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Dynamic Earth

Dynamic Earth. Class 16 2 March 2006. The Flow of the Continents (Chapter 5) Building Mountains: New Zealand and Tibet. Deformation of the Continental Crust. Deformation of continental crust. Since continents are not destroyed by subduction, we look here for the ancient history of Earth.

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Dynamic Earth

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  1. Dynamic Earth Class 16 2 March 2006

  2. The Flow of the Continents (Chapter 5)Building Mountains:New Zealand and Tibet

  3. Deformation of the Continental Crust

  4. Deformation of continental crust • Since continents are not destroyed by subduction, we look here for the ancient history of Earth. • orogeny: sum of the tectonic forces (i.e., deformation, magmatism, metamorphism, erosion)that produce mountain belts

  5. Mountains and Mountain Building Mountains are one part of the continuum of plate tectonics—the most evident one. Example: Limestones at the top of Mount Everest.

  6. Structures of continents 1) Continents are made and deformed by plate motion. 2) Continents are older than oceanic crust. 3) Lithosphere floats on a viscous layer below (isostasy).

  7. Age of the Continental Crust Blue areas mark continental crust beneath the ocean

  8. Continental characteristics • Granitic-andesitic composition • 30–70 km thick • 1/3 of Earth surface • Complex structures • Up to 4.0 Ga old

  9. Three basic structural components of continents • Shields • Stable platforms • Folded mountain belts

  10. Shields (e.g., Canada) • Low elevation and relatively flat • ”Basement complex" of metamorphic and igneous rocks • Composed of a series of zones that were once highly mobile and tectonically active

  11. Stable platforms • Shields covered with a series of horizontal sedimentary rocks • Sandstones, limestones, and shales deposited in ancient shallow seas • Many transgressions, regresssions caused by changes in spreading rate

  12. Mountain belts • Relatively narrow zones of folded, compressed rocks (and associated magmatism) • Formed at convergent plate boundaries • Two major active belts: Cordilleran (Rockies-Andes), Alps-Himalayan • Older examples: Appalachians, Urals

  13. Mountain types Folded—Alps, Himalaya, Appalachians Fault block—Basin and Range Upwarped—Adirondacks Volcanic—Cascades

  14. Stacked Sheets of Continental Crust Due to Convergence of Continental Plates

  15. Volcanic Origin, e.g. Cascades

  16. Upwarped with Reverse Faults,e.g. Central Rocky Mountians

  17. Tilted Normal Fault Blocks,e.g. Basin and Range Province

  18. Folded Rocks,e.g. the Appalachian Ridge and Valley

  19. Uplift Formed by Removal of Ice Sheet

  20. Uplift Caused by HeatingSubsidence Caused by Cooling

  21. Uplift Caused by HeatingSubsidence Caused by Extension

  22. Uplift Caused by Rising Mantle Plume

  23. Building fold mountains (1)

  24. Building fold mountains (2)

  25. The Applachians

  26. Northern Valley and Ridge Southern Valley and Ridge

  27. Valley and Ridge in Pennsylvania

  28. Valley and Ridge in Tennessee

  29. Stages in the formation of the Southern Appalachians Fig. 17.30

  30. Overlapping Thrust Faults,e.g. the Himalayas

  31. Tibet—not just mountains, a huge plateau too

  32. India has collided with Asia

  33. Continent–ContinentConvergent Boundary

  34. Indian plate subductsbeneath Eurasian plate 60 million years ago

  35. Indian subcontinentcollides with Tibet 40–60 million years ago

  36. Accretionary wedge and forearc deposits thrust northward onto Tibet Approximately 40–20 million years ago

  37. Main boundary fault develops 10–20 million years ago

  38. Exotic terranes

  39. Faults galore…

  40. …and earthquakes

  41. Himalayan collision ideas

  42. A complicated explanation emerges

  43. The drooling lithosphere

  44. So now we think we have figured it out

  45. Indian climate before Himalayas

  46. Monsoons – Circulation in ITCZ • ITCZ shifts with seasons • Circulation driven by solar heating • Circulation affected by seasonal heat transfer between tropical ocean and land • Heat capacity and thermal inertia of land < water

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