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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
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Landform and Endogenetic Processes
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Part 1 Plate Tectonics

• History of Development
• Basic Concepts
• Earths 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

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1. From Continental Drift to Plate Tectonics
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Alfred Wegener

• Paleoclimate
• Fossil evidence
• Geological evidence
• Coastline geometry

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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

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Plate Boundaries, Earthquakes and Major Volcanoes
of the World
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Note new designation of plate boundary at Japan.
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Plate Boundaries
Note associated landforms axial rift at
mid-ocean ridge, sea trench at subduction zone,
sea mounts and island arc.
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A paradigm shift - A unifying theory accounting
for

• Earths interior structure
• Origin of atmosphere hydosphere
• Crustal structures and provinces
• Volcanism earthquakes
• Rock record
• Fossil record
• Sedimentary basins
• Petroleum and mineral formation
• Geophysical fields

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2. Earths Interior Structure
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Studying Earths Interior
Earth scientists use the following techniques to
determine Earths interior structure

• Earthquake waves
• Whole-earth free oscillation
• Rock records
• Meteorite compositions
• Geomagnetism
• Heat flow geothermal gradient
• Lab experimentation
• Numerical modeling

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Earths Abundance

• Four major elements O, Fe, Si, Mg 85
• Only 3 S
• Earths crust depleted in siderophile (Fe, Ni, Cu
  etc.) but enriched in K and Al
• Mantle - Mg silicate
• Core FeS, FeO and Fe

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Earths Interior Model
Mantle is not liquid convection occurs due to
material rheology.
Shell Name Name Depth (km) Composition State
A Crust Crust 0-30 Al-rich silicate solid
B Noncrustal Lithosphere Upper Mantle 30-100 Mg-rich silicate (olivine) solid
C Asthenosphere Upper Mantle 100-640 Mg-rich silicate (olivine) near melting
D Lower Mantle Lower Mantle 640-2800 Mg-rich silicate (olivine) solid
D Mantle-Core Transition Mantle-Core Transition 2800-2890 Mg-rich silicate (olivine) soild (softer)
E Outer Core Outer Core 2890-4600 FeSFe liquid
F OC-IC Transition OC-IC Transition 4600-5160 FeFeO liquidsolid
G Inner Core Inner Core 5160-6370 FeFeO solid
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Earlier idea on crustal structure
The concepts of sial and sima are old and
imprecisely describe current understanding of
crustal structure.
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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
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3. Crustal Provinces Structures
Crustal provinces and structures at different
scales are results of tectonic evolution and
associated stress system
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Growth of North America Continent
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Most folded mountain belts are continental suture
zones
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Structures on smaller scale
Tension gashes
Overturned syncline
Plunging S-fold
Graben structure
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4. Rock Formations
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Rock Cycle in Plate Tectonics Context
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Igneous Metamorphic Rocks
Most magmas form from melting of mantle and
crustal material in the overriding plate and not
the descending plate.
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Ophiolite suite of oceanic crust and mantle
rocks
Pillow basalt intruded by mafic dikes, Cyprus
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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.
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5. The Energy Source
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Earths Source of Energy

• Primordial heat
• Radioactivity
• Gravitational heat
• Phase changes

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Outer Core-Inner Core Relation
Phase change, not radioactivity, is the primary
energy source for plate motion.
Outer core condenses gradually to become part of
inner core. The process probably involves also a
compositional change.
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Mantle Convection heat energy from core
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Not all spreading ridges are located above
mantle divergence.
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6. Mineral and oil Formations
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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

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7. Tectonic Evolution of Hong Kong Region
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Geological Map of Hong Kong (Geological Survey,
GEO)
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End of Part 1 chanls_at_hku.hk Department of Earth
Sciences, University of Hong Kong
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Useful Web Links
pubs.usgs.gov/publications/text/dynamic.html geol
ogy.er.usgs.gov/eastern/tectonic.html www.school.
discovery.com www.geolsoc.com.hk