Presentation on theme: "Plate Tectonics Theory: Basic Concepts & Some Common Misconceptions Chan Lung Sang Department of Earth Sciences Faculty of Science, HKU Refresher Programme."— Presentation transcript:
Plate Tectonics Theory: Basic Concepts & Some Common Misconceptions Chan Lung Sang Department of Earth Sciences Faculty of Science, HKU Refresher Programme for Geography Teachers
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]
1. From Continental Drift to Plate Tectonics
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
* Note new designation of plate boundary at Japan.
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
2. Earth’s Interior Structure
Studying Earth’s Interior Earthquake waves Whole-earth free oscillation Rock records Meteorite compositions Geomagnetism Heat flow & geothermal gradient Lab experimentation Numerical modeling Earth scientists use the following techniques to determine Earth’s interior structure
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
Earth’s Interior Model ShellNameDepth (km)CompositionState ACrust0-30Al-rich silicatesolid B Noncrustal Lithosphere Upper Mantle Mg-rich silicate (olivine) solid C Asthenosphere near melting D’Lower Mantle solid D”Mantle-Core Transition soild (softer) EOuter Core FeS+Feliquid FOC-IC Transition Fe+FeO liquid+solid GInner Core solid * Mantle is not liquid; convection occurs due to material rheology.
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
Growth of North America Continent
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
Most folded mountain belts are continental suture zones
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.
5. The Energy Source
Earth’s Source of Energy Primordial heat Radioactivity Gravitational heat Phase changes
Outer Core-Inner Core Relation Outer core condenses gradually to become part of inner core. The process probably involves also a compositional change. * Phase change, not radioactivity, is the primary energy source for plate motion.
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.
6. Mineral and oil Formations
ACTIVE VS PASSIVE MARGIN ACTIVE MARGIN magmatic activity mountain belt with thick continental crust narrow continental shelf active seismicity mineral deposit PASSIVE MARGIN Stable Wide continental shelf Continental crust thins out gradually Oil and gas resources
7. Tectonic Evolution of Hong Kong Region
Geological Map of Hong Kong (Geological Survey, GEO) Department of Earth Sciences, HKU
End of Part 1 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