Geology Plate Tectonics Mid-Ocean Ridge System

1. Geology • Plate Tectonics • Mid-Ocean Ridge System • Discovered from sea floor mapping with SONAR during and after World War II • Largest geological feature on Earth • Ridges displaced in some areas by transform faults • Trenches • Conspicuous sea floor features • Especially common in the Pacific Ocean

2. http://www.ngdc.noaa.gov/mgg/image/global_topo_large.gif

3. Fig. 2.5

4. Geology • Plate Tectonics - Evidence • “Ring of Fire” • Geological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges and with trenches

5. Fig. 2.6

6. Geology • Plate Tectonics - Evidence • “Ring of Fire” • Geological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges and with trenches • Closer to ridges • Younger rock • Thinner covering of sediment • Magnetic anomalies • Caused by magnetic field reversals • Symmetrical on either side of ridge axis

7. Fig. 2.7

8. Geology • Plate Tectonics - Mechanism • Sea-Floor Spreading • Mid-ocean ridges contain rifts where two pieces of crust are moving apart and new oceanic crust is being created (spreading rate ca. 2-18 cm y-1) • As rift widens, hot mantle material rises through rift, cools and solidifies to form new oceanic crust • Ridges = spreading centers • Theory generated by induction explains observations • Younger rock closer to ridges • Thinner sediment closer to ridges • Patterns of magnetic anomalies

9. Fig. 2.8

10. Geology • Plate Tectonics - Mechanism • Sea-Floor Spreading • Lithosphere made up of lithospheric plates • Plates may contain continental crust, oceanic crust, or both • Plates rest on asthenosphere (plastic upper mantle) • Plate boundaries correspond to locations of mid-ocean ridges and to trenches • Not all plates completely characterized yet Fig. 2.9

11. Geology • Plate Tectonics - Mechanism • Subduction • Old crust destroyed when one plate dips below another • Oldest oceanic crust ~200 million years old • Denser plate subducted beneath less dense plate • Locations – oceanic trenches = subduction zones • Recycles crust and supports volcanic activity • May result from collisions between • Continental plate and oceanic plate (oceanic plate subducted; usually forms volcanoes) • Two oceanic plates (denser plate subducted; usually forms island arc)

12. Fig. 2.10

13. Fig. 2.11

14. Geology • Geological History • Continental Drift • All continents joined together ~200 mya • Pangaea – “supercontinent” • Panthalassa – single ocean  Pacific Ocean • Tethys Sea – Shallow sea between Eurasia & Africa  Mediterranean Sea • Sinus Borealis  Arctic Ocean • Laurasia separated from Gondwana ~180 mya

15. Fig. 2.14

16. Fig. 2.14

17. Fig. 2.14

18. Fig. 2.14

19. Fig. 2.14

20. Global Plate TectonicsJurassic to Present Day By L.A. Lawver, M.F. Coffin, I.W.D. Dalziel L.M. Gahagan, D.A. Campbell, and R.M. Schmitz 2001, University of Texas Institute for Geophysics February 9, 2001

44. We wish to thank the PLATES’ sponsorsfor their support:Conoco, TotalFinaElf, Exxon-Mobil, Norsk Hydro, and Statoil.

45. For more information, contact:Lisa M. GahaganInstitute for Geophysics4412 Spicewood Springs Rd., Bldg. 600Austin, TX 78759plates@ig.utexas.edu

46. Earth – Future Drift

47. Earth – Future Drift

48. Earth – Future Drift

49. Earth – Future Drift

50. Earth – Future Drift Link