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Plate Tectonics Theory: Basic Concepts & Some Common Misconceptions

Refresher Programme for Geography Teachers. Plate Tectonics Theory: Basic Concepts & Some Common Misconceptions. Chan Lung Sang Department of Earth Sciences Faculty of Science, HKU. 地殼 (固態，大陸地殼為花崗質，海洋地殼為玄武質) 地幔 (固態，超基質) 地核 (外核液態，硫化鐵質。內核固態，純鐵質。). Landform and Endogenetic Processes.

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Plate Tectonics Theory: Basic Concepts & Some Common Misconceptions

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  1. Refresher Programme for Geography Teachers Plate Tectonics Theory: Basic Concepts & Some Common Misconceptions Chan Lung Sang Department of Earth Sciences Faculty of Science, HKU

  2. 地殼 (固態，大陸地殼為花崗質，海洋地殼為玄武質) 地幔 (固態，超基質) 地核 (外核液態，硫化鐵質。內核固態，純鐵質。) Landform and Endogenetic Processes

  3. Part 1: Plate Tectonics • History of Development • Basic Concepts • Earth’s interior model • Crustal provinces & structures • Rock formation • Energy sources • Mineral and oil formation • Tectonics and Geology of Hong Kong Region [MANY OF THE FIGURES USED IN THIS PRESENTATION WERE DOWNLOADED FROM THE INTERNET. THEIR CREATORS , OFTEN ANONYMOUS, ARE GRATEFULLY ACKNOWLEDGED]

  4. 1. From Continental Drift to Plate Tectonics

  5. Alfred Wegener • Paleoclimate • Fossil evidence • Geological evidence • Coastline geometry

  6. Birth of the Plate Tectonics Theory Plate tectonics theory was founded upon the following new findings in the late 1960s: • Ocean floor topography • Marine magnetic anomalies • Paleomagnetism & geomagnetic field reversals • Sea floor spreading

  7. Plate Boundaries, Earthquakes and Major Volcanoes of the World

  8. * Note new designation of plate boundary at Japan.

  9. Plate Boundaries * Note associated landforms: axial rift at mid-ocean ridge, sea trench at subduction zone, sea mounts and island arc.

  10. A paradigm shift - A unifying theory accounting for Earth’s interior structure Origin of atmosphere & hydosphere Crustal structures and provinces Volcanism & earthquakes Rock record Fossil record Sedimentary basins Petroleum and mineral formation Geophysical fields

  11. 2. Earth’s Interior Structure

  12. Studying Earth’s Interior Earth scientists use the following techniques to determine Earth’s interior structure • Earthquake waves • Whole-earth free oscillation • Rock records • Meteorite compositions • Geomagnetism • Heat flow & geothermal gradient • Lab experimentation • Numerical modeling

  13. Earth’s Abundance • Four major elements: O, Fe, Si, Mg 85% • Only 3% S • Earth’s crust depleted in siderophile (Fe, Ni, Cu etc.) but enriched in K and Al • Mantle - Mg silicate • Core – FeS, FeO and Fe

  14. * Mantle is not liquid; convection occurs due to material rheology. Earth’s Interior Model

  15. Earlier idea on crustal structure * The concepts of sial and sima are old and imprecisely describe current understanding of crustal structure.

  16. *Lithosphere includes the crust and part of the upper mantle. Asthenosphere is not a molten layer. *Note deepening of Moho beneath mountains due to isostasy. * The distinction between lithosphere and asthenosphere is by means of physical strength, not composition

  17. 3. Crustal Provinces & Structures Crustal provinces and structures at different scales are results of tectonic evolution and associated stress system

  18. Growth of North America Continent

  19. 板塊俯衝形成火山弧 弧後地區形成摺曲山脈 大陸板塊碰撞形成巨型造山帶

  20. Most folded mountain belts are continental suture zones

  21. Structures on smaller scale Tension gashes Overturned syncline Plunging S-fold Graben structure

  22. 4. Rock Formations

  23. Rock Cycle in Plate Tectonics Context

  24. Igneous & Metamorphic Rocks * Most magmas form from melting of mantle and crustal material in the overriding plate and not the descending plate.

  25. Ophiolite: suite of oceanic crust and mantle rocks Pillow basalt intruded by mafic dikes, Cyprus

  26. The Obsolete Concept of Geosyncline *What formerly called geosynclines are now known to be mountains that formed in active continental margins *The term should not be used anymore.

  27. 5. The Energy Source

  28. Earth’s Source of Energy • Primordial heat • Radioactivity • Gravitational heat • Phase changes

  29. *Phase change, not radioactivity, is the primary energy source for plate motion. Outer Core-Inner Core Relation Outer core condenses gradually to become part of inner core. The process probably involves also a compositional change.

  30. Mantle Convection heat energy from core 地幔對流 熱源來自地核 * Not all spreading ridges are located above mantle divergence.

  31. 6. Mineral and oil Formations

  32. ACTIVE VS PASSIVE MARGIN PASSIVE MARGIN • Stable • Wide continental shelf • Continental crust thins out gradually • Oil and gas resources ACTIVE MARGIN • magmatic activity • mountain belt with thick continental crust • narrow continental shelf • active seismicity • mineral deposit

  33. 7. Tectonic Evolution of Hong Kong Region

  34. Department of Earth Sciences, HKU http://www.hku.hk/earthsci Geological Map of Hong Kong (Geological Survey, GEO)

  35. End of Part 1 chanls@hku.hk Department of Earth Sciences, University of Hong Kong

  36. Useful Web Links pubs.usgs.gov/publications/text/dynamic.html geology.er.usgs.gov/eastern/tectonic.html www.school.discovery.com www.geolsoc.com.hk

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