Basic concepts some common misconceptions

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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 地地 ( 地地地地地地地地地地地地地地地地地地地地 ) 地地 ( 地地地地地地 ) 地地 ( 地地地地地地地地地地地地地地地地地地地 ) 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] 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 Rock Formations Rock Cycle in Plate Tectonics Context 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 *What formerly called geosynclines are now known to be mountains that formed in active continental margins *The term should not be used anymore The Obsolete Concept of Geosyncline The Energy Source 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 地地地地 地地地地地地 * Not all spreading ridges are located above mantle divergence Mineral and oil Formations ACTIVE VS PASSIVE MARGIN ACTIVE MARGIN PASSIVE MARGIN • • Stable • Wide continental shelf • Continental crust thins out gradually • Oil and gas resources • magmatic activity mountain belt with thick continental crust • narrow continental shelf • active seismicity • mineral deposit Tectonic Evolution of Hong Kong Region Geological Map of Hong Kong (Geological Survey, GEO) Department of Earth Sciences, HKU End of Part Department of Earth Sciences, University of Hong Kong Useful Web Links [...]... 2890-4600 F OC-IC Transition 4600-5160 G Inner Core 5160-6370 solid Mg-rich silicate (olivine) near melting solid soild (softer) FeS+Fe Fe+FeO liquid liquid+solid solid 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
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