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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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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
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]
Alfred Wegener • Paleoclimate • Fossil evidence • Geological evidence • Coastline geometry
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
Plate Boundaries, Earthquakes and Major Volcanoes of the World
Plate Boundaries * Note associated landforms: axial rift at mid-ocean ridge, sea trench at subduction zone, sea mounts and island arc.
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
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
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
* Mantle is not liquid; convection occurs due to material rheology. Earth’s Interior Model
Earlier idea on crustal structure * The concepts of sial and sima are old and imprecisely describe current understanding of crustal structure.
*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
3. Crustal Provinces & Structures Crustal provinces and structures at different scales are results of tectonic evolution and associated stress system
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
Structures on smaller scale Tension gashes Overturned syncline Plunging S-fold Graben structure
Igneous & Metamorphic Rocks * Most magmas form from melting of mantle and crustal material in the overriding plate and not the descending plate.
Ophiolite: suite of oceanic crust and mantle rocks Pillow basalt intruded by mafic dikes, Cyprus
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.
Earth’s Source of Energy • Primordial heat • Radioactivity • Gravitational heat • Phase changes
*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.
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.
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
Department of Earth Sciences, HKU http://www.hku.hk/earthsci Geological Map of Hong Kong (Geological Survey, GEO)
End of Part 1 chanls@hku.hk Department of Earth Sciences, University of Hong Kong
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