Download The Theory of Plate Tectonics

The Theory of Plate
Tectonics
Earth’s Internal Layers
• The crust varies in thickness (4-60 km) oxygen,
silicon, magnesium and iron
• The mantle (2885 km) silicon & oxygen
• Outer core (2270 km) iron & nickle – liquid
• Inner core (1218 km) iron & nickle - solid
The Rock Cycle
• Three types of rock found in the crust are:
– Igneous: cooled magma/lava
– Sedimentary: particles deposited by water
flow. Organic/inorganic matter (fossils)
– Metamorphic: as layers build up, this rock is
formed when pressure and heat become
great enough to change the rock chemically
• The rock cycle is completed through the tectonic
process. Rock returns to the mantle, remelt,
become magma, return to the crust as igneous
rock.
Pangaea
• Pangaea is the name given to the single
giant continent (Wegener 1912)
• Panthalassa (single ocean)
• The theory of continental drift states
that the continents were once a single
landmass that drifted apart and are still
doing so.
The Theory of Seafloor Spresding
• New crust emerges from the rift valley in a
mid-ocean ridge.
• Magma from the mantle pushes up
through the rift and solidifies into new
crust.
• New seafloor forms at the rift valleys and
mid-ocean ridges, spreading away from
the ridges until it returns as part of the rock
cycle at subduction zones (trenches)
Magnetic polarity
EM field reverses from time to time
Seafloor spreading and continental drift combined
by theory of plate tectonics
• More than 12 separate plates
– Divergent boundary: two plates moving apart
– Convergent boundary: two plates push
together
– Transform boundary: two plates moving past
each other (earthquakes)
Boundary Interactions
• Divergent boundary (normal)
– Tectonic plates moves in opposite directions
– Mid-oceanic ridge forms as seafloor spreading creates new crust and
seafloor as magma fills the gap created over geologic time.
• Convergent boundary (reverse)
– Tectonic plates move towards each other
– Oceanic subduction under continental: volcanoes, earthquakes
• Andes
– Continental /continental convergence: Mountains
• Himaylayas – Mt. Everest
• Oceanic/oceanic: Trenches – Mariana trench, tsunamis
• Transform boundary (strike-slip)
– Tectonic plates move past each other: Earthquakes
– San Andeas fault in San Francisco
Bridge across the Álfagjá rift valley in southwest Iceland, the boundary
between the Eurasian and North American continental tectonic plates.
Hot Spots
• The hot spot theory states that hot spots are
small melting areas within the mantle where
thermal plumes cause magma columns to push
up, breaking the crust
• Hot spots do not move with tectonic plates
because they originate in the mantle
• Volcanic isalnd chains are the result of the plate
moving over a hot spot (Hawaii, Galapagos, etc.)
Hot Spots
Plate movement
• Convection is the primary force driving
seafloor spreading
– Convection currents form as hot material rises
and cold materials sink
• A second driving force comes from the
seafloor spreading
– As new seafloor forms, the plates tend to slide
away from the elevated mid-ocean ridge
The end