

  23. How thick do you like your crust?

  24. Making the Earth move Mantle convection

  25. Seismology and the Moho Andrija Mohorovicic, seismologist

  26. Seismology and the Moho Base of brittle lithosphere at ~1300° C

  27. Thin, young oceans

  28. Geomagneticoceans Symmetric bands of magnetized minerals in ocean crust

  29. Spreading ridges Oceanic crust formed by extension; Upwelling of mafic magma

  30. Spreading ridges

  31. Convergence Oceanic-continental (e.g. Andes)

  32. Convergence Continental-continental (e.g. Himalayas) Oceanic-oceanic (e.g. Japan)

  33. The full picture Ocean birth to death = Wilson Cycle

  34. Iapetus - the Old Lost Sea

  35. The Ordovician Atlantic

  36. Iapetus in Wales The Welsh Basin Palaeozoic marine mudstones (Many now slate)

  37. Iapetus in Scotland Glens and highlands

  38. Caledonian orogeny

  39. Old Lost Sea in Newfoundland An Iapetan slice of upper mantle

  40. W is for Williams • Appalachians-Caledonides GrosMorne National Park

  41. Avalonia A micro-continent of the Iapetus Ocean Colony of Avalon, Newfoundland

  42. Iapetus (1)

  43. Iapetus (2)

  44. Iapetus (3)

  45. The Iapetus of Man Niarbyl Fault, nr Dalby, south-west Isle of Man

  46. The Iapetus of Man NORTH AMERICA (Laurentia) EUROPE (Avalonia)

  47. Next week

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