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

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

10. Shields (e.g., Canada) Low elevation and relatively flat Low elevation and relatively flat ”Basement complex" of metamorphic and igneous rocks ”Basement complex" of metamorphic and igneous rocks Composed of a series of zones that were once highly mobile and tectonically active 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 Shields covered with a series of horizontal sedimentary rocks Sandstones, limestones, and shales deposited in ancient shallow seas Sandstones, limestones, and shales deposited in ancient shallow seas Many transgressions, regresssions caused by changes in spreading rate Many transgressions, regresssions caused by changes in spreading rate

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

21. Uplift Caused by Heating Subsidence Caused by Extension

22. Uplift Caused by Rising Mantle Plume

23. Building fold mountains (1)

24. Building fold mountains (2)

25. The Applachians

26. Southern Valley and Ridge Northern 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

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

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

34. India has collided with Asia

35. Continent–Continent Convergent Boundary

36. Indian plate subducts beneath Eurasian plate 60 million years ago

37. Indian subcontinent collides with Tibet 40–60 million years ago

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

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

41. Exotic terranes

42. Faults galore…

43. …and earthquakes

44. Himalayan collision ideas

45. A complicated explanation emerges

46. The drooling lithosphere

47. So now we think we have figured it out

49. Indian climate before Himalayas

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

51. Atmospheric Circulation Atmosphere has no distinct upper boundary Atmosphere has no distinct upper boundary Air becomes less dense with increasing altitude Air becomes less dense with increasing altitude Air is compressible and subject to greater compression at lower elevations, density of air greater at surface Air is compressible and subject to greater compression at lower elevations, density of air greater at surface What drives atmospheric circulation? What drives atmospheric circulation?

52. Free Convection Atmospheric mixing related to buoyancy Atmospheric mixing related to buoyancy Localized parcel of air is heated more than nearby air Localized parcel of air is heated more than nearby air Warm air is less dense than cold air Warm air is less dense than cold air Warm air is therefore more buoyant than cold air Warm air is therefore more buoyant than cold air Warm air rises Warm air rises

53. Water Vapor Content of Air Saturation vapor density Saturation vapor density Warm air holds 10X more water than cold Warm air holds 10X more water than cold

54. General Circulation of the Atmosphere Tropical heating drives Hadley cell circulation Tropical heating drives Hadley cell circulation Warm wet air rises along the equator Warm wet air rises along the equator Transfers water vapor from tropical oceans to higher latitudes Transfers water vapor from tropical oceans to higher latitudes Transfers heat from low to high latitudes Transfers heat from low to high latitudes

55. Summer Monsoon Air over land heats and rises drawing moist air in from tropical oceans Air over land heats and rises drawing moist air in from tropical oceans

56. Winter Monsoon Air over land cools and sinks drawing dry air in over the tropical oceans Air over land cools and sinks drawing dry air in over the tropical oceans

58. Monsoon Climate: Tibet heats up and rises Moist Indian Ocean air sucked in Clouds form as moist air blocked by mts

59. Uplift Weathering Hypothesis Uplift Weathering Hypothesis Uplift Weathering Hypothesis Chemical weathering is the active driver of climate change Chemical weathering is the active driver of climate change Rate of supply of CO 2 constant, rate of removal changes Rate of supply of CO 2 constant, rate of removal changes Global mean rate of chemical weathering depends on availability of fresh rock and mineral surfaces Global mean rate of chemical weathering depends on availability of fresh rock and mineral surfaces Rate of tectonic uplift controls/enhances exposure of fresh rock surfaces Rate of tectonic uplift controls/enhances exposure of fresh rock surfaces

60. Source of Greenhouse Gases Input of CO 2 and other greenhouse gases from volcanic emissions Input of CO 2 and other greenhouse gases from volcanic emissions

61. Is Volcanic CO 2 Earth’s Thermostat? If volcanic CO 2 emissions provide greenhouse, has volcanic activity been continuous through geologic time? No, but… If volcanic CO 2 emissions provide greenhouse, has volcanic activity been continuous through geologic time? No, but… Carbon input balanced by removal Carbon input balanced by removal Near surface carbon reservoirs Near surface carbon reservoirs Stop all volcanic input of CO 2 Stop all volcanic input of CO 2 Take 270,000 years to deplete atmospheric CO 2 Take 270,000 years to deplete atmospheric CO 2 Surface carbon reservoirs (41,700 gt) divided by volcanic carbon input (0.15 gt y -1 ) Surface carbon reservoirs (41,700 gt) divided by volcanic carbon input (0.15 gt y -1 ) Rate of volcanic CO 2 emissions have potential to strongly affect atmospheric CO 2 levels on billion-year timescale Rate of volcanic CO 2 emissions have potential to strongly affect atmospheric CO 2 levels on billion-year timescale

62. Removal of Atmospheric CO 2 Slow chemical weathering of continental rocks balances input of CO 2 to atmosphere Slow chemical weathering of continental rocks balances input of CO 2 to atmosphere Chemical weathering reactions important Chemical weathering reactions important Hydrolysis and Dissolution Hydrolysis and Dissolution

63. Hydrolysis Main mechanism of chemical weathering that removes atmospheric CO 2 Main mechanism of chemical weathering that removes atmospheric CO 2 Reaction of silicate minerals with carbonic acid to form clay minerals and dissolved ions Reaction of silicate minerals with carbonic acid to form clay minerals and dissolved ions Summarized by the Urey reaction Summarized by the Urey reaction CaSiO 3 + H 2 CO 3  CaCO 3 + SiO 2 + H 2 O CaSiO 3 + H 2 CO 3  CaCO 3 + SiO 2 + H 2 O Atmospheric CO 2 is carbon source for carbonic acid in groundwater Atmospheric CO 2 is carbon source for carbonic acid in groundwater Urey reaction summarizes atmospheric CO 2 removal and burial in marine sediments Urey reaction summarizes atmospheric CO 2 removal and burial in marine sediments Accounts for 80% of CO 2 removal Accounts for 80% of CO 2 removal

64. Dissolution Kinetics of dissolution reactions faster than hydrolysis Kinetics of dissolution reactions faster than hydrolysis Dissolution reaction neither efficient nor long term Dissolution reaction neither efficient nor long term Dissolution of exposed limestone and dolostone on continents and precipitation of calcareous skeletons in ocean Dissolution of exposed limestone and dolostone on continents and precipitation of calcareous skeletons in ocean CaCO 3 + H 2 CO 3  CaCO 3 + H 2 O + CO 2 CaCO 3 + H 2 CO 3  CaCO 3 + H 2 O + CO 2 Although no net removal of CO 2 Although no net removal of CO 2 Temporary removal from atmosphere Temporary removal from atmosphere

65. Atmospheric CO 2 Balance Slow silicate rock weathering balances long-term build-up of atmospheric CO 2 Slow silicate rock weathering balances long-term build-up of atmospheric CO 2 On the 1-100 million-year time scale On the 1-100 million-year time scale Rate of chemical hydrolysis balance rate of volcanic emissions of CO 2 Rate of chemical hydrolysis balance rate of volcanic emissions of CO 2 Neither rate was constant with time Neither rate was constant with time Earth’s long term habitably requires only that the two are reasonably well balanced Earth’s long term habitably requires only that the two are reasonably well balanced

66. Tectonic Uplift and Weathering Uplift causes several tectonic and climatic effects that affects weathering by fragmenting fresh rock Uplift causes several tectonic and climatic effects that affects weathering by fragmenting fresh rock

67. Testing the Hypothesis Times of continental collision coincide with times of glaciations Times of continental collision coincide with times of glaciations Uplift weathering hypothesis consistent with geologic record Uplift weathering hypothesis consistent with geologic record

68. Earth’s High Topography Only a few regions with elevations above 1 km Only a few regions with elevations above 1 km Most young tectonic terrains Most young tectonic terrains Exception is E. African plateau Exception is E. African plateau

69. India-Asia Collision Formation of Tibetan Plateau Formation of Tibetan Plateau Large geographic region elevated Large geographic region elevated Initial collision about 55 mya Initial collision about 55 mya Uplift continues today Uplift continues today No large continental collisions between 100-65 mya No large continental collisions between 100-65 mya

70. Elevation on Earth Most high elevation caused by subduction of oceanic crust and volcanism Most high elevation caused by subduction of oceanic crust and volcanism Mountain ranges associates with subduction common throughout geologic time Mountain ranges associates with subduction common throughout geologic time Deep-seated heating and volcanism Deep-seated heating and volcanism East African plateau East African plateau Mechanism of uplift not unique to last 55 my Mechanism of uplift not unique to last 55 my Existence of uplifted terrains like the Tibetan Plateau Existence of uplifted terrains like the Tibetan Plateau Not common through geologic time Not common through geologic time Conclude – amount of high elevation terrain is unusually large during last 55 my Conclude – amount of high elevation terrain is unusually large during last 55 my

71. Physical Weathering High Does the amount of high elevation terrain result in unusual physical weathering? Does the amount of high elevation terrain result in unusual physical weathering? Most likely given 10 fold increase of sediment to the Indian Ocean Most likely given 10 fold increase of sediment to the Indian Ocean Steep terrain along southern Himalayan margin Steep terrain along southern Himalayan margin Presence of powerful South Asian monsoon Presence of powerful South Asian monsoon

72. Tuesday Video: Winds of Change Homework #5 Due

73. Next Thursday Exam #2 (March 9 th )