Plate Tectonics GEOL 101 Lecture 22 How Are Mountains Built?

Transcription

1 Plate Tectonics GEOL 101 Lecture 22 How Are Mountains Built? The Grand Tetons, Wyoming First a Brief Review of Sea Floor Spreading Prop: Test 3 Invitations Break-Up of a Continent and Origin of an Ocean Basin Spread Centers Feed Subduction Zones 1

2 Missing Mechanisms for Continental Drift: Sea Floor Spreading & Subduction Continents are Passive Boats Subduction Zones: Ocean-Ocean Margin Subduction Zones: Ocean-Continent Margin 2

3 Orogeny Associated with Subduction Zone Single Figure with Some Vertical Exaggeration Plummer et al. 10 th ed, Figure 20.6 Orogeny Associated with Subduction Zone Single Figure with More Vertical Exaggeration Orogeny Associated with Subduction Zone 3

4 Orogeny Flipped for East Coast View Craton Fold and Thrust Belt Orogeny Associated with Subduction Zone Single Figure Flipped & Tilted to Match Eastern US Shenandoah Natl. Park Sea Level Today Younger Sed Rx Orogeny in the Himalayas 4

5 Continental Lithosphere Will NOT Flush Down Subduction Zones Orogeny Folds Rocks Review: New Lithosphere (Crust + Upper Mantle) is Created at Spread Centers, Consumed at Subduction Zones 5

6 What About Offsets in Spread Centers? Transform Faults & Fracture Zones Transform Faults 6

7 San Andreas Fault: Right-Lateral Transform Fault Left-Lateral Offset!! Why?: Fault is Produced by Offset, vs. Offset Produced by Fault Plate Margins: Spread Centers (Mid-Ocean Ridges) Subduction Zones (Trenches) Transform Faults Plate Margins: 7

8 The Plates: Atlantic-Centered View The Plates: Pacific-Centered View (Distorted by Mercator Map Projection) What Drives Plate Tectonics? 1. Convection Cells in Mantle 2. Sinking of Cool, Dense Plates 3. Mantle Plumes - Hot Spots 8

9 Convection Cells Convection Cells in Mantle 9

10 Mantle Plumes Mantle Plumes Under Continents 10

11 Known Hot Spots Hawaiian Islands Mantle Plumes - Hot Spots Numbers = Age of Rock in Millions of Years 11

12 Sinking of Cool, Dense Plates Seamount Volcanoes Surrounded by Fringing Coral Reefs Atolls: Submerged Volcanos Support Reefs Only in Warm Clear Seas Tuamoto Islands NASA 12

13 Plate Tectonic Evolution of Eastern North America The Craton Suspect Terranes Continental Accretion The Craton: The Old Core of the Continent Mostly Exposed in the Canadian Shield Craton Craton Accreted or Suspect Terranes in Western USA, Canada 13

14 History of Suspect Terrane Accretion in Western North America suspect terranes (AK) Plate Tectonic Evolution of North America: Accretion of Terranes 3 North American Orogenies in a 5 frame cartoon 14

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17 Taconic Orogeny Continent-Arc Collision Orogeny: Eastern N. Amer. Mirror Image of West Coast 17

18 Taconic Orogeny Acadian Orogeny Continent- Terrane Collision 18

19 Acadian Orogeny 19

20 Alleghenian Orogeny Continent-Continent Collision Allegehenian Orogeny Folded Appalachian Rocks Mirror Image of West Coast Pangaea = Gondwanaland + Laurasia Penn.jpg 20

21 Alleghenian Orogeny Pangaea = Gondwanaland + Laurasia Ice Sheet Perm.jpg Erosion and Isostatic Uplift of the Appalachians Since End of Alleghenian Orogeny 21

22 160_1st.jpg Laurasia Gondwanaland 22

23 Laurasia: North America, Europe, most of Asia glg.nau.edu/ rcb/jur.jpg Gondwanaland: Antarctica, South America, Africa, Australia and India 23

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